Abstract 788: Correlation of elevated phosphorylated / total AKT ratio, chemoresistance and survival in ovarian cancer ascites samples

Abstract

Abstract Background: AKT pathway activation is commonly described in ovarian cancer, and implicated in preclinical models of chemoresistance. Ascites occurs in a high proportion of patients at some stage in their illness. Purpose: To study the relationship between activation of the AKT pathway in human ovarian cancer ascites specimens (measured by the ratio of phosphorylated (P) to total (T) AKT pathway proteins) to patient survival and response to chemotherapy. In addition we studied the correlation of P/T AKT ratio to carboplatin sensitivity in a human ovarian cancer cell line panel. Method. 99 samples of ascites from 75 patients with ovarian cancer and a known treatment history were purified using anti-EpCam antibody coated magnetic beads (Dynal Biotech), stored at −80 degrees C, and then analysed with Mesoscale Discovery (MSD) ELISA for P/T AKT, GSK3β and p70S6K, and Pathscan ELISA for P/T 4EBP1 . Differences in survival in patient subgroups were analysed by logrank tests. Five cell lines (A2780, CH1, IGROV1, OVCAR3, SKOV3) were analysed in triplicate by sulphurhodamine B colorimetric assay to establish half maximal inhibitory concentration (IC50) for carboplatin and PI3K-AKT-mTOR pathway inhibitors (rapamycin, LY 294002, PI103, and Merck AKT inhibitor VIII), and the results correlated with baseline AKT pathway protein activation ratios. Results: Samples from patients who responded to chemotherapy (n=32) subsequent to sample collection had a lower median P/T S6K ratio (0.43) than those (n=28) who progressed (0.71, p=0.026, Mann-Whitney test; 39 samples were from patients who received no subsequent chemotherapy). Analysing the first sample for each patient, (n=75), those with a P/T AKT ratio above median (0.140) had a statistically significantly longer survival than those patients below median (28.0 months (m) vs 49.7 m, HR 1.74 (95% CI 1.01-3.01), p=0.048). A similar trend for P/T S6K ratio was also found, however this was not statistically significant (22.0 m vs 47.5 m, HR 1.56 (95%CI 0.90-2.71), p=0.112). In the ovarian cell line panel studied, a high P/T AKT ratio was found in the cells most resistant to carboplatin, whereas there was no relationship between AKT pathway activation and resistance to the AKT pathway inhibitors. Potential reasons for activation of the AKT pathway include amplification and mutation of PIK3CA and AKT2. Fluorescence in-situ hybridisation and sequencing of somatic DNA from these samples are ongoing. Conclusion: Patients who responded to subsequent chemotherapy had a significantly lower P/T S6K ratio than those who progressed. A P/T AKT ratio greater than 0.144 in malignant ascites predicts a statistically significant poorer prognosis. In vitro cell line models suggest a trend of P/T AKT ratio to correlate with carboplatin resistance. P/T AKT ratio should be studied prospectively as a prognostic and predictive biomarker in ovarian cancer. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 788.