Combined treatment of mitoxantrone sensitizes breast cancer cells to rapalogs through blocking eEF-2K-mediated activation of Akt and autophagy

Abstract

Oncogenic activation of the mTOR signaling pathway occurs frequently in tumor cells and contributes to the devastating features of cancer, including breast cancer. mTOR inhibitors rapalogs are promising anticancer agents in clinical trials; however, rapalogs resistance remains an unresolved clinical challenge. Therefore, understanding the mechanisms by which cells become resistant to rapalogs may guide the development of successful mTOR-targeted cancer therapy. In this study, we found that eEF-2K, which is overexpressed in cancer cells and is required for survival of stressed cells, was involved in the negative-feedback activation of Akt and cytoprotective autophagy induction in breast cancer cells in response to mTOR inhibitors. Therefore, disruption of eEF-2K simultaneously abrogates the two critical resistance signaling pathways, sensitizing breast cancer cells to rapalogs. Importantly, we identified mitoxantrone, an admitted anticancer drug for a wide range of tumors, as a potential inhibitor of eEF-2K via a structure-based virtual screening strategy. We further demonstrated that mitoxantrone binds to eEF-2K and inhibits its activity, and the combination treatment of mitoxantrone and mTOR inhibitor resulted in significant synergistic cytotoxicity in breast cancer. In conclusion, we report that eEF-2K contributes to the activation of resistance signaling pathways of mTOR inhibitor, suggesting a novel strategy to enhance mTOR-targeted cancer therapy through combining mitoxantrone, an eEF-2K inhibitor.

Insights Into the Pathologic Roles and Regulation of Eukaryotic Elongation Factor-2 Kinase

“…Combination treatment with an eEF2K inhibitor and an AKT inhibitor (MK-2206) exert a highly anticancer effect on nasopharyngeal carcinoma and glioma ( Cheng et al, 2011 ; Zhao et al, 2018 ). An anticancer drug, mitoxantrone, a potential inhibitor for eEF2K, can disrupt mTOR inhibitors to enhance the efficacy of anticancer effects in breast cancer cells ( Guan et al, 2020 ).…”

Inhibiting Eukaryotic Elongation Factor 2 Kinase: An Update on Pharmacological Small-Molecule Compounds in Cancer

“…52 In addition, four small-molecule compounds from the FDAapproved drug library have been screened as new hit that directly binds to eEF2K and inhibits the phosphorylation of eEF2, followed by Akt inhibition. 54 Drug repurposing may expand the sources of eEF2K inhibitors while reducing costs and time compared to newly designed eEF2K inhibitors (Table 2).…”

“…Subsequently, compound 29, an FDA-approved drug, was shown to restrain the growth of breast cancer in vitro and in vivo when combined with the mTOR inhibitor rapamycin (Figure 5, 30). 54 As mentioned above, combination strategies can enhance drug efficacy and reduce single drug doses to alleviate side effects, ultimately promoting the employment of eEF2K inhibitors in cancer treatment.…”

“…However, only entecavir and pemetrexed inhibited eEF2 phosphorylation in experimental validation studies, and further investigation is needed to verify their efficacy on breast cancer . Mitoxantrone (Figure , 29 ) has been shown to be a new eEF2K inhibitor that directly binds to eEF2K and inhibits the phosphorylation of eEF2, followed by Akt inhibition . Drug repurposing may expand the sources of eEF2K inhibitors while reducing costs and time compared to newly designed eEF2K inhibitors (Table ).…”

“…More recently, eEF2K has been reported to participate in Akt activation and autophagy evoked by mTOR inhibitors induces drug resistance in breast cancer, indicating that combination of an eEF2K inhibitor and mTOR inhibitor warrants further investigation. Subsequently, compound 29 , an FDA-approved drug, was shown to restrain the growth of breast cancer in vitro and in vivo when combined with the mTOR inhibitor rapamycin (Figure , 30 ) . As mentioned above, combination strategies can enhance drug efficacy and reduce single drug doses to alleviate side effects, ultimately promoting the employment of eEF2K inhibitors in cancer treatment.…”