Effect of epirubicin on 3H-thymidine labelling index in cultured L-strain cells.

The effect of epirubicin (EPI) on 3H-thymidine labelling index (3H-TdR LI) of L-strain cells in culture was investigated. EPI concentrations of 0.001 microg/ml, 0.01 microg/ml and 0.1 microg/ml were applied to the cells for 4, 8, 16 and 32 hours. Following the treatment with EPI, labelling process in 3H-TdR medium continued for 0, 2, 4, 8, 16, 20, 22, 25 and 30 hours. The results showed that EPI diminished labelling index of L-strain cells depends on time and applied concentrations. When compared to control this decrease was found statistically significant (p<0.001) in each group.

Combined effects of epirubicin and tamoxifen on the cell-cycle phases in estrogen-receptor-negative Ehrlich ascites tumor cells.

Laboratory and clinical data suggest some interactions between cytotoxic agents and tamoxifen. The mechanisms of these interactions differ in estrogen-receptor-negative cell lines. The ability of tamoxifen to modify the effects of epirubicin on the cell-cycle phases of estrogen-receptor-negative Ehrlich's carcinoma ascitic cells (EATC) was studied in mice. The results showed that combination of tamoxifen with epirubicin decreased the thymidine labelling index more effectively than did either drug alone. Adding tamoxifen to epirubicin treatment induced both an early S-phase and G2-M-phase arrest and a later G0-G1-phase arrest in EATC. An increase of S0 cells in the quiescent fraction could play a role in these changes, and some of these quiescent cells may not be viable, causing them to die later. In conclusion, the data suggest that continuous exposure to tamoxifen might modify the effects of epirubicin via cell-cycle perturbations.