Induction of apoptosis by the angucyclinone antibiotic chemomicin in human tumor cells

Chemomicin (CHM), an angucyclinone antibiotic extracted from the fermentation broth of Nocardia Mediterranei subsp. Kanglensis 1747-64, shows immunosuppressive activity. However, whether it can inhibit growth of tumor cells remains elusive. In the present study, we show that CHM potently inhibited the proliferations of eight various types of human tumor cell lines and non-cross resistant to multidrug-resistant cells. In contrast to action of doxorubicin, the generation of reactive oxygen species was observed as early as 30 min after addition of CHM and its process did not involve iron. The apoptotic cells with chromatin condensation and Annexin V staining markedly increased after the human hepatoma HepG2 was exposed to 1, or 2 microg/ml CHM for 24 h. In the CHM-induced apoptosis, robust increment of p53 expression, activation of caspase-3, -7, -8, -9, cleavage of PARP and the phosphorylation of p38 and JNK, were detected by Western blot analysis. Further investigation revealed the disruption of mitochondrial membrane potential in the cells with CHM incubation for 4 h. Taken together, the results demonstrated that potent proliferation inhibitory effect of CHM on tumor cells is due to activation of the apoptotic pathway.