Sirolimus With Cyclophosphamide and Topotecan for Pediatric/Adolescent Relapsed and Refractory Solid Tumors

The combination of cyclophosphamide and topotecan is well-tolerated and provides an oral therapy option for heavily pre-treated patients. The toxicity profile and activity level suggest that this combination will provide a useful platform onto which novel compounds may be added. Sirolimus has been shown to demonstrate single-agent activity in preclinical models of rhabdomyosarcoma, Ewing sarcoma, medulloblastoma, glioblastoma, neuroblastoma, and osteosarcoma. Sirolimus has also been shown to have additive effects in pre-clinical models of solid tumors when combined with cyclophosphamide. This trial therefore will evaluate the combination of sirolimus with cyclophosphamide and topotecan. Pharmacokinetic studies of sirolimus as well as pharmacodynamic studies to assess antiangiogensis and inhibition of the mTOR pathway will be done. Patients will be accrued to dose levels in cohorts of 3 using a 3 + 3 design. Patients will initially be enrolled on dose level 1. Patients will receive daily oral sirolimus and cyclophosphamide on days 1 - 21 in a 28 day cycle. This will be combined with oral topotecan given on days 1 - 14. Sirolimus will be dosed based on steady-state plasma trough concentrations with a goal level in dose level 1 of 3-7.9 ng/ML and goal levels in subsequent dose levels of 8-12.0 ng/ML. Dosing of cyclophosphamide and topotecan will be 25 mg/m2/dose and 0.8 mg/ m2 /dose respectively for dose levels 1 and 2. Level 3 dosing will escalate cyclophosphamide to 50 mg/ m2/dose. If level 1 dosing is not tolerated, patients will then be enrolled in a level -1 cohort with cyclophosphamide and sirolimus administered only on days 1 - 14. If level -1 is not tolerated, patients will be enrolled in level -2 with topotecan administration limited to days 1 - 7.