Identification of a novel S6K1 inhibitor, rosmarinic acid methyl ester, for treating cisplatin-resistant cervical cancer

Jee Hun Park,Kang Ro Lee,Jong Woo Park,Gibeom Nam,Hyun-Ju Park,Jae Sung Noh,Ki Hong Nam,Jieun Lee,Hwamok Oh,Jeung-Whan Han,Sang Ah Yi,Jaecheol Lee,Min Gyu Lee

doi:10.1186/s12885-019-5997-2

Abstract

BackgroundThe mTOR/S6K1 signaling pathway is often activated in cervical cancer, and thus considered a molecular target for cervical cancer therapies. Inhibiting mTOR is cytotoxic to cervical cancer cells and creates a synergistic anti-tumor effect with conventional chemotherapy agents. In this study, we identified a novel S6K1 inhibitor, rosmarinic acid methyl ester (RAME) for the use of therapeutic agent against cervical cancer.MethodsCombined structure- and ligand-based virtual screening was employed to identify novel S6K1 inhibitors among the in house natural product library. In vitro kinase assay and immunoblot assay was used to examine the effects of RAME on S6K1 signaling pathway. Lipidation of LC3 and mRNA levels of ATG genes were observed to investigate RAME-mediated autophagy. PARP cleavage, mRNA levels of apoptotic genes, and cell survival was measured to examine RAME-mediated apoptosis.ResultsRAME was identified as a novel S6K1 inhibitor through the virtual screening. RAME, not rosmarinic acid, effectively reduced mTOR-mediated S6K1 activation and the kinase activity of S6K1 by blocking the interaction between S6K1 and mTOR. Treatment of cervical cancer cells with RAME promoted autophagy and apoptosis, decreasing cell survival rate. Furthermore, we observed that combination treatment with RAME and cisplatin greatly enhanced the anti-tumor effect in cisplatin-resistant cervical cancer cells, which was likely due to mTOR/S6K1 inhibition-mediated autophagy and apoptosis.ConclusionsOur findings suggest that inhibition of S6K1 by RAME can induce autophagy and apoptosis in cervical cancer cells, and provide a potential option for cervical cancer treatment, particularly when combined with cisplatin.

Highlights

The mammalian target of rapamycin (mTOR)/Ribosomal protein S6 kinase 1 (S6K1) signaling pathway is often activated in cervical cancer, and considered a molecular target for cervical cancer therapies
rosmarinic acid methyl ester (RAME) is identified as a novel S6K1 inhibitor by virtual screening of the natural product compound library To identify novel S6K1 inhibitors, we conducted a virtual screening of the in-house library containing 519 compounds isolated from natural products
The conventional mTOR inhibitor inevitably caused unpleasant side effects because of the additional inhibition of Akt, we here present that RAME blocks the mTORC1/S6K1 signaling pathway without extra inhibition of Akt

Summary

Introduction

The mTOR/S6K1 signaling pathway is often activated in cervical cancer, and considered a molecular target for cervical cancer therapies. Cervical cancer is one of the most common malignant gynaecological tumors and is primarily caused by persistent human papilloma virus (HPV) infection [1]. Effective vaccines against high-risk HPV strains significantly lower the occurrence of cervical cancer, these vaccines have only prophylactic effects without therapeutic effects against HPV-infected lesions [2, 3]. The HPV infection-mediated pathogenesis of cervical cancer is closely related to the activation of multiple intracellular signaling pathways [7, 8]. The mammalian target of rapamycin (mTOR) is one such signaling molecule that has been reported to be activated in cervical cancer [8,9,10,11,12]. Immunostaining analyses have shown that p-mTOR, pp70S6K1, and p-S6 are highly detected in HPV-positive lesions and cervical cancer cell lines [9,10,11,12], and these contribute to the survival of cervical cancer cells [11].

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