Retroviral transfer of a chimeric multidrug resistance-adenosine deaminase gene.

A fusion between a selectable multidrug resistance (MDR1) cDNA and an adenosine deaminase (ADA) cDNA concomitantly confers multidrug resistance and ADA activity on transfected cells. We have produced a Harvey murine sarcoma virus-derived, replication-defective, recombinant retrovirus to transduce this chimeric MDR-ADA gene efficiently into a great variety of cells. Infection with the MDR-ADA retrovirus conferred the multidrug resistance phenotype on drug-sensitive cells, therefore allowing selection in the presence of colchicine. Colchicine-resistant cells synthesized large amounts of a membrane-associated 210-kDa MDR-ADA fusion protein that preserved both MDR and ADA functional activities. To monitor expression of the chimeric gene in vivo, Kirsten virus-transformed NIH cells were infected with the MDR-ADA retrovirus, and after drug-selection, injected into athymic nude mice. Tumors developed that contained the bifunctionally active MDR-ADA fusion protein. When these mouse tumor cells were placed in tissue culture without the selecting drug, they did not lose the bifunctionally active MDR-ADA fusion protein. The replication-defective, recombinant MDR-ADA retrovirus should be useful to stably introduce the chimeric MDR-ADA gene into a variety of cell types for biological experiments in vitro and in vivo.