Activity of dolastatin 10 against small-cell lung cancer in vitro and in vivo: induction of apoptosis and bcl-2 modification.
OBJECTIVE
Dolastatin 10 is a natural cytotoxic peptide which acts through the inhibition of microtubule assembly. Studies have suggested that such agents can induce apoptosis in association with bcl-2 phosphorylation. Since bcl-2 overexpression is common in small-cell lung cancer (SCLC), we evaluated the activity of dolastatin 10 in SCLC cell lines and xenografts.


METHODS
In vitro growth inhibition was evaluated with a standardized MTT assay and apoptosis with fluorescent microscopy and a TUNEL assay. Immunoblot analysis and phosphatase digestion were used to determine bcl-2 modification. In vivo activity was evaluated in subcutaneous and metastatic SCLC xenograft models in SCID mice.


RESULTS
Dolastatin 10 had growth inhibitory activity against four SCLC cell lines (NCI-H69, -H82, -H446, -H510) with IC50 values ranging from 0.032 to 0.184 nM. All four cell lines exhibited evidence of apoptosis after 48 h of exposure to 1.3 nM dolastatin 10. Immunoblot analysis revealed that 1.3 nM dolastatin 10 altered the electrophoretic mobility of bcl-2 in NCI-H69 and -H510 cells within 16 h of treatment. Incubation of protein extract from dolastatin 10-treated NCI-H69 and -H510 cells with calcineurin resulted in the disappearance of the altered mobility species, suggesting dolastatin 10-induced bcl-2 phosphorylation. In in vivo studies, 450 microg/kg of dolastatin 10 IV x 2 given after intravenous injection of NCI-H446 cells completely inhibited tumor formation. In established subcutaneous NCI-H446 xenografts, 450 microg/kg of dolastatin 10 IV induced apoptosis in the majority of tumor cells within 96 h, resulting in a log10 cell kill of 5.2 and an increase in median survival from 42 to 91 days.


CONCLUSIONS
These findings suggest that dolastatin 10 has potent activity against SCLC and that the modulation of apoptotic pathways deserves further evaluation as an anticancer strategy.
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D047630:Depsipeptides; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D009842:Oligopeptides / Q000494:pharmacology* / Q000627:therapeutic use; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured