RESISTANCE TO CYTOSINE-ARABINOSIDE BY RETROVIRALLY MEDIATED GENE-TRANSFER OF HUMAN CYTIDINE DEAMINASE INTO MURINE FIBROBLAST AND HEMATOPOIETIC-CELLS

Dose-limiting hematopoietic toxicity produced by the cytosine nucleosi de analogue cytosine arabinoside (ARA-C) is one of the major factors t hat limit its use in the treatment of neoplastic diseases. An interest ing approach to overcome this problem would be to insert a gene for dr ug resistance to ARA-C in normal hematopoietic cells to protect them f rom drug toxicity. The deamination of ARA-C by cytidine deaminase resu lts in a loss of its antineoplastic activity. The objective of this st udy was to determine if gene transfer of human cytidine deaminase into murine fibroblast and hematopoietic cells would confer drug resistanc e to ARA-C. Retrovirally mediated transfer of the human cytidine deami nase gene into 3T3 fibroblasts resulted in efficient expression of the proviral RNA for this gene and in increased cytidine deaminase activi ty in cytoplasmic extracts. These cells showed marked resistance to AR A-C as determined by the effects of this drug on colony formation, cel l growth, and DNA synthesis. The transfer of the human cytidine deamin ase gene into murine bone marrow cells by the retroviral vector confer red a high level of drug resistance to ARA-C in clonogenic assays. The se studies indicate that the cytidine deaminase gene could be used in cancer gene therapy by protecting normal hematopoietic cells against t he cytotoxic effects of ARA-C and related cytosine nucleoside analogue s.