MODULATION OF CYTOTOXICITY OF CHEMOTHERAPEUTIC DRUGS BY ACTIVATED H-RAS

Cells from a single MCF-7 clone were transfected with an isopropyl-1-t hio-beta-D-galactopyranoside (IPTG)-inducible construct containing act ivated human H-ras with a Gly(12) --> Val(12) mutation. Expression of H-ras was induced by the presence of IPTG with low background. MCF-7-r as clones were examined for sensitivity to a wide variety of drugs und er both induced and non-induced conditions. When expression of the act ivated ras was induced, these clones showed markedly increased resista nce to cisplatin and mitomycin C, moderately increased resistance to m ethotrexate and trimetrexate, and no increased resistance to other dru gs including taxol, doxorubicin, and etoposide. A DNA fragmentation as say revealed that DNA in MCF-7-ras cells treated with cisplatin under induced conditions was intact, whereas extensive degradation of DNA oc curred in similarly treated cells under non-induced conditions. This r esult, along with the fact that MCF-7-ras cells, upon induction of the activated H-ras, showed increased resistance to drugs that bind DNA, indicates that the activated H-ras may play a role in the DNA repair p rocess. (C) 1997 Elsevier Science Inc.