In Vitro Evaluation of the Dual Pharmacological Action of Vitamin D₃ as Cardio-protectant and Anti-cancer Agent

Background/Aim: Doxorubicin (DOX) is a potent and widely used chemotherapeutic; however, DOX-induced cardiotoxicity (DIC) remains a major clinical challenge. This study evaluated the cardio-protective and cytotoxic activities of vitamin D₃ in combination with DOX and as a single agent.

Materials and Methods: Immortalized human cardiomyocytes (AC16) and breast and liver cancer cells (JIMT-1, Huh-7) were exposed to DOX, vitamin D₃, and their simultaneous (Sim) or sequential (Seq) combinations for 48 and 72 h. The maximum inhibitory effects (I_max) and concentrations leading to 50% of I_max (IC₅₀) for each drug were estimated with Hill equation using Monolix2016R1 software. Combination indices (CI) for Sim and Seq were calculated using CompuSyn software.

Results: The concentration-effect relationships revealed that cardiomyocytes were more sensitive to DOX than cancer cells, with IC₅₀ at 0.01 μM (AC16), 0.07 μM (Huh-7), and 0.125 μM (JIMT-1). Moreover, vitamin D₃ concentrations maintained the baseline AC16 cell viability up to 10 μM, above which cardiomyocyte viability began to decline (IC₅₀=34.5 μM). The anti-cancer action of vitamin D₃ occurs at supra-physiological concentrations with IC₅₀ at 22.8 μM (Huh-7) and 40.9 μM (JIMT-1). The CI analysis in cardiomyocytes revealed a time-dependent shift in drug interaction from antagonistic (CI>1, 48 h) towards synergistic (CI<1, 72 h) for Sim, whereas it was antagonistic and independent of vitamin D₃ concentration for Seq.

Conclusion: The changes in cancer cell viability in Sim and Seq were not significantly different from that of DOX, suggesting no added benefit from adding vitamin D₃ to DOX-containing treatment regimens.