Kinetics of Cyclophosphamide Biotransformation in

with its ring-opened tautomer, aldophosph$mide. it is generally agreed that, as such, 4-hydroxycyclopho$phamide-aldophos phamide is without significant antitumor aCtivity and that it can undergo 2 fates: conversion to relatively floncytotoxic metab olites, namely, 4-ketocyclophosphamide,; carboxyphospham ide, and alcophosphamide; and conversioVito cytotoxic metab olites, namely, acrolein, phosphoramide mustard, and bls(2chloroethyl)amine. Still subject to controversy is whether 4-hydroxycyclophos phamide-aldophosphamide serves as a relatively long-lived transport form of the ultimate cytotoxic metabolites or as a short-lived intermediate that gives rise @ to these and other metabolites almost as quickly as it is forr@ied. Previous investi gations in our laboratory (14), although n4t definitive, indicated the presence of detectable amounts of @4-hydroxycyclophos phamide-aldophosphamide in the bloodl of rats given a very high dose of cyclophosphamide, namel@,400 mg/kg. Struck et a!. (21) were unable to detect 4-hydro@ycycIophosphamlde aldophosphamide in the blood of cyclc@phosphamide-treated (300 mg/kg) mice. They concluded that@upon its formation in the liven, 4-hydroxycyclophosphamid@aldophosphamlde is quickly converted to other metabolites $o that it never enters the circulation in appreciable amounts ar@i that, therapeutically, the significant circulating metabolite is@phosphoramide mus tard. Voelcker et a!. (24) were unable to @Jetect the presence of 4-hydroxycyclophosphamide-aldophos@hamide in the serum or urine of humans given cyclophosph@nide but did report its presence in the serum and urine of cyc@phosphamide-treated rats and mice. Wagner et a!. (25) trea@edblood and urine of humans given cyclophosphamide and blood of cyclophospha mide-treated rats and mice with benz@flmercaptanand were able to detect the 4-(S-benzyI)mercapto@denivativeof 4-hydrox ycyclophosphamide. Moreover, Fensel@uet a!. (8) treated the plasma of a human given cyclophosphámidewith cyanide and were able to detect the cyanohydnin derivative of aldophos phamide. However, attempts by Struck et a!. (22) to detect 4hydnoxycyclophosphamide-aidophospt@amideas a stabilized cyanohydninderivative in cyclophosph@mide-treatedmice were unsuccessful. These discrepancies raise question@concerning the validity and/on sensitivity of the various as@aysthus far used. An independent procedure was utilized @nthe experiments re ported herein in an attempt to resolve this controversy.