Protection of committed murine haemopoietic progenitors against BCNU toxicity does not predict protection of primitive, multipotent spleen colony-forming cells – implications for chemoprotective gene therapy

Abstract

The effect of expression of an O⁶-benzylguanine (O⁶-beG)-resistant mutant (hATPA/GA) of human O⁶-alkylguanine-DNA alkyltransferase (ATase) on the in vivo toxicity and clastogenicity of the anti-tumour agent N,N′-bis(2-chloroethyl)-N-nitrosourea (BCNU) to murine bone marrow has been investigated. When compared with control animals, the bipotent granulocyte–macrophage colony-forming (GM-CFC) progenitor population of the hATPA/GA transduced mice were somewhat more resistant to BCNU (1.4-fold, P = 0.047) and this effect was more significant in the presence of the ATase inactivator O⁶-beG (3.5-fold, P = 0.001). The polychromatic erythrocytes were also significantly protected against BCNU-induced clastogenicity both in the presence (P < 0.001) and absence of O⁶-beG (P < 0.05). the primitive, multipotent spleen colony-forming cells (cfu-s) in these animals also showed moderate (1.6-fold, P = 0.034) protection in the absence of O⁶-beG but in the presence of the inactivator they remained as sensitive to BCNU toxicity as those in the control animals (P = 0.133). This result contrasts with previous findings demonstrating significant hATPA/GA-mediated, O⁶-beG-resistant protection against the toxicity and clastogenicity of a number of O⁶-alkylating agents, including temozolomide, fotemustine and chlorozotocin. The possibility that our strategy for protective gene therapy may be highly agent and cell-type specific is unexpected and has possible implications for clinical trials of this approach using BCNU or related agents.