title: Phosphorylation of mTOR Ser2481 is a key target limiting the efficacy of rapalogs for treating hepatocellular carcinoma.
abstract: Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Although recent studies facilitate the identification of crucial genes and relevant regulatory pathways, therapeutic approaches against advanced HCC are insufficiently effective. Therefore, we aimed here to develop potent therapeutics to provide a reliable biomarker for the therapeutic efficacy in patients with HCC. To this end, we first compared the cytotoxic effects of various anti-cancer drugs between well differentiated (HAK-1A) and poorly differentiated (HAK-1B) cell lines established from a single HCC tumor. Of various drug screened, HAK-1B cells were more sensitive by a factor of 2,000 to the mTORC1 inhibitors (rapalogs), rapamycin and everolimus, than HAK-1A cells. Although rapalogs inhibited phosphorylation of mTOR Ser2448 in HAK-1A and HAK-1B cells, phosphorylation of mTOR Ser2481 was specifically inhibited only in HAK-1B cells. Silencing of Raptor induced apoptosis and inhibited the growth of only HAK-1B cells. Further, three other cell lines established independently from the tumors of three patients with HCC were also approximately 2,000-fold times more sensitive to rapamycin, which correlated closely with the inhibition of mTOR Ser2481 phosphorylation by rapamycin. Treatment with everolimus markedly inhibited the growth of tumors induced by poorly differentiated HAK-1B and KYN-2 cells and phosphorylation of mTOR Ser2481 in vivo. To our knowledge, this is the first study showing that the phosphorylation of mTOR Ser2481 is selectively inhibited by rapalogs in mTORC1-addicted HCC cells and may be a potential reliable biomarker for the therapeutic efficacy of rapalogs for treating HCC patients.
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Watari
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Nishitani
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Noda
authors.affiliation: Department of Diagnostic Pathology, Kurume University Hospital, Kurume, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kawahara
authors.affiliation: Department of Pathology, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Akiba
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.|Cancer Translational Research Center, St. Mary's Institute of Health Sciences, Kurume, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Murakami
authors.affiliation: Department of Pathology, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Yano
authors.affiliation: Cancer Translational Research Center, St. Mary's Institute of Health Sciences, Kurume, Japan.
authors.forename: Michihiko
authors.initials: M
authors.lastname: Kuwano
authors.affiliation: Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Ono
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy*; D045744:Cell Line, Tumor; D000068338:Everolimus / Q000494:pharmacology; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy*; D000076222:Mechanistic Target of Rapamycin Complex 1 / Q000037:antagonists & inhibitors*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D000068338:Everolimus; D000076222:Mechanistic Target of Rapamycin Complex 1; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human
keywords: Raptor; hepatocellular carcinoma; mTOR Ser2481; mTORC1; rapalogs