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PURPOSE Although chemoimmunotherapy is widely used for treatment of children with relapsed high-risk neuroblastoma (HRNB), little is known about timing, duration, and evolution of response after irinotecan/temozolomide/dinutuximab/granulocyte-macrophage colony-stimulating factor (I/T/DIN/GM-CSF) therapy. PATIENTS AND METHODS Patients eligible for this retrospective study were age < 30 years at diagnosis of HRNB and received ≥ 1 cycle of I/T/DIN/GM-CSF for relapsed or progressive disease. Patients with primary refractory disease who progressed through induction were excluded. Responses were evaluated using the International Neuroblastoma Response Criteria. RESULTS One hundred forty-six patients were included. Tumors were MYCN-amplified in 50 of 134 (37%). Seventy-one patients (49%) had an objective response to I/T/DIN/GM-CSF (objective response; 29% complete response, 14% partial response [PR], 5% minor response [MR], 21% stable disease [SD], and 30% progressive disease). Of patients with SD or better at first post-I/T/DIN/GM-CSF disease evaluation, 22% had an improved response per International Neuroblastoma Response Criteria on subsequent evaluation (13% of patients with initial SD, 33% with MR, and 41% with PR). Patients received a median of 4.5 (range, 1-31) cycles. The median progression-free survival (PFS) was 13.1 months, and the 1-year PFS and 2-year PFS were 50% and 28%, respectively. The median duration of response was 15.9 months; the median PFS off all anticancer therapy was 10.4 months after discontinuation of I/T/DIN/GM-CSF. CONCLUSION Approximately half of patients receiving I/T/DIN/GM-CSF for relapsed HRNB had objective responses. Patients with initial SD were unlikely to have an objective response, but > 1 of 3 patients with MR/PR on first evaluation ultimately had complete response. I/T/DIN/GM-CSF was associated with extended PFS in responders both during and after discontinuation of treatment. This study establishes a new comparator for response and survival in patients with relapsed HRNB.

Detailed methods, description of supplemental tables, and supplemental figures.

Supplementary Table S1

Pediatric sarcomas represent a heterogeneous group of malignancies that exhibit variable response to DNA-damaging chemotherapy. Schlafen family member 11 protein (SLFN11) increases sensitivity to replicative stress and has been implicated as a potential biomarker to predict sensitivity to DNA-damaging agents (DDA). SLFN11 expression was quantified in 220 children with solid tumors using IHC. Sensitivity to the PARP inhibitor talazoparib (TAL) and the topoisomerase I inhibitor irinotecan (IRN) was assessed in sarcoma cell lines, including SLFN11 knock-out (KO) and overexpression models, and a patient-derived orthotopic xenograft model (PDOX). SLFN11 was expressed in 69% of pediatric sarcoma sampled, including 90% and 100% of Ewing sarcoma and desmoplastic small round-cell tumors, respectively, although the magnitude of expression varied widely. In sarcoma cell lines, protein expression strongly correlated with response to TAL and IRN, with SLFN11 KO resulting in significant loss of sensitivity in vitro and in vivo. Surprisingly, retrospective analysis of children with sarcoma found no association between SLFN11 levels and favorable outcome. Subsequently, high SLFN11 expression was confirmed in a PDOX model derived from a patient with recurrent Ewing sarcoma who failed to respond to treatment with TAL + IRN. Selective inhibition of BCL-xL increased sensitivity to TAL + IRN in SLFN11-positive resistant tumor cells. Although SLFN11 appears to drive sensitivity to replicative stress in pediatric sarcomas, its potential to act as a biomarker may be limited to certain tumor backgrounds or contexts. Impaired apoptotic response may be one mechanism of resistance to DDA-induced replicative stress.

Key Points CPX-351 treatment is well tolerated and results in morphologic remission in newly diagnosed pediatric secondary myeloid malignancies.Favorable outcomes are achieved despite the presence of high-risk genetic lesions and previous therapies., Visual Abstract, Secondary myelodysplastic syndromes and acute myeloid leukemia (sMDS/AML) are rare in children and adolescents and have a dismal prognosis. The mainstay therapy is hematopoietic cell transplantation (HCT), but there has been no innovation in cytoreductive regimens. CP X-351, a fixed 5:1 molar ratio of liposomal cytarabine to daunorubicin, has shown favorable safety and efficacy in elderly individuals with secondary AML and children with relapsed de novo AML. We report the outcomes of 7 young patients (6 with newly diagnosed sMDS/AML and 1 with primary MDS/AML) uniformly treated with CP X-351. Five patients had previously received chemotherapy for osteosarcoma, Ewing sarcoma, neuroblastoma, or T-cell acute lymphoblastic leukemia; 1 had predisposing genomic instability disorder (Cornelia de Lange syndrome) and 1 had MDS-related AML and multiorgan failure. The median age at diagnosis of myeloid malignancy was 17 years (range, 13-23 years). Patients received 1 to 3 cycles of CP X-351 (cytarabine 100 mg/m2 plus daunorubicin 44 mg/m2) on days 1, 3, and 5, resulting in complete morphologic remission without overt toxicity or treatment-related mortality. This approach allowed for adding an FLT3 inhibitor as individualized therapy in 1 patient. Six patients were alive and leukemia-free at 0.5 to 3.3 years after HCT. One patient died as a result of disease progression before HCT. To summarize, CP X-351 is an effective and well-tolerated regimen for cytoreduction in pediatric sMDS/AML that warrants prospective studies.

Supplementary Figures and Tables

This figure demonstrates the relationship between prior treatment with chimeric or humanized 14.18 K322A antibody and A) the area under the concentration curve for the antibody (AUC); B elimination half-life of the antibody (T1/2 Beta); and C) the highest observed concentration of the antibody (Cmax). Although the data in panels A and B suggest that prior exposure to ch14.18 or hu14.18K322A tends to increase the AUC and the elimination half-life, there is no significant difference between prior treatment groups using the Kruskal-Wallis non-parametric test. The data in panel C do not suggest an association between prior exposure and the peak serum concentration of the hu14.18K322A antibody.

Box and whisker plot showing absolute NK cells per mm3 in samples. NK cells were identified by flow cytometry as CD14 negative, CD56 positive, CD3 negative and percentage of total WBC was computed from flow cytometry results. Absolute WBC count was obtained using a Sysmex{trade mark, serif} KX-21 blood cell analyzer, and final absolute NK count was obtained by multiplying percent NK by absolute WBC. Sample identifiers and associated N are: DONOR (N=10) blood sample drawn at or before time of first NK cell donation; CS1_PRE (N=13), Patient blood drawn prior to first treatment course; CS1_14 (N=9); Patient on day +14 of first treatment course; CS1_21 (N=14), Patient on day +21 of first treatment course; CS2_NK_07 (N=11), Patient on day +7 following NK cell administration in second treatment course; CS2_NK_14 (N=11), Patient on day +14 following NK cell administration in second treatment course; CS3_14 (N=7), Patient on day +14 of third treatment course; CS3_21 (N=9), Patient on day +21 of third treatment course; CS4_NK_07 (N=9), Patient on day +7 following NK cell administration in fourth treatment course; CS4_NK_14 (N=10), Patient on day +14 following NK cell administration in fourth treatment course; CS5_14 (N=3), Patient on day +14 of fifth treatment course; CS5_21 (N=8), Patient on day +21 of fifth treatment course; CS6_PRE (N=1), Patient blood drawn prior to initiation of 6th treatment course; CS6_NK_07 (N=7), Patient on day +7 following NK cell administration in sixth treatment course; CS6_NK_14 (N=7), Patient on day +14 following NK cell administration in sixth treatment course. Central Point (ï�¯) - median; Box - Inner quartiles (25th percentile to 75th percentile) of data; Whiskers - non-outlier min and max data; Outliers (ï,¡) - data points outside of median {plus minus} inner quartile range; Extreme Outliers (*) - data points outside of median {plus minus} 1.5 X inner quartile range.

Human anti-human antibody (HAHA) level and peak hu14.18K322A serum level by course and prior antibody therapy.

Purpose: Anti-GD2 mAbs, acting via antibody-dependent cell-mediated cytotoxicity, may enhance the effects of chemotherapy. This pilot trial investigated a fixed dose of a unique anti-GD2 mAb, hu14.18K322A, combined with chemotherapy, cytokines, and haploidentical natural killer (NK) cells.Experimental Design: Children with recurrent/refractory neuroblastoma received up to six courses of hu14.18K322A (40 mg/m2/dose, days 2–5), GM-CSF, and IL2 with chemotherapy: cyclophosphamide/topotecan (courses 1,2), irinotecan/temozolomide (courses 3,4), and ifosfamide/carboplatin/etoposide (courses 5,6). Parentally derived NK cells were administered with courses 2, 4, and 6. Serum for pharmacokinetic studies of hu14.18K322A, soluble IL2 receptor alpha (sIL2Rα) levels, and human antihuman antibodies (HAHA) were obtained.Results: Thirteen heavily pretreated patients (9 with prior anti-GD2 therapy) completed 65 courses. One patient developed an unacceptable toxicity (grade 4 thrombocytopenia >35 days). Four patients discontinued treatment for adverse events (hu14.18K322A allergic reaction, viral infection, surgical death, second malignancy). Common toxicities included grade 3/4 myelosuppression (13/13 patients) and grade 1/2 pain (13/13 patients). Eleven patients received 29 NK-cell infusions. The response rate was 61.5% (4 complete responses, 1 very good partial response, 3 partial responses) and five had stable disease. The median time to progression was 274 days (range, 239–568 days); 10 of 13 patients (77%) survived 1 year. Hu14.18K322A pharmacokinetics was not affected by chemotherapy or HAHA. All patients had increased sIL2Rα levels, indicating immune activation.Conclusions: Chemotherapy plus hu14.18K322A, cytokines, and NK cells is feasible and resulted in clinically meaningful responses in patients with refractory/recurrent neuroblastoma. Further studies of this approach are warranted in patients with relapsed and newly diagnosed neuroblastoma. Clin Cancer Res; 23(21); 6441–9. ©2017 AACR.

The left panel plots the calculated area under the concentration vs time curve (AUC) of hu14.18K322A and the right panel plots the highest observed serum concentration of hu14.18K322A (Cmax) against the pre-treatment concentration of HAHA antibodies, reported in units of optical density. There is no clear association between the concentration of HAHA at the start of treatment and the AUC of hu14.18K322A and the peak concentration of hu14.18K322A using the Spearman test.

Plot of ADCC assay reports comparing 6 lots of hu14.18K322A in comparison to dinutuximab (unituxin). M21 cells, expressing the GD2 cell surface epitope, served as the target cells. Engineered Jurkat cells, with a cell-surface FcyRIIIa (V158) receptor, served as the effector cells. Crosslinking of the two cells by either hu14.18K322A or dinutuximab led to gene transcription through NFAT (nuclear factor of activated T-cells) with subsequent NFAT response element (RE) driving expression of a firefly luciferase reporter protein. The luciferase reporter substrate was converted to a luminescent product and quantified as relative luminescence units (RLU) on a plate reader.

Purpose:We sought to evaluate whether combining a humanized antidisialoganglioside mAb (hu14.18K322A) with induction chemotherapy improves early responses and outcomes in children with newly diagnosed high-risk neuroblastoma.Patients and Methods:We conducted a prospective nonrandomized, single-arm, two-stage, phase II clinical trial. Six courses of induction chemotherapy were coadministered with hu14.18K322A and followed with granulocyte–macrophage colony-stimulating factor (GM-CSF) and low-dose IL2. Consolidation was performed with a busulfan/melphalan preparative regimen. An additional course of hu14.18K322A was administered with parent-derived natural killer cells, when available, during consolidation. Hu14.18K322A, GM-CSF, IL2, and isotretinoin were then administered. Secondary outcomes included reduced tumor volume and semiquantitative 123I-metaiodobenzylguanidine scoring [i.e., Curie scores (CS)] at the end of induction.Results:Forty-two patients received hu14.18K322A and induction chemotherapy. This regimen was well tolerated, with continuous-infusion narcotics adjusted to patient tolerance. Partial responses (PR) or better after the first two chemoimmunotherapy courses occurred in 32 patients [76.2%; 95% confidence interval (CI), 60.6–88.0]. This was accompanied by primary tumor volume reductions (median, –76%; range, –100% to 5%). Of 35 patients with stage IV disease who completed induction, 31 had end-of-induction CSs of 2 or less. No patients experienced progression during induction. Two-year event-free survival (EFS) was 85.7% (95% CI, 70.9–93.3).Conclusions:Adding hu14.18K322A to induction chemotherapy produced early PR or better in most patients, reduced tumor volumes, improved CSs at the end of induction, and yielded an encouraging 2-year EFS. These results, if validated in a larger study, may change the standard of care for children with high-risk neuroblastoma.

Tables of antibody infusion times and Curie Scores

Individual pharmacokinetic parameters in 3 subpopulations (no prior 14.18 mAb, prior dinutuximab mAb, prior hu14.18K322A mAb).

Purpose:To determine the pharmacokinetics and skin toxicity profile of sorafenib in children with refractory/relapsed malignancies.Patients and Methods:Sorafenib was administered concurrently or sequentially with clofarabine and cytarabine to patients with leukemia or with bevacizumab and cyclophosphamide to patients with solid tumor malignancies. The population pharmacokinetics (PPK) of sorafenib and its metabolites and skin toxicities were evaluated.Results:In PPK analysis, older age, bevacizumab and cyclophosphamide regimen, and higher creatinine were associated with decreased sorafenib apparent clearance (CL/f; P < 0.0001 for all), and concurrent clofarabine and cytarabine administration was associated with decreased sorafenib N-oxide CL/f (P = 7e−4). Higher bilirubin was associated with decreased sorafenib N-oxide and glucuronide CL/f (P = 1e−4). Concurrent use of organic anion-transporting polypeptide 1B1 inhibitors was associated with increased sorafenib and decreased sorafenib glucuronide CL/f (P < 0.003). In exposure–toxicity analysis, a shorter time to development of grade 2–3 hand–foot skin reaction (HFSR) was associated with concurrent (P = 0.0015) but not with sequential (P = 0.59) clofarabine and cytarabine administration, compared with bevacizumab and cyclophosphamide, and with higher steady-state concentrations of sorafenib (P = 0.0004) and sorafenib N-oxide (P = 0.0275). In the Bayes information criterion model selection, concurrent clofarabine and cytarabine administration, higher sorafenib steady-state concentrations, larger body surface area, and previous occurrence of rash appeared in the four best two-predictor models of HFSR. Pharmacokinetic simulations showed that once-daily and every-other-day sorafenib schedules would minimize exposure to sorafenib steady-state concentrations associated with HFSR.Conclusions:Sorafenib skin toxicities can be affected by concurrent medications and sorafenib steady-state concentrations. The described PPK model can be used to refine exposure–response relations for alternative dosing strategies to minimize skin toxicity.

ADCC EC50 values of hu14.18K322A and dinutuximab.

Donor characteristics, dose and chimerism of NK cells infused.

Although outcomes for patients with high-risk neuroblastoma improved after the addition of a chimeric anti-GD2 monoclonal antibody (dinutuximab) as treatment for minimal residual disease, nearly half of these patients die of disease. Recent studies demonstrated efficacy of the combination of chemotherapy with anti-GD2 mAb in patients with relapsed or newly diagnosed disease. This retrospective case series describes 6 patients treated at St Jude Children's Research Hospital with an induction regimen containing dinutuximab and chemotherapy, followed by consolidation and postconsolidation therapy. The treatment was well tolerated with expected toxicities. All patients completed induction therapy and demonstrated a clinical response. Further studies are warranted.

Background Talazoparib combined with irinotecan and temozolomide demonstrated efficacy in a murine Ewing sarcoma model. Based on these data, we conducted a phase I trial of talazoparib and irinotecan with/without temozolomide in paediatric patients with recurrent/refractory solid malignancies. Patients and methods Cohorts of 3–6 patients with recurrent/refractory solid malignancies received escalating doses of oral talazoparib and intravenous irinotecan (arm A) and oral talazoparib, oral temozolomide and intravenous irinotecan (arm B) in a 3 + 3 design. Talazoparib was administered on days 1–6, and intravenous irinotecan and oral temozolomide were administered on days 2–6, of a 21-day course. Serum for talazoparib and irinotecan pharmacokinetics was obtained during course 1. UGT1A1 polymorphism and Schlafen family member 11 (SLFN11) immunohistochemical staining were performed. Results Forty-one patients (20 males; median age, 14.6 years; 24 with recurrent disease) were evaluable for dose escalation. Twenty-nine and 12 patients were treated on arm A and arm B, respectively, for a total of 208 courses. The most common diagnosis was Ewing sarcoma (53%). The most common ≥grade III haematologic toxicities in arms A and B included neutropenia (78% and 31%, respectively) and thrombocytopenia (42% and 31%, respectively). In arms A and B, febrile neutropenia (24% and 14%, respectively) and diarrhoea (21% and 7%, respectively) were the most common ≥grade III non-hematologic toxicities. Six patients (Ewing sarcoma [5 patients] and synovial sarcoma [1 patient]) had a response (1 with a complete response, 5 with a partial response). The objective response rates were 10.3% (arm A) and 25% (arm B). Pharmacokinetic testing demonstrated no evidence of drug-drug interaction between talazoparib and irinotecan. UGT1A1 was not related to response. SLFN11 positivity was associated with best response to therapy. Conclusions The combination of talazoparib and irinotecan with/without temozolomide is feasible and active in Ewing sarcoma, and further investigation is warranted.

Background Angiogenesis is critical for tumour growth and metastasis. Dual inhibition of vascular endothelial growth factors and platelet-derived growth factor receptors suppresses angiogenesis. This expansion cohort of a phase I study targeted angiogenesis with sorafenib, bevacizumab and low-dose cyclophosphamide in children and young adults with recurrent solid tumours. Methods An expansion cohort including patients with refractory or recurrent solid tumours was enrolled and received bevacizumab (15 mg/kg IV, day 1), sorafenib (90 mg/m2 po twice daily, days 1–21) and low-dose cyclophosphamide (50 mg/m2 po daily, days 1–21). Each course was 21 days. Toxicities were assessed using Common Terminology Criteria for Adverse Events, v3.0, and responses were evaluated by Response Evaluation Criteria in Solid Tumors criteria. Serial bevacizumab pharmacokinetic (PK) studies were performed during course 1. Results Twenty-four patients (15 males; median age 14.5 yrs; range 1–22 yr) received a median of 6 courses (range 1–18). Twelve patients had a bone or soft tissue sarcoma. The most common grade III/IV non-haematologic toxicities were hypertension (N = 4), hand/foot rash (N = 3) and elevated lipase (N = 3). The most common grade III/IV haematologic toxicities were neutropenia (N = 7) and lymphopenia (N = 17). Three patients (2 synovial sarcoma, 1 rhabdoid tumour) achieved a partial response and 18 had stable disease. The progression-free survival at 3 and 6 months were 78.1% (95% confidence interval [CI] 60.6–95.6%) and 54% (95% CI 30.2–78.2%), respectively. Bevacizumab PKs in 15 patients was similar to published adult PK results. Conclusions Intravenous bevacizumab combined with oral sorafenib and low-dose cyclophosphamide was tolerated and demonstrated promising activity in a subset of childhood solid tumours.

Background/Purpose MYCN-amplification in neuroblastoma is associated with an aggressive clinical phenotype. We evaluated the association of MYCN amplification with tumor response to neoadjuvant chemotherapy. Methods Primary tumor response, assessed by percentage volume change on CT scan and degree of tumor resection, assessed by the operating surgeon, were retrospectively compared in 84 high-risk neuroblastoma patients. There were thirty-four (40%) with MYCN-amplified tumors and fifty (60%) with non-amplified tumors treated at our institution from 1999 to 2016. Metastatic disease response was assessed on MIBG scan by change in Curie score. Results MYCN-amplification was associated with a greater mean percentage reduction in primary tumor volume after neoadjuvant chemotherapy (72.27% versus 46.83% [non-amplified tumors], p = 0.001). The percentage of patients with a Curie score > 2 at diagnosis who then had a score ≤ 2 after neoadjuvant chemotherapy was not significantly different (8 [61.5%] and 8 [34.8%], respectively, p = 0.37). Twenty-eight (85.7%) patients with MYCN-amplification had ≥ 90% surgical resection compared to 45 (91.84%) patients with non-amplified tumors (p = 0.303). Conclusions MYCN-amplification in high-risk neuroblastoma was associated with a better response of the primary tumor to neoadjuvant chemotherapy, but not metastatic sites, than in patients with non-amplified tumors. This did not significantly impact the ability to resect ≥ 90% of the primary tumor/locoregional disease. Type of Study Treatment Study Level of Evidence Level III

PURPOSEWe evaluated whether combining a humanized antidisialoganglioside monoclonal antibody (hu14.18K322A) throughout therapy improves early response and outcomes in children with newly diagnosed high-risk neuroblastoma.PATIENTS AND METHODSWe conducted a prospective, single-arm, three-stage, phase II clinical trial. Six cycles of induction chemotherapy were coadministered with hu14.18K322A, granulocyte-macrophage colony-stimulating factor (GM-CSF), and low-dose interleukin-2 (IL-2). The consolidation regimen included busulfan and melphalan. When available, an additional cycle of parent-derived natural killer cells with hu14.18K322A was administered during consolidation (n = 31). Radiation therapy was administered at the end of consolidation. Postconsolidation treatment included hu14.18K322A, GM-CSF, IL-2, and isotretinoin. Early response was assessed after the first two cycles of induction therapy. End-of-induction response, event-free survival (EFS), and overall survival (OS) were evaluated.RESULTSSixty-four patients received hu14.18K322A with induction chemotherapy. This regimen was well tolerated, with continuous infusion narcotics. Partial responses (PRs) or better after the first two chemoimmunotherapy cycles occurred in 42 of 63 evaluable patients (66.7%; 95% CI, 55.0 to 78.3). Primary tumor volume decreased by a median of 75% (range, 100% [complete disappearance]-5% growth). Median peak hu14.18K322A serum levels in cycle one correlated with early response to therapy ( P = .0154, one-sided t-test). Sixty of 62 patients (97%) had an end-of-induction partial response or better. No patients experienced progressive disease during induction. The 3-year EFS was 73.7% (95% CI, 60.0 to 83.4), and the OS was 86.0% (95% CI, 73.8 to 92.8), respectively.CONCLUSIONAdding hu14.18K322A to induction chemotherapy improved early objective responses, significantly reduced tumor volumes in most patients, improved end-of-induction response rates, and yielded an encouraging 3-year EFS. These results, if validated in a larger study, may be practice changing.

PURPOSE: Image-defined risk factors (IDRFs) are associated with surgical risks in neuroblastoma. We sought to evaluate the impact of neoadjuvant therapy on IDRFs and associated ability to achieve gross total resection of locoregional disease in patients with high-risk neuroblastoma. METHODS: We retrospectively reviewed charts of patients treated on four consecutive high-risk neuroblastoma protocols over a 20-year period at a single institution. The number of IDRFs at diagnosis and just prior to surgery, and the percent decrease of tumor volume from just prior to surgery to the end of induction were determined. RESULTS: Eighty-eight patients were included. There were 438 IDRFs (average 5.0±3.1/patient) at diagnosis and 198 (average 2.3±1.9/patient) after neoadjuvant chemotherapy (p90% GTR at 9.33 (95%CI 3.14–31.5). CONCLUSION: Neoadjuvant chemotherapy reduced the number of IDRFs in the majority of patients with high-risk neuroblastoma. The number of IDRFs present after neoadjuvant therapy correlated with the extent of resection.

Purpose: To determine the pharmacokinetics and skin toxicity profile of sorafenib in children with refractory/relapsed malignancies. Patients and Methods: Sorafenib was administered concurrently or sequentially with clofarabine and cytarabine to patients with leukemia or with bevacizumab and cyclophosphamide to patients with solid tumor malignancies. The population pharmacokinetics (PPK) of sorafenib and its metabolites and skin toxicities were evaluated. Results: In PPK analysis, older age, bevacizumab and cyclophosphamide regimen, and higher creatinine were associated with decreased sorafenib apparent clearance (CL/f; P < 0.0001 for all), and concurrent clofarabine and cytarabine administration was associated with decreased sorafenib N-oxide CL/f (P = 7e−4). Higher bilirubin was associated with decreased sorafenib N-oxide and glucuronide CL/f (P = 1e−4). Concurrent use of organic anion-transporting polypeptide 1B1 inhibitors was associated with increased sorafenib and decreased sorafenib glucuronide CL/f (P < 0.003). In exposure–toxicity analysis, a shorter time to development of grade 2–3 hand–foot skin reaction (HFSR) was associated with concurrent (P = 0.0015) but not with sequential (P = 0.59) clofarabine and cytarabine administration, compared with bevacizumab and cyclophosphamide, and with higher steady-state concentrations of sorafenib (P = 0.0004) and sorafenib N-oxide (P = 0.0275). In the Bayes information criterion model selection, concurrent clofarabine and cytarabine administration, higher sorafenib steady-state concentrations, larger body surface area, and previous occurrence of rash appeared in the four best two-predictor models of HFSR. Pharmacokinetic simulations showed that once-daily and every-other-day sorafenib schedules would minimize exposure to sorafenib steady-state concentrations associated with HFSR. Conclusions: Sorafenib skin toxicities can be affected by concurrent medications and sorafenib steady-state concentrations. The described PPK model can be used to refine exposure–response relations for alternative dosing strategies to minimize skin toxicity.

Purpose: We sought to evaluate whether combining a humanized antidisialoganglioside mAb (hu14.18K322A) with induction chemotherapy improves early responses and outcomes in children with newly diagnosed high-risk neuroblastoma. Patients and Methods: We conducted a prospective nonrandomized, single-arm, two-stage, phase II clinical trial. Six courses of induction chemotherapy were coadministered with hu14.18K322A and followed with granulocyte–macrophage colony-stimulating factor (GM-CSF) and low-dose IL2. Consolidation was performed with a busulfan/melphalan preparative regimen. An additional course of hu14.18K322A was administered with parent-derived natural killer cells, when available, during consolidation. Hu14.18K322A, GM-CSF, IL2, and isotretinoin were then administered. Secondary outcomes included reduced tumor volume and semiquantitative 123I-metaiodobenzylguanidine scoring [i.e., Curie scores (CS)] at the end of induction. Results: Forty-two patients received hu14.18K322A and induction chemotherapy. This regimen was well tolerated, with continuous-infusion narcotics adjusted to patient tolerance. Partial responses (PR) or better after the first two chemoimmunotherapy courses occurred in 32 patients [76.2%; 95% confidence interval (CI), 60.6–88.0]. This was accompanied by primary tumor volume reductions (median, –76%; range, –100% to 5%). Of 35 patients with stage IV disease who completed induction, 31 had end-of-induction CSs of 2 or less. No patients experienced progression during induction. Two-year event-free survival (EFS) was 85.7% (95% CI, 70.9–93.3). Conclusions: Adding hu14.18K322A to induction chemotherapy produced early PR or better in most patients, reduced tumor volumes, improved CSs at the end of induction, and yielded an encouraging 2-year EFS. These results, if validated in a larger study, may change the standard of care for children with high-risk neuroblastoma.

Pediatric sarcomas represent a heterogeneous group of malignancies that exhibit variable response to DNA-damaging chemotherapy. Schlafen family member 11 protein (SLFN11) increases sensitivity to replicative stress and has been implicated as a potential biomarker to predict sensitivity to DNA-damaging agents (DDA). SLFN11 expression was quantified in 220 children with solid tumors using IHC. Sensitivity to the PARP inhibitor talazoparib (TAL) and the topoisomerase I inhibitor irinotecan (IRN) was assessed in sarcoma cell lines, including SLFN11 knock-out (KO) and overexpression models, and a patient-derived orthotopic xenograft model (PDOX). SLFN11 was expressed in 69% of pediatric sarcoma sampled, including 90% and 100% of Ewing sarcoma and desmoplastic small round-cell tumors, respectively, although the magnitude of expression varied widely. In sarcoma cell lines, protein expression strongly correlated with response to TAL and IRN, with SLFN11 KO resulting in significant loss of sensitivity in vitro and in vivo. Surprisingly, retrospective analysis of children with sarcoma found no association between SLFN11 levels and favorable outcome. Subsequently, high SLFN11 expression was confirmed in a PDOX model derived from a patient with recurrent Ewing sarcoma who failed to respond to treatment with TAL + IRN. Selective inhibition of BCL-xL increased sensitivity to TAL + IRN in SLFN11-positive resistant tumor cells. Although SLFN11 appears to drive sensitivity to replicative stress in pediatric sarcomas, its potential to act as a biomarker may be limited to certain tumor backgrounds or contexts. Impaired apoptotic response may be one mechanism of resistance to DDA-induced replicative stress.

Introduction: Diffuse alveolar hemorrhage (DAH) is an early pulmonary complication of hematopoietic cell transplantation (HCT) associated with severe hypoxemic respiratory failure and mortality. Extracorporeal membrane oxygenation (ECMO) support is often used for respiratory failure refractory to conventional interventions; however, its use has been limited in HCT patients with DAH due to potential for worsening alveolar hemorrhage and reported high mortality.Case Presentation: We report two cases of DAH following HCT who developed refractory hypoxemic respiratory failure despite cessation of bleeding and were successfully supported with ECMO.Conclusion: DAH after HCT should not automatically preclude ECMO support; rather, these patients must be evaluated individually for ECMO within the context of their overall clinical picture.

Pediatric sarcomas represent a heterogeneous group of malignancies that exhibit variable response to DNA damaging chemotherapy. Schlafen family member 11 protein (SLFN11) increases sensitivity to replicative stress, and SLFN11 gene silencing has been implicated as a common mechanism of drug resistance in tumors in adults. We found SLFN11 to be widely expressed in our cohort of pediatric sarcomas. In sarcoma cell lines, protein expression strongly correlated with response to the PARP inhibitor talazoparib (TAL) and the topoisomerase I inhibitor irinotecan (IRN), with SLFN11 knockout resulting in significant loss of sensitivity in vitro and in vivo. However, SLFN11 expression was not associated with favorable outcomes in a retrospective analysis of our patient cohort; instead, the protein was retained and promoted tumor growth and evasion. Furthermore, we show that pediatric sarcomas develop resistance to TAL and IRN through impaired intrinsic apoptosis, and that resistance can be reversed by selective inhibition of BCL-XL.Statement of SignificanceThe role of SLFN11 in pediatric sarcomas has not been thoroughly explored. In contrast to its activity in adult tumors, SLFN11 did not predict favorable outcomes in pediatric patients, was not silenced, and promoted tumor growth. Resistance to replicative stress in SLFN11-expressing sarcomas was reversed by selective inhibition of BCL-XL.

For children with neuroblastoma, the likelihood of cure varies widely according to age at diagnosis, disease stage, and tumor biology. Treatments are tailored for children with this clinically heterogeneous malignancy on the basis of a combination of markers that are predictive of risk of relapse and death. Sequential risk-based, cooperative-group clinical trials conducted during the past 4 decades have led to improved outcome for children with neuroblastoma. Increasingly accurate risk classification and refinements in treatment stratification strategies have been achieved with the more recent discovery of robust genomic and molecular biomarkers. In this review, we discuss the history of neuroblastoma risk classification in North America and Europe and highlight efforts by the International Neuroblastoma Risk Group (INRG) Task Force to develop a consensus approach for pretreatment stratification using seven risk criteria including an image-based staging system—the INRG Staging System. We also update readers on the current Children’s Oncology Group risk classifier and outline plans for the development of a revised 2021 Children’s Oncology Group classifier that will incorporate INRG Staging System criteria to facilitate harmonization of risk-based frontline treatment strategies conducted around the globe. In addition, we discuss new approaches to establish increasingly robust, future risk classification algorithms that will further refine treatment stratification using machine learning tools and expanded data from electronic health records and the INRG Data Commons.

BackgroundNatural killer (NK) cells are one of the main effector populations of immunotherapy with monoclonal antibody and cytokines, used in combination with chemotherapy to treat children with high-risk neuroblastoma on this phase II trial. However, the impact of chemoimmunotherapy on NK cell kinetics, phenotype, and function is understudied.MethodsWe prospectively examined NK cell properties from 63 children with newly diagnosed neuroblastoma enrolled in a phase II trial (NCT01857934) and correlated our findings with tumor volume reduction after 2 courses of chemoimmunotherapy. NK cell studies were conducted longitudinally during chemoimmunotherapy and autologous hematopoietic cell transplantation (autoHCT) with optional haploidentical NK cell infusion and additional immunotherapy.ResultsChemoimmunotherapy led to significant NK cytopenia, but complete NK cell recovery reliably occurred by day 21 of each therapy course as well as after autoHCT. Haploidentical NK cell infusion elevated the NK cell count transiently during autoHCT. NK cell cytotoxicity increased significantly during treatment compared with diagnosis. In addition, NK cells maintained their ability to respond to cytokine stimulation in culture longitudinally. Unsupervised cluster analysis of CD56brightNK cell count and tumor volume at diagnosis and after two courses of chemoimmunotherapy identified two patient groups with distinct primary tumor sizes and therapy responses.ConclusionAfter profound NK cytopenia due to chemoimmunotherapy, endogenously reconstituted NK cells exhibit enhanced NK cytotoxicity compared with pretherapy measurements. Our data suggest a relationship between CD56brightexpression and tumor size before and after two courses of chemoimmunotherapy; however, future studies are necessary to confirm this relationship and its predictive significance.Trial registration numberNCT01857934.

Aggressive cancers often have activating mutations in growth-controlling oncogenes and inactivating mutations in tumor-suppressor genes. In neuroblastoma, amplification of the MYCN oncogene and inactivation of the ATRX tumor-suppressor gene correlate with high-risk disease and poor prognosis. Here we show that ATRX mutations and MYCN amplification are mutually exclusive across all ages and stages in neuroblastoma. Using human cell lines and mouse models, we found that elevated MYCN expression and ATRX mutations are incompatible. Elevated MYCN levels promote metabolic reprogramming, mitochondrial dysfunction, reactive-oxygen species generation, and DNA-replicative stress. The combination of replicative stress caused by defects in the ATRX–histone chaperone complex, and that induced by MYCN-mediated metabolic reprogramming, leads to synthetic lethality. Therefore, ATRX and MYCN represent an unusual example, where inactivation of a tumor-suppressor gene and activation of an oncogene are incompatible. This synthetic lethality may eventually be exploited to improve outcomes for patients with high-risk neuroblastoma., In most cancers, mutations that lead to oncogene activation and tumor suppressor inactivation synergize to promote tumorigenesis. However, in neuroblastomas, MYCN amplification and ATRX mutations are mutually exclusive and incompatible.

BACKGROUND Patients with metastatic Ewing sarcoma experience poor outcomes despite intensive systemic and local therapy. Early chemotherapy response of pulmonary metastases has been associated with prognosis in other pediatric malignancies. We reviewed the outcomes of patients with Ewing sarcoma and pulmonary metastases treated at our institution based on therapy received and early pulmonary response. MATERIALS AND METHODS We retrospectively reviewed patients with newly diagnosed Ewing sarcoma and pulmonary metastases at St. Jude Children's Research Hospital between 1979 and 2015. Data obtained included demographic and treatment characteristics including chemotherapy, local control measures, whole lung irradiation (WLI) administration, autologous stem cell transplantation, and outcomes. Patients were evaluated for radiographic post-induction pulmonary complete response (CR). We estimated event-free survival (EFS) and overall survival (OS) and used Cox proportional hazards regression to examine the effects of clinical and treatment factors on outcomes. RESULTS Fifty-four patients (median age, 12.9 years) were evaluated. Post-induction pulmonary CR was observed in 33 (61%) patients. WLI was delivered to 16 patients (4/33 with pulmonary CR and 12/21 with non-CR). At median 3.6 years follow-up, five-year EFS and OS were 30.8% ± 6.4% and 49.6% ± 7.1%, respectively. Post-induction pulmonary CR was associated with prolonged EFS (P

Secondary myelodysplastic syndromes and acute myeloid leukemia (sMDS/AML) are rare myeloid neoplasms in children/adolescents and have a dismal prognosis. The mainstay therapy is hematopoietic cell transplantation (HCT) but there has been little therapeutic innovation for decades and outcomes remain poor. CPX-351, a fixed 5:1 molar ratio of liposomal cytarabine/daunorubicin, has shown favorable safety and efficacy in elderly individuals with sAML and children with relapsed de novo AML, which led the FDA to recently expand the label of CPX-351 to include pediatric patients with secondary AML, however, no data has been reported in this patient group. We report the outcomes of seven young patients with newly diagnosed sMDS/AML uniformly treated with CPX-351. Five patients had previously received chemotherapy for osteosarcoma, Ewing sarcoma, neuroblastoma, or T-ALL; one had predisposing genomic instability disorder (Cornelia de Lange syndrome); and one presented with MDS-related AML and multi-organ failure. The median age at diagnosis of myeloid malignancy was 17 (13-23) years. We identified somatic mutations and copy-number changes across 16 leukemia driver genes in six cases (including TP53 in two), abnormal karyotypes in six cases and rearrangements involving MECOM or NIM1K-TERT in two patients. Additional genomic studies identified pathogenic germline mutations in CHEK2 and SMC3 each in a single patient . Patients received 1-3 cycles of CPX-351 (100 units/m 2 on days 1, 3, and 5) resulting in complete morphologic remission without overt toxicity or treatment-related mortality. This approach allowed for adding FLT3 inhibitor as individualized therapy in one patient. Six patients were alive and leukemia-free at 0.51-3.25 years after HCT. One patient died from disease progression before HCT. Concluding, CPX-351 is an effective and well-tolerated regimen for cytoreduction in pediatric secondary myeloid malignancies warranting further investigation Figure 1 Figure 1. Disclosures Triplett: Miltenyi: Other: Travel, meeting registration.

Purpose: Anti-GD2 mAbs, acting via antibody-dependent cell-mediated cytotoxicity, may enhance the effects of chemotherapy. This pilot trial investigated a fixed dose of a unique anti-GD2 mAb, hu14.18K322A, combined with chemotherapy, cytokines, and haploidentical natural killer (NK) cells. Experimental Design: Children with recurrent/refractory neuroblastoma received up to six courses of hu14.18K322A (40 mg/m2/dose, days 2–5), GM-CSF, and IL2 with chemotherapy: cyclophosphamide/topotecan (courses 1,2), irinotecan/temozolomide (courses 3,4), and ifosfamide/carboplatin/etoposide (courses 5,6). Parentally derived NK cells were administered with courses 2, 4, and 6. Serum for pharmacokinetic studies of hu14.18K322A, soluble IL2 receptor alpha (sIL2Rα) levels, and human antihuman antibodies (HAHA) were obtained. Results: Thirteen heavily pretreated patients (9 with prior anti-GD2 therapy) completed 65 courses. One patient developed an unacceptable toxicity (grade 4 thrombocytopenia >35 days). Four patients discontinued treatment for adverse events (hu14.18K322A allergic reaction, viral infection, surgical death, second malignancy). Common toxicities included grade 3/4 myelosuppression (13/13 patients) and grade 1/2 pain (13/13 patients). Eleven patients received 29 NK-cell infusions. The response rate was 61.5% (4 complete responses, 1 very good partial response, 3 partial responses) and five had stable disease. The median time to progression was 274 days (range, 239–568 days); 10 of 13 patients (77%) survived 1 year. Hu14.18K322A pharmacokinetics was not affected by chemotherapy or HAHA. All patients had increased sIL2Rα levels, indicating immune activation. Conclusions: Chemotherapy plus hu14.18K322A, cytokines, and NK cells is feasible and resulted in clinically meaningful responses in patients with refractory/recurrent neuroblastoma. Further studies of this approach are warranted in patients with relapsed and newly diagnosed neuroblastoma. Clin Cancer Res; 23(21); 6441–9. ©2017 AACR.

Paediatric solid tumours arise from endodermal, ectodermal, or mesodermal lineages. Although the overall survival of children with solid tumours is 75%, that of children with recurrent disease is below 30%. To capture the complexity and diversity of paediatric solid tumours and establish new models of recurrent disease, here we develop a protocol to produce orthotopic patient-derived xenografts at diagnosis, recurrence, and autopsy. Tumour specimens were received from 168 patients, and 67 orthotopic patient-derived xenografts were established for 12 types of cancer. The origins of the patient-derived xenograft tumours were reflected in their gene-expression profiles and epigenomes. Genomic profiling of the tumours, including detailed clonal analysis, was performed to determine whether the clonal population in the xenograft recapitulated the patient's tumour. We identified several drug vulnerabilities and showed that the combination of a WEE1 inhibitor (AZD1775), irinotecan, and vincristine can lead to complete response in multiple rhabdomyosarcoma orthotopic patient-derived xenografts tumours in vivo.

Introduction: Venetoclax is a selective BCL2 inhibitor approved for the treatment of CLL and AML in adults and is currently being evaluated in several hematologic and solid malignancies. While plasma pharmacokinetics (PK) of venetoclax is well documented, data regarding the accumulation of venetoclax into the central nervous system (CNS) are limited. Venetoclax has a molecular weight of 868.44 which was hypothesized to limit its passage through the tight junctions of the blood brain barrier (BBB). Moreover, venetoclax is a substrate of the P- glycoprotein (P-gp) and breast cancer resistance protein (BCRP) efflux transporters, expressed by endothelial cells at the BBB, which presents an extra hurdle for penetration into the CNS. In this analysis we characterized the passage of venetoclax into the CNS using PK samples collected during a phase 1 study (NCT03236857) of pediatric patients with relapsed and refractory acute leukemia receiving venetoclax in combination with chemotherapy. Methods: PK samples from cerebrospinal fluid (CSF) were collected at screening and if a lumbar puncture was performed as standard of care during treatment. Plasma PK samples were collected throughout the study. CSF and plasma concentrations of venetoclax were determined using liquid-liquid extraction followed by liquid chromatography (LC) with tandem mass spectrometric detection (MS/MS). The lower limit of quantitation for venetoclax was 2.14 ng/mL in plasma and 0.1ng/mL in CSF. Results: There was a total of 66 samples from 33 patients with relapsed or refractory AML or ALL. The venetoclax concentration in CSF ranged between Conclusion: To our knowledge this is the first study reporting venetoclax CSF pharmacokinetics in the AML and ALL setting. The lower disposition observed in humans is contrary to our expectation, given the significantly higher expression of P-gp in mice BBB compared to humans and suggests that other factors are involved in venetoclax disposition to the CSF. The ability of venetoclax to cross the blood brain barrier may explain the reported activity of venetoclax in treatment of hematologic malignancies with CNS involvement1,2. References: Reda G, Cassin R, Dovrtelova G, et al. Venetoclax penetrates in cerebrospinal fluid and may be effective in chronic lymphocytic leukemia with central nervous system involvement. Haematologica. 2019;104(5):e222-e223. doi:10.3324/haematol.2018.213157 Beziat G, Gauthier M, Protin C, et al. Venetoclax with high-dose methotrexate and rituximab seem effective and well-tolerated in the treatment of central nervous system involvement of chronic lymphocytic leukemia: A case report. Clin Case Rep. 2020;8(2):269-273. Published 2020 Jan 10. doi:10.1002/ccr3.2580 Disclosures Salem: AbbVie Inc.: Current Employment, Other: may hold stock or other options. Badawi:AbbVie Inc.: Current Employment, Other: may hold stock or other options. Place:Novartis: Consultancy, Other: Institutional Research Funding; AbbVie: Consultancy. Palenski:AbbVie: Current Employment, Other: may hold stock or other options. Arrendale:AbbVie Inc.: Current Employment, Other: may hold stock or other options. Kim:AbbVie, Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months, Other: may hold stock or other options. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019). Menon:AbbVie Inc.: Current Employment, Other: may hold stock or other options.

Secondary hemophagocytic syndrome (HPS) has been described after autologous hematopoietic cell transplant (AutoHCT). We report two cases of secondary HPS after novel consolidation therapy for high-risk neuroblastoma as part of an institutional phase 2 trial incorporating immunotherapy into a "standard" AutoHCT regimen. Both patients developed liver dysfunction beyond expected course of hepatic veno-occlusive disease, coagulopathy, hyperferritinemia, and when evaluated, elevated soluble interleukin-2 receptor and hemophagocytosis. These cases highlight the need for clinicians to have a high index of suspicion for immune-related complications in patients receiving immune therapies.

// Andrew D.J. Pearson 1 , Sara M. Federico 2 , Isabelle Aerts 3 , Darren R. Hargrave 4 , Steven G. DuBois 5 , Robert Iannone 6 , Ryan D. Geschwindt 6 , Ruixue Wang 7 , Frank G. Haluska 8 , Tanya M. Trippett 9 , Birgit Geoerger 10 1 Paediatric Drug Development Unit, Children and Young People’s Unit, Institute of Cancer Research, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom (Retired) 2 Department of Pediatric Oncology, St. Jude Children’s Research Hospital, Memphis, TN, USA 3 Department of Pediatric, Adolescent and Young Adult Oncology, Institut Curie, Paris, France 4 Haematology and Oncology Department, Great Ormond Street Hospital for Children, London, United Kingdom 5 Department of Pediatrics, University of California San Francisco School of Medicine, and Benioff Children’s Hospital, San Francisco, CA, USA (current affiliation: Dana-Farber/Boston Children’s Cancer and Blood Disorders Center and Harvard Medical School, Boston, MA, USA) 6 Clinical Research, Merck & Co., Inc., North Wales, PA, USA 7 BARDS, MSD RD 18 were evaluable for dose-limiting toxicities. One dose-limiting toxicity (grade 3 increased alanine aminotransferase) occurred in 1 patient at 33 mg/m 2 . Dose escalation concluded at 33 mg/m 2 ; the maximum tolerated dose was not determined. The most common treatment-related adverse events (frequency ≥40%) were manageable grade 1–2 stomatitis, thrombocytopenia, hypertriglyceridemia, increased alanine aminotransferase, fatigue, hypercholesterolemia, anemia, and increased aspartate aminotransferase. Ridaforolimus exposure at 28 mg/m 2 and 33 mg/m 2 exceeded adult target levels. The RP2D for oral ridaforolimus in children was defined as 33 mg/m 2 . Four patients received at least 4 cycles; 2 with pineoblastoma and diffuse intrinsic pontine glioma had stable disease for 12 and 46 cycles, respectively. Conclusions: Ridaforolimus is orally bioavailable and well tolerated in children with advanced solid tumors. The RP2D (33 mg/m 2 , 5 days/week) exceeds the adult RP2D. The favorable toxicity and pharmacokinetic profiles may allow for combination therapy, a promising therapeutic option in pediatric malignancies.

Significant advances have been made over the past 25 years in our understanding of the most common adult solid tumors such as breast, colon, lung and prostate cancer. Much less is known about childhood solid tumors because they are rare and because they originate in developing organs during fetal development, childhood and adolescence. It can be very difficult to study the cellular origins of pediatric solid tumors in developing organs characterized by rapid proliferative expansion, growth factor signaling, developmental angiogenesis, programmed cell death, tissue reorganization and cell migration. Not only has the etiology of pediatric cancer remained elusive because of their developmental origins, but it also makes it more difficult to treat. Molecular targeted therapeutics that alter developmental pathway signaling may have devastating effects on normal organ development. Therefore, basic research focused on the mechanisms of development provides an essential foundation for pediatric solid tumor translational research. In this article, we describe new resources available for the developmental biology and oncology research communities. In a companion paper, we present the detailed characterization of an orthotopic xenograft of a pediatric solid tumor derived from sympathoadrenal lineage during development.

Recent advances in T cell-based immunotherapies have revolutionized treatment strategies for several types of cancers; however, approaches that rely on endogenous T cell responses have experienced limited success in pediatric populations, a pattern primarily attributed to the relatively low mutational burden characteristic of pediatric tumors. Here, we report our analysis of CD8 T cells isolated from a diverse set of pediatric solid tumors, documenting an enrichment of CD8 T cells with an antigen-experienced phenotype (i.e., high PD1 expression). The limited ability of immune checkpoint blockade therapy (ICBT) to trigger anti-tumor responses in pediatric populations, despite the presence of activated CD8 T cells in these tumors prompted us to explore alternative mechanisms restricting the endogenous T cell response. Using a novel, transplantable mouse tumor model that expresses a well-characterized epitope coupled to a mCherry marker, we identified antigen cross-presentation by tumor-infiltrating myeloid cells as a key mediator of CD8 T cell effector function in tumors. Specifically, we show that tumor microenvironment (TME)-mediated suppression of CD8 T cell polyfunctionality occurs even in the absence of direct antigen-presentation by tumor cells, suggesting that antigen cross-presentation is sufficient to enforce this dysfunctional state. Strikingly, age-related changes in the TME had a significant impact on the differentiation of tumor-specific CD8 T cells. Cross-presentation of tumor antigens in the young animals skewed the effector differentiation of tumor-specific CD8 T cells toward a TCF7lowGzmBhi terminally differentiated state. Profiling of tumor-infiltrating antigen-presenting cells by scRNAseq revealed the differential polarization of the myeloid compartment towards M1 and M2 phenotypes between the young and adult tumors, respectively. Consistent with our mouse findings, analysis of immune infiltrates from human pediatric solid tumors revealed a strong correlation between the expression of PDL1 on myeloid cells and enrichment of tumor-associated CD8 T cells with an exhaustion phenotype (PD1hiTim3+). Collectively, these data indicate that the “young” microenvironment of an actively developing tissue/individual contributes to the generation of an immune response skewed towards a terminally differentiated state with limited plasticity, thus narrowing the window for immunotherapeutic interventions. Citation Format: Ardiana Moustaki, Jeremy Chase Crawford, Shanta Alli, Anthony Zamora, Yiping Fan, Shannon Boi, Natalie M. McDonald, Paul G. Thomas, Alberto S. Pappo, Michael A. Dyer, Elizabeth Stewart, Sara Federico, Ben Youngblood. Antigen-cross presentation promotes development of terminally differentiated CD8 T cells in young individuals [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 LB-074.

Despite making significant advances over the past 25 years in our understanding of the most common adult solid tumors, much less is known about childhood solid tumors. We have previously described a protocol to produce orthotopic patient-derived xenografts (O-PDX) at diagnosis, recurrence and autopsy. These O-PDX models provide both in vivo and in vitro systems to study mechanisms of disease origin, tumor progression and preclinical testing. Here, we present an innovative cloud-based all-in-one data portal to explore various biological features of these pediatric O-PDX models. The vast diversity of the collected childhood solid tumors is represented in 166 O-PDX models, consisting of 21 diagnoses including Neuroblastoma, Osteosarcoma, Rhabdomyosarcoma, and a large number of rare solid tumors including Ewing Sarcoma, Desmoplastic Small Cell Round Tumor, Fibrosarcoma, High Grade Sarcoma, Liposarcoma, Retinoblastoma, Rhabdoid Tumor and Synovial Sarcoma. The O-PDX models have been characterized and compared to the original patient tumor using various methods and assays including histology, electron microscopy, short tandem repeat DNA profiling, chemical compound screening as well as genomic sequencing (whole genome sequencing, whole exome sequencing, and RNA Sequencing) and clonal analysis to determine the clonal population in the O-PDX. Somatic genetic mutations as well as clonal architecture is retained in the majority of O-PDX tumors. The data on O-PDX models can now be visualized and compared in our web-based CSTN data portal on St Jude Cloud (www.stjude.cloud). The user-friendly interface allows both gene and sample level search and visualization. For genomics variations, the presence or absence of a particular variant can be observed through interactive heatmaps. In addition to genomic and transcriptomic profiles, some of these models have extensive epigenomic and proteomic profiling which are integrated into the portal. We have also included chemical sensitivity heatmaps and dose response curves for common oncology drugs using primary cultures of the O-PDXs and cell lines. Importantly, the raw genomics sequencing data is also available from St Jude Cloud, following a straightforward application and approval process for access. In summary, the integration of data from multi-omics and beyond at the CSTN data portal provides a rich resource for both academic and industrial research community to find the appropriate models to advance the knowledge and therapeutic solutions to the catastrophic childhood solid tumors. *co-first #co-corresponding Citation Format: Asa Karlstrom, Ti-Cheng Chang, Darrell Gentry, Xin Zhou, Elizabeth Stewart, Brittney Gordon, Sara M. Federico, Rachel Brennan, Michael R. Clay, Sharon Frase, Armita Bahrami, Xiang Chen, Anang A. Shelat, Nathaniel R. Twarog, Daniel Alford, Anthony Woodard, Edgar Sioson, Irina McGuire, Cynthia Williams, Nedra Robison, Brandon McMahan, Ashok K. Boddu, Swapnali Mohite, Kirby Birch, Clay McLeod, Michael Rusch, Alberto Pappo, Keith Perry, Gang Wu, Ed Suh, Michael A. Dyer. An innovative integrated cloud-based data portal for orthotopic patient-derived xenografts (O-PDX) available through the Childhood Solid Tumor Network (CSTN) [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 6149.

10524 Background: Dependence on the prosurvival protein B-cell lymphoma 2 (BCL-2) occurs in certain pediatric solid tumors, resulting in tumorigenesis and resistance to therapies. Venetoclax (VEN), an orally administered BCL-2-selective inhibitor, has preclinical anticancer activity in human-derived neuroblastoma models. Reported here are preliminary results from pediatric patients (pts) with recurrent or refractory (R/R) solid tumors treated with VEN monotherapy or VEN with cyclophosphamide and topotecan (Cy-Topo). Methods: This phase 1 open-label, 2-part study (NCT03236857) enrolled pts < 25 yr old with R/R malignancies; we report only on pts with solid tumors. Following a dose ramp-up, pts received 800 mg VEN (age/weight-adjusted adult equivalent) once daily for the first 8 wk; Cy-Topo was added optionally after wk 8. Dose-limiting toxicities (DLTs) were assessed during the first 21 days of VEN therapy or cycle 1 of VEN-Cy-Topo. Objectives included safety, toxicity, and preliminary efficacy. Results: As of Dec 17, 2019, 11 solid tumor pts were enrolled: neuroblastoma (n = 6), rhabdomyosarcoma (n = 2), Wilms’ tumor, Carney-Stratakis syndrome, and low-grade fibromyxoid sarcoma (n = 1 each). Median age was 11 yr (range 3–22); median time on study was 6.9 mo (range 1.2–17.8). All pts experienced ≥1 treatment-emergent adverse event (TEAE); vomiting (72%; all grades) was most common. Grade ≥3 TEAEs were reported in 82% of pts; febrile neutropenia (64%), decreased blood cell count, and neutropenia (36% each) were the most common. Seven pts received 800-mg monotherapy for 8 wk; 3 of these pts did not receive Cy-Topo after monotherapy. Of the 7 pts who received VEN-Cy-Topo, 3 pts received 400 mg VEN with Cy-Topo. DLTs of grade 4 neutropenia/thrombocytopenia with delayed count recovery occurred in 2 pts on 800 mg VEN-Cy-Topo, necessitating a dose de-escalation (to 400 mg VEN). Grade 4 neutropenia occurred in 2 pts on 400 mg VEN with Cy-Topo, leading to the addition of myeloid growth factor to the therapy regimen. The best response after 8 wk of VEN monotherapy was stable disease (SD). Six pts were evaluable for tumor response with VEN-Cy-Topo; 1 neuroblastoma pt had a complete response after 5 cycles of 400 mg VEN, 4 pts had SD (3 on 800 mg and 1 on 400 mg VEN) and 1 (800 mg VEN) had progressive disease as best response. Conclusions: Continuous dosing of VEN with Cy-Topo was not tolerated due to cytopenias in 4/7 pts with solid tumors. Discontinuous dosing of VEN with Cy-Topo is being explored. Clinical trial information: NCT03236857.

ATRX alterations occur at high frequency in neuroblastoma of adolescents and young adults. Particularly intriguing are the large N-terminal deletions of ATRX (Alpha Thalassemia/Mental Retardation, X-linked) that generate in-frame fusion (IFF) proteins devoid of key chromatin interaction domains, while retaining the SWI/SNF-like helicase region. We demonstrate that ATRX IFF proteins are redistributed from H3K9me3-enriched chromatin to promoters of active genes and identify REST as an ATRX IFF target whose activation promotes silencing of neuronal differentiation genes. We further show that ATRX IFF cells display sensitivity to EZH2 inhibitors, due to derepression of neurogenesis genes, including a subset of REST targets. Taken together, we demonstrate that ATRX structural alterations are not loss-of-function and put forward EZH2 inhibitors as a potential therapy for ATRX IFF neuroblastoma.

Purpose: The use of celiac plexus block (CPB) for abdominal pain has been extensively reported in adults. However, pediatric literature is limited to three single case reports and a series of three cases. This study evaluated the effectiveness of CPB in children and young adults (aged 8–20 years) with abdominal malignancies. Methods: Pain outcomes after CPB were evaluated in four children and young adults with cancer. Mean daily pain score (PS, 0–10) and morphine consumption (intravenous morphine equivalent daily [MED], mg/kg/day) before and after CPB were used to assess effectiveness. Results: Mean daily PS reduced after CPB in all patients. In one patient, this reduction was sustained up to 6 months of follow-up, and analgesics were discontinued 1 week after CPB. The other three patients had limited survival (6, 16, and 37 days) after CPB. One patient had a PS of 0 over the last few days of life, but the MED was escalated from 0.74 before the block to 5.4 mg/kg/day at the end of life. In the other two patients, MED was lower during the first week after CPB than that before CPB (4.55 vs. 1.59 and 2.88 vs. 1.51 mg/kg/day, respectively). As these two patients had disease progression during their last days of life, the MED was increased to 4.75 and 263.9 mg/kg/day, respectively. Conclusions: Our results suggest that CPB may contribute to reducing PS and MED. We observed the use of CPB rather late in the disease trajectory.