HPLC AND P-31 NMR CHARACTERIZATION OF THE REACTION BETWEEN ANTITUMOR PLATINUM AGENTS AND THE PHOSPHOROTHIOATE CHEMOPROTECTIVE AGENT S-2-(3-AMINOPROPYLAMINO)ETHYLPHOSPHOROTHIOIC ACID (WR-2721)

In prior studies, we examined the effects of the radioprotective and c hemoprotective agent WR-2721 [S-2-(3-aminopropylamino)ethylphosphoroth ioic] on the in vivo biotransformation of the cisplatin [cisdiamminedi chloroplatinum(II)] analog ormaplatin ans-1,2-diaminocyclohexanetetrac hloroplatinum(IV), Pt(dach)Cl-4, (formerly called tetraplatin)]. Those data suggested that a direct interaction between WR-2721 and ormaplat in and/or the corresponding Pt(II) drug, Pt(dach)Cl-2, may be occurrin g in vivo. This would be in contrast to the generally accepted hypothe sis that WR-2721 is a prodrug that must first be converted by alkaline phosphatase to a free thiol compound, WR-1065, before any appreciable reactivity would be evident. However, the major biotransformation pro duct observed in the peritoneal fluid, plasma, and all tissues was Pt( dach)(WR-1065). We report here on further investigations into the in v itro reactivity of Pt(dach) compounds with WR-2721 and WR-1065. Separa tion of reaction products resulting from incubation of Pt(dach)(malona to) with either WR-2721 or WR-1065 under physiological conditions gave profiles that were indistinguishable by reverse phase HPLC and cation exchange HPLC at two different pHs. P-31 NMR characterization of the dephosphorylation of WR-2721 revealed essentially no loss of inorganic phosphate for up to 24 hr when incubated in unbuffered water at 30 de grees. In contrast, when incubated with a 1:1 molar ratio of cisplatin under the same conditions, the WR-2721 signal was decreased markedly in the first 5 min, and had disappeared almost completely by 1 hr. The signal corresponding to inorganic phosphate increased in parallel to the decrease in the WR-2721 signal. No intermediate formation of a com plex containing both platinum and phosphate could be detected at any t ime. These data suggest that the reaction between WR-2721 and platinum complexes results in rapid dephosphorylation of WR-2721, and, consequ ently, that the reaction products formed with either WR-2721 or WR-106 5 and Pt(II) complexes are identical.