A BICISTRONIC RETROVIRAL VECTOR FOR PROTECTING HEMATOPOIETIC-CELLS AGAINST ANTIFOLATES AND P-GLYCOPROTEIN EFFLUXED DRUGS

Chemoresistance gene transfer is an experimental method to protect hem atopoietic cells from the toxicity of anticancer drugs, Because multip le drugs are usually given together in cancer therapy, this strategy w ill ultimately require vectors expressing multiple chemoresistance gen es, For this reason, we designed a bicistronic retroviral vector (HaMI D) containing a modified human multidrug resistance-1 cDNA and a mutan t human dihydrofolate reductase cDNA bearing a leucine to tyrosine sub stitution at codon 22 (L22Y). To determine if this vector would confer dual drug resistance to hematopoietic cells, recombinant retrovirus w as used to transduce the human CEM T lymphoblastic cell line as well a s primary murine myeloid progenitors, Growth suppression assays, using polyclonal transduced CEM cells, demonstrated increased resistance to taxol (13-fold), trimetrexate (8.9-fold), vinblastine (5.6-fold), met hotrexate (2.5-fold), and etoposide (1.5-fold) when used as single age nts, HaMID-transduced cells also grew at a logarithmic rate in the sim ultaneous presence of 25 nM taxol and 100 nM trimetrexate while contro l cells were entirely growth inhibited by this drug combination, Simil arly, HaMID-transduced murine myeloid progenitors acquired increased r esistance to taxol (2.9-fold) and trimetrexate (140-fold), and were ab le to form colonies in the simultaneous presence of both drugs, Our re sults suggest that retroviral transfer of HaMID into primary hematopoi etic cells should reduce the myelosuppression associated with the comb ined use of antifolates and P-glycoprotein-effluxed drugs.