Yoshihiro Shibata

The Role of Extrahepatic Metabolism in the Pharmacokinetics of the Targeted Covalent Inhibitors Afatinib, Ibrutinib, and Neratinib

Despite the fact that much progress has been made recently in the development of targeted covalent inhibitors (TCIs), their pharmacokinetics (PK) have not been well characterized in the light of extrahepatic clearance (CLextH) by glutathione (GSH)/glutathione S-transferase (GST)-dependent conjugation attributable to the unique electrophilic structure (e.g., acrylamide moiety) of TCI compounds. In the present study, CLextH values were examined in rat, dog, and monkey to predict the contribution of CLextH to the PK of the TCIs afatinib, ibrutinib, and neratinib in humans. Afatinib and neratinib both underwent extensive conjugation with GSH in buffer and cytosol fractions of liver and kidney, whereas ibrutinib showed much lower reactivity/susceptibility to GSH/GST-dependent conjugation. The CLextH in each species was calculated from the difference between observed total body clearance and predicted hepatic clearance (CLH) in cryopreserved hepatocytes suspended in 100% serum of the corresponding species. The power-based simple allometry relating the CLextH for the unbound compound to animal body weight was applicable across species for afatinib and neratinib (R2 ≥ 0.9) but not for ibrutinib (R2 = 0.04). The predicted AUC after oral administration of afatinib and neratinib agreed reasonably closely with reported values in phase I dose-escalation studies. Comparisons of CLextH and CLH predicted that CLextH largely determined the PK of afatinib (>90% as a proportion of total body clearance) and neratinib (∼34%) in humans. The present method can serve as one of the tools for the optimization of PK in humans at the discovery stage for the development of TCI candidates.

TAS-116, a Highly Selective Inhibitor of Heat Shock Protein 90α and β, Demonstrates Potent Antitumor Activity and Minimal Ocular Toxicity in Preclinical Models

The molecular chaperone HSP90 plays a crucial role in cancer cell growth and survival by stabilizing cancer-related proteins. A number of HSP90 inhibitors have been developed clinically for cancer therapy; however, potential off-target and/or HSP90-related toxicities have proved problematic. The 4-(1H-pyrazolo[3,4-b]pyridine-1-yl)benzamide TAS-116 is a selective inhibitor of cytosolic HSP90α and β that does not inhibit HSP90 paralogs such as endoplasmic reticulum GRP94 or mitochondrial TRAP1. Oral administration of TAS-116 led to tumor shrinkage in human tumor xenograft mouse models accompanied by depletion of multiple HSP90 clients, demonstrating that the inhibition of HSP90α and β alone was sufficient to exert antitumor activity in certain tumor models. One of the most notable HSP90-related adverse events universally observed to differing degrees in the clinical setting is visual disturbance. A two-week administration of the isoxazole resorcinol NVP-AUY922, an HSP90 inhibitor, caused marked degeneration and disarrangement of the outer nuclear layer of the retina and induced photoreceptor cell death in rats. In contrast, TAS-116 did not produce detectable photoreceptor injury in rats, probably due to its lower distribution in retinal tissue. Importantly, in a rat model, the antitumor activity of TAS-116 was accompanied by a higher distribution of the compound in subcutaneously xenografted NCI-H1975 non–small cell lung carcinoma tumors than in retina. Moreover, TAS-116 showed activity against orthotopically transplanted NCI-H1975 lung tumors. Together, these data suggest that TAS-116 has a potential to maximize antitumor activity while minimizing adverse effects such as visual disturbances that are observed with other compounds of this class. Mol Cancer Ther; 14(1); 14–22. ©2014 AACR.

A novel class of cycloalkano[b]pyridines as potent and orally active opioid receptor-like 1 antagonists with minimal binding affinity to the hERG K+ channel.

A series of compounds based on 7-{[4-(2-methylphenyl)piperidin-1-yl]methyl}-6,7,8,9-tetrahydro-5 H-cyclohepta[ b]pyridine-9-ol ( (-)-8b), a potent and selective opioid receptor-like 1 (ORL1) antagonist, was prepared and evaluated using structure-activity relationship studies with the aim of removing its affinity to human ether-a-go-go related gene (hERG) K (+) channel. From these studies, 10l was identified as an optimized structure with respect to ORL1 antagonist activity, and affinity to the hERG K (+)channel. Furthermore, 10l showed good in vivo antagonism with a wide therapeutic index in regards to adverse cardiovascular effects.

Abstract C112: Characterization of TAS-121, a novel mutant-specific EGFR-TKI, on pharmacokinetics, pharmacodynamics, and antitumor activity.

Background: Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), Gefitinib and Erlotinib, show good responsiveness in non-small cell lung cancer (NSCLC) patients with EGFR activating mutations. Notably, skin rash and diarrhea, the most common EGFR-TKIs-related adverse effects, are due to wild type EGFR inhibition in dermal and intestinal tissue, respectively. Acquired resistance to EGFR-TKIs, however, arises in most cases and is caused in about half the cases by a secondary gatekeeper T790M mutation of EGFR. Therefore, an EGFR-TKI that specifically inhibits EGFR harboring mutations including T790M without affecting wild-type EGFR represents an attractive therapeutic agent. Materials and Methods: Pharmacokinetics studies were performed in mice, rats, dogs and monkeys, and tumor growth and pharmacodynamics evaluation was analyzed in athymic nude mice bearing NSCLC cell lines, NCI-H1975 (harboring the EGFR T790M/L858R mutation) and HCC827 (harboring the EGFR exon 19 deletion). Results: TAS-121 is a newly synthesized compound which is a mutant selective EGFR inhibitor with improved oral bioavailability in various animal species and in vivo antitumor potency compared to the previously described prototype compound, TAS-2913. TAS-121 showed a higher plasma concentration than TAS-2913 following oral administration in mice. Once daily dosing of TAS-121 inhibited NCI-H1975 (EGFR T790M/L858R) tumor growth at a low dose, with an ED50 of less than 12.5 mg/kg/day. TAS-121 also showed tumor growth inhibition of HCC-827 cells, harboring an EGFR activating mutation. In an orthotopic lung xenograft model, TAS-121 significantly prolonged survival in mice compared to first- and second-generation EGFR-TKIs. Pharmacodynamics analysis revealed that TAS-121 dose-dependently inhibited phosphorylation of EGFR T790M/L858R in a xenografted tumor, whereas it did not inhibit that of wild-type EGFR in mouse skin. Conclusion: Our study demonstrates that TAS-121 is a highly potent and mutant-specific EGFR-TKI with a favorable oral bioavailability, and provides a promising therapeutic option for patients harboring T790M mutation after the failure of pre-existing EGFR-TKIs. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C112. Citation Format: Masanori Kato, Kazutaka Miyadera, Yoshihiro Shibata, Kimihiro Ito, Yoshimi Aoyagi, Masato Chiba, Kazuhiko Yonekura, Yoshikazu Iwasawa, Teruhiro Utsugi. Characterization of TAS-121, a novel mutant-specific EGFR-TKI, on pharmacokinetics, pharmacodynamics, and antitumor activity. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C112.

Abstract A272: Intermittent treatment with TAS-120, an irreversible FGFR inhibitor, is effective in tumors harboring a FGFR gene abnormality.

Background: FGFs (fibroblast growth factors) and their receptors (FGFRs) play crucial roles in regulation of cell proliferation, survival, migration and differentiation. Deregulation of FGFR expression has been reported in multiple cancers, including breast, bladder, lung, gastric, endometrial and multiple myeloma. FGFRs are overactivated by several mechanisms such as gene amplification, translocation and mutations. FGFR gene alterations are reported in a variety of cancers. We have identified a highly potent, irreversible and selective FGFR inhibitor, TAS-120 (1). In this report, we investigated FGFR turnover in human cancer cell lines. Moreover, we present the antitumor efficacy and pharmacodynamic (PD) activity of TAS-120 in xenograft tumor models to determine the optimal dosing schedule. Materials and Methods: For in vitro turnover experiments, cell lines were treated with Brefeldin A which suppresses de novo protein synthesis. The cellular level of FGFR was determined by ELISA. For in animal efficacy studies, FGFR2 gene amplified human tumor cell lines were subcutaneously transplanted into the side flank of nude mice or rats. Dosing of compound was started when transplanted tumor size reached > ∼ 200 mm3. For antitumor efficacy, tumor size was measured with digital calipers. To determine the optimal dosing schedule of TAS-120 in a human tumor xenograft model, we orally administered TAS-120 by daily, every other day and other intermittent dosing schedule. The time course of phospho-FGFR inhibition in tumor after single dosing of TAS-120 was also examined as a pharmacodynamic marker. Results: FGFR turnover was investigated in 2 human cancer cell lines, OCUM-2M (gastric cancer cell line with FGFR2 amplification) and OPM-2 (multiple myeloma cell line with FGFR3 gene translocation). When cells were treated with Brefeldin A, cellular FGFR levels were reduced to < 20% at 4 and 6 hr respectively. FGFR turnover in these cells is rapid as most FGFR protein was replaced within 4 or 6 hr. In animal studies, we determined the PD/efficacy correlation. The time course of phosphor-FGFR inhibition in tumor at efficacious doses suggests that continuous inhibition of the target is not necessary to maintain efficacy. Additional studies in OCUM-2MD3 and SNU-16 models demonstrated that TAS-120 is efficacious even with intermittent dosing schedules of every other day or twice/week schedule. Conclusion: TAS-120 is a highly potent, selective, irreversible FGFR inhibitor, which demonstrated strong tumor growth inhibition across continuous and intermittent dosing schedules in mice and rat xenograft models. 1) 24th EORTC-NCI-AACR Symposium (2012) abstract #380 & #383 Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A272. Citation Format: Yoko Nakatsuru, Hiroaki Ochiiwa, Hiroshi Sootome, Hidenori Fujita, Akihiro Hashimoto, Yoshihiro Shibata, Masato Chiba, Yayoi Fujioka, Kazuhiro Yonekura, Hiroshi Hirai, Teruhiro Utsugi. Intermittent treatment with TAS-120, an irreversible FGFR inhibitor, is effective in tumors harboring a FGFR gene abnormality. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A272.