Cinnamomum zeylanicum Blume Essential Oil Inhibits Metastatic Melanoma Cell Proliferation by Triggering an Incomplete Tumour Cell Stress Response

Given the known pro-oxidant status of tumour cells, the development of anti-proliferative strategies focuses on products with both anti- and pro-oxidant properties that can enhance antitumour drug cytotoxicity. We used a C. zeylanicum essential oil (CINN-EO) and assessed its effect on a human metastatic melanoma cell line (M14). Human PBMCs and MDMs from healthy donors were used as normal control cells. CINN-EO induced cell growth inhibition, cell cycle perturbation, ROS and Fe(II) increases, and mitochondrial membrane depolarization. To assess whether CINN-EO could affect the stress response, we analysed iron metabolism and stress response gene expression. CINN-EO increased HMOX1, FTH1, SLC7A11, DGKK, and GSR expression but repressed OXR1, SOD3, Tf, and TfR1 expression. HMOX1, Fe(II), and ROS increases are associated with ferroptosis, which can be reversed by SnPPIX, an HMOX1 inhibitor. Indeed, our data demonstrated that SnPPIX significantly attenuated the inhibition of cell proliferation, suggesting that the inhibition of cell proliferation induced by CINN-EO could be related to ferroptosis. Concurrent treatment with CINN-EO enhanced the anti-melanoma effect of two conventional antineoplastic drugs: the mitochondria-targeting tamoxifen and the anti-BRAF dabrafenib. We demonstrate that CINN-EO-mediated induction of an incomplete stress response specifically in cancer cells affects the proliferation of melanoma cells and can enhance drug cytotoxicity.