Liu, Xiaowei

10051 Background: CBL0137 is a novel agent that targets the FAcilitates Chromatin Transcription complex (FACT), a histone chaperone that regulates chromatin remodeling during transcription, replication, and DNA repair. CBL0137 has been shown to have anti-tumor activity in multiple preclinical models of pediatric cancer. We report the phase 1 trial of CBL0137 in children with relapsed or refractory solid tumors including central nervous system (CNS) tumors or lymphoma (NCT04870944). Methods: Patients (age 12 months to 21 years) with relapsed/refractory solid tumors, central nervous system tumors or lymphoma were eligible. In the dose escalation phase, a rolling-six design was used to evaluate CBL0137 administered intravenously (IV) once per week on Days 1 and 8 of a 21-day cycle. The starting dose was 400 mg/m 2 , with escalation to the adult phase 2 dose (RP2D) of 540 mg/m 2 . The maximum tolerated dose (MTD) was determined based on cycle 1 dose limiting toxicity (DLT) using Common Toxicity Criteria for Adverse Events (v5). Pharmacokinetics (PK) and cytokine analyses were performed during cycle 1. Seven additional patients ( < 18 years old) were accrued to a PK expansion cohort at the RP2D. Results: Sixteen patients were enrolled; 14 were evaluable for DLT assessment (12 at 400mg/m 2 [6 in dose escalation and 6 in PK expansion] and 2 at 540mg/m 2 ). The median (range) age was 10 (4-20) years. Diagnoses included high grade glioma (n = 6), osteosarcoma (n = 5), ependymoma (n = 2), neuroblastoma, hepatoblastoma and Burkitt’s lymphoma (1 each). One of 12 evaluable patients treated at 400 mg/m 2 experienced a DLT: Grade 3 photosensitivity. At 540 mg/m 2 , the two evaluable patients both had fever and dose limiting Grade 3 hypotension. Non-dose limiting Grade 3-4 toxicities included anemia, lymphopenia, neutropenia, thrombocytopenia, hypokalemia, anorexia, photosensitivity and fever. For both dose levels, a total of 12 patients were reported to have at least one episode of Grades 1-3 fever and/or Grade 1 cytokine release syndrome (CRS). PK parameters (mean±SD) for CBL0137 (400 mg/m 2 ) were T max = 0.7 ± 0.5 h, C max = 1310 ± 417 ng/mL, and AUC 0-24h = 15300 ± 6790 h·ng/mL. Given the unexpected toxicities of fever, hypotension, and CRS, cytokine samples were collected in patients enrolled in the PK expansion cohort; all had Grade 1 CRS and significantly elevated levels of both IL-10 (adj p = 0.001) and IL-1RA (adj p < 0.001) at 24 hours vs pre-infusion. Conclusions: The RP2D and MTD of CBL0137 in children and adolescents with solid or CNS tumors is 400mg/m 2 IV weekly on Days 1 and 8 of 21-day cycles. CBL0137 leads to immune activation, with cytokine elevation and the possibility of CRS, an unexpected toxicity not previously reported in adults. A Phase 2 cohort in patients with Diffuse Midline Glioma is ongoing and includes further assessment of immune activation. Clinical trial information: NCT04870944 .

AbstractPurposePepinemab, a humanized IgG4 monoclonal antibody, targets the SEMA4D (CD100) antigen to inhibit binding to its high‐affinity receptors (plexin B1/PLXNB1, plexin B2/PLXNB2) and low‐affinity receptor (CD72). SEMA4D blockade leads to increased cytotoxic T‐cell infiltration, delayed tumor growth, and durable tumor rejection in murine tumor models. Pepinemab was well tolerated and improved T cell infiltration in clinical studies in adults with refractory tumors. SEMA4D was identified as a strong candidate proto‐oncogene in a model of osteosarcoma. Based on these preclinical and clinical data, we conducted a phase 1/2 study to determine the recommended phase 2 dose (RP2D), pharmacokinetics, pharmacodynamics, and immunogenicity, of pepinemab in pediatric patients with recurrent/refractory solid tumors, and activity in osteosarcoma.Experimental designPepinemab was administered intravenously on Days 1 and 15 of a 28‐day cycle at 20 mg/kg, the adult RP2D. Part A (phase 1) used a Rolling 6 design; Part B (phase 2) used a Simon 2‐stage design in patients with osteosarcoma. Pharmacokinetics and target saturation were evaluated in peripheral blood.ResultsPepinemab (20 mg/kg) was well tolerated and no dose‐limiting toxicities were observed during Part A. There were no objective responses. Two patients with osteosarcoma achieved disease control and prolonged stable disease. Pepinemab pharmacokinetics were similar to adults.ConclusionsPepinemab (20 mg/kg) is safe, well tolerated and resulted in adequate and sustained target saturation in pediatric patients. Encouraging disease control in two patients with osteosarcoma warrants further investigation with novel combination strategies to modulate the tumor microenvironment and antitumor immune response.Clinical trial registryThis trial is registered as NCT03320330 at Clinicaltrials.gov.DisclaimerThe content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

AbstractBackgroundRamucirumab is a monoclonal antibody that binds the extracellular domain of vascular endothelial growth factor receptor (VEGFR‐2) and prevents binding of VEGF ligands. Based on population pharmacokinetic (PK) analysis and correlation with efficacy in adults, a target steady state trough concentration (Css,min) ≥ 50 µg/mL was established.ProceduresThis phase 1 trial (ADVL1416) used a rolling six design and a PK primary endpoint to define the recommended phase 2 dose (RP2D) of ramucirumab in children with recurrent/refractory solid tumors. Two dose levels (DL) were planned (DL1: 8 mg/kg, DL2: 12 mg/kg administered intravenously [IV] every 2 weeks). Toxicity during the initial 6 weeks was used to assess maximum tolerated dose (MTD). Cycle 1 Day 42 trough (Cmin) ≥ 50 µg/mL was the target concentration for the PK endpoint. At the RP2D, cohorts for PK expansion and children with central nervous tumors were planned.ResultsTwenty‐nine patients were enrolled; 28 were eligible; median age [range] = 13.5 [1–21] years; 22 were evaluable for the PK endpoint. Dose‐limiting proteinuria occurred at both DLs; however, the MTD was not exceeded. At DL2 (12 mg/kg), the median Day 42 Cmin (n = 16) was 87.8 µg/mL; 15 of 16 patients achieved a Cmin ≥ 50 µg/mL.ConclusionRamucirumab was well tolerated in children and adolescents with solid tumors. The RP2D for ramucirumab was 12 mg/kg IV every 2 weeks. This trial demonstrates the feasibility of incorporating a primary PK endpoint to determine dose escalation and the RP2D in children. Studies of ramucirumab in children with selected solid tumors are ongoing.

AbstractBackgroundOutcomes for children with relapsed/refractory (R/R) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) are poor, and new therapies are needed. Pevonedistat is an inhibitor of the NEDD‐8 activating enzyme, a key regulator of the ubiquitin proteasome system that is responsible for protein turnover, with protein degradation regulating cell growth and survival.ProcedureWe evaluated the feasibility, toxicity, and pharmacokinetics (PK) of pevonedistat (20 mg/m2 days 1, 3, 5) in combination with azacitidine, fludarabine, cytarabine (aza‐FLA) in children with R/R AML and MDS (NCT03813147). Twelve patients were enrolled, median age was 13 years (range 1–21). Median number of prior chemotherapeutic regimens was two (range one to five), and two (25%) patients had prior hematopoietic cell transplantation. Diagnoses were AML NOS (n = 10, 83%), acute monocytic leukemia (n = 1), and therapy‐related AML (n = 1).ResultsOverall, three of 12 (25%) patients experienced DLTs. The day 1 mean ± SD (n = 12) Cmax, VSS, T1/2, and CL were 223 ± 91 ng/mL, 104 ± 53.8 L/m2, 4.3 ± 1.2 hours, and 23.2 ± 6.9 L/h/m2, respectively. T1/2, VSS, and Cmax, but not CL, were significantly different between age groups. The overall response rate was 25%, with n = 3 patients achieving a complete remission with incomplete hematologic recovery (CRi).ConclusionsPevonedistat 20 mg/m2 combined with Aza‐FLA was tolerable in children with R/R AML with similar toxicity profile to other intensive AML regimens. However, within the confines of a phase 1 study, we did not observe that the pevonedistat + Aza‐FLA combination demonstrated significant anti‐leukemic activity.

e15131 Background: Elimusertib is a highly selective oral inhibitor of the Ataxia telangiectasia and Rad3 related (ATR) kinase, which is required for efficient end-joining repair of double-stranded breaks, particularly during DNA replication. Many pediatric cancers involve potential ATR susceptibilities such as increased replication stress due to oncogenic fusions, specific DNA damage repair (DDR) deficiencies, oncogenic activation of DNA damage and nucleases such as PGBD5, as well as alternative lengthening of telomeres. We report the initial phase 1 results of PEPN2112 (NCT05071209), an ongoing pediatric phase 1/2 clinical trial of elimusertib monotherapy. Methods: Eligible patients (pts) included children, adolescents, and young adults with relapsed or refractory tumors with: (1) Ewing sarcoma or related EWSR1 fusion positive tumors (EWS), (2) alveolar rhabdomyosarcoma, PAX3-FOXO1 fusion positive (aRMS), or (3) non-CNS primary tumors exhibiting specific DDR pathway defects anticipated to sensitize to ATR inhibition. For pts < 18 years (yrs), a rolling-six design was used to evaluate elimusertib administered BID x3 days/week of a 28-day cycle starting at the adult equivalent recommended phase 2 dose (RP2D) of 24 mg/m2/dose (max 40 mg) with a potential de-escalation to 18 mg/m2/dose (max 30 mg). The pediatric RP2D determination was based upon dose limiting toxicity (DLT) criteria (CTCAEv5) during cycle 1. Pharmacokinetic (PK) studies were performed. Pts > 18 yrs could enroll onto the phase 2 cohorts at the adult RP2D simultaneously with the pediatric phase 1. Once the pediatric RP2D was defined, pts < 18 yrs accrued to the phase 2 cohorts and a PK expansion for pts < 12 yrs was opened. Results: 8 eligible pts were enrolled (4 males) on the phase 1 part of the study. 2 pts were inevaluable for DLT as they received < 75% of protocol therapy. Median (range) age was 13 (10-17) yrs. Diagnoses included: EWS (n = 4) and 1 pt each with aRMS, adrenocortical carcinoma, clear cell sarcoma, and osteosarcoma. At 24 mg/m2/dose, no DLTs were observed. Toxicities were hematologic, with grade 3 toxicities including anemia (n = 3), neutropenia (n = 4), and decreased white blood cells (n = 1). One pt experienced grade 4 lymphopenia. There were no grade 3/4 non-hematologic toxicities. Day 1 mean ± SD values of Tmax, Cmax, AUC0-8h and t1/2 were 1.6 ± 0.5 h, 1532 ± 385 ng/mL, 5863 ± 1841 h*ng/mL and 3.6 ± 0.9 h, respectively. Conclusions: Elimusertib-related toxicities were primarily hematologic. The RP2D for elimusertib monotherapy in pediatric pts is 24 mg/m2/dose (max 40 mg) orally BID x3 days/week continuously, analogous to dosing in adults with similar PK. Phase 2 and PK expansion cohorts as well as pharmacodynamic studies are ongoing. Clinical trial information: NCT05071209 .

AbstractBackgroundInhibition of the WEE1 kinase by adavosertib (AZD1775) potentiates replicative stress from genomic instability or chemotherapy. This study reports the pediatric solid tumor phase 2 results of the ADVL1312 trial combining irinotecan and adavosertib.MethodsPediatric patients with recurrent neuroblastoma (part B), medulloblastoma/central nervous system embryonal tumors (part C), or rhabdomyosarcoma (part D) were treated with irinotecan and adavosertib orally for 5 days every 21 days. The combination was considered effective if there were at least three of 20 responses in parts B and D or six of 19 responses in part C. Tumor tissue was analyzed for alternative lengthening of telomeres and ATRX. Patient's prior tumor genomic analyses were provided.ResultsThe 20 patients with neuroblastoma (part B) had a median of three prior regimens and 95% had a history of prior irinotecan. There were three objective responses (9, 11, and 18 cycles) meeting the protocol defined efficacy end point. Two of the three patients with objective responses had tumors with alternative lengthening of telomeres. One patient with pineoblastoma had a partial response (11 cycles), but parts C and D did not meet the protocol defined efficacy end point. The combination was well tolerated and there were no dose limiting toxicities at cycle 1 or beyond in any parts of ADVL1312 at the recommended phase 2 dose.ConclusionThis is first phase 2 clinical trial of adavosertib in pediatrics and the first with irinotecan. The combination may be of sufficient activity to consider further study of adavosertib in neuroblastoma.

Abstract Introduction: Tegavivint is a first in class small molecule inhibitor of Wnt-ß-catenin signaling that functions by disrupting the interaction of ß-catenin and TBL1/TBLR1 resulting in degradation of nuclear ß-catenin. Aberrant Wnt signaling has been identified as a key mechanism of cancer biology, resulting in uncontrolled transcription of pro-oncogenic Wnt target genes. Pre-clinical in vivo studies of tegavivint demonstrated anti-tumor activity in a variety of pediatric solid tumors, including osteosarcoma, Ewing sarcoma, and lymphoma. Methods: We conducted a phase 1 dose-escalation study of single agent tegavivint in children aged ≥12 months to ≤21 years with relapsed or refractory solid tumors including lymphoma and desmoid tumors. The dose escalation was conducted using a rolling six design starting with the recommended phase 2 dose (RP2D) in adults, 5 mg/kg, administered intravenously over four hours on days 1, 8 and 15 of a 28 day cycle. A single de-escalation to 4 mg/kg and escalations to 6.5 mg/kg and 8 mg/kg if pharmacokinetic (PK) parameters indicated were planned. Once the RP2D is defined a PK cohort and phase 2 cohorts including Ewing sarcoma, desmoid tumor, osteosarcoma, liver tumors, Wilms tumor and a disease agnostic cohort including cancers with Wnt alterations will be evaluated. Results: A total of 15 patients were enrolled on the phase 1 part of the study. Two patients were not treated due to pre-therapy DEXA scan demonstrating grade 1 osteoporosis; therefore, 13 patients received treatment with tegavivint on 2 dose levels (5 mg/kg and 6.5 mg/kg). The median age of treated patients was 16 years (range 3-21). Patient diagnoses included desmoid tumor (5), Wilms tumor (3), and one each of Ewing sarcoma, osteosarcoma, CIC::DUX4 sarcoma, neuroblastoma, and hepatocellular carcinoma. There were no dose limiting toxicities among 4 DLT-evaluable patients at DL1 and 6 at DL2. The maximum tolerated dose was not determined. Grade three or higher adverse events at least possibly related to treatment included anemia (2) and lymphopenia (2). A single patient had a grade 3 QT prolongation requiring cessation of tegavivint after cycle 3. At 5 mg/kg, the mean AUC was 94,900 hr*ng/mL (range 52,000-136,000), and at 6.5 mg/kg was 91,200 hr*ng/mL (range 28,400-144,000). The pediatric RP2D dose was determined to be 6.5 mg/kg based on the pre-specified objective of achieving pharmacologically relevant plasma concentrations and less than 20% difference in mean AUC between the two tested dose levels. Conclusions: Tegavivint is well tolerated in children with refractory solid tumors, the pediatric RP2D is 6.5 mg/kg demonstrating pharmacologically relevant plasma concentrations. The study is currently enrolling patients to a pharmacokinetic expansion cohort and will then proceed to phase 2. Citation Format: Sarah B. Whittle, Joseph G. Pressey, Xiaowei Liu, Charles G. Minard, Kristina Z. Denic, Joel M. Reid, Stacey L. Berg, Elizabeth Fox, Brenda J. Weigel. PEPN2011: a phase 1/2 study of tegavivint in children, adolescents, and young adults with recurrent or refractory solid tumors, including lymphomas and desmoid tumors: a report from the pediatric early phase clinical trials network [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT090.

10022 Background: nab-Sirolimus (formerly know ABI-009 and nab-rapamycin) is a novel human albumin-bound preparation of sirolimus, a potent mTOR inhibitor. We report results of a Phase I study of ABI-009 alone and in combination with irinotecan and temozolomide in children with relapsed/refractory solid or CNS tumors. Methods: Patients (age 1-21 years) with relapsed/refractory solid or CNS tumors were eligible. Using a rolling 6 design, ABI-009 was administered intravenously as a single agent on Days 1 and 8 of cycle 1 (cycle = 21d), then subsequent cycles ABI-009 was administered in combination with temozolomide (125 mg/m2/dose, maximum 250 mg/dose) orally once daily x 5 on Days 1-5 and irinotecan 90 mg/m2/dose orally once daily x 5 on Days 1-5. Three dose levels (DL) of ABI-009 were investigated (DL1: 35mg/m2/dose, DL-1: 20mg/m2/dose, and DL-2: 15mg/m2/dose). The maximum tolerated dose (MTD) or Recommended Phase 2 Dose (RP2D) was established based on dose limiting toxicity (DLT) observed during Cycle 1 and 2. At the RP2D, additional patients were enrolled for pharmacokinetics (PK). Results: 33 patients were enrolled (32 eligible and 1 ineligible); 11 did not experience DLT but were not evaluable for toxicity due to progressive disease or physician decision to discontinue protocol therapy prior to completion of cycle 2; 17 [median age 13 (2-20) years] were evaluable for determination of MTD during dose escalation, 6 were enrolled on the PK cohort, of which 3 were evaluable to toxicity. At DL1, 2/5 patients experienced DLT (thrombocytopenia during cycle 1 (n = 1) and cycle 2 (n = 1)); at DL-1, 2/6 patients experienced DLT (thrombocytopenia in cycle 1); at DL-2, 1/6 patients experienced DLT (thrombocytopenia in cycle 1). PK expansion enrolled at DL-2 and 1/3 participants evaluable for toxicity had a DLT (mucositis). Overall, at DL-2, 2/9 patients (22%) had DLT. One patient with Ewing Sarcoma had a partial response and remained on study for 35 cycles; Patients (one each) with Ewing Sarcoma, Wilms Tumor, and Pineoblastoma had stable disease, ranging from 3-6 cycles. Conclusions: Thrombocytopenia was dose limiting for ABI-009 alone and in combination with temozolomide and irinotecan. The MTD for ABI-009 is 15mg/m2/dose days 1 and 8 in combination with 5 daily doses of temozolomide 125 mg/m2/dose and oral irinotecan 90 mg/m2/dose. One patient had a partial response, 3 patients had prolonged stable disease. Pharmacokinetics and pharmacodynamics are pending and will inform future trials. Clinical trial information: NCT02975882.

AbstractBackgroundChildren with diffuse intrinsic pontine gliomas (DIPG) have a dismal prognosis. Adavosertib (AZD1775) is an orally available, blood-brain barrier penetrant, Wee1 kinase inhibitor. Preclinical efficacy against DIPG is heightened by radiation induced replication stress.MethodsUsing a rolling six design, 7 adavosertib dose levels (DLs) (50 mg/m2 alternating weeks, 50 mg/m2 alternating with weeks of every other day, 50 mg/m2, then 95, 130, 160, 200 mg/m2) were assessed. Adavosertib was only given on days of cranial radiation therapy (CRT).The duration of CRT (54 Gy over 30 fractions; 6 weeks) constituted the dose limiting toxicity (DLT) period. Endpoints included tolerability, pharmacokinetics, overall survival (OS) and peripheral blood γH2AX levels as a marker of DNA damage.ResultsA total of 46 eligible patients with newly diagnosed DIPG [median (range) age 6 (3–21) years; 52% female] were enrolled. The recommend phase 2 dose (RP2D) of adavosertib was 200 mg/m2/d during days of CRT. Dose limiting toxicity included ALT elevation (n = 1, DL4) and neutropenia (n = 1, DL7). The mean Tmax, T1/2 and Clp on Day 1 were 2 h, 4.4 h, and 45.2 L/hr/m2, respectively. Modest accumulation of adavosertib was observed comparing day 5 versus day 1 AUC0-8h (accumulation ratio = 1.6). OS was 11.1 months (95% CI: 9.4, 12.5) and did not differ from historical control.ConclusionAdavosertib in combination with CRT is well tolerated in children with newly diagnosed DIPG, however, compared to historical controls, did not improve OS. These results can inform future trial design in children with high-risk cancer.

Abstract Introduction: Selinexor is a first-in-class, central nervous system (CNS) penetrant, oral inhibitor of exportin 1 (XPO1), the sole nuclear exporter of many key tumor suppressors. Selinexor is FDA-approved for refractory multiple myeloma and DLBCL and has been evaluated in a phase 1 trial in children with leukemia. We report a phase 1 trial of selinexor in children and adolescents with recurrent CNS and solid tumors, including lymphoma (NCT02323880). Methods: A rolling-six design was used to evaluate selinexor (10 or 25 mg tablets) administered twice or once weekly during a 28-day cycle. Dose determination was based on protocol-defined dose limiting toxicity (DLT) using CTCAEv4 during cycle 1. First dose pharmacokinetics (PK) were performed. Results: 43 subjects were enrolled (17 males); median (range) age was 15 (6-20) years. 27 (63%) had CNS tumors, most commonly high-grade glioma (n=12); 16 (37%) had extracranial solid tumors. 42 were evaluable for DLT. At the starting dose (35 mg/m2/dose, twice weekly), no DLTs were observed in 6 subjects, however, 2 subjects had unexpected late myelosuppression delaying initiation of cycle 2. The dosing schedule was amended to twice weekly for 3 weeks followed by a 1 week break. 12 subjects received 35 mg/m2/dose; 4 experienced DLTs [grade 3 fatigue (n=2), grade 3 thrombocytopenia (n=1), or grade 3 ALT increase (n=1)]. The dose was de-escalated to 20 mg/m2/dose, 3 weeks on, 1 week off. 12 subjects enrolled; 3 experienced a DLT [grade 3 increased AST/ALT, acute reversible neurologic changes, or neutropenia (each n=1)]. At the 20 mg/m2 (n=12) and 35 mg/m2 (n=19) dose levels, respectively, the mean ± SD Cmax (ng/ml) was 324±116 and 535±174, and AUC (hr•ng/ml) was 3092 ± 842 and 5156 ± 1227. This was comparable to PK in adults receiving 35 and 50 mg/m2. Based on a desire to achieve a higher Cmax and avoid breaks in schedule, and emerging evidence for similar effectiveness with decreased toxicity in adults receiving continuous once weekly dosing, we evaluated a dosing schedule with once weekly dosing for all 4 weeks of each cycle. At the initial dose level (45 mg/m2 weekly), 2 of 6 subjects had DLTs [prolonged grade 2 thrombocytopenia or grade 3 seizure in a primary CNS tumor patient]. Six subjects received 35 mg/m2/dose once weekly; 1 DLT [grade 3 thrombocytopenia] was observed. Non-dose-limiting toxicity (Grade ≥2 occurring in &gt;10% of subjects during cycle 1) included lymphopenia, leukopenia, neutropenia, thrombocytopenia, anorexia, fatigue, hypophosphatemia, nausea, and vomiting. Subjects received a median (range) of 1 (1-9) cycle; 13 received 2-3 cycles, and 6 received 5-9 cycles. Conclusions: Selinexor-related toxicities were primarily hematological and gastrointestinal. The maximum tolerated dose (MTD) of selinexor in children and adolescents with recurrent solid and CNS tumors is 20 mg/m2/dose twice weekly for 3 weeks followed by one week off. On a continuous once weekly schedule, the MTD and recommended phase 2 starting dose of selinexor is 35 mg/m2/dose. Citation Format: Adam L. Green, Charles G. Minard, Xiaowei Liu, Joel M. Reid, Kerice Pinkney, Stephan Voss, Marvin D. Nelson, Elizabeth Fox, Brenda J. Weigel, Julia Glade Bender. Phase 1 trial of selinexor in children and adolescents with recurrent/refractory solid and CNS tumors (ADVL1414): A Children’s Oncology Group Phase 1 Consortium trial [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P162.