Application of capsaicin as a potential new therapeutic drug in human cancers.

WHAT IS KNOWN AND OBJECTIVE: Capsaicin, the major active ingredient of chili pepper, may play a "dual role" in tumourigenesis, acting as a carcinogen or as a cancer preventive agent. The aim of this study was to investigate the anticancer mechanisms of capsaicin and the effects of capsaicin on traditional chemotherapeutic drugs and radiotherapy in various cancer types and the potential for clinical application in cancer therapy. METHODS: We conducted extensive literature searches through PubMed to collect representative studies of capsaicin in different cancer types. These studies investigated the anticancer molecular mechanisms of capsaicin. We then searched for the effects of capsaicin on traditional chemotherapeutic drugs or radiotherapy. Finally, in terms of clinical application, we searched for the advances of capsaicin-loaded nanoparticles in malignant tumours. RESULTS AND DISCUSSION: In most studies, capsaicin is a potential anti-tumour compound and the anti-cancer mechanisms are mainly related to anti-proliferation, induction of apoptosis and autophagy, anti-angiogenesis and anti-metastasis. It is worth noting that the biological functions of capsaicin are greatly affected by its concentration and the effective concentration in different malignant tumours varies considerably. Furthermore, capsaicin can affect the anti-cancer activity of conventional chemotherapeutic drugs or radiation therapy and more and more capsaicin-loaded nanoparticles have been developed to prolong the drug retention of capsaicin in the blood circulation and allow active targeting of specific cancer cells to enhance its accurate delivery and targeting specificity, suggesting that capsaicin may be used as a potential chemopreventive or a new auxiliary therapeutic drug for cancer. However, there is still a need for well-controlled studies to assess the safety and efficacy of capsaicin, and further preclinical and clinical trials are needed to elucidate its anti-tumour effects when combined with other standard drugs or radiotherapy. WHAT IS NEW AND CONCLUSION: Capsaicin exhibits strong anti-cancer properties in various cancer types. The combination of capsaicin with conventional chemotherapy drugs or radiotherapy can improve the sensitivity, reduce the side effects and enhance the tolerance of patients to cancer treatment. The development of capsaicin-loaded nanoparticles may provide a very promising approach to chemotherapy for malignant tumours.