Toshimi Okada

Squalene synthase inhibitors reduce plasma triglyceride through a low-density lipoprotein receptor-independent mechanism

Inhibitors of squalene synthase are considered to be candidate drugs to reduce both plasma cholesterol and triglyceride. However, little is known about the mechanism of squalene synthase inhibitor-specific effect on plasma triglyceride. In this study, we confirmed the triglyceride-lowering effect of ER-27856, a potent squalene synthase inhibitor prodrug, in rhesus monkeys. To determine the role of low-density lipoprotein (LDL) receptor in the triglyceride-lowering effect of squalene synthase inhibitors, we intravenously administered ER-28448, the active form of ER-27856, to Watanabe heritable hyperlipidemic (WHHL) rabbits for 4 days. In heterozygotes, ER-28448 reduced plasma cholesterol and triglyceride by 52% and 37%, respectively. In homozygous rabbits, in contrast, ER-28448 lowered plasma triglyceride by 40% but did not lower plasma cholesterol. Orally administered ER-27856 reduced plasma triglyceride in homozygous animals but atorvastatin and bezafibrate did not. In hepatocytes isolated from homozygous WHHL rabbits, squalene synthase inhibitors but not atorvastatin reduced triglyceride biosynthesis. These data demonstrate that squalene synthase inhibitors reduced plasma triglyceride through an LDL receptor-independent mechanism, which was distinct from that of the triglyceride-lowering action of atorvastatin or bezafibrate. The reduction of hepatic triglyceride biosynthesis may play an important role in the hypotrigyceridemic action of squalene synthase inhibitors.

A novel carbazole topoisomerase II poison, ER-37328: potent tumoricidal activity against human solid tumors in vitro and in vivo

We have discovered a novel topoisomerase II (topo II) poison, ER‐37328 (12,13‐dihydro‐5‐[2‐(dimethylamino)ethyl]‐4H‐benzo[c]py‐rimido[5,6,1‐jk]carbazole‐4,6,10(5H, 11H)‐trione hydrochloride), which shows potent tumor regression activity against Colon 38 cancer inoculated s.c. Here, we describe studies on the cell‐killing activity against a panel of human cancer cell lines and the antitumor activity of ER‐37328 against human tumor xenografts. In a cell‐killing assay involving 1‐h drug treatment, ER‐37328 showed more potent cell‐killing activity (50% lethal concentrations (LC50s) ranging from 2.9 to 20 μM) than etoposide (LC50s>60 μM) against a panel of human cancer cell lines. ER‐37328 induced double‐stranded DNA cleavage, an indicator of topo II‐DNA cleavable complex formation, within 1 h in MX‐1 cells, and the extent of cleavage showed a bell‐shaped relationship to drug concentration, with the maximum at 2.5 μM. After removal of the drug (2.5 μM) at 1 h, incubation was continued in drug‐free medium, and the amount of cleaved DNA decreased. However, at 10 μM, which is close to the LC50 against MX‐1 cells, DNA cleavage was not detected immediately after 1‐h treatment, but appeared and increased after drug removal. This result may explain the potent cell‐killing activity of ER37328 in the 1‐h treatment. In vivo, ER‐37328 showed potent tumor regression activity against MX‐1 and NS‐3 tumors. Moreover, ER‐37328 had a different antitumor spectrum from irinotecan or cisplatin against human tumor xenografts. In conclusion, ER‐37328 is a promising topo II poison with strong cell killing activity in vitro and tumor regression activity in vivo, and is a candidate for the clinical treatment of malignant solid tumors. (Cancer Sci 2003; 94: 119–124)

E7090, a Novel Selective Inhibitor of Fibroblast Growth Factor Receptors, Displays Potent Antitumor Activity and Prolongs Survival in Preclinical Models

The FGFR signaling pathway has a crucial role in proliferation, survival, and migration of cancer cells, tumor angiogenesis, and drug resistance. FGFR genetic abnormalities, such as gene fusion, mutation, and amplification, have been implicated in several types of cancer. Therefore, FGFRs are considered potential targets for cancer therapy. E7090 is an orally available and selective inhibitor of the tyrosine kinase activities of FGFR1, -2, and -3. In kinetic analyses of the interaction between E7090 and FGFR1 tyrosine kinase, E7090 associated more rapidly with FGFR1 than did the type II FGFR1 inhibitor ponatinib, and E7090 dissociated more slowly from FGFR1, with a relatively longer residence time, than did the type I FGFR1 inhibitor AZD4547, suggesting that its kinetics are more similar to the type V inhibitors, such as lenvatinib. E7090 showed selective antiproliferative activity against cancer cell lines harboring FGFR genetic abnormalities and decreased tumor size in a mouse xenograft model using cell lines with dysregulated FGFR. Furthermore, E7090 administration significantly prolonged the survival of mice with metastasized tumors in the lung. Our results suggest that E7090 is a promising candidate as a therapeutic agent for the treatment of tumors harboring FGFR genetic abnormalities. It is currently being investigated in a phase I clinical trial. Mol Cancer Ther; 15(11); 2630–9. ©2016 AACR.

Abstract 770: E7090: A potent and selective FGFR inhibitor with activity in multiple FGFR-driven cancer models with distinct mechanisms of activation

The fibroblast growth factor (FGF) signaling pathway comprises 18 ligands and 4 FGF receptor subtypes, FGFR1, 2, 3 and 4, which are known as receptor-type tyrosine kinases corresponding to those ligands. Upon ligand binding, FGFRs activate an array of downstream signaling pathways, such as the mitogen activated protein kinase (MAPK) and the phosphoinositide-3-kinase (PI3K)/Akt pathways. Genetic abnormalities (gene fusion, mutation and amplification) of FGFRs are known to cause constitutive activation of their signaling pathways, which play an important role in proliferation, survival and migration of cancer cells, tumor angiogenesis, drug resistance, etc. These abnormalities have also been reported to be involved in different cancer types including lung, breast, endometrial, gastric, and bladder cancer so far. Therefore, FGFRs are considered as one of potential targets for cancer therapy. E7090 is an orally available, selective and potent inhibitor of FGFR1, 2 and 3 tyrosine kinase activities. E7090 displayed inhibition of FGFR1, 2, and 3 kinase activities with the IC50 values of approximately 1 nmol/L. E7090 also inhibited the growth of SNU-16, human gastric cancer cell line harboring FGFR2 amplification with an IC50 value of 3 nmol/L. This activity was about 60-fold stronger than that against VEGF-stimulated HUVEC growth. Kinase profiling assay consisting of 93 kinases including non-receptor and serine/threonine kinases, also demonstrated that E7090 inhibited limited kinases including FGFR-1, -2 and -3. In addition, E7090 inhibited proliferation of human cancer cell lines harboring various types of FGFRs gene abnormalities such as amplification, mutation, or translocation in vitro, which are confirmed by the inhibition of FGFR signaling. E7090 also showed significant antitumor activities on various human xenografts harboring FGFRs gene abnormalities in a dose dependent manner and demonstrated tumor shrinkage at several doses in some models. Furthermore, pharmacodynamics analysis revealed that E7090 inhibited phosphorylation of FGFRs in SNU-16 xenograft tumors in a dose-dependent manner. Overall, the in vitro and in vivo studies confirm that E7090 is a potent and selective FGFRs inhibitor, showing promising antitumor activities with wider therapeutic windows in preclinical cancer models harboring FGFRs gene abnormalities. E7090 has been advanced through preclinical development and we disclose here the first details of its preclinical profile. Citation Format: Saori Watanabe Miyano, Yuji Yamamoto, Kotaro Kodama, Setsuo Funasaka, Satoshi Nagao, Naoko Hata Sugi, Hiroko Kuramochi, Katsuyuki Ishikawa, Kiyoshi Okamoto, Yukinori Minoshima, Takayuki Nakagawa, Yusuke Nakatani, Yuki Karoji, Isao Ohashi, Yoshinobu Yamane, Keigo Tanaka, Toshimi Okada, Tomohiro Matsushima, Junji Matsui, Masao Iwata, Akihiko Tsuruoka, Toshimitsu Uenaka. E7090: A potent and selective FGFR inhibitor with activity in multiple FGFR-driven cancer models with distinct mechanisms of activation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 770. doi:10.1158/1538-7445.AM2015-770