Abstract 5732: PI3K/Akt activity regulates androgen receptor expression and predicts poor clinical outcome in non-metastatic hormone-naïve prostate cancer

Activation of PI3K/Akt pathway is associated with adverse outcome and aggressive disease in many cancers. In prostate cancer (PCa), the activity of this pathway has been shown to promote disease progression and metastasis. However, it is still controversial how PI3K/Akt regulates androgen receptor (AR), a central signaling molecule in prostate pathophysiology, and whether it has an active role in hormone naïve non-metastatic PCa. Here, we show using immunohistochemistry (IHC) and advanced quantitative multiplexed IHC that the expression of phosphorylated-Akt(S473) and AR are highly correlated in clinical PCa, even at the cellular level. Furthermore, we found that high expression of p-Akt(S473) predicts poor clinical outcome in two independent hormone-naïve non-metastatic PCa cohorts. To study whether PI3K/Akt regulates AR expression, we performed an in vitro drug screen with 32 PI3K/Akt/mTOR inhibitors in PC346C, an AR expressing cell line derived from a hormone-naïve primary tumor of prostate. We observed a strong correlation between p-Akt(S473) and AR also in vitro in individual cells independent of the inhibitor used. Although both PI3K and Akt specific inhibition reduced cell viability, the response in nuclear expression of AR was highly dependent on the target of inhibition: Akt specific inhibition reduced AR nuclear expression and resulted in large, spindle-shaped cells, whereas PI3K specific inhibition increased AR nuclear expression and resulted in smaller, round-shaped cells. These data suggest that PI3K and Akt have different roles in sustaining AR activity in PCa as perturbations of the two components leads to differential responses in terms of AR nuclear expression and cell morphology. In conclusion, activated Akt associates with AR expression and predicts poor clinical outcome in hormone-naïve non-metastatic PCa. Furthermore, the differing roles of PI3K and Akt in AR regulation warrants for further studies as it may have implications in the design of PCa therapy targeting PI3K/Akt, especially when the inhibitors are administered in combination with anti-androgens. Citation Format: Sami Blom, Petra Mäki-Teeri, Andrew Erickson, Lassi Paavolainen, Tuomas Mirtti, Antti Rannikko, Swapnil Potdar, Päivi Östling, Wytske van Weerden, Olli Kallioniemi, Teijo Pellinen. PI3K/Akt activity regulates androgen receptor expression and predicts poor clinical outcome in non-metastatic hormone-naïve prostate cancer [abstract]. In: Proceedings of the American Asso