[Growth-inhibitory activity of minocycline on various tumor cell lines in vitro]

In order to investigate the possible mechanism for the therapeutic efficacy of tetracycline antibiotics against malignant pleural effusion, the effect of minocycline (MC), one of this type of antibiotic, on in vitro growth of tumor cells was examined. As a result, it was found that MC caused complete growth inhibition of various tumor cell lines at concentration of 10-20 micrograms/ml, but this action was reversible, suggesting that considerably long exposure time would be needed for these drugs to kill the tumor cells in vivo at a relatively low concentration. On the other hand, when a relatively high concentration of 100 micrograms/ml was applied, MC induced irreversible inhibition of cell growth even if the exposure time was comparatively short. Since 4 human lung tumor cell lines examined exhibited high sensitivity to these antibiotics, it seems possible that their direct administration in the form of a high-concentration solution into the pleural cavity would result in a direct cytostatic effect on tumor cells in clinical therapy.