New ifosfamide analogs designed for lower associated neurotoxicity and nephrotoxicity with modified alkylating kinetics leading to enhanced in vitro anticancer activity.

Ifosfamide is a well known prodrug for cancer treatment with cytochrome P450 metabolism. It is associated with both antitumor activity and toxicities. Isophosphoramide mustard is the bisalkylating active metabolite, and acrolein is a urotoxic side product. Because acrolein toxicity is limited by coadministration of sodium mercaptoethanesulfonate, the incidence of urotoxicity has been lowered. Current evidence suggests that chloroacetaldehyde, a side-chain oxidation metabolite, is responsible for neurotoxicity and nephrotoxicity. The aim of our research is to prevent chloroacetaldehyde formation using new enantioselectively synthesized ifosfamide analogs, i.e., C7,C9-dimethyl-ifosfamide. We hypothesize that reduced toxicogenic catabolism may induce less toxicity without changing anticancer activity. Metabolite determinations of the dimethyl-ifosfamide analogs were performed using liquid chromatography and tandem mass spectrometry after in vitro biotransformation by drug-induced rat liver microsomes and human microsomes expressing the main CYP3A4 and minor CYP2B6 enzymes. Both human and rat microsomes incubations produced the same N-deschloroalkylated and 4-hydroxylated metabolites. A coculture assay of 9L rat glioblastoma cells and rat microsomes was performed to evaluate their cytotoxicity. Finally, a mechanistic study using (31)P NMR kinetics allowed estimating the alkylating activity of the modified mustards. The results showed that C7,C9-dimethyl-ifosfamide exhibited increased activities, although they were still metabolized through the same N-deschloroalkylation pathway. Analogs were 4 to 6 times more cytotoxic than ifosfamide on 9L cells, and the generated dimethylated mustards were 28 times faster alkylating agents than ifosfamide mustards. Among these new ifosfamide analogs, the 7S,9R-enantiomer will be assessed for further in vivo investigations for its anticancer activity and its toxicological profile.