Purpose: To evaluate the antitumor activity of gemcitabine (GEM), incorporated in microemulsions with varying surfactant-to-oil (S/O) ratio, against MCF-7 breast cancer cells and HCT 116 colon cancer cells.

Methods: The microemulsion formulations consisted of Tween 80, Span 20, isopropyl myristate (IPM) and aqueous ethanol (40 %). Anticancer assessment involved determination of hemolysis activity, screening for cytotoxicity using sulphorhodamine B assay and determination of the mechanism of cell death using light microscope and ApopNexin FITC apoptosis detection kit.

Results: Hemolysis activity of all the microemulsion formulations, either blank or drug-loaded, was significantly less than that of GEM solution.  On average, MCF-7 cell viability significantly (p < 0.05) decreased from 38.53 ± 6.04 to 30.1 ± 4.66 % when the administered microemulsion concentration in modified eagle medium (MEM),  increased from 0.03 to 0.3 % v/v but significantly (p < 0.05) increased by 1.4-fold when exposed to GEM solution at equivalent concentrations. In contrast, the cytotoxicity of the microemulsion formulation against HCT116 cells was similar to that of 0.03 % v/v GEM solution but greater than that of GEM solution by 1.5-fold when their concentration in MEM increased to 0.3 %v/v. Microscopic studies show that the microemulsions stimulated apoptosis in MCF-7 and HCT116 cell within 48 h and at low concentration (0.03 %v/v).

Conclusion: Microemulsion formulations improved the efficacy of GEM and induced apoptosis in MCF-7 and HCT116 cells.