Therapeutic application of natural medicine monomers in cancer treatment

Natural medicine monomers (NMMs) isolated from plants have been recognized for their roles in treating different human diseases including cancers. Many NMMs exhibit effective anti-cancer activities and can be used as drugs or adjuvant agents to enhance the efficacy of chemotherapy and radiotherapy. Some NMMs, such as paclitaxel and camptothecin, have been extensively studied for decades and are now used as anti-cancer medicines due to their remarkable curative effects, such as inhibiting cancer cell proliferation and metastasis, and inducing cell death and differentiation. Methods: After extensively reviewing papers related to NMM studies in cancers, we grouped NMMs into six categories based on their chemical structures. We summarized the anti-cancer activities of these NMMs and current knowledge of molecular mechanisms for them to exert their functions. Results and Conclusion: Many NMMs from plants can effectively inhibit cancer cells with low or tolerable toxicity to patients. Some NMMs have been well-characterized for their anti-cancer activities and have already been used as clinical drugs or adjuvant agents; however, the mechanisms underlying the cancer suppressive activities of most NMMs remain poorly understood. Many NMMs can be used as initial structural scaffolds to design and develop novel therapeutics against cancers. This review summarizes reports related to signaling pathways mediated by different NMMs and can provide a theoretical basis for clinical application and new drug development of NMMs.