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Clear cell ovarian carcinoma (CCOC) is an aggressive form of epithelial ovarian cancer that exhibits low response rates to systemic therapy and poor patient outcomes. Multiple studies in CCOC have revealed expression profiles consistent with increased hypoxia, and our previous data suggest that hypoxia is correlated with increased autophagy in CCOC. Hypoxia-induced autophagy is a key factor promoting tumor cell survival and resistance to therapy. Recent clinical trials with the molecular-targeted receptor tyrosine kinase (RTK) inhibitor sunitinib have demonstrated limited activity. Here, it was evaluated whether the hypoxia–autophagy axis could be modulated to overcome resistance to sunitinib. Importantly, a significant increase in autophagic activity was found with a concomitant loss in cell viability in CCOC cells treated with sunitinib. Pharmacologic inhibition of autophagy with the lysosomotropic analog Lys05 inhibited autophagy and enhanced sunitinib-mediated suppression of cell viability. These results were confirmed by siRNA targeting the autophagy-related gene Atg5. In CCOC tumor xenografts, Lys05 potentiated the antitumor activity of sunitinib compared with either treatment alone. These data reveal that CCOC tumors have an autophagic dependency and are an ideal tumor histotype for autophagy inhibition as a strategy to overcome resistance to RTK inhibitors like sunitinib. Implications: This study shows that autophagy inhibition enhances sunitinib-mediated cell death in a preclinical model of CCOC. Mol Cancer Res; 15(3); 250–8. ©2017 AACR.

Accumulating evidence indicates that therapies designed to trigger apoptosis in tumor cells cause mitochondrial depolarization, nuclear damage, and the accumulation of misfolded protein aggregates, resulting in the activation of selective forms of autophagy. These selective forms of autophagy, including mitophagy, nucleophagy, and ubiquitin-mediated autophagy, counteract apoptotic signals by removing damaged cellular structures and by reprogramming cellular energy metabolism to cope with therapeutic stress. As a result, the efficacies of numerous current cancer therapies may be improved by combining them with adjuvant treatments that exploit or disrupt key metabolic processes induced by selective forms of autophagy. Targeting these metabolic irregularities represents a promising approach to improve clinical responsiveness to cancer treatments given the inherently elevated metabolic demands of many tumor types. To what extent anticancer treatments promote selective forms of autophagy and the degree to which they influence metabolism are currently under intense scrutiny. Understanding how the activation of selective forms of autophagy influences cellular metabolism and survival provides an opportunity to target metabolic irregularities induced by these pathways as a means of augmenting current approaches for treating cancer.

Hypoxia is a signature feature of growing tumors. This cellular state creates an inhospitable condition that impedes the growth and function of all cells within the immediate and surrounding tumor microenvironment. To adapt to hypoxia, cells activate autophagy and undergo a metabolic shift increasing the cellular dependency on anaerobic metabolism. Autophagy upregulation in cancer cells liberates nutrients, decreases the buildup of reactive oxygen species, and aids in the clearance of misfolded proteins. Together, these features impart a survival advantage for cancer cells in the tumor microenvironment. This observation has led to intense research efforts focused on developing autophagy-modulating drugs for cancer patient treatment. However, other cells that infiltrate the tumor environment such as immune cells also encounter hypoxia likely resulting in hypoxia-induced autophagy. In light of the fact that autophagy is crucial for immune cell proliferation as well as their effector functions such as antigen presentation and T cell-mediated killing of tumor cells, anticancer treatment strategies based on autophagy modulation will need to consider the impact of autophagy on the immune system.

Despite a significant body of literature identifying the main regulators of autophagy in model organisms, there are gaps in our understanding of the precise molecular and biochemical modulators that control this adaptive process in metazoans. Two studies in this issue of EMBO reports provide new insight into the autophagic process. Mauvezin and colleagues (2010) show that a nuclear protein, known as DOR, is a new player in stress‐induced autophagy, and the Dikic lab reports that the mitochondrial protein Nix is a selective autophagy receptor that mediates mitochondrial clearance (Novak et al , 2010). Autophagy is a conserved catabolic cellular process in which macromolecules and organelles are degraded, either as a means to eliminate long‐lived, damaged, or faulty cellular components, or in response to stresses such as hypoxia, endoplasmic reticulum stress, or nutrient deprivation. Cells can use the products of autophagic degradation to generate energy or other essential proteins required for cell survival. When cellular conditions are favourable, autophagy is negatively regulated by the nutrient sensor mammalian target of rapamycin (mTOR). In the presence of stress, mTOR is inhibited and autophagy is induced (Fig 1). In this setting, beclin 1 forms a complex with Vps34, which is a class III phosphatidylinositol 3‐kinase (PI3K). Through a poorly defined process, this complex initiates the nucleation of the autophagosome membrane. The autophagy‐related (Atg) proteins Atg5, Atg12 and Atg16 also have a role in this process, by promoting the formation of the autophagosome precursor, the phagophore. The proteins LC3 and GATE16 localize to the autophagosomal membrane during autophagosome formation and remain bound as it fuses with a lysosome and becomes an autolysosome, the end organelle where …