ACTIVE VERSUS PASSIVE ABSORPTION KINETICS AS THE BASIS FOR SELECTIVE PROTECTION OF NORMAL-TISSUES BY S-2-(3-AMINOPROPYLAMINO)-ETHYLPHOSPHOROTHIOIC ACID
Through an in vivo and in vitro analysis of the absorption kinetics of S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721) in the normal tissues and solid tumors of mice, rats and rabbits, it was demonstrated that normal tissues actively concentrate WR-2721 against a concentration gradient, whereas solid tumors passively absorb it, or, if active concentration of WR-2721 is present in tumors, it operates at a far reduced rate relative to normal tissues. These observations can account for the ability of WR-2721 to selectively protect normal tissues against radiation and alkylating agent injury. [The use of WR-2721 in cancer therapy was discussed.].