Rasagiline Inhibits Human Melanoma Cell Viability and Interacts Synergistically with Mitoxantrone and Antagonistically with Cisplatin—In Vitro Isobolographic Studies

<b>Background:</b> The increased incidence of malignant melanoma is observed in patients with Parkinson's disease. <b>Methods:</b> The anti-proliferative effects of carbidopa and rasagiline on four human malignant melanoma cell lines (A375, SK-MEL28, FM55P and FM55M2) were determined in MTT assay. The interaction profiles of rasagiline in combinations with cisplatin (CDDP) and mitoxantrone (MTX) in four human melanoma cell lines (A375, SK-MEL28, FM55P and FM55M2) were assessed by means of the isobolographic analysis in the MTT test; <b>Results:</b> Rasagiline, but not carbidopa, produced clear-cut anti-proliferative effects on various melanoma cell lines. The median inhibitory concentrations (IC₅₀ values) of rasagiline in the MTT were 280.69 µM for A375, 402.89 µM for SK-MEL28, 349.44 µM for FM55P, and 117.45 µM for FM55M2, respectively. The experimentally-derived selectivity index for rasagiline ranged from 8.22 to 28.18. Flow cytometry assay revealed, in two melanoma cell lines (FM55P and A375), a significant increase in the number of cells in the G0/G1 (up to 76.48% and 75.46% for cell lines, respectively), accompanied by a decrease in the percentage of cells in the S phase (decrease to 9.91% and 10.83% for cell lines, respectively), which may indicate potential cytostatic properties of rasagiline. The combinations of rasagiline with CDDP (at the fixed-ratio of 1:1) exerted either antagonistic interactions (<i>p</i> < 0.05) in the A375 and SK-MEL28, or additive interactions, with a tendency toward antagonism in the FM55P and FM55M2 cell lines in the MTT test. In contrast, the combinations of rasagiline with MTX (ratio of 1:1) produced either synergistic interaction (<i>p</i> < 0.05) in the FM55P cell line or additive interactions with a tendency toward synergy in the FM55M2, SK-MEL28, and A375 cell lines in the MTT test. <b>Conclusions:</b> Rasagiline combined with MTX exerted the most desirable synergistic interactions in relation to the anti-proliferative effects in four malignant melanoma cell lines, as assessed isobolographically. In contrast, rasagiline should not be combined with CDDP during the treatment of malignant melanoma due to the antagonistic interactions in the MTT assay.