Rosmarinic Acid Potentiates Cytotoxicity of Cisplatin against Colorectal Cancer Cells by Enhancing Apoptotic and Ferroptosis

Rosmarinic acid (RA) has demonstrated anticancer effects on several types of malignancies. However, whether RA promotes the anticancer effect of cisplatin on colorectal cancer cells remains sketchy. This study aimed to explore whether RA potentiates the cytotoxicity of cisplatin against colon cancer cells and the underlying mechanism. Cell viability, cell cycle progression, and apoptosis was evaluated using sulforhodamine B (SRB) assay, flow cytometric analysis, and propidium iodide/Annexin V staining, respectively. Western blotting was utilized to analyze signaling pathways. Our findings showed that RA significantly enhanced the inhibitory effect on cell viability and the induction of apoptosis on the colon cancer cell lines DLD-1 and LoVo. Signaling cascade analysis revealed that the combination of RA and cisplatin jointly induced Bax and caspase activation while downregulating Bcl-2, glutathione peroxidase 4 (GPX4), and SLC7A11 in DLD-1 cells. Moreover, caspase inhibitor and ferroptosis inhibitor significantly reversed the inhibition of cell viability in response to RA combined with cisplatin. Collectively, these findings demonstrate that RA enhances the cytotoxicity of cisplatin against colon cancer cells, attributing to the promotion of apoptosis and ferroptosis.