This study focuses on children who have a solid tumor that has come back (relapsed) or has not responded to standard treatments (refractory). The purpose of the study is to determine whether a drug called PEEL-224 (SN22), a topoisomerase 1 inhibitor, is safe and effective when given both as monotherapy (drug given by itself) and as part of a combination therapy together with other chemotherapy drugs. PEEL-224 will be given as an infusion into the vein. The study consists of 2 parts (phases). The goal of Phase 1 is to determine whether different doses of the study drug are safe and tolerable for people with solid tumors. PEEL-224 will be given to some participants as monotherapy and to others as part of a combination therapy together with other chemotherapy drugs. Researchers will also examine how the body handles different doses of the drug. The results of Phase 1 will help determine which dose of PEEL-224 to use in Phase 2. The goal of Phase 2 is to evaluate the effectiveness of PEEL-224 in treating people with rhabdomyosarcoma and neuroblastoma when given in combination with routine chemotherapy drugs (vincristine and temozolomide). The use of PEEL-224 in this study is considered experimental.
EIIT-2025-PEEL-224: A phase 1/2 clinical trial of the novel topoisomerase I inhibitor PEEL-224 as a single agent and in combination with vincristine and temozolomide in children with refractory, progressive or relapsed solid tumors *^