Autophagy is a homeostatic, catabolic degradation process whereby cellular proteins and organelles are engulfed by autophagosomes, digested in lysosomes, and recycled to sustain cellular metabolism. Autophagy has dual roles in cancer, acting as both a tumor suppressor by preventing the accumulation of damaged proteins and organelles and as a mechanism of cell survival that can promote the growth of established tumors. Tumor cells activate autophagy in response to cellular stress and/or increased metabolic demands related to rapid cell proliferation. Autophagy-related stress tolerance can enable cell survival by maintaining energy production that can lead to tumor growth and therapeutic resistance. As shown in preclinical models, inhibition of autophagy restored chemosensitivity and enhanced tumor cell death. These results established autophagy as a therapeutic target and led to multiple early phase clinical trials in humans to evaluate autophagy inhibition using hydroxychloroquine in combination with chemotherapy or targeted agents. Targeting autophagy in cancer will provide new opportunities for drug development, because more potent and specific inhibitors of autophagy are needed. The role of autophagy and its regulation in cancer cells continues to emerge, and studies aim to define optimal strategies to modulate autophagy for therapeutic advantage.
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