Drug Transporter-independent Liver Cancer Cell Killing by a Marine Steroid Methyl Spongoate via Apoptosis Induction

Yi Jiang,Ze-Hong Miao,Lei Xu,Bing Yu,Jing-Xu Gong,Lin-Jiang Tong,Yi Chen,Zhao-Li Zhou,Hong-Chun Liu,Yi Wang,Yue-Wei Guo,Jian Ding

doi:10.1074/jbc.m111.232728

Abstract

Hepatocellular carcinoma (HCC) is inherently resistant to the majority of clinical anticancer drugs. To obtain drugs that can circumvent or evade such inherent drug resistance of HCC, we investigated the effect of the marinely derived steroid methyl spongoate (MESP) on HCC cells. MESP displayed potent cell killing against a panel of six HCC cell lines, independent of their expression of drug transporters. MESP did not change the function of the drug transporters, and its cell killing was not impaired in multidrug-resistant cancer cells overexpressing the transporters. The cell killing of MESP was irrelevant to estrogen or androgen signaling and was not associated with cell cycle progression, inhibition of microtubules, and topoisomerases. In contrast, MESP potently induced apoptosis via activation of a proapoptotic caspase cascade and relief of the suppression of antiapoptotic signal transducers and activators of transcription 3 (STAT3) signaling. MESP inhibited the phosphorylation of STAT3, a critical survival signaling factor that reduced the expression of the antiapoptotic protein x-linked inhibitor of apoptosis protein but enhanced the expression of the proapoptotic protein Bax, thus promoting caspase-dependent apoptosis. These data reveal that MESP may well serve as an important candidate drug lead for HCC therapy.

Highlights

Patients have a poor prognosis because of their advanced-stage disease, which is inherently resistant to clinical anticancer drugs, largely because Hepatocellular carcinoma (HCC) cells express drug transporters, including P-glycoprotein (P-gp), multidrug resistance protein (MRP), and/or breast cancer resistance protein (BCRP) [1,2,3]
To examine whether those proteins affect the cellular sensitivity to methyl spongoate (MESP), we detected whether multidrug resistance (MDR) tumor cells that overexpress drug transporter proteins were resistant to MESP
As a marinely derived steroid with a unique 21-oic acid methyl ester moiety in 20R configuration [16], in this study, MESP displays the following impressive characteristics: 1) MESP possesses a potent capability of nonselectively killing HCC cells with the IC50s of several ␮M, an ideal anticancer

Summary

Introduction

Patients have a poor prognosis because of their advanced-stage disease, which is inherently resistant to clinical anticancer drugs, largely because HCC cells express drug transporters, including P-glycoprotein (P-gp), multidrug resistance protein (MRP), and/or breast cancer resistance protein (BCRP) [1,2,3]. To clarify the relationship between the HCC cell killing of MESP and the expression of drug transporter proteins, we detected the levels of P-gp, MRP1, and BCRP in the tested HCC cells. MESP was revealed to disrupt the integrity of mitochondria membrane as evidenced by the loss of MMP [20] and the release of cytochrome C into the cytosols, followed by the cleavage of procaspase-9 (Fig. 4C), indicating activation of the intrinsic pathway.

Results

Conclusion