Meeting the metabolic demands of a tumor cell is challenging due to increased energy utilization and reliance on aerobic glycolysis, making the targeting of metabolism an attractive therapeutic approach for investigation. Autophagy, a regulated cellular process of self digestion, may function to sustain cell survival under conditions of nutrient limitation, or, alternatively, if allowed to continue, result in cell death. We hypothesized that understanding the role of autophagy during treatment of inhibitors of metabolism such as 2-deoxyglucose (2DG), which we are currently studying in an ongoing clinical trial, will be critical to develop future approaches to induce metabolic catastrophe in tumor cells. We found that 2DG induced cytotoxicity in PC-3 and LNCaP cells in a dose dependent fashion. Using a transfected pEGFP-LC3 autophagy reporter construct, we found that 2DG induced LC3 membrane translocation, characteristic of autophagy. Furthermore, knockdown of beclin-1, an essential regulator of autophagy, abrogated the 2DG induced induction of autophagy. Using Western analysis for LC3 protein, we also found increased LC3 expression, again consistent with autophagy. Using immortalized rat prostate cells expressing constituitively active Akt, which activates mTOR and thereby inhibits autophagy, we also demonstrated that the cytotoxic effect of 2DG increased with increased expression of Akt. In an effort to develop markers of autophagy for assessment in clinical trials, we stained human prostate tumors (n=13) and normal tissue (n=35) for Beclin-1 by IHC. Beclin-1 staining was noted in tumor cells, as well as normal epithelial cells, but was increased in tumor tissue compared to normal tissue (p=.003). These data support the potential importance of autophagy as modulating the response of tumor cells to metabolic stress and for the use of metabolic therapeutic approaches; Beclin-1 is an easily measurable marker that requires further study to determine if expression will predict response to studies with agents such as 2DG, which we have ongoing.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA