Rationally designed hydrolytically activated etoposide prodrugs, a novel strategy for the treatment of neuroblastoma

Effective chemotherapy in neuroblastoma is limited by poor anti-tumor efficacy, systemic toxicity and the induction of drug resistance. Here, we provide further evidence that a hydrolytic activated prodrug design may overcome these problems. For this purpose, VP-16 was functionally blocked by a carbonate linker to generate two novel chemically stable prodrugs of VP-16, ProVP-16 I and II. We demonstrate profoundly different biological effects in vitro and in vivo of the prodrugs compared to parental VP-16. First, we established an up to >2 log higher in vitro toxicity of the two prodrugs compared to VP-16 on a panel of neuroblastoma cell lines. The highest increase of prodrug mediated cytotoxicity was observed in multi drug resistant cell lines. Second, in vivo studies showed a maximum tolerated dose (MTD) of ProVP-16 II (60 mg/kg), which was at least threefold higher than that of VP-16 (20 mg/kg). Tests of ProVP-16 II in a syngeneic NXS2 neuroblastoma model indicated that mice treated with this prodrug at 1/3 of the MTD was as effective as VP-16 parental compound used at the MTD in suppression of tumor growth. In summary, the etoposide prodrugs proved effective and less toxic and are therefore highly promising new anti-neuroblastoma compounds.