Study On The Mechanism Of Mitotic Cell Death Induced By Lidamycin

Lidamycin (also designated C1027) is a member of the enediyne antibiotic family, has highly potent cytotoxicities toward tumor cells. It consists of a chromophore and an apoprotein, and the former has the ability to attack DNA, whereas the latter plays the role as a protecting protein. It has been observed that lidamycin can directly cleave DNA strands with preference of nucleotide and sequence. In addition to antitumor activities, lidamycin can inhibit the replication of viruses. The accumulation evidences indicate that lidamycin is a promising drug for clinical usage and valuable to be further studied.Mitotic cell death has been focused on in tumor therapy. However, the precise mechanisms underlying it remain unclear. We have reported previously that enediyne antibiotic lidamycin induces mitotic cell death at low concentrations in human epithelial tumor cells. The aim of this study was to investigate the molecular mechanism and signal transduction of lidamycin-induced mitotic cell death.With 0.1 nmol/L or 0.5 nmol/L lidamycin for 2 h, followed by a 72-hour incubation in drug-free medium, the treated human hepatoma BEL-7402 cells and normal human liver L-02 cells both displayed mitotic cell death characterized by enlargement of cell volume, appearance of multinucleation, and arrest in G2-M phase of cell cycle. We measured the cells growth curves by the MTT assay. Compared with the control cells, the treated cells showed the marked growth rate decrease and the delay in double time of proliferation. Subconfluent cells were continuously incubated for 72 h after exposure to low concentration of lidamycin for 2 h, and then were co-stained with the DNA-specific fluorescent dyes Hoechst 33342 and propidium iodide. A unique and atypical chromatin condensation occurred. The cells with this kind of condensation are characterized by integrated karyotheca, adhering on the bottom, and appearance of small "dots" representing segregated condensed chromatin without apoptotic bodies. The genomic DNA samples were extracted from the BEL-7402 cells and L-02 cells incubated continuously for 72 h after 2-hour treatments of lidamycin. The DNA ladder was never obtained in each sample whatever the exposure to 0.1 nmol/L or 0.5 nmol/L lidamycin. Neither BEL-7402 cells nor L-02 cells displayed apoptotic peaks after treatment of lidamycin at a low concentration. With Giemsa staining, the multinucleation was observed in BEL-7402 cells at the 12th hour after lidamycin treatment, whereas the appearance of...