Use and Mechanism of Action of ASI01 in Protecting Bone Marrow Colony Forming Units-Granulocyte-Macrophage following Purging with ASTA-Z 75571

Ammonium trichloro(dioxoethylene-O,O')tellurate (AS101) has been shown previously to provide radioprotective effects when given to mice 24 h prior to irradiation and to protect mice from lethal and sublethal doses of cyclophosphamide (CTX). In this study we examined the ability of AS101 to protect mice bone marrow colony forming units-granulocytemacrophage treated in vitro with various doses of ASTA-Z 7557, a potent derivative of cyclophosphamide. We demonstrate that prior incubation with AS101 protects colony forming units-granulocyte-macrophage from toxic effects of ASTA-Z. This protection can also be conferred by injection of mice with AS101 prior to incubation of their bone marrow in vitro with ASTA-Z. Prior incubation with AS101 was shown not to protect K562 leukemic cells or HI ,-60 cells from the toxic effects of ASTA-Z. We show that AS101 protection from the toxic effects of ASTA-Z in vitro and CTX in vivo can be partially ascribed to increased aldehyde dehydrogenase (ALDH) activity induced by AS101. This was shown directly by measuring cellular ALDH activity and indirectly by measuring the toxicity of ASTA-Z and CTX in the presence of cyana mide, an inhibitor of ALDH. AS101 is also demonstrated in this study to protect spleen cells from the toxic effects of 5-fluorouraciL, probably through a different mechanism. These properties of AS101 make it a useful candidate for increasing the qualitative potential of bone marrow used for autologous transplantation after purging with ASTA-Z. In addition, the results suggest an increase in ALDH activity by AS101 as one of the mechanisms of protection from the toxic effects of ASTA-Z and CTX. However, the chemoprotectiveness of AS101 was found not to be restricted to cyclophosphamide, since as shown in this study, AS101 helped by other mechanisms to reconstitute the number of spleen cells after 5-fluorouracil treatment.