The effect of AKT pathway inhibition on reversal of platinum resistance in ovarian cancer: a translational approach

Abstract

Dysregulation of the phosphotidylinositol-3-kinase (PI3-kinase)/AKT signalling pathway is one of the most frequent mutational events in various human malignancies, including ovarian cancer. Increased PI3K/AKT activity in malignant cells is associated with resistance to chemotherapeutic agents.

GSK2141795 is a potent pan-AKT kinase inhibitor, being developed for ovarian and other cancers. The aim of the present study was to evaluate the ability of GSK2141795 to restore platinum sensitivity to platinum-resistant ovarian cancer cell lines. Effective pharmacodynamic (PD) biomarkers are critical for the implementation and assessment of targeted therapeutics. The second aim of this study was to explore the utility of using fluoro-deoxy-glucose positron emission tomography (FDG-PET) imaging as a PD marker by correlating changes in glucose metabolism (as measured by changes in FDG uptake) with changes in AKT pathway biomarkers, as an alternative to invasive tumour biopsies. The third aim of this study was to assess the role of DNA-PK mediated activation of AKT, compared to PI3K, in mediating drug resistance.

The results demonstrate that GSK2141795 synergistically enhances cisplatin induced apoptosis in platinum-resistant ovarian cancer cells, grown as either 2-dimensional monolayers or 3-dimensional multi-cellular tumour spheroids (MTS). Similar results were achieved when cisplatin was combined with the DNA-PK inhibitor NU7441, but not in combination with the selective PI3K inhibitor GSK2126458 in vitro. In vivo, combination of GSK2141795 or NU7441 with cisplatin led to superior tumour growth inhibition in murine xenografts, compared to either agent alone. In all three model systems (2D monolayers 3D MTS and in vivo xenografts), GSK2141795 decreased levels of phospho-PRAS40 and FDG uptake. FDG uptake and pPRAS40 expression were strongly correlated. In addition, reverse phase protein arrays (RPPA) was used to study the effects of GSK2141795 on cell signalling pathways in vitro, in vivo and using tumour biopsies from a phase I clinical trial of GSK2141795 in ovarian cancer. This identified a signature of AKT-pathway inhibition that includes consistent changes in phosphorylation of S6, 4E-BP1 and AKT itself.

Taken together, this report shows that GSK2141795 inhibits AKT signalling in platinum-resistant ovarian cancer cells, and can reverse platinum resistance in pre-clinical systems, and merits clinical exploration. In addition, the results demonstrate significant differences in the role of DNA-PK and PI3K mediated AKT activation in modulating the response to platinum chemotherapy, and support further clinical development of AKT or DNA-PK inhibitors in combination with cisplatin to overcome platinum resistance in ovarian cancer. FDG uptake was also found to be potential non-invasive PD biomarker, subject to clinical validation, for guiding dose selection in ovarian cancer patients. RPPA also identified a proteomic PD signature that could be used for pre-clinical development and applied to clinical tumour biopsies.