Abstract

4-S-(hexane-6-ol)-sulfidocyclophosphamide (monomer) and a compound composed of this derivative covalently bound to divinylether-maleic acid copolymer (DIVEMA) spontaneously hydrolyze in vitro with half-lives of hydrolysis of 9 and 48 min respectively, to form 4-hydroxycyclophosphamide. In turn, 4-hydroxycyclophosphamide further degrades to phosphoramide mustard with a half-life of 312 min. Sulfido-CP (cyclophosphamide) monomer, DIVEMA-sulfido-CP polymer, and phosphoramide mustard are qualitatively similar in producing DNA interstrand cross-links, as measured by alkaline elution, when incubated with mouse L1210 leukemia cells for 20 min. DNA interstrand cross-linking in L1210 cells increases for up to 6 hr following drug treatment and then decreases until it is completely removed within 18 hr for all three drugs. However, quantitatively more phosphoramide mustard (150 µM) is required than monomer (30 µM) to produce comparable amounts of cross-linking. An equivalent amount of monomer hydrolytically released by the polymer within 20 min is one-half as potent as monomer alone in producing crosslinks. Similar concentration relationships are observed in cytotoxicity assays (L1210 soft agar colony formation). These in vitro data suggest that (a) the activated monomer or some degradation product prior to phosphoramide mustard is taken up by L1210 cells; (b) the polymer hydrolyzes extracellularly to a monomeric species before cellular uptake; and (c) tumor endocytotic uptake of polymer appears negligible in L1210 cells. In vivo antitumor studies with ascites L1210 in BGD2F₁ mice indicate that the monomer (200 mg/kg, LD₁₀) is cytotoxic to tumor cells (5 log tumor cell kill). However, the polymer at a dose equitoxic to the mice (100 mg/kg, LD₁₀) is less cytotoxic than monomer to tumor cells (1 log tumor cell kill).