Low-Dose Metronomic Topotecan and Pazopanib (TOPAZ) in Children with Relapsed or Refractory Solid Tumors: A C17 Canadian Phase I Clinical Trial

Oral metronomic topotecan represents a novel approach to chemotherapy delivery which, in preclinical models, may work synergistically with pazopanib in targeting angiogenesis. A phase I and pharmacokinetic (PK) study of this combination was performed in children with relapsed/refractory solid tumors. Oral topotecan and pazopanib were each administered daily without interruption in 28-day cycles at five dose levels (0.12 to 0.3 mg/m topotecan and 125 to 160 mg/m pazopanib powder for oral suspension (PfOS)), with dose escalation in accordance with the rolling-six design. PK studies were performed on day 1 and at steady state. Thirty patients were enrolled, with 26 evaluable for dose-limiting toxicity (DLT), with median age 12 years (3-20). Toxicities were generally mild; the most common grade 3/4 adverse events related to protocol therapy were neutropenia (18%), thrombocytopenia (11%), lymphopenia (11%), AST elevation (11%), and lipase elevation (11%). Only two cycle 1 DLTs were observed on study, both at the 0.3/160 mg/m dose level comprising persistent grade 3 thrombocytopenia and grade 3 ALT elevation. No AEs experienced beyond cycle 1 required treatment discontinuation. The best response was stable disease in 10/25 patients (40%) for a median duration of 6.4 (1.7-45.1) months. The combination of oral metronomic topotecan and pazopanib is safe and tolerable in pediatric patients with solid tumors, with a recommended phase 2 dose of 0.22 mg/m topotecan and 160 mg/m pazopanib. No objective responses were observed in this heavily pre-treated patient population, although 40% did achieve stable disease for a median of 6 months. While this combination is likely of limited benefit for relapsed disease, it may play a role in the maintenance setting.