Cotreatment Of Gefitinib With Mk-2206 Also Caused A Reduction Of Antiapoptotic Protein

In this study, we evaluated whether or not combining the novel allosteric Akt inhibitor, MK-2206, with gefitinib could enhance the antiglioma activity. The results showed that gefitinib in combination with MK-2206 produced a synergistic effect against glioma cells and enhanced the antitumor activity in an orthotopic glioma mouse model.

The synergism between MK-2206 and gefitinib seems to be associated with the modulation of autophagy and apoptosis in the cells subjected to the combinatory treatment of gefitinib and MK-2206. To explore the mechanism underlying the synergism between gefitinib and MK-2206 in killing tumor cells, we examined the activity of both apoptosis and autophagy in the glioma cells subjected to combinatorial treatment of the 2 agents. We observed that gefitinib simultaneously induced apoptosis and autophagy and that in the presence of MK-2206, both of apoptosis and autophagy were increased in the tumor cells treated with gefitinib for 48 hours. As autophagy may contribute to either cell survival or cell death, we then assessed the role of autophagy in determining the efficacy of the treatments. We found that suppression of autophagy significantly enhanced the cytocidal activity of the combinatorial treatments, suggesting that induction of autophagy is a compensatory response to therapeutic stress. Interestingly, 48 hours after the cotreatments, autophagic activity began to decrease but apoptosis was further activated, and this shift did not occur in the glioma cells treated with gefitinib alone. Cotreatment of gefitinib with MK-2206 also caused a reduction of antiapoptotic protein, survivin, but led to an elevation of proapoptotic protein, Bim. It has been reported that Bim is required for apoptosis induced by certain targeted therapy in cancer cells with oncogenic EGFR and that the downregulation of survivin plays a pivotal role in the gefitinib-induced apoptosis. Thus, our results are consistent with those reported observations. More importantly, our study suggests that Akt inhibitors such as MK-2206 may play a therapeutically beneficial role in promoting functional switch from autophagy to apoptosis, and this switch may account for the synergistic effect of MK-2206 on cytocidal activity of gefitinib. Evidence of a switch from autophagy to apoptosis was previously reported for temozolomide, a chemotherapeutic drug commonly used in treatment of GBM, and targeting autophagy has been proposed as a new approach to treating apoptosis-resistant GBM. In addition, we found that mTORS6K pathway, which locates downstream of Akt and normally plays a role in suppressing autophagy, was involved in the induction of autophagy in the cells cotreated with gefitinib and MK-2206, as evidenced by a decrease in the levels of p-mTOR and p-S6K. As mTOR and S6K are downstream effectors of Akt, and their inhibition might cause deinhibition of a negative feedback loop, how precisely this pathway affects the targeted therapy might be worth further study.

Considering that the majority of human malignant gliomas harbor mutations that result in activation of PI3K/Akt pathway, and that aberrant EGFR signaling is a primary contributor to the pathogenesis of gliomas, the results provide a rationale and basis for further clinical investigation of the combinatorial use of MK-2206 and egfr inhibitor gefitinib in the treatment of this disease, and thus may have potential impact in cancer therapy.