Therapeutic starvation and autophagy in prostate cancer: A new paradigm

Abstract

10530 The metabolic fragility of cancer cells is magnified with the preferential utilization of glycolysis that metabolizes glucose inefficiently rather than oxidative phosphorylation (the “Warburg effect”) and from impaired mechanisms of survival. In fact, one pathway by which cells survive metabolic stress is thought to be autophagy, a catabolic process of organelle digestion, which creates ATP during periods on nutrient limitation. Remarkably, autophagy is often impaired in human prostate cancers, due to either activation of the PI-3 kinase/Akt/mTOR pathway, which normally inhibits autophagy, or through allelic loss of the essential autophagy gene beclin1. This suggests that prostate cancers may be susceptible to metabolic stress that can be exploited therapeutically. Using immortalized mouse epithelial prostate cells, as well as PC-3 and LNCaP cell lines, we demonstrated the cytotoxic effect of 2-deoxyglucose (2DG), as an inhibitor of glycolysis. We found that 2DG induced membrane translocation in cells characteristic of autophagy using a transfected pEGFP-LC3 autophagy marker construct. We then demonstrated that induction of autophagy was dependent on Beclin1 expression in these cell models using Beclin1 siRNA. Based on these data, we initiated a phase I/II clinical trial with 2DG in patients with advanced malignancies and prostate cancer, which is now ongoing. In an effort to develop markers of autophagy for assessment in a clinical trial, we stained a human prostate TMA (>35 patient cores) for Beclin1 by IHC. Beclin1 staining was increased in tumor tissue compared to normal tissue. Staining was imaged and digitized using a 40x volume scan on a high- throughput MedMicro whole slide scanner. The imaged specimens were stored in multi-tiled TIFF format on a redundant array of independent devices (RAID); staining will be analyzed using a color decomposition algorithm and compared to tumor characteristics as we have previously done (Foran DJ et al., IEEE Trans Inf Technol Biomed, 8:89–96, 2004). These data further support the rationale to inhibit metabolism in cancer and the potential importance of autophagy with metabolic approaches to therapy. Further imaging assessment and analysis of markers of autophagy such as Beclin1 are ongoing. No significant financial relationships to disclose.