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Comparison of tumor PD-L1 expression and tumor immune infiltrate between baseline biopsies and at 8 weeks on treatment (UPS/DDLPS only)

Purpose:We recently reported a 17.5% objective RECIST 1.1 response rate in a phase II study of pembrolizumab in patients with advanced sarcoma (SARC028). The majority of responses occurred in undifferentiated pleomorphic sarcoma (UPS) and dedifferentiated liposarcoma (DDLPS). We sought to determine whether we can identify immune features that correlate with clinical outcomes from tumor tissues obtained pre- and on-treatment.Patients and Methods:Pretreatment (n = 78) and 8-week on-treatment (n = 68) tumor biopsies were stained for PD-L1 and multiplex immunofluorescence panels. The density of positive cells was quantified to determine associations with anti–PD-1 response.Results:Patients that responded to pembrolizumab were more likely to have higher densities of activated T cells (CD8+ CD3+ PD-1+) and increased percentage of tumor-associated macrophages (TAM) expressing PD-L1 pre-treatment compared with non-responders. Pre-treatment tumors from responders also exhibited higher densities of effector memory cytotoxic T cells and regulatory T cells compared with non-responders. In addition, higher density of cytotoxic tumor-infiltrating T cells at baseline correlated with a better progression-free survival (PFS).Conclusions:We show that quantitative assessments of CD8+ CD3+ PD-1+ T cells, percentage of TAMs expressing PD-L1, and other T-cell densities correlate with sarcoma response to pembrolizumab and improved PFS. Our findings support that multiple cell types present at the start of treatment may enhance tumor regression following anti–PD-1 therapy in specific advanced sarcomas. Efforts to confirm the activity of pembrolizumab in an expansion cohort of patients with UPS/DDLPS are underway.

Comparison of tumor PD-L1 expression and tumor immune infiltrate between baseline tumor biopsies from responders and nonresponders (STS only)

Comparison of tumor PD-L1 expression and tumor immune infiltrate between baseline biopsies and at 8 weeks on treatment (STS only)

Response to anti-PD1 therapy is associated with higher levels of PD-L1 expression by (A) tumor cells and (B) tumor infiltrating macrophages and higher density of sarcoma-associated immune infiltrates at baseline. Tumor biopsies obtained from patients who responded to pembrolizumab therapy had higher baseline density (cell count/mm2) of tumor infiltrating (C) T lymphocytes, (D) cytotoxic T lymphocytes, (E) antigen experience T lymphocytes, (F) antigen experienced cytotoxic T lymphocytes, (G) activated cytotoxic T lymphocytes, (H) effector memory cytotoxic T lymphocytes, and (I) regulatory T lymphocytes. Baseline tumor samples available for immune profiling by IHC were obtained prior to anti-PD1 treatment (8 responder and 58 non-responder patients). Error bars represent SEM. * = p{less than or equal to}0.05, ** = p{less than or equal to}0.01, *** = p{less than or equal to}0.001, n.s. = not significant.

Comparison of tumor PD-L1 expression and tumor immune infiltrate between baseline biopsies and at 8 weeks on treatment (bone only)

SARC028 tumor biopsies obtained at baseline and after 8 weeks treatment and associated patient response to pembrolizumab

Supplemental Legend

Demographic and clinical characteristics of 84 eligible, treated patients

Comparison of tumor PD-L1 expression and tumor immune infiltrate between baseline tumor biopsies from responders and nonresponders (UPS/DDLPS only)

Osteosarcoma (OS) frequently metastasizes to lung where it greatly contributes to patient mortality. Frustratingly, OS treatment options have remained static due to a paucity of strong pre-clinical evidence to motivate clinical trials. To identify therapeutic targets, we assessed a number of FDA approved therapies for their cytotoxic effects. We found that histone deacetylase (HDAC) inhibitors (panobinostat and romidepsin) limited OS viability at low nM and were highly effective for the treatment of lung metastatic disease in vivo. Although clinically approved, HDAC inhibitors have noted toxicities. Therefore, we next examined the potential mechanisms through which HDAC controlled OS growth. Gene expression analyses on romidepsin treated OS cells revealed key up and downregulated targets. We found that SLC17A7, a vesicular glutamate transporter, was highly and consistently induced in response to romidepsin (greater than 100 fold more than base line) across multiple OS cell lines. Functionally, SLC17A7 traps glutamate in cytoplasmic synaptic vesicles that are then released via exocytosis. Our data show that HDAC inhibition reduces glutamate secretion from OS cells while SLC17A7 overexpression significantly impaired OS viability. Further, we showed that the glutamate export inhibitor, riluzole, significantly impairs the OS growth in vitro and is highly effective for the treatment of lung metastatic OS in vivo. Taken together, we conclude that HDAC1/2 suppression of SLC17A7 ensures high cytoplasmic glutamate levels that can be leveraged for OS growth. We posit that targeting glutamate usage by OS cells using FDA approved inhibitors such as riluzole will be highly effective for the treatment of lung metastatic OS. Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Ryan T. Bishop, Diana Yu, Damon R. Reed, Conor C. Lynch. Delineating the role of vesicular glutamate transporter SLC17A7 in osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 276.

Osteosarcoma is an orphan disease with only 900 patients diagnosed each year in US. Most patients are adolescents with small number of older patients. The 5-survival rates for those with metastatic disease is only 30%. Frustratingly, there has been little change in treatment options (chemotherapy, surgery and radiotherapy) due to the difficulty of conducting clinical trials in this rare but deadly cancer. To address this, strong pre-clinical trial information is required to motivate clinical trial design. In vitro and in vivo, we identified that the pan-HDAC inhibitor, panobinostat is highly effective in limiting osteosarcoma growth and metastasis. Panobinostat is approved for the treatment of other malignancies but has noted toxicities. Therefore, to identify therapeutic targets, we explored the HDACs responsible for driving osteosarcoma metastasis and the specific genes through which those HDACs mediated their effects. Our data shows that HDAC1 and HDAC2 are key for osteosarcoma survival using siRNA approaches. Use of the HDAC1/2 selective inhibitor romidepsin in vitro and in vivo supported this finding. To identify targets being regulated by HDAC1/2, we performed microarray and proteomics analyses on romidepsin treated osteosarcoma cells. We found and validated independently that, SLC17A7, a metabolic vesicular glutamate transporter to be highly induced in response to romidepsin treatment; >100 fold more than base line in multiple osteosarcoma cell lines. Functionally, SLC17A7 allows entry of glutamate into the synaptic vesicles from cytoplasm and releases the glutamate from the cells via exocytosis. In our studies, we have seen that romidepsin treatment leads to reduced glutamate levels in the conditioned media and cell death indicating key roles for SLC17A7 in driving osteosarcoma progression and metastasis. In conclusion, our data shows that HDAC1/2 suppression of SLC17A7 is a novel means of promoting osteosarcoma progression and metastasis. Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Diana Yu, Damon R. Reed, Conor C. Lynch. Epigenetic silencing of SLC17A7 promotes osteosarcoma growth [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-044.

Osteosarcoma (OS) is the most common bone malignancy in adolescents. At the time of initial diagnosis, approximately 15% of the patients present with metastatic disease in lungs. Prognosis for this cohort is grim with 5-year overall survival rates at 30%. Frustratingly, these statistics have changed little over the past three decades, in part due to the lack of progress in identifying effective therapies and difficulty in coordinating robust clinical trials in this relatively rare malignancy. To address this, we previously screened 54 FDA approved drugs against 5 different OS cell lines and identified the histone deacetylase inhibitor (HDAC), panobinostat (Pano) as having potent effects in vitro. Here, we explore whether Panobinostat is effective in preventing multiple stages of OS progression in vivo using the K7M2 and SAOS2LM7 pre-clinical models of the disease. Pano prevents the growth of primary OS and lung metastasis. Mice were intratibially inoculated with K7M2-Luc cells and then treated with vehicle (n=11) or panobinostat (n=10; 10 mg/kg for all in vivo studies). Tumor growth was measured by bioluminescence (RLU). The clinical endpoint was 1x106RLU (IVIS-200). Primary OS growth was significantly slower in the panobinostat treated group (p Citation Format: Niveditha Nerlakanti, Jeremy McGuire, Diana Yu, Damon R. Reed, Conor C. Lynch. HDAC inhibition significantly reduces primary and lung metastatic osteosarcoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2016.

Background: Relapsed Acute Lymphoblastic Leukemia (ALL) remains a major cause of cancer-related deaths in children. We identified the AMP activated protein kinase (AMPK) as a potential target for ALL therapy due to its regulatory effects on the unfolded protein response (UPR), leading to increased vulnerability of ALL cells to endoplasmic reticulum (ER) stress inducers. In vitro, metformin leads to ALL cell death via AMPK-mediated inhibition of the UPR. Methods: Metformin was administered twice daily continuously on a 28 day cycle in addition to the Vincristine, Dexamethasone, PEG-Asparaginase and Doxorubicin (VPLD) systemic regimen and CNS-directed therapy in pediatric patients with relapsed/refractory ALL. Metformin doses were increased in a standard 3+3 phase I design with three dose levels evaluated, 666, 1,000 and 1,333 mg/m2/day. Pharmacokinetic (PK) and pharmacodynamic (PD) evaluation of the AMPK and ER stress/UPR pathways were ascertained on days 1 and 7, and treatment response was assessed on day 29. Results: Fourteen patients were enrolled, 11 evaluable. DL3 was the maximum administered dose with 2 related DLT’s of diarrhea and acidosis. A single DLT of hypoglycemia and acidosis during an episode of sepsis was observed in DL2. Infectious SAE’s occurred in 7 patients. Two patients had posterior reversible encephalopathy syndrome; both died of disease progression within 30 days of coming off study. A single patient had stable disease, 2 had a partial response, and 3 achieved a complete response. PK studies demonstrated levels within the therapeutic range for patients with diabetes, and PD evaluation showed induction of ER stress and inhibition of the UPR. Conclusions: This trial has been completed. We found induction of ER stress with inhibition of UPR consistent with that observed in vitro leading to metformin-induced apoptosis. The chemotherapeutic backbone was tolerable and the combination with metformin yielded responses in a heavily pretreated population. Toxicities attributable to metformin occurred in all dose levels, but DLT’s were only observed in dose levels above the standard dosing for diabetes. Clinical trial information: NCT01324180 Citation Format: Matteo Trucco, Julio Barredo, John Goldberg, Gregory Hale, Jonathan Gill, Bhuvana Setty, Tiffany Smith, Jae Lee, Damon Reed. A phase I window, dose escalating and safety trial of Metformin in combination with induction chemotherapy (VPLD)in relapsed/refractory acute lymphoblastic leukemia: NCT01324180 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT145. doi:10.1158/1538-7445.AM2017-CT145

Background: Ewing Sarcoma (ES) is the second most common primary bone cancer affecting children and young adults. Despite advances in treatment that have led to survival rates of approximately 73% for localized disease, outcomes for patients with metastatic or recurrent ES remain poor. A distinguishing feature of ES is the presence of the EWS/FLI1 fusion in 85% of cases. The fusion has been shown to alter expression of a number of oncogenic genes. Mechanistic studies have demonstrated that the NuRD co-repressor complex interacts with EWS/FLI1. The associated protein LSD-1 contributes to the repressive function by histone modifications. While reversible LSD1 inhibitors demonstrate single agent activity, in preclinical models, a system to evaluate combinations may be needed for optimizing effect in clinical trials. Methods: Here, we seek to confirm promising single drug activity and evaluate combination therapies using active chemotherapies currently utilized in ES care (4-HC, etoposide, SN-38, vincristine and doxorubicin) along with the LSD1 Inhibitors SP2509 and SP2577 and romidepsin, an HDAC inhibitor. We evaluated these combinations in high-throughput screening platforms and well-established cell line models for ES (A-673, TC-32, RD-ES, TC-71). Taking into consideration past lessons learned from in vitro experiments, we designed stringent screening conditions that assess the candidate compounds and combinations at clinically-relevant concentrations and exposure times that mimic the in vivo pharmacokinetics in an effort to maximize the translational potential of these results to the clinical setting. All combinations of agents were studied in two-drug combinations to evaluate for synergy in addition to efficacy. Results: IC50 for SP2509 was found to be in the submicromolar range across cell lines with SP2577 being more potent. A-673 and TC-71 were 5-10 fold less sensitive than RD-ES and TC-32. Agents currently utilized in clinic were universally active at clinically achievable concentrations and exposure times. Combinations showed additivity frequently and demonstrated promising activity that can be used to inform further decision making once LSD1 inhibition toxicities are better known. These findings suggest potentially promising opportunities for developing combination clinical trials to maximize development of LSD1 inhibitors. Citation Format: Darcy Welch, Elliot Kahen, Christopher L. Cubitt, Damon R. Reed. LSD1 inhibition alone and in combination with chemotherapy in Ewing sarcoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2034. doi:10.1158/1538-7445.AM2017-2034

Background: Malignant Peripheral Nerve Sheath Tumor (MPNST) is a malignant sarcoma that derives from a peripheral nerve or plexiform neurofibroma. Neurofibromatosis type 1 (NF-1) patients are particularly susceptible, with a higher risk, earlier onset, and worse prognosis. The major factor associated with MPNST and NF-1 is Neurofibromin 1, coded by the NF1 gene. NF1 mutation results in RAS hyperactivation. Chemotherapy for MPNST is currently limited, with poor prognosis for metastatic or unresectable tumors. Thus, the development of promising treatment solutions for MPNST to translate to clinical trials is required. Methods: Here, we seek to identify efficacious chemotherapeutic treatments for MPNST with a combination of drug screening and biological pathway analysis. We used our previously established preclinical system to test FDA approved or promising developmental agents against five cell line models for MPNST. We screened sixty agents with diverse mechanisms of action below published maximum plasma concentrations, and measured effects with a CellTiter-Glo viability assay. Promising agents were then tested in two-drug combinations, allowing for determination of synergism. We then examined the molecular effects of the top candidates with use of antibody arrays that permit detection of a series of phosphorylated proteins. Results: The group of most efficacious drugs was enriched with agents that target factors downstream of RAS, including MEK, mTOR, and PI3K inhibitors, with microtubule inhibitors, genotoxics, and HDAC inhibitors also demonstrating good results. Strong synergism was observed across our cell line models particularly in combinations containing the dual mTORC1/2 inhibitor INK128. Interestingly, drug sensitivity varied greatly between cell lines, correlating with relative NF1 protein and RAS-GTP levels. We analyzed the activation of the RAS pathway in response to drug treatment with antibody arrays and found that, following treatment, relative phosphorylation signal was more decreased compared to controls in cell lines with lower relative NF1 protein levels. Doxorubicin was able to reduce phosphorylation signal compared to controls to a level near comparable to targeted inhibitors, which could contribute to doxorubicin’s current usefulness against MPNSTs. Importantly, we identified combination treatments that were able to greatly reduce the relative phosphorylation signal of RAS pathway members versus control. Combinations containing INK128 resulted in the most pathway shutdown. These findings suggest that MPNSTs may be susceptible to combination treatments targeting RAS pathway members. Moreover, it may be possible to use pathway analysis as a diagnostic tool to predict drug tolerance. Citation Format: Elliot Kahen, Darcy Welch, Diana Yu, Christopher Cubitt, Jae Lee, Andrew Brohl, Damon R. Reed. RAS pathway activation and sensitivity to therapeutic agents is correlated with NF1 residual activity in malignant peripheral nerve sheath tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1340. doi:10.1158/1538-7445.AM2017-1340

Background: Alveolar Soft Part Sarcoma (ASPS) is a rare soft tissue sarcoma subtype occurring mainly in children and young adults. Malignant tumors develop in the connective tissues, typically in the lower extremities of the legs and thighs, but can also be found in the head and neck regions. ASPS is slow growing, highly angiogenic, and may have unique metabolic properties. ASPS is characterized by an unbalanced translocation between the ASPSCR1 gene (whose product tethers GLUT4 transporters) and the TFE3 gene (encoding a transcription factor). The resulting ASPSCR1-TFE3 fusion gene is responsible for an aberrant transcription factor that is thought to be involved in the pathogenesis of the disease. Methods to assess a number of different agents in combination are needed for practical use in clinical trials. Methods: Here, we seek to examine the therapeutic activity of single agent and combinations of epigenetic, anti-angiogenic and a diverse mix of other mechanisms of action agents using high-throughput screening platforms and well-established cell line models for ASPS (ASPS-1 and ASPS-KY). We designed stringent screening conditions that assess the compounds at clinically-relevant concentrations and time of exposures that mimic the in vivo pharmacokinetics in an effort to maximize the translational potential of these results to the clinical setting. 54 agents were screened across the 2 cell lines with attention to existing clinical data and angiogenesis inhibitors. The cell titer glo assay was used to determine cell viability at three clinically achievable concentrations for all agents. The most promising 8 agents were then studied in all two-drug combinations to evaluate for synergy. Results: The results of our screening showed that several agents significantly reduced cell viability at clinically relevant concentrations and exposure times with belinostat (an HDAC inhibitor) and dinaciclib (a CDK 1, 2, 5 and 9 inhibitor) in particular having good activity. Several combinations with doxorubicin showed good efficacy and synergy. Belinostat and doxorubicin affected both ASPS-KY and ASPS-1 cell lines similarly, with an average fraction affected (FA) of 0.87. The combination index (CI) indicated strong synergy in the ASPS-KY (CI = 0.09) and some synergy in ASPS-1 (CI = 0.74). Similarly, dinaciclib and doxorubicin produced a FA of 0.85 with good synergy (CI of 0.51-0.66). In addition, the combination of belinostat and tivantinib showed additive effects in both cell lines (CI of 0.88-1.2) with a FA of ∼0.8. These findings suggest potentially promising opportunities for developing combinational approach to treating childhood soft tissue sarcomas. Citation Format: Justine Clark, Elliot Kahen, Diana X. Yu, Christopher L. Cubitt, Daniel M. Sullivan, Damon R. Reed. Assessing combinations of chemotherapy in alveolar soft part sarcoma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 274.

Background: Sarcomas are a heterogeneous group of mesenchymal malignant tumors that make up approximately 15% of all childhood tumors and represent the fourth most common group of malignancies in children, remaining common in young adults with cancer as well. While over 35 agents have been FDA approved for adult carcinomas in the past 3 years, little progress has been made in incorporating new agents into the chemotherapy plans for pediatric sarcomas in the past few decades. A system to rapidly evaluate many agents and combinations of agents which can immediately be translated into clinical trials in a clinically relevant manner is needed. Methods: Here, we seek to examine the therapeutic activity of single agent and combinations of FDA approved chemotherapy agents using high-throughput screening platforms, based on well-established childhood cancer cell line models for most prevalent forms of pediatric bone sarcomas (osteosarcoma and Ewing sarcoma). Taking into consideration past lessons learned from in vitro experiments, we designed stringent screening conditions that assess the candidate compounds at clinically-relevant concentrations and time of exposures that mimic the in vivo pharmacokinetics in an effort to maximize the translational potential of these results to the clinical setting. Fifty-four agents, mainly FDA approved but also including agents with promising mechanism of action or preclinical data were screened across 5 cell lines for each histology. Caspace glo and cell titer glo assays were used to determine apoptosis and cell viability at the maximal achievable serum concentration from phase I studies and at two lower concentrations. Promising agents were then studied in 2 drug combinations to evaluate for synergy with careful attention to metabolism pathways, existing clinical data for combinations, and non-overlapping toxicities. Combinations of FDA approved agents with promising therapeutic efficacy and predicated non-overlapping toxicities will be translated to the clinic using the established Sunshine Project network. Results: Our screening results indicate that a number of FDA approved chemotherapy agents, evaluated at clinically relevant concentrations and exposure times, significantly reduced cell viability and induced up regulation of caspase3/7 activities across all cell lines. These findings suggest promising opportunities for developing combinational approach to treating childhood bone sarcomas and can be utilized to explore other pediatric tumors with existing cell lines. Citation Format: Diana Yu, Christopher Cubitt, Daniel Sullivan, Damon Reed. Assessing combinations of FDA approved chemotherapy in childhood sarcoma cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 812. doi:10.1158/1538-7445.AM2014-812

The number of effective drugs available for the treatment of soft tissue and bone sarcomas is limited to a small group of antineoplastic agents. Previously, we have identified synergistic anti-tumor activities when the HDAC inhibitor Vorinostat was used in combination with FDA approved chemotherapies. With newer and more selective HDAC inhibitors entering clinical trials we examined the effectiveness of SNDX-275, an inhibitor of HDAC I, II & III when combined with Akt inhibitors and other FDA approved drugs. CT-Blue cell viability experiments were performed to first obtain IC50s for 72 hour treatments. IC50s for SNDX-275 ranged from 0.84 to 11.4 μM (Table). SNDX-275 alone and in combination with the drugs listed in the Table showed synergistic cooperativity in viability experiments. Using Chou and Talalay's Combination Index (CI) analyses (ED levels of 0.7, 0.9 & 0.95), a synergistic or strongly synergistic reduction in cell viability (CI Table. IC50s and Chou and Talalay Combination Index (CI) Synergy Analysis. Inhibitory concentration of SNDX-275 required for 50% reduction in viable cells after 72 hour treatment (IC50). CI values represent the level of synergy resulting from concurrent SNDX-275 plus indicated combination treatment. +/- symbols indicate calculated CI synergy level. SNDX-275 MK-2206 Triciribine Carboplatin Cisplatin Etoposide sarcoma type cell line IC50 (μM) CI Syn CI Syn CI Syn CI Syn CI Syn osteosarcoma MNNG HOS 4.9 0.393 +++ 0.384 +++ 0.214 ++++ 0.037 +++++ 0.252 ++++ U2-OS 1.8 1.025 +/− 0.391 +++ 0.379 +++ rhabdomyosarcoma A-204 2.4 0.305 +++ 0.328 +++ 0.908 +/− 0.815 ++ Ewing type A-673 11.4 0.350 +++ 0.029 +++++ 0.185 ++++ RD-ES 1.5 0.962 +/− SK-ES-1 0.84 0.284 ++++ 0.293 ++++ 0.459 +++ 0.593 +++ 1.278 −− leiomyosarcoma SK-LMS-1 4.3 0.029 +++++ 0.510 +++ SK-UT-1 3.4 0.332 +++ 0.845 ++ 0.099 +++++ 0.082 +++++ 0.985 +/− liposarcoma SW-872 1.6 0.286 ++++ 0.540 +++ 0.511 +++ 0.457 +++ 0.617 +++ fibrosarcoma HT-1080 5.7 0.179 ++++ 0.060 +++++ 0.038 +++++ 0.267 ++++ Citation Format: Christopher L. Cubitt, Jillaina Menth, Jana Dawson, John M. Goldberg, Damon Reed, Daniel M. Sullivan. SNDX-275 synergistically inhibits the growth of sarcoma cells when combined with AKT inhibitors, platinum drugs and Topo II poisons. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2072. doi:10.1158/1538-7445.AM2013-2072

Sarcomas are rare and heterogeneous mesenchymal tumors affecting both pediatric and adult populations with more than 70 recognized histologies. Doxorubicin and ifosfamide have been the main course of therapy for treatment of sarcomas; however, the response rate to these therapies is about 10-20% in metastatic setting. Toxicity with the drug combination is high, response rates remain low, and improvement in overall survival, especially in the metastatic disease, remains negligible. Accordingly, new agents are needed for the treatment of this heterogeneous group of diseases. Wee1 is a critical component of the G2/M cell cycle checkpoint control and mediates cell cycle arrest by regulating the phosphorylation of CDC2. Inhibition of Wee1 by a selective small molecule inhibitor MK1775 has been reported to to enhance the cytotoxic effect of DNA damaging agents. However, its role in the treatment of mesenchymal tumors has not been explored. In this study we investigated the therapeutic efficacy of MK1775 in various sarcoma cell lines and patient-derived tumor explants ex vivo both alone and in combination with other chemotherapeutic drugs frequently used in the treatment of sarcomas. Our data demonstrate that MK1775 treatment as a single agent at clinically relevant concentrations leads to unscheduled entry into mitosis and initiation of apoptotic cell death in all sarcomas tested. Additionally, MK1775 significantly enhances the cytotoxic effect of the DNA damaging agents, gemcitabine and doxorubicin. In MK1775 treated cells CDC2 activity was enhanced and G2/M ceheckpoint was impaired as assessed by increased expression of phosphorylated histone H3, a marker of mitotic entry. The cytotoxic effect of Wee1 inhibition on sarcoma cells appears to be independent of p53 status as all sarcoma cell lines with different p53 mutation were highly sensitive to treatment. Additionally, in patient-derived bone and soft tissue sarcoma samples we showed that MK1775 in combination with gemcitabine causes significant apoptotic cell death suggesting that this treatment may represent a novel approach in the treatment of sarcomas. In patient-derived xenograft mouse models of sarcoma we are currently analyzing the therapeutic efficacy of MK1775 in vivo by utilizing magnetic resonance imaging (MRI) and diffusion MRI methods. Our results together with the high safety profile of MK1775 strongly suggest that this drug can be used as a potential therapeutic agent in the treatment of both adult as well as pediatric sarcoma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3047. doi:1538-7445.AM2012-3047

The number of effective drugs available for the treatment of soft tissue and bone sarcomas is limited to a small group of antineoplastic agents. The goal of this study was to determine the effectiveness of MK-2206 (Akt inhibitor) when used in combination with Ridaforolimus (mTor inhibitor), Cisplatin, Topotecan or Etoposide in a panel of ten cell lines. Six different types of sarcomas are represented in the panel, including rhabdo-, osteo-, Ewing, leiomyo-, lipo- and fibrosarcomas. Cell Titer-Blue cell viability experiments were performed to test dilutions of MK-2206 alone and in combination at various molar ratios over a 72 hour time period. The observed IC50s for MK-2206 or Ridaforolimus alone ranged from 4.2 to 12.9 µM or 23.7 to 62.3 µM, respectively. The observed IC50 range for Etoposide was 0.5 to 7.5 µM. To determine the relative potentiation of drug combinations, Excess over Highest Single Agent (HSA) analysis was performed (Table). The average Excess HSA score for MK-2206 combinations with Ridaforolimus or Etoposide were 0.17 and 0.15 respectively with levels of significance (p value) < 0.032. This was in contrast to MK-2206 combinations containing Cisplatin or Topotecan with average HSA scores of 0.084 and 0.085, respectively, indicating less potentiation. Using Chou and Talalay combination index (CI) analyses (effective dose levels of 0.7, 0.9 and 0.95), a synergistic to strongly synergistic reduction in cell viability was observed in 5 cell lines for MK-2206 plus Ridaforolimus and MK-2206 plus Etoposide combinations. Ongoing experiments are underway to identify the effects of MK-2206 combinations on apoptosis and the effect of drug sequencing on growth inhibition. The results of this study indicate that a MK-2206 plus Ridaforolimus or a MK-2206 plus Etoposide combination may be an effective treatment regimen for sarcoma patients. This work was funded by the Pediatric Cancer Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3513. doi:10.1158/1538-7445.AM2011-3513