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Autologous hematopoietic stem cell transplantation (ASCT) improves survival in multiple myeloma (MM). However, many individuals are unable to collect optimal CD34+ hematopoietic stem and progenitor cell (HSPC) numbers with granulocyte colony-stimulating factor (G-CSF) mobilization. Motixafortide is a novel cyclic-peptide CXCR4 inhibitor with extended in vivo activity. The GENESIS trial was a prospective, phase 3, double-blind, placebo-controlled, multicenter study with the objective of assessing the superiority of motixafortide + G-CSF over placebo + G-CSF to mobilize HSPCs for ASCT in MM. The primary endpoint was the proportion of patients collecting ≥6 × 106 CD34+ cells kg–1 within two apheresis procedures; the secondary endpoint was to achieve this goal in one apheresis. A total of 122 adult patients with MM undergoing ASCT were enrolled at 18 sites across five countries and randomized (2:1) to motixafortide + G-CSF or placebo + G-CSF for HSPC mobilization. Motixafortide + G-CSF enabled 92.5% to successfully meet the primary endpoint versus 26.2% with placebo + G-CSF (odds ratio (OR) 53.3, 95% confidence interval (CI) 14.12–201.33, P P + HSPC numbers within two apheresis procedures versus placebo + G-CSF while preferentially mobilizing increased numbers of immunophenotypically and transcriptionally primitive HSPCs. Trial Registration: ClinicalTrials.gov, NCT03246529

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Purpose: The potential of the high-affinity CXCR4 antagonist BL-8040 as a monotherapy-mobilizing agent and its derived graft composition and quality were evaluated in a phase I clinical study in healthy volunteers (NCT02073019).Experimental Design: The first part of the study was a randomized, double-blind, placebo-controlled dose escalation phase. The second part of the study was an open-label phase, in which 8 subjects received a single injection of BL-8040 (1 mg/kg) and approximately 4 hours later underwent a standard leukapheresis procedure. The engraftment potential of the purified mobilized CD34+ cells was further evaluated by transplanting the cells into NSG immunodeficient mice.Results: BL-8040 was found safe and well tolerated at all doses tested (0.5–1 mg/kg). The main treatment-related adverse events were mild to moderate. Transient injection site and systemic reactions were mitigated by methylprednisolone, paracetamol, and promethazine pretreatment. In the first part of the study, BL-8040 triggered rapid and substantial mobilization of WBCs and CD34+ cells in all tested doses. Four hours postdose, the count rose to a mean of 8, 37, 31, and 35 cells/μL (placebo, 0.5, 0.75, and 1 mg/kg, respectively). FACS analysis revealed substantial mobilization of immature dendritic, T, B, and NK cells. In the second part, the mean CD34+ cells/kg collected were 11.6 × 106 cells/kg. The graft composition was rich in immune cells.Conclusions: The current data demonstrate that BL-8040 is a safe and effective monotherapy strategy for the collection of large amounts of CD34+ cells and immune cells in a one-day procedure for allogeneic HSPC transplantation. Clin Cancer Res; 23(22); 6790–801. ©2017 AACR.

Supplemented Table 4A: Absolut number of different subsets of hematopoietic stem cells Supplemented Table 4B: Percentages of different subpopulations of BL-8040 mobilized cells as compared to G-CSF mobilized cells

Purpose:Pancreatic ductal adenocarcinoma (PDAC) is largely unresponsive to checkpoint inhibitors. Blockade of the CXCR4/CXCL12 axis increases intratumoral trafficking of activated T cells while restraining immunosuppressive elements. This study evaluates dual blockade of CXCR4 and PD1 with chemotherapy in PDAC.Patients and Methods:Multicenter, single-arm, phase II study to evaluate the safety and efficacy of motixafortide and pembrolizumab combined with chemotherapy in patients with de novo metastatic PDAC and disease progression on front-line gemcitabine-based therapy (NCT02826486). Subjects received a priming phase of motixafortide daily on days 1–5, followed by repeated cycles of motixafortide twice a week; pembrolizumab every 3 weeks; and nanoliposomal irinotecan, fluorouracil, and leucovorin every 2 weeks (NAPOLI-1 regimen). The primary objective was objective response rate (ORR). Secondary objectives included overall survival (OS), progression-free survival (PFS), disease control rate (DCR), safety, and tolerability.Results:A total of 43 patients were enrolled. The ORR according to RECISTv1.1 was 21.1% with confirmed ORR of 13.2%. The DCR was 63.2% with median duration of clinical benefit of 5.7 months. In the intention-to-treat population, median PFS was 3.8 months and median OS was 6.6 months. The triple combination was safe and well tolerated, with toxicity comparable with the NAPOLI-1 regimen. Notably, the incidence of grade 3 or higher neutropenia and infection was 7%, lower than expected for this chemotherapy regimen.Conclusions:Triple combination of motixafortide, pembrolizumab, and chemotherapy was safe and well tolerated, and showed signs of efficacy in a population with poor prognosis and aggressive disease.

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The transcription factor β-catenin is a key player in many cellular processes, including stem cell renewal, cellular homeostasis and inflammation. Deregulation of β-catenin occurs frequently in several cancer types by mutation or overexpression of the β-catenin gene or mutation of negative regulators such as Adenomatous Polyposis Coli (APC). ST316 is a novel peptide antagonist that specifically interferes with the association of β-catenin with its co-activator BCL9, disrupting β-catenin nuclear localization and attenuating target gene expression. In an orthotopic triple-negative breast cancer (TNBC) model, ST316 demonstrates potent anti-tumor activity, resulting in 84% tumor growth inhibition (TGI) (p Citation Format: Claudio Scuoppo, Lila Ghamsari, Erin Gallagher, Siok Leong, Mark Koester, Rick Ramirez, Jerel Gonzales, Gene Merutka, Barry Kappel, Abi Vainstein-Haras, Jim Rotolo. Immunotherapeutic potential of ST316, a peptide antagonist of β-catenin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB016.

CCAAT/Enhancer Binding Protein β (C/EBPβ) is a basic leucine zipper (bZIP) transcription factor that causes aberrant gene expression in many cancers. Upregulated or overactivated C/EBPβ drives oncogenesis by promoting tumor survival and proliferation and is a critical regulator of the immunosuppressive tumor microenvironment (TME). Specifically, C/EBPβ regulates macrophage differentiation, activating a transcriptional program driving macrophage polarization toward immunosuppressive M2-type myeloid-derived suppressor cells (MDSCs). Consistently, activation of C/EBPβ correlates with poor prognosis in several types of human cancer. Thus, targeting C/EBPβ to reprogram tumor-associated macrophages (TAMs) from the M2 toward the immune-promoting M1 phenotype represents an attractive strategy to enhance antitumor immunity. ST101 is a novel peptide antagonist of C/EBPβ dimerization that inhibits C/EBPβ-dependent gene expression. Here we evaluated the impact of ST101 on macrophage differentiation, cytotoxic T-cell activation, and in vivo anti-tumor activity. Primary human macrophages cultured from Peripheral Blood Mononuclear Cells (hPBMCs) were activated toward the M1 or M2 phenotype by LPS and IFNγ or IL-4, respectively. ST101 exposure dose-dependently suppressed expression of M2 markers (CD163, CD206) while inducing M1 markers (CD80, CD86) by flow cytometry and quantitative PCR, resulting in a 40-fold increase in the M1/M2 ratio without substantial impact on cell viability. Next, in co-cultures of T cells with M2 macrophage, ST101 exposure resulted in a 4-fold increase in T-cell activation compared to control M2/T cell co-cultures, as measured by intracellular IFN-γ staining. Importantly, ST101 did not suppress proliferation or activity of T cells cultured alone. Finally, in an orthotopic TNBC model in vivo, ST101 in combination with anti-PD-1 treatment enhanced anti-tumor activity compared to either single agent alone. The observed increase in tumor growth inhibition was accompanied by a reduced TAM fraction and increased intratumoral and peripheral M1/M2 ratios. ST101 is being evaluated in a Phase 1-2 clinical study in patients with advanced unresectable and metastatic solid tumors (NCT04478279). Initial gene expression analysis performed on 8 paired patient biopsies (prior to ST101 exposure and within 24 hrs of ST101 administration during cycle 2 of therapy) collected during dose escalation (4 mg/kg ST101 or greater) indicates a significant decrease in expression of multiple factors involved in M2 polarization, including CD209, SIGLEC5 and IL-24, and T cell suppression, including FoxP3 and inhibitory KIR proteins. The result is a decrease in intratumoral regulatory T cell (Treg) vs. TIL ratio, indicating a shift towards a more immunoactive TME. Overall, these results support a novel, macrophage-driven mechanism of action for ST101 as anticancer agent and suggest the exploration of ST101 in immune-oncology therapeutic strategies. Citation Format: Claudio Scuoppo, Rick Ramirez, Siok Leong, Lila Ghamsari, Gina Capiaux, Rob Michel, Steve Kaesshaefer, Gene Merutka, Barry Kappel, Abi Vainstein-Haras, Alice Bexon, Jim Rotolo. ST101, a peptide antagonist of novel I/O target CEBPβ,reprograms MDSCs and promotes an immunoactive tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB236.

Programmed cell death 1 (PD-1) inhibitors have limited effect in pancreatic ductal adenocarcinoma (PDAC), underscoring the need to co-target alternative pathways. CXC chemokine receptor 4 (CXCR4) blockade promotes T cell tumor infiltration and is synergistic with anti-PD-1 therapy in PDAC mouse models. We conducted a phase IIa, open-label, two-cohort study to assess the safety, efficacy and immunobiological effects of the CXCR4 antagonist BL-8040 (motixafortide) with pembrolizumab and chemotherapy in metastatic PDAC (NCT02826486). The primary outcome was objective response rate (ORR). Secondary outcomes were overall survival (OS), disease control rate (DCR) and safety. In cohort 1, 37 patients with chemotherapy-resistant disease received BL-8040 and pembrolizumab. The DCR was 34.5% in the evaluable population (modified intention to treat, mITT; N = 29), including nine patients (31%) with stable disease and one patient (3.4%) with partial response. Median OS (mOS) was 3.3 months in the ITT population. Notably, in patients receiving study drugs as second-line therapy, the mOS was 7.5 months. BL-8040 increased CD8+ effector T cell tumor infiltration, decreased myeloid-derived suppressor cells (MDSCs) and further decreased circulating regulatory T cells. In cohort 2, 22 patients received BL-8040 and pembrolizumab with chemotherapy, with an ORR, DCR and median duration of response of 32%, 77% and 7.8 months, respectively. These data suggest that combined CXCR4 and PD-1 blockade may expand the benefit of chemotherapy in PDAC and warrants confirmation in subsequent randomized trials. Results from the phase IIa COMBAT trial combining CXCR4 and PD-1 inhibition in patients with metastatic cancer show encouraging clinical responses in association with enhanced antitumor immune activation.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is largely unresponsive to checkpoint inhibitors. Blockade of the CXCR4/CXCL12 axis increases intratumoral trafficking of activated T cells while restraining immunosuppressive elements. This study evaluates dual blockade of CXCR4 and PD1 with chemotherapy in PDAC. Patients and Methods: Multicenter, single-arm, phase II study to evaluate the safety and efficacy of motixafortide and pembrolizumab combined with chemotherapy in patients with de novo metastatic PDAC and disease progression on front-line gemcitabine-based therapy (NCT02826486). Subjects received a priming phase of motixafortide daily on days 1–5, followed by repeated cycles of motixafortide twice a week; pembrolizumab every 3 weeks; and nanoliposomal irinotecan, fluorouracil, and leucovorin every 2 weeks (NAPOLI-1 regimen). The primary objective was objective response rate (ORR). Secondary objectives included overall survival (OS), progression-free survival (PFS), disease control rate (DCR), safety, and tolerability. Results: A total of 43 patients were enrolled. The ORR according to RECISTv1.1 was 21.1% with confirmed ORR of 13.2%. The DCR was 63.2% with median duration of clinical benefit of 5.7 months. In the intention-to-treat population, median PFS was 3.8 months and median OS was 6.6 months. The triple combination was safe and well tolerated, with toxicity comparable with the NAPOLI-1 regimen. Notably, the incidence of grade 3 or higher neutropenia and infection was 7%, lower than expected for this chemotherapy regimen. Conclusions: Triple combination of motixafortide, pembrolizumab, and chemotherapy was safe and well tolerated, and showed signs of efficacy in a population with poor prognosis and aggressive disease.

Background CXCR4 mediates the retention and survival of acute myelogenous leukemia blasts in bone marrow and contributes to their resistance to chemotherapy. The authors evaluated a combination of the high-affinity CXCR4 antagonist BL-8040 with high-dose cytarabine (HiDAC) chemotherapy in a phase 2a study of patients with relapsed and refractory AML. Methods Forty-two patients received treatment with BL-8040 monotherapy for 2 days followed by a combination of BL-8040 with HiDAC for 5 days. Six escalating BL-8040 dose levels were investigated (0.5, 0.75, 1.0, 1.25, 1.5, and 2.0 mg/kg), and 1.5 mg/kg was selected as the dose for the expansion phase (n = 23). Results BL-8040 in combination with HiDAC was safe and well tolerated at all dose levels. Clinical response was observed with BL-8040 doses ≥1.0 mg/kg. The composite response rate (complete remissions plus complete remissions with incomplete hematologic recovery of platelets or neutrophils) was 29% (12 of 42) in all patients and 39% (9 of 23) in the 1.5-mg/kg phase. The median overall survival was 8.4 months for all patients, 10.8 months in the 1.5-mg/kg phase, and 21.8 months for responding patients in the 1.5-mg/kg cohort. Two days of BL-8040 monotherapy triggered the mobilization of blasts into peripheral blood, with significantly higher mean fold-changes in responders versus nonresponders. This was accompanied by a decrease in bone marrow blasts. Conclusions The current results demonstrate the efficacy of CXCR4 targeting with BL-8040 and support continued clinical development in acute myelogenous leukemia.

Introduction: Regulatory T (Treg) cells, an immunosuppressive subset of CD4+ T cells characterized by the expression of the master transcription factor forkhead box protein P3 (FOXP3), are a component of the immune system with essential roles in maintaining self-tolerance. Treg cells which are indispensable for preventing autoimmunity, also suppress effective tumor immunity (Togashi et al. Nat Rev Clin Oncol 2019) Treg cells abundantly infiltrate into tumor tissues, present in the tumor microenvironment where they promote tumor development and progression by dampening antitumor immune responses. The abundantly infiltrate of Treg cells into tumor tissues is often associated with poor prognosis in cancer patients (Tanaka et al Eur. J. Immunol. 2019). The chemokine receptor CXCR4 and its ligand, stromal cell-derived factor-1 (SDF-1/CXCL12) are critically involved in immune cell trafficking. CXCR4 overexpression, which has been identified in multiple cancer types, also supports cancer metastasis, recurrence and therapeutic resistance. More importantly, CXCR4 was shown to enhance tumor immune evasion by recruiting Treg (Santagata et al. Oncotarget. 2017) Objective: To study the effect of the high affinity CXCR4 antagonist, BL-8040, on the biology of Treg cells. To study how BL-8040 affects the ability of these cells to penetrate into the tumors, their migratory ability, their survival and also the differentiation of naive T cells towards Treg. Methods:C57BL/6 mice bearing LivMet pancreatic tumors and control mice were used for in-vivo study. In-vitro study was done with CD4 +CD25 hiFOXP3 + (Treg) cells which were isolated from fresh whole blood. CD4 +CD25 - cells were served as T conventional cells (Tconv). Differentiation of Treg cells was done from Naïve CD4+ T cells which were isolated from cord blood and stimulated with anti-CD3/CD28, TGF-b, IL-2 with or without BL-8040 for 6 days. Results: When mice bearing pancreatic cancer were treated with BL-8040, we found a significant reduction in the number of infiltrating Treg into the tumor. Following treatment with BL-8040 there was no alteration in the number of Treg in the blood neither in control mice nor in mice bearing tumors. To further understand the mechanism by which BL-8040 effected Treg cells we isolated Treg and Tconv cells and found that Treg cells express lower level of CXCR4, as compared to Tconv (Figure1). Further to, when we compared their motility, we found that Treg migration less efficiently towards CXCL12. Despite this, BL8040 more efficiently suppressed CXCL12 induced migration of Treg compared to Tconv. 100 nM of BL8040 was found to inhibits the migration of 82 % from the Treg compared to only 56.6% of Tconv cells (Figure 2). CXCR4 involves classical pathways of cell survival. In order to study the role of CXCR4 in the viability of Treg, we incubated Treg and Tconv cells in the presence of BL-8040 for 24 hr. We found that Treg cells are more sensitive to BL-8040 treatment with 19.2% of cell death compared to only 3.5% of Tconv cell death (Figure 3). Treg are one of the lineages of T helper (Th) cells which differentiated from naïve CD4 T cells. We found that BL-8040 inhibits the differentiation of naive CD4 T cells toward Treg. 10uM of BL-8040 shows a 5-fold inhibition in Treg differentiation from naïve CD4 T cells (Figure 4). Conclusions: In this work we show that the CXCR4 antagonist, BL-8040, can act as an immunomodulator by affecting the biology of regulatory T cells. BL8040 reduce the amount of infiltrating Treg into the tumors, impaired the migratory capacity of Treg toward CXCL12 and induces their cell death. Furthermore, BL-8040 was found to inhibit the differentiation of naïve CD4 T cells toward Treg. Taking all these together, BL-8040 may therefore improve the anticancer immune response, without impairing the activity of Tconv and thus can potentially serve as an effective immunomodulatory agent for cancer. Figure 1 Figure 1. Disclosures Abraham: Biokine Therapeutics: Current Employment. Vainstein: BioLineRx LTD: Current Employment. Shemesh-Darvish: BioLineRx LTD: Current Employment. Sorani: BioLineRx LTD: Current Employment. Eizenberg: Biokine Therapeutics Ltd: Current Employment. Peled: Biokine Therapeutics Ltd: Current Employment; Gamida Cell: Research Funding.

Background: Autologous stem cell transplantation (ASCT) in multiple myeloma (MM) has been shown to improve survival compared to conventional chemotherapy alone. However, the ability to perform ASCT relies, in part, on collecting a sufficient number (#) of CD34+ hematopoietic stem cells (HSCs), typically from peripheral blood. The ideal HSC mobilization regimen would enable collection of optimal #s of HSCs (5-6x10 6 CD34+ cells/kg) within the minimum # of apheresis sessions possible. Yet, despite currently available G-CSF (G) based mobilization regimens and multiple apheresis days, many remain unable to collect optimal #s of HSCs. Motixafortide (M) is a novel CXCR4 inhibitor, with high affinity (IC 50 0.54-4.5 nM) and long receptor occupancy (>48 hours). Methods: In this prospective, phase 3, double blind, placebo controlled, multicenter trial, 122 patients were randomized (2:1) to receive either M+G or placebo (P)+G for HSC mobilization prior to ASCT for MM. All patients received G (10 mcg/kg) on days 1-5 (and 6-8, if needed). Patients received either M (1.25 mg/kg, subcutaneous injection) or P on day 4 (and 6, if needed). Apheresis began day 5, with the primary (PEP) and secondary (SEP) endpoints of collecting ≥6x10 6 CD34+ cells/kg in up to 2 apheresis days or 1 day, respectively. Apheresis continued on days 6-8 if needed. Total CD34+ cells/kg were analyzed on site to determine if patients mobilized to the goal and all samples were subsequently sent for assessment by central laboratory. Patients that did not collect ≥2x10 6 CD34+ cells/kg by day 8 proceeded to rescue mobilization. The # of CD34+ cells infused was determined independently by each investigator according to local practice (minimum ≥2x10 6 CD34+ cells/kg). Analyses of the PEP/SEPs were performed on an intent-to-treat basis. Results: Demographics between the 2 treatment arms were similar. Mobilization with M+G resulted in 92.5% of patients collecting ≥6x10 6 CD34+ cells/kg within 2 apheresis days vs 26.2% with P+G (Odds Ratio (OR) 53.3, 95% CI 14.12-201.33, p Conclusions: A single injection of M on top of G significantly increased the proportion of patients mobilizing ≥6x10 6 CD34+ cells/kg for ASCT (92.5%) vs G (26.2%) in up to 2 apheresis days (p Figure 1 Figure 1. Disclosures Crees: BioLineRx Ltd.: Research Funding. Larson: TORL biotherapeutics: Current holder of individual stocks in a privately-held company; Bioline: Research Funding; Abbvie: Research Funding; BMS: Research Funding; Celgene: Research Funding; GSK: Research Funding; Janssen: Research Funding; Juno: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; Takeda: Research Funding. Illés: Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees. Stiff: Incyte: Research Funding; Cellectar: Research Funding; Seagen: Research Funding; Gamida Cell: Research Funding; Cellectar: Research Funding; Actinium: Research Funding; Bristol Myers Squibb: Research Funding; BioLineRX: Research Funding; Macrogenics: Research Funding; CRISPR Therapeutics: Consultancy, Honoraria; Amgen: Research Funding; Janssen: Research Funding; Kite, a Gilead Company: Research Funding; Karyopharm: Consultancy, Honoraria; MorphoSys: Consultancy, Honoraria. Sborov: Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy; Sanofi: Consultancy; SkylineDx: Consultancy. Pereira: Jazz Pharmaceutical: Membership on an entity's Board of Directors or advisory committees. Mikala: Novartis: Consultancy; Takeda: Consultancy; Abbvie: Consultancy; Krka: Consultancy; Janssen: Consultancy; Amgen: Consultancy; Celgene: Consultancy. Holtick: Celgene: Honoraria; Sanofi: Honoraria. Qazilbash: Amgen: Research Funding; Oncopeptides: Other: Advisory Board; Bristol-Myers Squibb: Other: Advisory Board; Biolline: Research Funding; Angiocrine: Research Funding; NexImmune: Research Funding; Janssen: Research Funding. Hardy: American Gene Technologies, International: Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Membership on an entity's Board of Directors or advisory committees; InCyte: Membership on an entity's Board of Directors or advisory committees. Vainstein: BioLineRx LTD: Current Employment. Sorani: BioLineRx LTD: Current Employment. Gliko-Kabir: BioLineRx Ltd.: Current Employment. Goldstein: BioLineRx Ltd.: Current Employment. Kadosh: BioLineRx Ltd.: Current Employment.

Background: CD34+ hematopoietic stem and progenitor cell (HSPC) dose during hematopoietic cell transplantation (HCT) remains one of the most reliable clinical parameters to predict quality of engraftment. A minimum HSPC dose of 2-2.5x10 6 CD34+ cells/kg is considered necessary for reliable engraftment, while optimal doses of 5-6x10 6 CD34+ cells/kg are associated with faster engraftment, as well as fewer transfusions, infections, and antibiotic days. CXCR4 inhibition significantly improves the number (#) of CD34+ HSPCs mobilized for HCT, when added to G-CSF (G). Motixafortide (M), a novel CXCR4 antagonist, is a potent mobilizer of HSPCs recently evaluated in the phase 3, double blind, placebo controlled, multicenter GENESIS Trial as a mobilizing agent prior to autologous HCT (ASCT) in multiple myeloma (MM). Methods: Patients received G (10 mcg/kg) on days 1-5 (and days 6-8, if needed). On day 4 (and day 6, if needed), patients received either M (1.25 mg/kg) or placebo (P). Apheresis began day 5, with up to 4 days of apheresis if needed. The primary and secondary endpoints were collection of ³6x10 6 CD34+ cells/kg in up to 2 days of apheresis or 1 day, respectively. The # of CD34+ cells/kg infused was determined independently by each investigator according to local practice, but a minimum of ³2x10 6 CD34+ cells/kg was required. A post-hoc analysis was performed pooling data from both arms to evaluate time to platelet engraftment (TPE) (≥20x10 9/L without transfusions x7 days) and neutrophil engraftment (TNE) (ANC ≥0.5x10 9/L x3 days) based on total # of CD34+ cells/kg and # of specific CD34+ HSPC subsets infused. CD34+ HSPC immunophenotyping was performed via multicolor fluorescence-activated cell sorting (FACS). TPE/TNE was analyzed using Kaplan-Meier curves and Cox proportional hazards model. Results: 114 MM patients underwent apheresis, ASCT and were evaluable (M+G N=77; P+G N=37). M+G mobilization yielded a median of 10.8x10 6 CD34+ cells/kg collected in 1 apheresis vs 2.3x10 6 CD34+ cells/kg with P+G (p75 th percentile) of combined CD34+ HSC, MPP, CMP and GMP subsets was associated with faster TPE of 12 days vs 19 days with lower #s of these subsets (p=0.003) (Figure 2A). Furthermore, higher #s (>75 th percentile) of GMPs was individually associated with faster TPE of 13 days vs 19 days with lower GMP cell doses (p=0.0116) (Figure 2C). TNE was not impacted by increasing doses of total CD34+ HSPCs or any specific CD34+ HSPC subset (all p>0.05) (Figures 1B, 2B and 2D). Conclusions: M+G mobilization enabled significantly more CD34+ cells to be collected in 1 apheresis (median 10.8x10 6 CD34+ cells/kg) vs P+G (2.3x10 6 CD34+ cells/kg), as well as 3.5-5.6 fold higher #s of HSCs, MPPs, CMPs and GMPs (all p-values Figure 1 Figure 1. Disclosures Crees: BioLineRx Ltd.: Research Funding. Retting: BioLineRx Ltd.: Research Funding. Larson: TORL biotherapeutics: Current holder of individual stocks in a privately-held company; Abbvie, Bioline, BMS, Celgene, GSK, Janssen, Juno, Novartis, Pfizer, Takeda: Research Funding. Illes: Novartis, Janssen, Pfizer, Roche: Other: Travel, Accommodations, Expenses; Takeda, Seattle Genetics: Research Funding; Janssen, Celgene, Novartis, Pfizer, Takeda, Roche: Consultancy. Stiff: CRISPR: Consultancy; Gamida-Cell, Atara, Amgen, Incyte, Takeda, Macrogenetics, Eisai: Research Funding. Sborov: SkylineDx: Consultancy; GlaxoSmithKline: Consultancy; Sanofi: Consultancy; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Pereira: Jazz Pharmaceutical: Membership on an entity's Board of Directors or advisory committees. Mikala: Abbvie: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Janssen: Consultancy; Krka: Consultancy; Novartis: Consultancy; Takeda: Consultancy. Holtick: Sanofi: Honoraria; Celgene: Honoraria. Qazilbash: Janssen: Research Funding; Oncopeptides: Other: Advisory Board; Biolline: Research Funding; Bristol-Myers Squibb: Other: Advisory Board; NexImmune: Research Funding; Amgen: Research Funding; Angiocrine: Research Funding. Hardy: Kite/Gilead: Membership on an entity's Board of Directors or advisory committees; American Gene Technologies, International: Membership on an entity's Board of Directors or advisory committees; InCyte: Membership on an entity's Board of Directors or advisory committees. Sorani: BioLineRx LTD: Current Employment. Shemesh-Darvish: BioLineRx LTD: Current Employment. Vainstein: BioLineRx LTD: Current Employment; Enlivex: Consultancy. Kadosh: StatExcellence: Current holder of individual stocks in a privately-held company; BioLineRx: Honoraria.

Background: CD34 expression remains the most common immunophenotypic cell surface marker defining human hematopoietic stem and progenitor cells (HSPCs). Recently, use of multicolor fluorescence-activated cell sorting (mFACS) and single-cell RNA sequencing (scRNA seq) has illustrated the heterogenous nature of CD34+ HSPCs, with immunophenotypically and transcriptionally distinct subsets ranging from primitive hematopoietic stem cells (HSCs) capable of long-term multilineage potential to differentiated, lineage-committed progenitors. Meanwhile, the addition of CXCR4 inhibitors (CXCR4i) to G-CSF (G) has increased mobilization of CD34+ HSPCs for stem cell transplantation (SCT). Yet, the effect of CXCR4i +/- G on mobilization of specific immunophenotypic and transcriptional CD34+ HSPC subsets is not well-characterized. Motixafortide (M) is a novel cyclic peptide CXCR4i with a low receptor off rate and extended in vivo action vs plerixafor (Px). M was recently evaluated in the phase 3, double blind, placebo controlled GENESIS Trial as an HSPC mobilizer prior to autologous SCT (ASCT) in multiple myeloma (MM). Methods: GENESIS Trial patients were prospectively randomized (2:1) to receive either M+G or placebo (P)+G for HSPC mobilization. Demographically similar patients undergoing mobilization with Px+G prior to ASCT for MM were prospectively enrolled on a parallel tissue banking protocol. All patients received G (10 mcg/kg) on days 1-5 (and 6-8 if needed). Patients also received either M (1.25 mg/kg) or P on day 4 (and 6 if needed); or Px (0.24 mg/kg) on day 4 (and 5-7 if needed). Apheresis began day 5 (and 6-8 if needed). HSPCs were purified from apheresis product on day 5 via CD34+ immunomagnetic selection. CD34+ HSPC subset profiling was performed via mFACS and scRNA seq. CXCR4 expression and receptor occupancy was evaluated by antibody binding capacity of 12G5 and 1D9 clones. Results: Demographics were similar between the M+G (n=24), P+G (n=13) and Px+G (n=14) cohorts. By mFACS, M+G mobilized a 5.5 fold higher absolute number (#) of HSCs, multipotent progenitors (MPP) and common myeloid progenitors (CMP) vs P+G (p0.05). 1D9 binding to CXCR4 on CD34+ HSPCs was similar between all 3 arms (p-values 0.45-0.75). 12G5 binding (which competes with CXCR4i's for binding to CXCR4) was significantly lower with M+G (MFI:11) vs P+G (MFI:74; p By scRNA seq, UMAP clustering identified 3 transcriptionally similar HSC sub-clusters (HSC-I, -II and -III) mobilized by all 3 regimens; and 1 distinct HSC-PL cluster mobilized by P+G expressing heat shock protein genes (HSPA1 A/B) (Figure 1C). Differentially expressed genes (DEGs) of HSCs I-III included CD52, FTH1, HLA-E, KLF2 and LMNA. AVP was unique to HSC-I while EGR1, JUN and ZFP36 were unique to HSC-III. MPPs clustered into 3 sub-clusters (MPP-I, -II and -III). MPP-I clustered closely to HSC-II/III with low expression of genes of differentiation. MPP-II expressed DEGs (PLEK) on a continuum toward megakaryocyte-erythroid progenitors (MEP-I/II), which expressed DEGs of erythroid differentiation (HBD/HBB). MPP-I and -II contained cells from all 3 regimens. However, MPP-III was specific to M+G with DEGs (MT-ATP8, HIST1H1) associated with monocyte, lymphocyte and NK cell differentiation. Conclusions: Extended CXCR4i with M+G mobilized significantly higher #s of combined CD34+ HSCs, MPPs and CMPs vs Px+G and P+G (p-values Figure 1 Figure 1. Disclosures Crees: BioLineRx Ltd.: Research Funding. Retting: BioLineRx Ltd.: Research Funding. Jayasinghe: WUGEN: Consultancy; MMRF: Consultancy. Vainstein: BioLineRx LTD: Current Employment. Sorani: BioLineRx LTD: Current Employment. Ickowicz: BioLineRx Ltd.: Current Employment. Shemesh-Darvish: BioLineRx LTD: Current Employment. Kadosh: BioLineRx Ltd.: Current Employment.

Background: Improving outcomes of PDAC with checkpoint inhibitors (CPIs) have been ineffective, underscoring the need to co-target alternative pathways. Preclinical data showed that CXCR4-SDF1 axis modulates the tumor microenvironment (TME) in PDAC and that CXCR4 inhibition enhances T cell access to the TME, increasing tumor sensitivity to CPIs. This was confirmed in the COMBAT Cohort 1 (CC1) study showing that the dual combination M+P increases activated CD8+ T cells and decreases myeloid derived suppressor cells (MDSCs) within the TME. Moreover, our pre-clinical studies showed that adding C to M+P resulted in improved efficacy vs C alone. The COMBAT Cohort 2 (CC2) aims to test the safety and efficacy of the triple combination of M+P+C in 2L mPDAC. Methods: Single arm phase 2a study in mPDAC. In cohort 2, patients with stage IV PDAC at diagnose who had progressed to 1L gemcitabine-based C received 5 days M priming, followed by M BIW + P Q3W plus C [Irinotecan liposomal injection/5-FU/LV (OFL)] Q2W. The primary endpoint was RR. Results: A total of 43 patients with stage 4 PDAC, 98% of whom were diagnosed with stage 4 disease, were enrolled. Median age was 68 (40-85) and 74.4% had liver disease. The safety profile was consistent with the individual profiles of each treatment alone. Of note, the incidence of ≥G3 neutropenia (G3Neu) was 7% and ≥G3 infection was 7%, which is lower than expected for C (OFL) alone (20% and 17%, respectively). The levels of T-cells increased during M priming and returned to normal values, which remained stable across the study despite the OFL treatment. For the evaluable patients (N=38) the ORR was 21.1% with a 13.2% confirmed ORR (defined as two consecutive assessments showing PR) and a 63.2% DCR (PR+SD). Median duration of clinical benefit was 5.6 months. Median OS and PFS were 6.5 months and 4.0 months, respectively (6.6 months and 3.8 months, respectively, for the ITT population). Conclusions: The triple combination of M+P+C is tolerable and shows encouraging results with cORR 13.2%, mPFS 4.0 months and mOS 6.5 months (compared to 7.7%, ~3 months and 4.7 months, respectively, on a historical basis for OFL alone in the stage 4 diagnosis subpopulation). SD of 42.1% and DCR of 63.2% were also higher than historical data on SoC chemotherapy used in 2L patients. The incidence of severe neutropenia and infections is lower than the historical data on C. The results from the CC2 suggest that M+P may expand the efficacy and safety benefit of OFL in PDAC, and warrants further investigation in a randomized study. Citation Format: Manuel Hidalgo, Teresa Macarulla, Valerya Semenisty, Erkut Borazanci, Jaime Feliu, Mariano Ponz-Sarvise, David Gutierrez Abad, Paul Oberstein, Angela Alistar, Andres Muñoz, Ravit Geva, Carmen Guillén-Ponce, Mercedes Salgado Fernandez, Amnon Peled, Marya Chaney, Irit Glicko-Kabir, Liron Shemesh-Darvish, Debby Ickowicz, Ella Sorani, Shaul E. Kadosh, Abi Vainstein-Haras, Bruno Bockorny. A multi-center phase 2a trial of the CXCR4 inhibitor motixafortide (BL-8040) (M) in combination with pembrolizumab (P) and chemotherapy (C), in patients with metastatic pancreatic adenocarcinoma (mPDAC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT177.

Purpose: The potential of the high-affinity CXCR4 antagonist BL-8040 as a monotherapy-mobilizing agent and its derived graft composition and quality were evaluated in a phase I clinical study in healthy volunteers (NCT02073019). Experimental Design: The first part of the study was a randomized, double-blind, placebo-controlled dose escalation phase. The second part of the study was an open-label phase, in which 8 subjects received a single injection of BL-8040 (1 mg/kg) and approximately 4 hours later underwent a standard leukapheresis procedure. The engraftment potential of the purified mobilized CD34+ cells was further evaluated by transplanting the cells into NSG immunodeficient mice. Results: BL-8040 was found safe and well tolerated at all doses tested (0.5–1 mg/kg). The main treatment-related adverse events were mild to moderate. Transient injection site and systemic reactions were mitigated by methylprednisolone, paracetamol, and promethazine pretreatment. In the first part of the study, BL-8040 triggered rapid and substantial mobilization of WBCs and CD34+ cells in all tested doses. Four hours postdose, the count rose to a mean of 8, 37, 31, and 35 cells/μL (placebo, 0.5, 0.75, and 1 mg/kg, respectively). FACS analysis revealed substantial mobilization of immature dendritic, T, B, and NK cells. In the second part, the mean CD34+ cells/kg collected were 11.6 × 106 cells/kg. The graft composition was rich in immune cells. Conclusions: The current data demonstrate that BL-8040 is a safe and effective monotherapy strategy for the collection of large amounts of CD34+ cells and immune cells in a one-day procedure for allogeneic HSPC transplantation. Clin Cancer Res; 23(22); 6790–801. ©2017 AACR.

BackgroundTreatments that generate T cell-mediated immunity to a patient’s unique neoantigens are the current holy grail of cancer immunotherapy. In particular, treatments that do not require cumbersome and individualized ex vivo processing or manufacturing processes are especially sought after. Here we report that AGI-134, a glycolipid-like small molecule, can be used for coating tumor cells with the xenoantigen Galα1-3Galβ1-4GlcNAc (α-Gal) in situ leading to opsonization with pre-existing natural anti-α-Gal antibodies (in short anti-Gal), which triggers immune cascades resulting in T cell mediated anti-tumor immunity.MethodsVarious immunological effects of coating tumor cells with α-Gal via AGI-134 in vitro were measured by flow cytometry: (1) opsonization with anti-Gal and complement, (2) antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells, and (3) phagocytosis and antigen cross-presentation by antigen presenting cells (APCs). A viability kit was used to test AGI-134 mediated complement dependent cytotoxicity (CDC) in cancer cells. The anti-tumoral activity of AGI-134 alone or in combination with an anti-programmed death-1 (anti-PD-1) antibody was tested in melanoma models in anti-Gal expressing galactosyltransferase knockout (α1,3GT−/−) mice. CDC and phagocytosis data were analyzed by one-way ANOVA, ADCC results by paired t-test, distal tumor growth by Mantel–Cox test, C5a data by Mann–Whitney test, and single tumor regression by repeated measures analysis.ResultsIn vitro, α-Gal labelling of tumor cells via AGI-134 incorporation into the cell membrane leads to anti-Gal binding and complement activation. Through the effects of complement and ADCC, tumor cells are lysed and tumor antigen uptake by APCs increased. Antigen associated with lysed cells is cross-presented by CD8α+ dendritic cells leading to activation of antigen-specific CD8+ T cells. In B16-F10 or JB/RH melanoma models in α1,3GT−/−mice, intratumoral AGI-134 administration leads to primary tumor regression and has a robust abscopal effect, i.e., it protects from the development of distal, uninjected lesions. Combinations of AGI-134 and anti-PD-1 antibody shows a synergistic benefit in protection from secondary tumor growth.ConclusionsWe have identified AGI-134 as an immunotherapeutic drug candidate, which could be an excellent combination partner for anti-PD-1 therapy, by facilitating tumor antigen processing and increasing the repertoire of tumor-specific T cells prior to anti-PD-1 treatment.

Effective hematopoietic cell transplantation relies upon collecting adequate numbers of CD34+ hematopoietic stem cells, typically from peripheral blood. A minimum of ≥2 × 106 CD34+ cells/kg are necessary, while transplants of ≥5–6 × 106 CD34+ cells/kg are associated with improved hematopoietic recovery. Granulocyte colony stimulating factor (G-CSF) remains the gold standard for hematopoietic stem cell mobilization. However, in randomized trials for autologous-hematopoietic cell transplantation in multiple myeloma, approximately 45% of patients remain unable to optimally mobilize with G-CSF alone despite multiple injections and apheresis days. Therefore, reducing mobilization failures remains an unmet need. The study objective is to evaluate the superiority of one dose of BL-8040 plus G-CSF over placebo plus G-CSF to mobilize ≥6.0 × 106 CD34+ cells/kg in up to two apheresis days. ClinicalTrials.gov: NCT03246529

Additional file 1: Figure S1. Compound structures. (A) AGI-134 (functional head group is a galactose-α-1,3-galactosyl-beta-1,4-N-acetyl-glucosamine: α-Gal); (B) FSL-Fluorescein (functional group is fluorescein); (C) FSL-A (functional group is N-acetyl-galactosamine-α-1,3-fucosyl-α-1,2-galactose: blood group A antigen).

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy that accounts for 10-15% of pediatric and 25% of adult ALL cases. Prior studies have established that most cases pf T-ALL are addicted to CXCR4 signaling. Indeed, strong preclinical data demonstrating therapeutic activity of BL-8040, a potent CXCR4 antagonist, have led to a clinical trial of BL-8040 in combination with nelarabine for patients with relapsed/refractory T-ALL (NCT02763384). However, the molecular mechanisms by which CXCR4 blockade induces T-ALL cell death are unknown. Using a human T-ALL xenotransplantation model, we previously reported that treatment with BL-8040 killed T-ALL cells through a non-apoptotic mechanism. Transcriptome sequencing revealed that BL-8040 induced alterations in genes involved in oxidative phosphorylation and carbohydrate metabolism. Indeed, seahorse experiments show that BL-8040 markedly reduced both oxidative phosphorylation and glycolysis. However, metabolic tracing studies using 13C-labeled glucose show that BL-8040 treatment does not have a major effect on the contribution of glucose to either glycolysis or the citric acid cycle. Instead, the major alteration observed is the reduced entry of glucose into the pentose phosphate pathway (PPP). A major function of the PPP pathway is to generate NADPH, which regulates reactive oxygen species (ROS) by producing reduced glutathione (GSH). Indeed, BL-8040 treatment resulted in a significant decrease in the ratio of reduced glutathione to oxidized glutathione. Together, these data suggest that BL-8040 induces oxidative stress by inhibiting GSH production. One mechanism utilized by cancer cells to regulate GSH levels and oxidative stress is the system xc- amino acid antiporter that mediates the exchange of extracellular L-cystine and intracellular l-glutamate across the plasma membrane, resulting in the production of GSH and oxidative protection. We measured L-cystine levels in the media of T-ALL cells cultured for 24 hours with or without BL-8040. A significant decrease in L-cystine in the media was observed. These data, along with increased expression of the xc- transporter (SLC7A11), suggested that increased system xc- activity was compensating for the loss of GSH induced by BL-8040. To test this possibility, we cultured T-ALL cells in L-cystine deficient media. Loss of L-cystine in the media resulted in a modest decrease in T-ALL cell viability that was markedly increased, in a synergistic fashion, upon treatment with BL-8040. Interestingly, caspase 3 was not activated, suggesting that, similar to in vivo results, BL-8040 induces a non-apoptotic cell death. This observation, coupled with the reduction in GSH, suggested the hypothesis that BL-8040 induces ferroptosis. Consistent with the hypothesis, treatment of T-ALL cells with ACXT-3102, a novel system xc- inhibitor, significantly enhanced BL-8040 killing of T-ALL cells in vitro. Collectively, these data suggest that T-ALL cells are sensitive to perturbations of the glutathione axis. Combined inhibition of CXCR4 signaling and system xc- activity exploits this vulnerability and presents a promising new therapeutic approach for T-ALL. Disclosures Uy: Astellas Pharma: Honoraria; Jazz Pharmaceuticals: Consultancy; Genentech: Consultancy; Agios: Consultancy; Pfizer: Consultancy; Daiichi Sankyo: Consultancy. Sorani:BiolineRx Ltd: Current Employment. Vainstein:BiolineRx Ltd: Current Employment. Davish:BiolineRx Ltd: Current Employment. Hawkins:Accuronix Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Background: We recently conducted a clinical trial assessing Pembrolizumab (P) and BL-8040 (BL) in patients with pancreatic cancer. We prospectively collected serial biopsies to help understand the impact of this treatment on the tumor microenvironment (TME). Methods: Twenty patients were enrolled and were treated with BL8040 (1.25mg/kg) monotherapy for 2 weeks followed by dual therapy with BL8040 (d1, 4, 8, 11) plus Pembrolizumab (200 mg IV, d1) every 3 weeks. Biopsies were collected at baseline (T0) and during therapy. Some patients had biopsies after BL monotherapy (Tm) and some after combined therapy (Tc) due to a protocol change mid-study. Malignant cells expressing PD-L1 were assessed using immunohistochemistry (IHC) and TME was studied using 3 multiplex immunofluorescence panels including one each for T-cells subpopulations, macrophages and myeloid-derived suppressor cells (MDSCs). Median densities of the different phenotypes were analyzed in tumor and stromal compartments and correlated with serial biopsies. Results: Of 20 patients enrolled and 15 were evaluable for response of whom 2 had stability and 1 had a partial response. 17 patients had at least one viable biopsy; 4 had biopsies at T0 and Tm, 3 had biopsies at T0, Tm, and Tc, and 2 had biopsies at T0 and Tc. In general, we noted that cytotoxic T cells increased from baseline when measured at Tm or Tc. In contrast, MDSC counts and overall T cells decreased at Tm or Tc from baseline. Additionally, we saw an increase in CD 68+ and PD-L1 expressing macrophages (P=0.059 and P=0.046, respectively). Patients who had clinical benefit (PR/SD) had greater numbers of cytotoxic T-cells (CD3+CD8+, median, 226.08 cells/mm2) and regulatory T cells (CD3+FOXP3+, median, 48.20 cells/mm2) at baseline than PD patients (median, 26.15 cells/mm2, P=0.03; 13.31 cells/mm2, P=0.016, respectively). Conversely, at T0, the lowest numbers of tumor cytotoxic T-cells activated CD3+CD8+GB+ (median, 0.34 cells/mm2) and highest numbers of PMN-cells (CD66b+CD11b+, median, 16.66 cells/mm2) were observed in patients with PD when compared with PR or SD (median, 4.54 cells/mm2, P=0.097; 3.38 cells/mm2, P=0.023, respectively), suggesting that highest densities of PMN-cells may contribute to downregulation of T-cells in those cases. Conclusions: Higher cytotoxic T-cells or PMN-cell counts at T0 may predict changes in the TME and radiologic response to treatment with BL8040+Pembrolizumab therapy in metastatic pancreatic cancer. PMN-cells may play a role promoting immune suppression of T-cells, increase the risk of metastasis and interfering with the treatment. Trial Registration: NCT02907099, Ethics Approval: This study was approved by the M.D. Anderson Institutional Review Board, approval number 2016-0410. Citation Format: Carmelia M. Noia Barreto, Debora A. Ledesma, Swati Gite, Luisa M. Solis, Mei Jiang, Renganayaki K. Pandurengan, Robert Wolff, Milind Javle, Shubham Pant, Gauri Varadhachary, Rachna Shroff, Abi Vainstein-Haras, Ella Sorani, Tzipora M. Lustig, Osnat Kashtan, Yosi Gozlan, Steven M. Townson, Jeanne M. Fahey, James Yao, Ignacio I. Wistuba, Michael Overman, David Fogelman, Edwin R. Parra. High cytotoxic T-cell or polymorphonuclear cell infiltrates in the tumor microenvironment correlate with responses to BL8040 plus pembrolizumab combination therapy in metastatic pancreatic tumors: Scientific correlates of a phase II clinical trial [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT204.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy that accounts for 10-15% of pediatric and 25% of adult ALL cases. CXCL12 is a CXC chemokine that is constitutively expressed at high levels in the bone marrow. CXCR4 is the major receptor for CXCL12 and is by far the most highly expressed chemokine receptor on T-ALL cells. Two groups recently showed that genetic loss of CXCR4 signaling in murine or human T-ALL cells markedly suppressed their growth in vivo. We previously reported that BL-8040, a potent new CXCR4 antagonist with sustained receptor occupancy, is active as monotherapy against T-ALL in mice. Indeed, a 2-week course of daily BL-8040 resulted in a median reduction in tumor burden of 32.1-fold (range 6.8 to 176) across 5 different T-ALL xenografts. Preliminary data from a clinical trial of BL-8040 plus nelarabine for relapsed T-ALL also suggest therapeutic activity, with a complete remission rate observed in 4/8 patients (50%), which compares favorably to published response rates of approximately 30% with single agent nelarabine. Here, we explore molecular mechanisms by which CXCR4 blockade induces T-ALL death. NOD-scid IL2Rgammanull (NSG) mice were injected with P12-Ichikawa cells, a T-ALL cell line modified to express click beetle red luciferase and GFP. Following T-ALL engraftment, mice were treated with a single dose of BL-8040, and then leukemic cells in the bone marrow harvested 24-48 hours later. Treatment with BL-8040 resulted in a marked suppression of Akt and Erk1/2 phosphorylation, suggesting that signaling through CXCR4 is the major source of PI3 kinase pathway activation in T-ALL cells. Surprisingly, treatment with BL-8040 did not affect cellular proliferation, as measured by Ki67/FxCycle Violet staining or by EdU labeling. Moreover, no increase in apoptosis, as measured by annexin V or activated caspase 3 expression, was observed. These data suggest that CXCR4 blockade induces a non-apoptotic cell death. To explore this possibility further, we performed transcriptome sequencing on T-ALL cells recovered from mice 24 hours after 1 dose of BL-8040. A total of 151 differentially expressed genes (FDR of < 0.05% and ≥ 2-fold change) were identified. Gene set enrichment analysis was strongly positive for alterations in oxidative phosphorylation, ribosome biogenesis, and carbohydrate metabolism. Ribosome function was assessed using O-propargyl-puromycin (OPP), which monitors global protein translation. No difference in global protein synthesis in T-ALL cells was observed after CXCR4 blockade in vivo. T-ALL cells are dependent on glutamine as a source of carbon, and PI3 kinase signaling positively regulates glutaminolysis. Thus, we hypothesized that CXCR4 blockade may induce T-ALL cell death by reducing glutamine metabolism. However, treatment of T-ALL cells in vitro with BL-8040 did not alter the cellular levels of glutamine or glutamate, as measured using a commercial bioluminescent assay. Confirmatory metabolic tracing studies using 13C-labeled glutamine and glucose are in progress. Finally, to explore the reduction in oxidative phosphorylation, we examined mitochondria function using Mitotracker Green. Treatment of T-ALL cells in vitro with BL-8040 for 24-48 hours induced a significant decrease in mitochondria number, suggesting induction of mitophagy. Collectively, these data suggest that T-ALL cells are addicted to CXCR4 signaling in vivo. CXCR4 blockade with BL-8040 induces a non-apoptotic cell death that is characterized by a loss of mitochondria. Disclosures Uy: Astellas: Consultancy; Pfizer: Consultancy; Curis: Consultancy; GlycoMimetics: Consultancy. Bohana-Kashtan:BiolineRx: Employment, Equity Ownership. Sorani:BiolineRx: Employment, Equity Ownership. Vainstein:BiolineRx: Employment, Equity Ownership.

Background: The chemokine receptor, CXCR4, mediates the trafficking and retention of hematopoietic stem cells to the marrow through its interaction with the chemokine, CXCL12. CXCR4 is the most highly expressed chemokine receptor on T-ALL cells, and preclinical data demonstrate that CXCR4 is critical for the growth and survival of T-cell acute lymphoblastic lymphoma (T-ALL). Genetic loss or pharmacologic blockade of CXCR4 signaling suppresses T-ALL cell growth and leukemia initiating activity in murine models. BL-8040 is a novel synthetic peptide antagonist of the chemokine receptor, CXCR4. Compared to other CXCR4 inhibitors, BL-8040 is a more potent mobilizer of normal HSCs with sustained occupancy and inhibition of CXCR4. We previously reported that BL-8040 potently suppresses T-ALL cell growth in xenotransplantation models of T-ALL. To test the efficacy of BL-8040 in T-ALL by conducting a multicenter, open label pilot study of BL-8040 in combination with nelarabine in patients with relapsed or refractory disease (ClinicalTrials.gov: NCT0276338). Methods: Adults with relapsed or refractory T-ALL/LBL, age ≥18 years and ECOG PS ≤2, were eligible for the study. A peripheral blood lymphoblast count ≤50,000/mm3 was required prior to starting treatment. During cycle 1, subjects received daily subcutaneous administration of BL-8040 1.5 mg/kg from Day 1 to Day 6 with nelarabine 1,500 mg/m2 intravenously over 2 hours on Days 2, 4 and 6. In subsequent 21-day cycles, BL-8040 1.5 mg/kg was administered daily on days 1-5 with nelarabine 1,500 mg/m2 given on days 1, 3 and 5. Up to 4 cycles of treatment was allowed. Results: Nine patients with median age of 29 years (range 20-75) have been enrolled in the study out of which including fout patients were in untreated 1st relapse, one in 2nd relapse, two with relapsed and refractory disease, and two primary refractory patient. Two patients had failed prior allogeneic hematopoietic cell transplant. The rate of complete remission is 56% (5/9) with all responses occurring after 1 cycle of treatment. Adverse events occurred in 2 subjects requiring dose modification. Consistent with the known mechanism of BL-8040, one subject developed G3 leukocytosis after BL-8040 administration with the peripheral WBC increasing from 5.3 to 273 h/mm3 with evidence of spontaneous tumor lysis requiring interruption of BL-8040 and leukapheresis. A second patient developed injection site pain requiring omission of the final dose of BL-8040. Peripheral blood analyzed at baseline and 24 hours after the first dose of BL-8040 (prior to nelarabine) showed the following: 1) sustained blockade of CXCR4 on leukemic blasts; 2) mobilization of leukemic blasts into the blood; and 3) no induction of leukemia blast apoptosis as measured by activated caspase 3 expression. Conclusions: BL-8040 can be combined with nelarabine in subjects with relapsed or refractory T-ALL with encouraging CR rates. Evidence of on target effects on CXCR4 has been observed in this study with sustained CXCR4 receptor occupancy at 24 hours after administration along with tumor mobilization of ALL blasts into the peripheral circulation. Disclosures Uy: Astellas: Consultancy; Pfizer: Consultancy; Curis: Consultancy; GlycoMimetics: Consultancy. Kadia:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Bioline RX: Research Funding; BMS: Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Research Funding. Stock:Astellas: Membership on an entity's Board of Directors or advisory committees; Daiichi: Membership on an entity's Board of Directors or advisory committees; Research to Practice: Honoraria; UpToDate: Honoraria; Agios: Membership on an entity's Board of Directors or advisory committees; Kite, a Gilead Company: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees. Brammer:Verastem, Inc: Research Funding; Viracta Therapeutics, Inc.: Research Funding; Bioniz Therapeutics, Inc.: Research Funding. Bohana-Kashtan:BiolineRx: Employment, Equity Ownership. Vainstein:BiolineRx: Employment, Equity Ownership. Sorani:BiolineRx: Employment, Equity Ownership. Chen:BiolineRx: Employment. DiPersio:Bioline Rx: Research Funding, Speakers Bureau; Macrogenics: Research Funding, Speakers Bureau; Celgene: Consultancy; Amphivena Therapeutics: Consultancy, Research Funding; Magenta Therapeutics: Equity Ownership; NeoImmune Tech: Research Funding; RiverVest Venture Partners Arch Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Cellworks Group, Inc.: Membership on an entity's Board of Directors or advisory committees; WUGEN: Equity Ownership, Patents & Royalties, Research Funding; Incyte: Consultancy, Research Funding; Karyopharm Therapeutics: Consultancy. OffLabel Disclosure: BL-8040 for ALL

Background. Mobilized hematopoietic stem/progenitor cells (HSPCs) are the most commonly used graft source for hematopoietic cell transplantation (HCT). Current practices for harvesting HSPCs with G-CSF and/or plerixafor are costly, involve a multi-day procedure with suboptimal HSPC yields in up to 30% of patients and are associated with some morbidity and mortality. Here, we sought to test BL-8040, a high affinity CXCR4 antagonist with rapid mobilizing kinetics and long receptor occupancy, in donors for allogeneic HCT (alloHCT). Methods. The primary endpoint was to assess the efficacy of a single injection of BL-8040 to mobilize ≥ 2 x 106 CD34+ cells/kg of recipient weight after no more than two leukapheresis (LP) collections. Donors received BL-8040 by subcutaneous (SC) injection 3 hours prior to LP on day 1. The study was conducted in 2 parts. Part 1 enrolled HLA-identical pairs and 14 donors were treated with 1 mg/kg BL-8040. Part 2 enrolled HLA-identical and haploidentical pairs and treated 11 donors with 1.25 mg/kg BL-8040. When < 5x106 CD34+ cells/kg recipient weight were collected, a second injection of BL-8040 and LP collection was performed the next day. Immunophenotyping of lymphoid, myeloid, and HSPC subsets in the blood and LPs was performed by flow cytometry. Results. 25 donor-recipient pairs were enrolled in the study. The median age of donors was 55 years (range 20-69); 18 were fully HLA-matched siblings, and 7 were haploidentical donors. One donor was replaced per protocol because of problems with vascular access. All 11 donors treated at the 1.25 mg/kg dose and 22/24 (92%) patients overall collected the minimum goal of 2 x 106 CD34+ cells/kg recipient weight in 2 LPs. 9/11 donors treated with 1.25 mg/kg BL-8040 collected the target of 5 x 106 CD34+ cells/kg recipient weight. The median CD34+ cell count was 15 cells/µL blood at 3-4 hours after BL-8040 and was maintained for > 24 hours. BL-8040-adverse related events consisted primarily of grade 1-2 injection site reactions and transient systemic reactions (hives). Recipients were a median of 58 years of age (26-71) with an ECOG PS of 0-2 undergoing alloHCT for AML (n=16, 64%), ALL (n=4, 16%), MDS (n=3, 12%), MPN (n=1, 4%) or Hodgkin lymphoma (n=1, 4%). 22 recipients were transplanted with BL-8040-mobilized grafts. Time to neutrophil engraftment occurred at a median of 13 days (n=22, range 11-26) and platelet engraftment occurred at a median of 20 days (n=20, range 15-41; no platelet nadir for 1 pt and no engraftment in 1 pt). With a median follow-up of 258 days, 5 deaths have been observed on study. These deaths were due to sepsis (Day +84), complications of sepsis in setting of grade 3 GVHD (Day+67), AML relapse (Day+143,+166), and complications of intrabdominal infection (Day+252). Grade II acute GVHD was observed in 2/22 recipients (9%) both of which resolved. Grade III-IV GVHD was observed in 5 out of 22 recipients (23%), of which 3 resolved. Flow cytometric evaluation of HSPCs purified from LPs by CD34 immunoselection revealed that BL-8040 preferentially mobilized CD34+ plasmacytoid dendritic cell (pDC) precursors (pre-pDCs) that express high levels of CXCR4 (Fig. 1A). These pre-pDCs are the immediate progenitors of pDCs; a distinct DC population capable of producing large amounts of type 1 interferons in response to viral infections. In contrast to plerixafor, BL-8040 remained bound (as determined by inhibition of anti-CXCR4 binding) to CXCR4 on all lymphoid, myeloid, and HSPCs after LP (Fig. 1B and data not shown). BL-8040 induced pan-mobilization of all major myeloid and lymphoid subsets, with maximum relative changes in the absolute numbers of circulating pDCs, B cells, basophils, myeloid DCs (mDCs), CD8+ T cells and CD14+HLA-DR+CD16lo classical monocytes (Fig. 1C). In general, the magnitude of mobilization of each subset correlated with the level of surface CXCR4 at baseline (Fig 1C, gray bars, R2 = 0.4; P = 0.02). Although there was pan mobilization of all CD8+ and CD4+ T cell subsets, BL-8040 preferentially mobilized naïve and central memory CD8+ T cells relative to the other T cell subsets (Fig. 1D). Conclusions. Treatment of normal donors with a single dose of BL-8040 results in rapid and sustained mobilization of HSPCs for use in allogeneic transplant. BL-8040 mobilized grafts result in rapid and reliable engraftment in transplant recipients. Additional data is required to assess the impact of BL-8040-mobilized grafts on rates of GVHD and relapse. Disclosures Rettig: Novimmune: Research Funding; Amphivena Therapeutics: Research Funding. Uy:Curis: Consultancy; GlycoMimetics: Consultancy. Devine:Kiadis Pharma: Consultancy. Jaglowski:Juno: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Kite Pharma: Consultancy, Research Funding. Vainstein:BioLineRx Ltd.: Employment. Sorani:BioLineRx Ltd.,: Employment. Chen:BioLineRx Ltd.,: Employment. Bohana-Kashtan:BioLineRx Ltd.,: Employment, Equity Ownership; Cell Cure Neurosciences: Equity Ownership. Shaw:BioLineRx Ltd.: Employment, Equity Ownership.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy that accounts for 10-15% of pediatric and 25% of adult ALL cases. Approximately 20-25% of pediatric and 50% of adult patients with T-ALL relapse following induction therapy, and the prognosis after relapse is dismal, with 3-year event-free survival of only 10-15%. Thus, there is a clear unmet clinical need for better therapies for T-ALL. CXCL12 (stromal-derived factor-1, SDF1) is a CXC chemokine that is constitutively expressed at high levels in the bone marrow. CXCR4 is the major receptor for CXCL12 and is by far the most highly expressed chemokine receptor on T-ALL cells. Two groups recently showed that genetic loss of CXCR4 signaling in murine or human T-ALL cells markedly suppressed their growth in vivo. Here we explore the hypothesis that inhibition of the CXCR4 signaling with a potent new CXCR4 antagonist, BL-8040 alone, or in combination with ABT263 (navitoclax), a BCL2/BCLXL antagonist, will have therapeutic activity against T-ALL. To test this hypothesis, we xenotransplanted a human T-ALL cell line (P12/Ichikawa cells) or 5 different patient-derived T-ALL xenografts into non-irradiated NSG mice. In each case, the T-ALL cells were allowed to engraft and then mice were randomly assigned to one of four treatment groups: 1) vehicle control; 2) BL-8040 alone; 3) ABT263 alone; 4) combined BL-8040 and ABT263. Treatment was given for 2 weeks, and leukemia burden monitored weekly by bioluminescent imaging or by flow cytometry to quantify human CD45+ T-ALL cells in the blood. A minimum of 10 mice in each cohort from two independent experiments were analyzed (Figure 1). A significant reduction in T-ALL burden was observed in all T ALL samples after treatment with BL8040 alone, with a mean fold-decrease compared with control mice after 2 weeks of treatment of 966 ± 651 (range 16-3,486). Consistent with a prior report, the response to ABT263 alone was more variable, with responses seen in 4 of 6 T-ALL samples. All T-ALL samples had a marked response to the combination of BL-8040 and ABT263, with a mean fold decrease of 4,389 ± 2,602 (range, 139-15,199). A previous study suggested that inhibition of CXCR4 signaling may suppress Myc expression (Pitt et al, Cancer Cell, 2015), which is relevant, since overexpression of Myc secondary to mutations in the Notch pathway are common in T-ALL. However, we observed no difference in Myc protein expression or expression of Myc target genes following BL-8040 treatment. Consistent with this observation, treatment with BL8040 had no impact on the cell cycle status of T-ALL cells in vivo. Of note, we observed a marked decrease in Akt and Erk phosphorylation following BL8040, suggesting that CXCR4 signaling may regulate T ALL survival in vivo by suppressing these pathways. Conclusion. Collectively, these data suggest that BL-8040, either alone or in combination with ABT263, is highly active in T-ALL and support our ongoing clinical trial of BL-8040 in combination with nelarabine for patients with relapsed T-ALL (NCT02763384). Figure 1. Figure 1. Disclosures Uy: GlycoMimetics: Consultancy; Curis: Consultancy. Vainstein:Biolinerx: Employment. Sorani:BioLineRx Ltd.,: Employment. Bohana-Kashtan:BioLineRx Ltd.,: Employment, Equity Ownership; Cell Cure Neurosciences: Equity Ownership. Shaw:BioLineRx Ltd.: Employment, Equity Ownership.

73 Background: C-X-C chemokine receptor type 4 (CXCR4) helps to retain the hematopoietic stem cells (HSC) in the bone marrow (BM). CXCR4 binds to its ligand CXCL12/SDF1 which is constitutively expressed in the BM thereby inhibiting the mobilization of CXCR4 expressing immune progenitor cells. Moreover, increased numbers of effector cells in the tumor microenvironment (TME) are directly correlated to enhanced immunotherapeutic efficacy. Therefore, we hypothesized that CXCR4 antagonism will result in movement of immune progenitor cells from BM to periphery leading to increased availability of T-cells in the periphery and better infiltration of effector cells into the TME. Methods: In TC-1 mouse tumor-model, we tested the effects of CXCR4 antagonist (BL-8040; 4 doses; 24 h apart; 20 mg/kg) on the tumor growth and mice survival in the presence of tumor-specific antigen priming using E7 peptide vaccine (3 doses, one week apart). Anti-tumor immune responses were determined in the tumor tissues obtained 3-4 days after the second vaccination using flow cytometry. Results: We found that BL-8040 given with specific antigenic stimulation results in significantly enhanced anti-tumor immune response, leading to a decrease in tumor growth (p≤0.001 at day 21) and prolonged mice survival. At day 35 after tumor implantation, 80% of mice survived in the BL-8040 + vaccine treatment group compared to 0% survival following BL-8040 or vaccine treatments. Interestingly, we also found that BL-8040 leads to a significant increase in the numbers of antigen-specific CD8+ T-cells in the TME. We also found that starting BL-8040 prior to or together with the priming of the mice did not affect the outcome, suggesting that the scheduling of BL-8040 does not affect the therapeutic outcomes. Conclusions: These results suggest that BL-8040 treatment enhances anti-tumor immune response by potentially increasing the immune progenitor cells in the periphery leading to a better immune response. These results also suggest that BL-8040, a CXCR4 antagonist, is a promising immune-modulatory agent with potent anti-tumor effects.

276 Background: BL-8040 is a novel CXCR4 antagonist being developed for multiple oncology indications. Preclinical studies demonstrated that BL-8040 increases the number of immune cells in peripheral blood and promotes CD8+ T cell infiltration into orthotropic pancreatic mouse tumors, reducing tumor load. BL-8040 is being evaluated in a Phase 2a, multicenter, open label trial in patients with metastatic pancreatic cancer (the COMBAT study). Patients are undergoing a 5-day period of monotherapy in which they receive daily doses of BL-8040, followed by 21-day cycles in which patients receive one dose of pembrolizumab and 3 doses/week of BL-8040 until disease progression or discontinuation. To date, 32 patients have been enrolled. Methods: On Day 1 and Day 5, blood samples were taken at pre- and post-dosing, to evaluate peripheral immune cell subset frequency by flow cytometry. In addition, core biopsies were taken from liver metastases, where possible, to assess immune cell infiltration into tumors and the tumor microenvironment (TME). Results: Here we present interim PD biomarker data from the BL-8040 monotherapy portion of the trial. Flow cytometry shows that BL-8040 monotherapy caused an approximately two-fold reduction in frequency of peripheral T regulatory cells, but had no effect on the frequency of T cells, NKT cells or cell populations that contain B cells (CD3- CD56-). Additionally, BL-8040 remained bound to CXCR4 on peripheral immune cells throughout the period of monotherapy. Analysis of available biopsies (N = 7) shows an up to 15-fold increase in the CD3+ population, and up to two-fold increase of CD8+ cells, in the tumor periphery and TME of 43% (3/7) of the patients after five days of BL-8040 monotherapy compared to baseline. Conclusions: In summary, the PD biomarker results in humans support the proposed mechanism of action for BL-8040 that was based on preclinical mouse models. Analysis of tumor biopsies is ongoing, with an emphasis on investigating the effects of BL-8040 on tumor-resident immune cells and the TME. Clinical trial information: NCT02826486.

68 Background: AGI-134 is a fully synthetic alpha-Gal glycolipid for intratumoral (i.t.) treatment of solid tumors to induce a patient-specific anti-tumor immune response. AGI-134 recruits pre-existing anti-Gal antibodies to the injected lesion, leading to complement activation and enhanced tumor antigen processing. Using the B16.F10 murine melanoma model, we have previously demonstrated that AGI-134 evokes a robust abscopal anti-tumor effect, with treatment of a primary lesion protecting mice from the growth of distant lesions. In the current study, we investigated the response of injected tumors to AGI-134 administration. Methods: Tumors were induced by s.c. injection of B16.F10 or ovalbumin expressing B16 (B16.OVA) cells into the flank of α1,3galactosyltransferase knock out mice. After reaching a treatable size, the tumors were injected twice, 24 hrs apart, with PBS or 1-1.25 mg AGI-134, and tumor growth monitored for up to 32 days. In addition, to measure the activation of complement after treatment with AGI-134, tumors were processed 2 hours after treatment and the i.t. concentration of complement fragment C5a determined by ELISA. Results: Almost 50% of AGI-134-treated B16.F10 tumors fully regressed vs. 24% in the PBS controls. Moreover, AGI-134 treatment had a significant survival benefit, with 23% of AGI-134-treated mice dying or requiring euthanisia due to tumor mass by Day 27 post treatment vs. 43% in the PBS groups (p < 0.05, Mantel-Cox test). In the B16.OVA model, 67% of the AGI-134 treated tumors fully regressed vs. 0% in PBS-treated mice in two independent assays. Comparison of C5a levels in B16.F10 tumors 2 hrs after AGI-134 or PBS treatment demonstrated that AGI-134 induced significant complement activation within injected tumors. Conclusions: Having previously shown that AGI-134 induces an abscopal effect that protects mice from the development of secondary tumors, we now show that AGI-134 also induces regression of injected tumors: AGI-134-treatment induces the activation of complement within the tumor and leads to complete regression of the tumor in significantly more AGI-134-treated mice than PBS-treated. Clinical trials with AGI-134 are planned for 2018.

TPS533 Background: Checkpoint inhibitors such as pembrolizumab are active against a variety of tumor types; however, pancreatic cancer patients generally do not see improvements in their disease from single agent treatment. Blocking CXCR4 may potentiate the activity of checkpoint inhibitors by (1) increasing mobilization of lymphocytes from bone marrow, (2) blocking production of SDF-1, in turn allowing better penetration of immune cells into the tumor, (3) reducing the entry of suppressor T cells into tumor, and (4) upregulating CCL20 in the tumor microenvironment, which may help attract dendritic cells into the tumor. We have launched a study combining BL8040, a CXCR4 antagonist, with pembrolizumab in order to determine the efficacy of this combination. Methods: Major inclusion criteria require patients with pancreatic adenocarcinoma whose tumors have progressed through at least one line of therapy. There must be sufficient disease to allow for pre- and post-treatment biopsy as well as measurement of response by RECIST criteria. Patients must be age 18 or older and ECOG 0-1. Liver function, renal, and hematologic criteria are fairly rigorous. Major exclusion criteria include patients with viral infections or those who require supraphysiologic steroid use. Treatment includes a two week cycle of single agent BL-8040 given on days 1-5 and 8-12. Cycles 2 and beyond include treatment on day 1 with pembrolizumab, 200 mg flat dose, plus BL-8040 given SQ on days 1,4,8, and 11 of a two week cycle. The primary endpoint is response rate; other major clinical objectives include progression free and overall survival. Scientific correlates include assessments of immune cell infiltrates into tumor via histology and immunoflourescence, histological assessment of stromal components, and gene expression signatures. Blood is likewise being collected for serum cytokine analysis, circulating free DNA analysis, circulating tumor cells, and exosome analysis. Clinical trial information: NCT02907099.

Introduction: Lifelong blood cell production is dependent on rare hematopoietic stem cells (HSCs) to perpetually replenish mature cells via a series of lineage-restricted intermediates. The bulk of HSCs are CD34+, however, most CD34+ cells are lineage-restricted progenitors and HSCs remain rare. HSCs can be enriched further based on CD45RA, Thy1 (CD90), and CD38 expression. Loss of CD90 expression was proposed to be sufficient to separate CD34+CD38−CD45RA− CD90+ HSCs from CD34+CD38−CD45RA− CD90- multipotent progenitors (MPPs). Recently, it was demonstrated that the expression CD49f is a specific HSC marker. Single CD49f(+) cells were highly efficient in generating long-term multilineage grafts, and the loss of CD49f expression identified transiently engrafting MPPs. Results: CD34+ cells were purified from BL-8040 and G-CSF mobilized grafts and stained for CD38, CD45RA, CD90, and CD49f. The percentage of CD34+CD38- hematopoietic stem and progenitors was similar in both grafts (Figure 1A). However, whereas 23.2 % of BL-8040 mobilized CD34+ CD38- cells did not express CD45RA; only 1.6% of G-CSF mobilized CD34+ CD38- cells did not express CD45RA (Figure 1B). The percentages of CD34+CD38−CD45RA−CD49f+CD90+/-, CD34+CD38−CD45RA−CD49f+ CD90+, and CD34+CD38−CD45RA− CD90+ HPCS were increased significantly by 45, 25 and 12 -fold in the BL-8040 graft compared to G-CSF graft derived CD34+CD38- cells (Figure 1C). To assess the long-term engraftment potential of the BL-8040 mobilized CD34+ cells, engraftment was allowed for 4, 8, and 22 weeks after transplantation. Successful and robust long-term human engraftment of CD45+ and CD45+CD34+ cells was observed at week 22 (Figure 2A, 2B). The % of human CD45 cells remained stable in the BM whereas the percentage of CD45 cells in the blood and spleen increased at week 22 (Figure 2C). At 4 weeks, human CD3+CD4+ T cells were only observed at a low percentage in the spleen but not in the BM, whereas no significant percentage of CD3+CD8+ cells were found neither in the BM nor in the spleen (Figure 2D, 2E). 22 weeks after transplantation, the percentage of human CD3+CD4+ and CD3+CD8+ T cells was significantly increased in the spleen (30% vs. 5%, respectively) and to much lower levels in the BM (Figure 2D, 2E). Furthermore, successful and robust long-term human engraftment of secondary recipient was observed 14 weeks following the second transplantation (Figure 2A and 2B). Conclusion: In association with the high percentage of HPCs in the BL-8040-derived graft, we found a robust myeloid and lymphoid long-term engraftment (week 22) of BL-8040 mobilized human CD34+ cells in NSG mice. The ability of BL-8040 to collect high numbers of HPCs may be beneficial for a variety of HPCs dependent therapeutics. Disclosures Abraham: Biokine: Employment. Oberkovitz: BiolineRx: Employment. Eizenberg: Biokine: Employment. Vainstein: BiolineRx: Employment. Benami: BiolineRx: Employment. Golan: BiolineRx: Employment. Or: Bioline: Consultancy. Peled: Biokine: Consultancy; Biosight: Consultancy.

e14544 Background: Cancer cells affect their micro-environment by recruiting immune cells that support tumor growth, metastasis and inhibition of anti-tumor effector T and NK cell recruitment. In this study, we investigated the role of BL-8040, a CXCR4 antagonist in cancer immunotherapy and its ability to modulate the immunosuppressive tumor micro-environment. Methods: The effect of BL8040 on tumor micro-environment was tested in 3 different cancer mouse models: lung cancer, pancreatic cancer and melanoma. The mobilization of immune cells to the periphery in response to BL8040 was tested, as well as the accumulation of immune cells both within and surrounding the tumor in the pancreatic cancer mouse model. Results: BL8040 was found to be a potent and robust mobilizer of immune cells. Immunophenotyping of the mobilized cells revealed that the mobilization of CD4 and CD8 T lymphocytes, as well as of dendritic cells (DC), was significantly increased in the cancer-bearing mice compared to their naïve counterparts. Importantly, a significant mobilization of effector CD8 T cells and activated CD8 T cells in the cancer-bearing mice was also detected following BL8040 treatment. Concomitantly, in the pancreatic cancer mouse model, treatment with BL8040 increased CD8 T cell accumulation within the tumor and inhibited tumor growth. Conclusions: The immune cell population that is mobilized in response to BL8040 treatment is different in cancer mouse models and naïve mice. The ability of BL8040 to induce mobilization of leukocytes, cytotoxic and activated CD8 T cells and DCs is affected by the presence of a tumor. In our models of pancreatic cancer, mobilization of immune cells from the bone marrow into the circulation and their accumulation within the tumor and tumor microenvironment resulted in inhibition of tumor growth. These results indicate that BL8040 may affect the tumor microenvironment and therefore can potentially synergize with immunomodulatory agents. In vivo pre-clinical studies as well as clinical studies are currently ongoing for testing the combination of BL8040 with immunomodulatory agents in different cancer models.

Background: Persistence of minimal residual disease (MRD) after induction, consolidation and salvage therapies is an independent poor prognostic marker in AML. The bone marrow (BM) microenvironment is a protective niche that promotes chemotherapy resistance of leukemia cells. This residual subset of chemotherapy-resistant cells present during remission eventually contributes to the leukemia relapse/persistence. Adhesion of AML cells to BM stroma is dependent on the CXCR4 receptor binding to its ligand CXCL12. High levels of CXCR4 expression correlate with poor survival in AML. It is postulated that blocking the CXCL12/CXCR4 axis will dislodge AML cells from the protective microenvironment and, when combined with chemotherapy, may improve the response to therapy. BL-8040 (BKT140) is a short peptide which inhibits the binding of CXCR4 to CXCL12, resulting in mobilization of leukemic blasts from the BM to the peripheral blood (PB). BL-8040 has strong affinity for the CXCR4 receptor with long receptor occupancy and as a single agent induces differentiation and apoptosis of leukemia cells in preclinical models. A clinical trial assessing the safety and efficacy of BL-8040 in combination with cytarabine (Ara-C) for the treatment of relapsed/refractory AML patients was recently completed (NCT01838395). Here we report results from correlative studies done on samples from patients who participated in this trial. Objective: To assess BL-8040 single agent anti leukemia effects in relapsed/refractory AML. Method: Patients received a once daily SC dose of BL-8040 monotherapy on days 1-2 followed by the same dose of BL-8040 plus Ara-C (1.5g/m2 for patients ≥60; 3g/m2 for patients Results: 45 patients (including 3 receiving compassionate use BL-8040) with a median age of 61 yrs were treated. The majority of patients had poor risk disease with 24% secondary AML and 17% with prior allogeneic stem-cell transplantation. Most patients were heavily pretreated with 19% relapsing after a short first remission (CR1 ≤12 months), 17% had ≥2 relapses and 45% refractory to 1-2 inductions. The CR+CRi rate was 38% in subjects receiving BL-8040 dose ≥1.0 mg/kg (n=39). Ongoing follow-up (FU) of responding patients (expansion phase; N=19) shows median EFS of 9.3 months (range 4.3-12.8 months). At the time of this analysis 10/19 patients are alive with a FU range of 0.96 - 12.8 months. FACS analysis revealed that BL-8040 monotherapy triggered an average 4.3-fold increase of immature AML blasts (CD45+Low/CD34+/CD117+/HLA-DR+) in PB (i.e., mobilization). Response to treatment was associated with more robust mobilization of AML blasts following BL-8040 monotherapy (responders 9.5 vs non-responders 1.7 fold median). Preferential mobilization of AML blasts over normal cells (4.7 fold vs. 1.4 fold, respectively) was confirmed by FISH analysis in a subset of patients with informative cytogenetic abnormalities. Induction of granulocytic differentiation of immature leukemia progenitors (2.5 fold) in the BM following BL-8040 monotherapy was noted. Finally, induction of AML blasts apoptosis (40% increase) by BL-8040 alone was evident by FACS in day 3 (pre-araC) bone marrow biopsies. Conclusions: The data demonstrate that sustained blockade of the CXCR4-CXCL12 axis with BL-8040 is safe and well tolerated and when given in combination with Ara-C improves the response rate achieved historically with Ara-C alone. In addition, treatment with BL-8040 as a single agent rapidly and efficiently induces mobilization, differentiation and cell death of AML blasts. This selective effect on chemotherapy-resistant cells may be translated into reduction of residual disease arguing for incorporation into front-line trials and such studies are ongoing. Disclosures Foran: Millennium Pharmaceuticals, Inc.: Research Funding; medscape: Honoraria; karyopharm: Honoraria; pfizer: Honoraria; novartis: Honoraria; boehringer ingelheim: Research Funding; agios: Research Funding; Cellerant: Research Funding. DiPersio:Incyte Corporation: Research Funding. Peled:Biokine Therapeutics: Employment. Abraham:Biokine Therapeutics Ltd: Employment. Pereg:BioLineRx Ltd: Employment. Vainstein:BioLineRx Ltd.: Employment. Oberkovitz:BioLineRx Ltd.: Employment. Aharon:BioLineRx Ltd.: Employment. Cortes:ARIAD: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Teva: Research Funding.

Background: The bone marrow (BM) niche protects acute myeloid leukemia (AML) cells from chemotherapy. BM homing of AML cells is dependent on CXCR4 and its ligand CXCL12; high levels of CXCR4 expression correlate with poor survival in AML. It is postulated that blocking the CXCL12/CXCR4 axis with a potent CXCR4 antagonist will disrupt the interaction of the leukemic blasts with the BM and augment the anti-leukemic effect of chemotherapy. BL-8040 (BKT140) is a short synthetic peptide which inhibits the binding of CXCR4 to CXCL12, resulting in the mobilization of leukemic blasts from the bone marrow to the peripheral blood. BL-8040 also inhibits CXCR4/CXCL12 mediated pro-survival ERK/Akt signaling and alters balance of pro/anti-apoptotic Bcl-2 proteins. BL-8040 has strong affinity for the CXCR4 receptor with long receptor occupancy, and, in contrast to other CXCR4 inhibitors, as a single agent induces apoptosis of leukemia cells ex-vivo in clinical samples. A clinical trial assessing the safety and efficacy of BL-8040 in combination with cytarabine (Ara-C) for the treatment of adult relapsed/refractory AML patients is currently ongoing (NCT01838395). Objective: To assess the safety, efficacy and pharmacodynamics/pharmacokinetic parameters of BL-8040 in combination with Ara-C in first or second relapse and refractory AML patients. Method: The study includes a dose escalation phase (3+3 design) followed by an expansion phase. Each patient receives a once daily SC dose of BL-8040 monotherapy on days 1-2 followed by the same dose of BL-8040 plus Ara-C (1.5 g/m2 for patients ≥60; 3 g/m2 for patients Results: Twenty two patients (median age, 61 y; range, 43-74 y) with relapsed/refractory AML were treated during the escalation phase. BL-8040 was escalated up to 1.5 mg/kg (recommended phase 2 dose) without reaching the MTD. Combination of BL-8040 with Ara-C was safe and well tolerated at all doses tested. Only one SAE (Sweet Syndrome) was reported as possibly related to study drug. The primary treatment related AEs were transient injection site and systemic reactions. The composite complete remission including complete remission (CR) and complete remission with incomplete blood count recovery (CRi) rate was 38% in subjects receiving BL-8040 doses of 1 mg/kg and higher (n=16). Two days of BL-8040 monotherapy triggered an average 40.2-fold (range 1.0-350.9) mobilization of immature AML progenitors (CD45+Low/CD34+/CD117+/HLA-DR+) from the BM to the PB. Moreover, a significant apoptotic effect on the immature leukemia progenitors in the BM following 2 days of BL-8040 monotherapy was noted. Flow cytometric evidence of apoptosis by BL-8040 was corroborated by an increase in cleaved caspase 3 positive blasts in day 3 bone marrow biopsies. In addition, BL-8040 treatment resulted in a median decrease of 57.7% (range, -10.4% to -96.2%) in the number of BM Leukemia progenitor cells (CD45+Low/CD34+/CD117+/HLA-DR+ out of total CD45+/CD34+ normal/progenitor cells) compared with the baseline biopsy. This decrease was accompanied with a 3.1 fold increase in granulocytes in the day 3 BM biopsy supporting differentiation effect. Finally, long receptor occupancy (up to 24 hours post dosing) was confirmed by FACS analysis measuring surface CXCR4 staining. Pharmacokinetics analysis confirmed dose incremental BL-8040 exposure with a short plasma half-life. Conclusions: The current data demonstrate that sustained blockade of the CXCR4-CXCL12 axis with BL-8040 has potent anti leukemic activity and in combination with Ara-C may improve the response typically achieved in this advanced AML population. Mechanistically, BL-8040 was able to induce apoptosis of leukemic progenitor cells, overcoming the stroma protection, inducing mobilization and differentiation. Disclosures Rowe: BioLineRx Ltd.: Consultancy; Amgen: Consultancy; BioSight Ltd.: Consultancy, Membership on an entity's Board of Directors or advisory committees. Uy:Novartis: Research Funding. Altman:Seattle Genetics: Consultancy; Novartis: Consultancy; Spectrum: Consultancy; Astellas: Consultancy; Ariad: Consultancy; BMS: Consultancy. Peled:Biokine Ltd.: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; BiolineRX: Consultancy, Research Funding. Pereg:BioLineRx: Employment. Vainstein:BioLineRx: Employment. Aharon:BioLineRx: Employment. Pemmaraju:Stemline: Research Funding; Incyte: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; LFB: Consultancy, Honoraria. Cortes:Teva: Research Funding; Pfizer: Consultancy, Research Funding; BMS: Consultancy, Research Funding; BerGenBio AS: Research Funding; Novartis: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Ambit: Consultancy, Research Funding; Arog: Research Funding; Celator: Research Funding; Jenssen: Consultancy.