Plant natural products as autophagy modulators to improve potential cancer therapy

Plant natural products are well-characterized to have pharmacological or biological activities that can be of therapeutic benefits for cancer therapy, which also provide an important source of inspiration for the discovery of potential novel small-molecule drugs. In the past 3 decades, accumulating evidence has revealed that plant natural products can modulate a series of key autophagic signaling pathways in different types of human cancer. Autophagy, an evolutionarily conserved, multi-step lysosomal degradation process in which a cell destroys long-lived proteins and damaged organelles, has been widely reported to play a crucial role in several pathological processes, most notably in cancer. In this chapter, we focus on highlighting several representative plant natural products, such as artemisinin, oridonin, curcumin, paclitaxel, resveratrol, quercetin, berberine, dihydroartemisinin, matrine, and celastrol, that may ultimately trigger cancer cell death through the regulation of some key autophagy signaling pathways, involved in PI3K-AKT-mTOR, RAS-RAF-MEK-ERK, SIRT1-AMPK-mTOR, Wnt/β-catenin, Beclin-1, and p53. Taken together, these inspiring findings would shed new light on exploiting more and more plant natural products as candidate small-molecule drugs by targeting the crucial pathways of autophagy for future cancer drug discovery.