Release of methyl isocyanate from the antitumor agent caracemide (NSC-253272).

In recent phase 1 clinical trials, caracemide [N-acetyl-N-(methylcarbamoyloxy)-N-methylurea; NSC-253272] has demonstrated a marked potential to produce severe central nervous system (CNS) toxicity. Recent in vitro studies of this antitumor agent have presented indirect evidence indicating that methyl isocyanate is a likely metabolite which results from incubation of caracemide with either phosphate buffer or human plasma. This report presents evidence that methyl isocyanate is formed from caracemide in a concentration- and time-dependent manner. These data implicate the caracemide-mediated formation of methyl isocyanate as at least a plausible explanation for the CNS toxicity exhibited by this drug.