AKT is a serine-threonine kinase implicated in tumorigenesis as a central regulator of cellular growth, proliferation, survival, metabolism, and migration. Activated AKT is overexpressed in 50-70% of NSCLC tumors and has exhibited an association with poor prognosis as well as chemotherapeutic resistance to platinum-based therapy. Accordingly, AKT inhibitors such as MK-2206 are currently undergoing clinical investigation for the treatment of human NSCLC however, these agents broadly target all three (1-3) AKT isoforms. Recent evidence suggests opposing roles of the AKT isoforms in tumorigenesis where loss of AKT-1 inhibits while the loss of AKT-2 enhances lung tumor development in transgenic mouse models. Based on these findings, we hypothesized that preferential inhibition of AKT-1 would warrant a more effective therapeutic strategy for NSCLC compared to the current clinical approach of broad AKT inhibition. WST-1 cell viability assays have revealed that a selective AKT-1 inhibitor A-674563 is a more potent regulator of survival in 6 NSCLC cell lines compared to a pan-AKT inhibitor MK-2206. Furthermore, off-target CDK2 inhibition likely contributes to the observed benefits of the AKT-1 inhibitor as the reduction in cell viability largely parallels the effects of a CDK2 inhibitor PHA-848125. In addition, the cell lines with higher endogenous CDK2 and p-CDK2 expression are more sensitive to the AKT-1 inhibitor relative to the pan-AKT inhibitor MK-2206. Basal protein and RNA levels in each of the cell lines have also shown that high AKT-3 expression may confer resistance to the pan-AKT inhibitor MK-2206. Thus, AKT-3 expression has the potential to serve as a predictive marker for patient response to AKT-1 versus broad AKT-inhibition. Cell cycle analysis demonstrated that the AKT-1 inhibitor decreases the proportion of cells in the Go/G1 phase and increases the proportion of cells in the S-phase, indicating a possible S-phase cell cycle arrest. These differences are also more significant in the cell lines with augmented sensitivity to the AKT-1 inhibitor. Therefore, altered cell cycle progression could be the major driver of the therapeutic benefits of the AKT-1 inhibitor. Overall, our findings suggest that AKT-1 inhibition is significantly more effective at reducing NSCLC cell viability in-vitro compared to pan-AKT inhibition. Furthermore, cell lines with higher CDK2 and AKT-3 expression have marginally increased sensitivity to the AKT-1 inhibitor A-674563 compared to the pan-AKT inhibitor MK-2206. Future research will focus on understanding the mechanism of action of the AKT-1 inhibitor through combined western blot, AKT antibody array, flow cytometry, and confocal microscopy data. Additionally, we will investigate the toxicity of these inhibitors on normal human small airway epithelial cells (HSAECs) to ensure preferential activity against malignant over somatic cells.
Citation Format: Paige M. Chorner, Roger A. Moorehead. Inhibition of AKT-1 for the treatment of human non-small cell lung cancer (NSCLC) in-vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 151. doi:10.1158/1538-7445.AM2017-151