Combined Antitumor Therapy with Metronomic Topotecan and Hypoxia-Activated Prodrug, Evofosfamide, in Neuroblastoma and Rhabdomyosarcoma Preclinical Models

Abstract

Purpose: Tumor cells residing in tumor hypoxic zones are a major cause of drug resistance and tumor relapse. In this study, we investigated the efficacy of evofosfamide, a hypoxia-activated prodrug, and its combination with topotecan in neuroblastoma and rhabdomyosarcoma preclinical models.Experimental Design: Neuroblastoma and rhabdomyosarcoma cells were tested in vitro to assess the effect of evofosfamide on cell proliferation, both as a single agent and in combination with topotecan. In vivo antitumor activity was evaluated in different xenograft models. Animal survival was studied with the neuroblastoma metastatic tumor model.Results: All tested cell lines showed response to evofosfamide under normoxic conditions, but when exposed to hypoxia overnight, a 2-to 65-fold decrease of IC 50 was observed. Adding topotecan to the evofosfamide treatment significantly increased cytotoxicity in vitro. In neuroblastoma xenograft models, single-agent evofosfamide treatment delayed tumor growth. Complete tumor regression was observed in the combined topotecan/evofosfamide treatment group after 2-week treatment. Combined treatment also improved survival in a neuroblastoma metastatic model, compared to singleagent treatments. In rhabdomyosarcoma xenograft models, combined treatment was more effective than single agents. We also showed that evofosfamide mostly targeted tumor cells within hypoxic regions while topotecan was more effective to tumor cells in normoxic regions. Combined treatment induced tumor cell apoptosis in both normoxic and hypoxic regions.Conclusions: Evofosfamide shows antitumor effects in neuroblastoma and rhabdomyosarcoma xenografts. Compared with single-agent, evofosfamide/topotecan, combined therapy improves tumor response, delays tumor relapse, and enhances animal survival in preclinical tumor models. Clin Cancer Res; 22(11); 2697-708. Ó2015 AACR.

Optimization of liposomal topotecan for use in treating neuroblastoma

“…Enhanced exposure times can be achieved using a number of approaches including continuous drug infusions , more frequent dosing (i.e. metronomic dosing ), PEGylation of camptothecin derivatives and through use of nano‐scale drug delivery systems such as the liposomal formulations described here. Furthermore, topotecan's activity depends on maintaining an intact lactone ring and the liposomal formulations of topotecan will help maintain the drug in the lactone form for extended time periods following administration.…”

Molecular Pathways: Hypoxia-Activated Prodrugs in Cancer Therapy

“…The activity of TH-302 in combination with conventional chemotherapy or targeted therapy has been reported in multiple preclinical solid tumor models and hematologic malignancies (32,35,37,38,49,50). In various xenograft models, the addition of TH-302 significantly increased DNA damage, apoptosis, and tumor necrosis and reduced stroma density and intratumoral hypoxia, without additive toxicity.…”

“…TH-302 also improved the efficacy of a gemcitabine and nab-paclitaxel combination in mouse xenograft models of human pancreatic ductal adenocarcinoma (PDAC) (51). The addition of TH-302 to topotecan improved tumor response and prolonged survival in neuroblastoma and rhabdomyosarcoma xenograft models (52). In a murine model of multiple myeloma, the combination of TH-302 with bortezomib significantly prolonged survival (40).…”

Metronomic therapy in pediatric oncology: A snapshot

“…Most of the clinical studies that have attempted to take metronomic chemotherapy from the bench to the clinic have been influenced by results from preclinical studies done on human xenograft models, or by preclinical models involving syngeneic transplantable tumors or genetically engineered mouse models of cancer . Cyclophosphamide was the most frequently used drug in preclinical evaluations; however, other drugs, for example topotecan, doxorubicin, and evofosphamide, and targeted agents have also been used in the laboratory . Not only this, preclinical models have also been instrumental in studying the efficacy of repurposed drugs such as propranolol and assess newer mechanistic biomarkers such as CECs and EPC .…”

“…46,47 Cyclophosphamide was the most frequently used drug in preclinical evaluations 48,49 ; however, other drugs, for example topotecan, doxorubicin, and evofosphamide, and targeted agents have also been used in the laboratory. 47,48,50,51 Not only this, preclinical models have also been instrumental in studying the efficacy of repurposed drugs such as propranolol and assess newer mechanistic biomarkers such as CECs and EPC. 11,12 However, recently scientists have realized that primary mice models and xenograft models do not truly recapitulate the milieu of metastatic human disease and this may be the reason for the limited success of certain regimens in Phase III trials.…”