Cannabidiol Differentially Modulates Salinomycin Cytotoxicity in Human Cell Lines

Salinomycin, an ionophore coccidiostat widely used in livestock production, has attracted growing interest as a potential anticancer agent, although its clinical application remains limited by pronounced organ-specific toxicity. Cannabidiol (CBD), a non-psychoactive cannabinoid with documented cytoprotective properties, is increasingly consumed, making concurrent exposure plausible, yet its interaction remains unexplored. This study evaluated the cytotoxicity of salinomycin (0.39–50 µg/mL), alone and combined with two non-cytotoxic CBD concentrations (1.56 and 3.125 µg/mL), in three human cell lines—embryonic kidney-derived HEK-293, hepatoblastoma-derived HepG2, and neuroblastoma-derived SH-SY5Y—using assays of mitochondrial and lysosomal activity, membrane integrity, total protein content, and DNA synthesis, complemented by ROS measurement, apoptosis/necrosis evaluation, morphology, and an exploratory combination index analysis. CBD modulated salinomycin cytotoxicity in a strictly cell-line-dependent manner. In HEK-293 cells, it attenuated cytotoxicity, as reflected by uniformly higher IC50 values, reduced ROS production, and lower median fluorescence intensities of Hoechst 33342 and propidium iodide, whereas in the tumor-derived HepG2 and SH-SY5Y lines, it enhanced cytotoxicity irrespective of the CBD concentration applied, accompanied by increased ROS generation and more pronounced cell death. As all three lines are immortalized or tumor-derived, these observations describe cell-line-specific responses and cannot be extrapolated to normal renal, hepatic, or neuronal tissue.