[Flow cytometric study of enhanced effect of anti-cancer drugs induced by nicardipine hydrochloride].

Flow cytometric analysis was used to study the effect of a calcium influx blocker, nicardipine hydrochloride, on the cytotoxicity of anti-cancer drugs in tumor cells. The parameters used for this study were DNA- and protein-cell distribution histograms. Cells and drugs used for this study were C6 cells from CD Fisher rat glioma and VCR, ADM and ACNU, respectively. The growth inhibitory effect estimated by concentration at ID50 on C6 cells was indicated as follows; VCR showed an 89-fold enhancement, while ACNU showed little enhancement following addition of nicardipine hydrochloride. DNA and protein histograms obtained by flow cytometry revealed almost the same effects as cells which were studied using high concentration of VCR without nicardipine hydrochloride. For the other drugs, ADM showed a small enhancement on histograms, while with ACNU, little enhancement was noted as well as the inhibitory effect of each drug described above. The results indicate that nicardipine hydrochloride greatly affects the cell cytotoxicity of VCR but not so much with ADM and ACNU. From these results, it appears that this drug enhances the action of anti-cancer drugs not only by merely blocking the efflux of drugs from cells but also by other mechanisms which remain to be clarified.