Abstract A19: Blocking autophagy using lysosomotropic agents sensitizes resistant prostate tumor cells to the novel Akt inhibitor AZD5363
Authors: Lamoureux Francois , Thomas Christian , Kumano Masafumi , Zhang Fan , Gleave Martin , Zoubeidi Amina 
Published: May 2013

Introduction and objective: Prostate cancer development is often associated with deletion or silencing of tumor suppressor phosphatase and tensin homologue (PTEN), a negative regulator of the PI3K-Akt pathway, leading to resistance to various therapies in both preclinical and clinical trials. Therefore, the PI3K/Akt pathway plays a central role in various cellular processes promoting survival signaling that can contribute to the malignant phenotype, and, consequently is an attractive pharmacological target. However, as single agents, AKT inhibitors have yet to demonstrate satisfactory results in the treatment of prostate cancer. Although therapeutically relevant concentrations of AKT inhibitors can effectively induce apoptosis as single agents in some prostate cancer cell lines, such as LNCaP, they induce minimal cell death in others, suggesting that there are intrinsic resistance mechanisms that limit their activity in these models.

Methods: We investigated the effects of the Akt inhibitor AZD5363 on cell proliferation, cell cycle, apoptosis and Akt downstream pathway. Survival mechanisms induced by AZD5363 were investigated. Then, we examined the impacts of pharmacologic or genetic inhibition of autophagy in combination with AZD5363 on cell proliferation and apoptosis. Furthermore, the anti-cancer activity of combination treatment of a lysosomotropic inhibitor of autophagy (chloroquine) with the Akt inhibitor AZD5363 was evaluated in PC-3 prostate cancer xenograft model.

Results: Here, we show that Akt inhibitor AZD5363 affected the Akt downstream pathway by reducing p-mTOR, p-P70S6K and p-S6K protein levels. Moreover, Akt inhibitor AZD5363 alone caused G2 growth arrest failed to induce significant apoptosis and increased autophagy in the PC3 and DU-145 prostate cancer cell lines. Blocking autophagy using pharmacological inhibitors (3-methyladenine, chloroquine and bafilomycin A) or genetic inhibitors (siRNA targeting Atg3 and Atg7) enhanced cell death induced by Akt inhibitor AZD5363 in these tumor prostate cell lines. Importantly, the combination of AZD5363 with chloroquine significantly reduced tumor volume by 84.9% compared with the control group and by 77.5% compared with either drug alone in the PTEN null prostate cancer PC3 xenograft model.

Conclusion: Taken together, these data demonstrate that Akt inhibitor AZD5363 synergized with the lysosomotropic inhibitor of autophagy, chloroquine, to induce apoptosis and delay tumor progression in a xenograft model of prostate cancer which was relatively resistant to monotherapy AZD5363. Hence, combination of an AKT inhibitor with an agent that inhibits autophagy provides a novel therapeutic approach which merits further evaluation.

Citation Format: Francois Lamoureux, Christian Thomas, Masafumi Kumano, Fan Zhang, Martin Gleave, Amina Zoubeidi. Blocking autophagy using lysosomotropic agents sensitizes resistant prostate tumor cells to the novel Akt inhibitor AZD5363 [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A19.