Effect of maytansine on the cell cycle of Ehrlich ascites carcinoma cells in mice

The effect of maytansine on the cell cycle of Ehrlich ascites carcinoma(EAC) cells in mice was studied by autoradiography Maytansine 0.1 mg/kg was injected ip on d 4 after ip inoculation of 10(7) cells, the metaphase labeling curve showed a prolongation of T(G2+M).The [3H] TdR pulse labeling index( LI) was markedly reduced in 8 h; but the effect of maytansine on the mitotic index was contrary to the pulse LI. However, the anaphase and telophase cells were not noticed in 6 h. The [3H]TdR continuous LI in 12 h was 96% in the untreated cells, but 81% at the same time and 96% at the 24th in the treated cells. The grain counts of EAC cells labeled by [3H]TdR and [3H]UR did not decrease. These results showed that maytansine was extremely effective in producing mitotic arrest of the EAC cells, and the cells blocked in M phase could partial-synchronously enter S phase. LI curve of [3H]TdR continuous label for the cells on d 11 of tumor growth indicated that EAC cells in Go phase could not re-enter the cell cycle after ip maytansine.