Maytansinol (GMP) refers to the GMP grade reagents of Maytansinol. Maytansinol (Ansamitocin P-0) inhibits microtubule assembly and causes microtubule disassembly in vitro.

Maytansinol inhibits the growth of HCT116 human colon cancer cells. Maytansinol causes apoptosis in imaginal discs of wild-type larvae but not p53 mutant larvae. Maytansinol induces apoptosis in imaginal discs of wild-type larvae but not p53 mutant larvae at 24 hours after exposure to the drug. Maytansinol decreases the growth and/or survival of HCT116 cells in a dose-dependent manner and that the effect was more severe for p53+/+ than for p53-/- cells at both low and high doses. Maytansinol disrupts the mitotic spindle and prevents mitotic exit in Drosophila. This parallels the finding in human HCT116 cells, in which Maytansinol was more effective when p53 was present, at least at some doses.