Inhibition of CAMKK2 impairs autophagy and castration-resistant prostate cancer via suppression of AMPK-ULK1 signaling

Abstract

Previous work has suggested androgen receptor (AR) signaling mediates cancer progression in part through the modulation of autophagy. Accordingly, we demonstrate that chloroquine, an inhibitor of autophagy, can inhibit tumor growth in preclinical mouse models of castration-resistant prostate cancer (CRPC). However, clinical trials testing chloroquine derivatives in men with CRPC have yet to yield promising results, potentially due to side effects. We hypothesized that identification of the upstream activators of autophagy in prostate cancer could highlight alternative, context-dependent targets for blocking this important cellular process during disease progression. Here, we used molecular (inducible overexpression and shRNA-mediated knockdown), genetic (CRISPR/Cas9), and pharmacological approaches to elucidate an AR-mediated autophagy cascade involving Ca2+/calmodulin-dependent protein kinase kinase 2 (CAMKK2; a kinase with a restricted expression profile), 5-AMP-activated protein kinase (AMPK) and Unc-51 like autophagy activating kinase 1 (ULK1). These findings are consistent with data indicating CAMKK2-AMPK-ULK1 signaling correlates with disease progression in genetic mouse models and patient tumor samples. Importantly, CAMKK2 disruption impaired tumor growth and prolonged survival in multiple CRPC preclinical mouse models. Finally, we demonstrate that, similar to CAMKK2 inhibition, a recently described inhibitor of AMPK-ULK1 signaling blocked autophagy, cell growth and colony formation in prostate cancer cells. Taken together, our findings converge to demonstrate that AR signaling can co-opt the CAMKK2-AMPK-ULK1 signaling cascade to promote prostate cancer by increasing autophagy. Further, we propose that an inhibitor of this signaling cascade could serve as an alternative, more specific therapeutic compared to existing inhibitors of autophagy that, to date, have demonstrated limited efficacy in clinical trials due to their toxicity and poor pharmacokinetics.