Combination of AKT inhibition with autophagy blockade effectively reduces ascites-derived ovarian cancer cell viability
Recent genomic analyses of high-grade serous epithelial ovarian cancer (EOC) have identified significant aberrations within the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway. These alterations lead to the upregulation of signaling activity, contributing to the aggressiveness of high-grade EOC. As such, the PI3K/AKT pathway presents a promising therapeutic target for treating this highly malignant cancer subtype. Our previous research demonstrated that treatment of malignant ascites-derived primary human EOC cells, along with established ovarian cancer cell lines, with the allosteric AKT inhibitor Akti-1/2 induced a dormancy-like, cytostatic response, although it did not significantly affect cell viability. In this study, we expand on these findings, showing that allosteric inhibition of AKT in these EOC cells triggers the activation of a cytoprotective mechanism known as autophagy.
We observed that when autophagy was inhibited, either using chloroquine (CQ) alone or in combination with Akti-1/2, there was a significant reduction in the number of viable cells. Moreover, the combination of Akti-1/2 with CQ led to a marked increase in the sensitivity of EOC cells to CQ-induced cell death, as evidenced by a substantial decrease in the effective concentration for 50% inhibition (EC50) values when compared to treatment with CQ alone. This suggests that Akti-1/2 enhances the susceptibility of EOC cells to autophagy inhibition and its subsequent cytotoxic effects.
Further investigation into the role of autophagy in this context involved the use of Spautin-1, a novel and potent autophagy inhibitor. We demonstrated that Spautin-1 inhibits autophagy in a manner independent of Beclin-1, a key protein involved in autophagy initiation, in both primary EOC cells and ovarian cancer cell lines. Multicellular EOC spheroids, which more accurately mimic the tumor microenvironment, were found to be highly sensitive to the combined treatment of Akti-1/2 and either CQ or Spautin-1. However, these spheroids showed resistance to treatment with either agent alone, highlighting the increased efficacy of combination therapies.
Moreover, combination index analysis revealed strong synergy between Akti-1/2 and Spautin-1, further supporting the potential of combining these agents to enhance their therapeutic effect on EOC cells. A similar synergistic effect was observed when Akti-1/2 was combined with CQ in most of the samples tested. These findings suggest that the combination of AKT inhibition and autophagy blockade could represent a highly effective strategy to reduce residual EOC cells and prevent ovarian cancer recurrence.
In conclusion, our data support the hypothesis that targeting both the PI3K/AKT pathway and autophagy simultaneously could provide a potent therapeutic approach for combating high-grade serous EOC. The observed synergistic interactions between AKT inhibitors and autophagy inhibitors pave the way for future clinical strategies aimed at improving the treatment outcomes for patients with this aggressive cancer subtype.