New Visions on Natural Products and Cancer Therapy: Autophagy and Related Regulatory Pathways

SIMPLE SUMMARY: In the past few years, clinical as well as regular scientists have been paying attention to medicinal applications of natural products. There are several investigations focusing on the potential beneficial effects of natural compounds in the treatment of different cancers. In the current comprehensive review paper, we first discuss three major mechanisms that control the effect of cancer therapy agents on tumor cells. This includes autophagy, apoptosis and the unfolded protein response. In the next step, we discuss how different natural compounds (more than 100 compounds) target cancer cells via the autophagy pathway and how this regulates stress response and cell death in cancer cells. ABSTRACT: Macroautophagy (autophagy) has been a highly conserved process throughout evolution and allows cells to degrade aggregated/misfolded proteins, dysfunctional or superfluous organelles and damaged macromolecules, in order to recycle them for biosynthetic and/or energetic purposes to preserve cellular homeostasis and health. Changes in autophagy are indeed correlated with several pathological disorders such as neurodegenerative and cardiovascular diseases, infections, cancer and inflammatory diseases. Conversely, autophagy controls both apoptosis and the unfolded protein response (UPR) in the cells. Therefore, any changes in the autophagy pathway will affect both the UPR and apoptosis. Recent evidence has shown that several natural products can modulate (induce or inhibit) the autophagy pathway. Natural products may target different regulatory components of the autophagy pathway, including specific kinases or phosphatases. In this review, we evaluated ~100 natural compounds and plant species and their impact on different types of cancers via the autophagy pathway. We also discuss the impact of these compounds on the UPR and apoptosis via the autophagy pathway. A multitude of preclinical findings have shown the function of botanicals in regulating cell autophagy and its potential impact on cancer therapy; however, the number of related clinical trials to date remains low. In this regard, further pre-clinical and clinical studies are warranted to better clarify the utility of natural compounds and their modulatory effects on autophagy, as fine-tuning of autophagy could be translated into therapeutic applications for several cancers.