TRANSFECTION OF MURINE FIBROBLAST CELLS WITH HUMAN CYTIDINE DEAMINASECDNA CONFERS RESISTANCE TO CYTOSINE-ARABINOSIDE

One of the major limitations in the use of cytosine arabinoside (Ara-C ) in cancer chemotherapy is the hematopoietic toxicity produced by thi s nucleoside analog, One approach to overcome this problem would be to insert a gene for drug resistance to Ara-C in normal hematopoietic ce lls to protect them from drug toxicity. An interesting candidate gene for this aim is cytidine deaminase which catalyzes the deamination of Arac-C, resulting in a significant loss of its antineoplastic activity , We have ligated the human cDNA for cytidine deaminase into the plasm id vector pMFG. Transfection of NIH 3T3-derived GP + E86 murine fibrob lasts cells with this vector resulted in a marked increase (> 50-fold) in the expression of cytidine deaminase. In addition, the transfected cells showed resistance to the cytotoxic action and to the inhibition of DNA synthesis produced by Ara-C. Northern and Western blot analysi s of the transfected cells showed increased expression of mRNA for cyt idine deaminase and increased immunologically detectable enzyme. The a bility to confer drug resistance to Ara-C through gene transfer of cyt idine deaminase may have the potential as a selectable marker and for the protection of the bone marrow from the toxicity produced by this a nalog so as to increase its effectiveness in cancer chemotherapy.