The Challenge of Developing Autophagy Inhibition as a Therapeutic Strategy.

The finding that cancer chemotherapeutic drugs and ionizing radiation often promote autophagy has provided the foundation for clinical trials combining autophagy-blocking agents with antitumor drugs and radiation. The premise driving these trials is that therapy-induced autophagy is cytoprotective; consequently, inhibition of autophagy is anticipated to sensitize malignancies to therapy. However, it is well-established that autophagy may also mediate the toxicity of antitumor drugs while evidence also exists for a nonprotective function of autophagy. Consequently, given that it cannot be predicted what form autophagy will take upon treatment with chemotherapy or radiation, the current ongoing clinical trials are likely to generate contradictory or inconsistent results, with the potential consequence that autophagy inhibition could be dismissed as therapeutic strategy based on what are essentially false-negative outcomes. Appropriate interpretation of the outcomes of these trials would require knowledge as to whether the drugs or radiation used promote the cytoprotective form of autophagy in the tumor cells as well as whether the chloroquine or hydroxychloroquine actually inhibit the autophagy. Ultimately, it will be necessary to identify those patients for whom the strategy of autophagy inhibition would be anticipated to improve the response to therapy. However, this is currently not feasible in the absence of appropriate bioassays or predictive markers for characterization of the autophagy or the effectiveness of pharmacologic approaches for autophagy inhibition in the clinic. Cancer Res; 76(19); 5610-4. ©2016 AACR. ©2016 American Association for Cancer Research.