Phosphorylation of Akt (Ser473) is an Excellent Predictor of Poor Clinical Outcome in Prostate Cancer

Abstract

We previously showed, by immunohistochemistry with phospho-specific antibodies, increased phosphorylation (activation) of Akt (Ser(473)) [phosphorylated Akt (pAkt)] in high-Gleason grade prostate cancer (Malik SN, et al., Clin Cancer Res 2002;8:1168-71). Elevation of pAkt was accompanied by decreased phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 (Thr(202)/Tyr(204)) [phosphorylated ERK (pERK)], indicative of inactivation. In this report, we determined whether increased pAkt and decreased pERK predicted clinical outcome. Prostate-specific antigen (PSA) failure (detectable and rising PSA) versus PSA non-failure (undetectable PSA 5 years after prostatectomy) was used as a surrogate for clinical outcome. Prostate tumors from cases of PSA failure versus non-failure were stained for pAkt and pERK. A significant increase in mean pAkt staining (P < 0.001) in the PSA failures versus non-failures was seen based on the Wilcoxon signed ranks test [222.18 +/- 33.9 (n = 37) versus 108.79 +/- 104.57 (n = 16)]. Using the best-fitting multiple logistic regression equation, a 100-point increase in pAkt staining resulted in a 160% increase in the odds of being a PSA failure. There was decreased staining for pERK in PSA failures versus non-failures: a 100-point decrease resulted in an 80% increase in the odds of being a PSA failure. Each of these effects assumed the other biomarker was held constant. The area under the receiver-operating characteristic curve for these two biomarkers predicting PSA failure was 0.84, indicating excellent discrimination between PSA failure and non-failure cases. These data indicate that increased pAkt, alone or together with decreased pERK, is an important predictor of probability of PSA failure. However, pERK alone was not a significant predictor of PSA failure.