P-glycoprotein Blockers Augment the Effect of Mitomycin C on Human Tenon's Fibroblasts

Mitomycin C (MMC), which induces apoptosis in human Tenon's fibroblasts (HTF), is frequently used to retard wound healing after glaucoma surgery. The aim of this in vitro study was to examine whether adjunctive Verapamil and Cyclosporine could augment the cytotoxic effect of MMC on HTF.

Fibroblast cell lines were established by explant culture from human tissue biopsy samples obtained during trabeculectomy procedures. Cells were exposed to MMC at varying concentrations (0.01-0.4 mg/ml) for 3 minutes, prior to washing in the presence or absence of the following drugs: Staurosporine (0.003mg/ml), Verapamil (2.5-0.25 mg/ml), or Cyclosporine (50-0.5 mg/ml). Following exposure, cells were cultured for 6 hours and surviving cells quantitated by haemocytometer counts.

Both Verapamil and Staurosporine exhibited mild toxic effects on their own, but greatly enhanced the apoptotic effect of MMC. Staurosporine is too toxic to be considered clinically, so its augmentive effect on the activity of MMC was not studied further here. Doses as low as 0.25 mg/ml of Verapamil continued to show significant augmentation of the apoptotic effect of MMC Cyclosporine at a clinically used concentration (5 mg/ml) exhibited modest augmentation of the effect of MMC.

Verapamil and Cyclosporine in clinically acceptable concentrations potentiate the effect of MMC and may obviate the need for high dose antimetabolites in trabeculectomy; however, further preclinical study is required.

Adjunctive Verapamil or Cyclosporine may allow lower dose MMC to be used in glaucoma filtration surgery while maintaining the same antifibrotic effects.