Concentration-Dependent Dual Effects of Ciprofloxacin on SB-590885-Resistant BRAF A375 Melanoma Cells.

BRAF inhibitors (BRAFi) have been applied to treat melanoma harboring V600E mutations. Several studies showed that BRAFi-resistant melanomas are dependent on mitochondrial biogenesis. Therefore, the present study aimed to investigate the influence of ciprofloxacin (CIP), a mitochondria-targeting antibiotic, on SB-590885-resistant BRAF A375 melanoma (A375/SB) cells. The cytotoxicity activity of CIP and SB-590885, a potent and specific BRAFi, on A375 and A375/SB cells was evaluated by MTT, colony formation, migration, and spheroid formation assays. Moreover, SB-590885-induced cell death in A375 cells was analyzed. SB-590885 showed time- and concentration-dependent cytotoxic effects on A375 cells. Twenty-five μg/mL CIP decreased the cell viability of A375 and A375/SB cells in a time-dependent manner. This concentration of CIP markedly decreased clonogenicity in both cells and caused a reduction in the growth of A375/SB spheroids. The cytotoxicity of 5 μg/mL CIP on A375/SB cells was less than that of A375 cells. The colony formation and migration ability of A375/SB cells was increased in the presence of 5 μg/mL CIP. Ten μM SB-590885 induced a massive vacuolization in A375 cells. Cell death assays suggested a simultaneous activation of autophagy, paraptosis, apoptosis, and necrosis. For the first time, this study reveals that CIP at the maximum concentration in serum (5 μg/mL) can enhance the colony formation and migration abilities in BRAFi-resistant melanoma cells, while it has cytotoxic activity against these cells at a higher concentration than serum level. This study suggests that CIP may promote aggressive growth properties in BRAFi-resistant melanomas, at a concentration present in serum.