Cyclosporine A enhanced the cytotoxicity of immunotoxin to the HER-2-overexpressing SK-OV-3 cells

Abstract

Abstract Background Cyclosporine A (CsA) is a calcium antagonist mainly used as an immune-suppressive agent, which can enhance the cytotoxicity of immunotoxins through an unknown mechanism. In this study, T-CUS245C was an immunotoxin conjugated with trastuzumab(T) and recombinant cucurmosin 245C (CUS245C), commonly used to induce apoptosis and differentiation in caner cells. Objectives To explore the synergistic effect of T-CUS245C combined with CsA, and to reveal it's initial mechanism. Methods We investigated the synergistic effect of CsA combined with T-CUS245C on cell proliferation inhibition and apoptosis in SK-OV-3 cells with HER-2-overexpressing by SRB assay and apoptosis assays. The effect of CsA on the intracellular distribution of T-CUS245C was observed by confocal microscopy and quantified by flow cytometry. Results The results showed that the combination therapy index (CI) of CsA combined with T-CUS245C was less than 0.7, indicating that CsA could significantly enhance the proliferation inhibition and apoptosis induced by T-CUS245C in SK-OV-3 cells. The result of confocal microscopy and flow cytometry showed that CsA could effectively increase the dispersion of FITC-T-CUS245C in the cytoplasm, suggesting that CsA might enhance the cytotoxicity of T-CUS245C by promoting the endolysosomal escape. Conclusion CsA might improve the cytotoxicity of T-CUS245C by facilitating the release of immunotoxin in the intracellular space, which could be a potencial strategy to transport antibody-based drugs from endolysosomes into the cytoplasm.