Gene amplification of human cytidine deaminase proviral cDNA and increasedlevels of its mRNA produces enhanced drug resistance to cytosine arabinoside in retroviral-transduced murine fibroblasts

Hematopoietic toxicity is one of the major problems that limits the effecti veness of many antineoplastic drugs. One approach to overcome this problem is to confer chemoresistance to the hematopoietic cells by gene transfer of drug resistance genes. Human cytidine deaminase (CD) inactivates the cytos ine nucleoside analogues, such as cytosine arabinoside (ARA-C), by deaminat ion, Pie have reported previously that retroviral-mediated gene transfer of CD conferred drug resistance to ARA-C in murine cells. One of the major pr oblems in the use of these vectors is to obtain adequate and prolonged expr ession of the transferred gene to produce a therapeutic effect in the trans duced cells. The objective of this investigation was to determine if it is possible to increase the expression of CD proviral DNA in transduced murine fibroblast cells. We observed that by the use of continuous exposure to in creasing concentrations of ARA-C it was possible to enhance drug resistance in the transduced cells. This drug resistance was found to be associated w ith increases in CD enzyme activity and CD proviral mRNA and by amplificati on of the proviral CD gene. (C) 1999 Elsevier Science Ireland Ltd. All righ ts reserved.