A Phase 1 Trial of Fimepinostat in Children and Adolescents with Relapsed and Refractory Solid and CNS Tumors

ABSTRACT Background Fimepinostat, an oral dual inhibitor of histone deacetylase (HDAC) and phosphatidylinositol‐4,5‐bisphosphate 3‐kinase (PI3K), has shown activity in preclinical models of Myc‐driven pediatric malignancies. This Phase 1 trial aimed to determine the recommended pediatric Phase 2 dose (RPP2D), describe the toxicity profile, and evaluate the pharmacokinetics of fimepinostat in children with relapsed and refractory solid and central nervous system (CNS) tumors. Methods This multicenter, Phase 1 study enrolled patients ages 1–21 years with relapsed or refractory solid tumors, CNS tumors, or lymphoma. The dose‐escalation phase followed a 3 + 3 design, starting at 27.5 mg/m2 and escalating to 45 mg/m2. Following dose escalation, three expansion cohorts were opened including cohorts for patients with Myc(n)‐driven neuroblastoma, Myc‐driven extracranial solid tumors, and diffuse large B‐cell lymphoma or Burkitt lymphoma. The pharmacokinetics of fimepinostat and its metabolites were studied after the first dose. Results Twenty‐six patients were enrolled, with 25 receiving treatment. The median age was 13.6 years (range: 4.1–20.9). In the dose‐escalation phase, 12 patients were evaluable for DLT assessment. The RPP2D was initially determined to be 45 mg/m2 but was revised to 35 mg/m2 after observing DLTs in the dose‐expansion phase. Treatment‐related adverse events were primarily hematologic and gastrointestinal. No objective responses were observed in 23 evaluable patients. Three patients had stable disease for over four cycles, including a patient with MYCN amplified neuroblastoma with stable disease for 24 cycles. Pharmacokinetic analysis showed significant interpatient variability and rapid conversion of fimepinostat to its metabolites. Conclusion Fimepinostat was tolerable at a dose of 35 mg/m2 in children with relapsed and refractory solid and CNS tumors, but lacked significant clinical activity. Discovery of drugs to target Myc continues to be a high priority for childhood cancers. Trial Registration ClinicalTrials.gov identifier: NCT02909777