TZT-1027, a newly synthesized
dolastatin 10 derivative, is a potent
antitumor agent which inhibits microtubule polymerization and perturbs microtubule dynamics. In this report, we investigated whether
TZT-1027 inhibited the growth of various human
cancer cells, and the cell death caused by
TZT-1027 was due to apoptosis. In addition, we elucidated the apoptosis machinery induced by treatment with
TZT-1027. The 50% growth-inhibitory concentrations (IC50 values) of
TZT-1027 on
cancer cells derived from various sources were not more than 5.9 ng/ml.
TZT-1027 showed superior cytotoxicity than any other
antitumor agents. Next, we evaluated morphological nuclear change, namely,
chromatin condensation and DNA fragmentation. We used three
cancer cell lines derived from different types in view of having apoptosis related
protein, human
leukemia HL-60 (in the presence of both
Caspase-3 and Bcl-2), human
breast cancer MCF-7 (in the absence of
Caspase-3), and human
prostate cancer DU145 (in the absence of Bcl-2).
TZT-1027 induced DNA fragmentation in the presence but not absence of
Caspase-3. Nevertheless, apoptic
chromatin condensation was observed in all
cancer cells even if there was no
Caspase-3. Furthermore, we examined whether
TZT-1027, microtubule-disrupting agent, influenced cell cycle progression. Flow cytometric analysis revealed the cells treated with
TZT-1027, and with the other antimicrotubule agents, to be arrested at the G2/M phase and subsequently to show fragmented
DNA smaller than that of G1 phase cells. Moreover, we tested
TZT-1027 for its ability to induce Bcl-2 phosphorylation in human
cancer cell lines.
TZT-1027 and other agents which interacted with microtubules induced Bcl-2 phosphorylation, whereas
DNA-damaging agents did not. The present results suggested an association of the growth-inhibitory effect of
TZT-1027 with the induction of apoptosis and indicated that the apoptosis induced by
TZT-1027 was followed by G2/M arrest even if there was no
Caspase-3 or Bcl-2.