INCREASE OF BETA(III)-TUBULIN AND BETA(IVA)-TUBULIN ISOTYPES IN HUMANPROSTATE CARCINOMA-CELLS AS A RESULT OF ESTRAMUSTINE RESISTANCE

Estramustine (EM), an antimicrotubule agent, is effective against horm one-refractory prostate cancer when used in combination with vinblasti ne or paclitaxel, To understand the effect of EM on beta-tubulin, a ce llular target for this class of drugs, human prostate carcinoma cells (DU-145) were made resistant to EM, and two cell lines were selected a t 12- (EM-12) and 15-mu M (EM-15) concentrations of the drug, These ce ll lines exhibited 8- to 9-fold resistance to EM and 2- to 4-fold cros s-resistance to paclitaxel, Immunofluorescent staining of the cells wi th beta-tubulin isotype-specific antibodies showed a similar to 6-fold increase in the beta(III)-tubulin levels and moderate increase in ove rall beta-tubulin levels in EM-resistant cells when compared to DU-145 cells, This increase of beta(III) isotype was confirmed by Western an alysis, A reverse transcriptase-PCR assay was also employed using beta -tubulin isotype-specific primers to quantify beta-tubulin isotype RNA , A 4-fold increase in beta(III) and a 3-fold increase in beta(IVa) tr anscript were seen in both EM-resistant cell lines, These results indi cate that overexpression of specific beta-tubulin isotypes may play a role in the cellular defense against EM and other antimicrotubule agen ts.