Discovery of 2-Sulfinyl-Diazabicyclooctane Derivatives, Potential Oral ß-Lactamase Inhibitors for Infections Caused by Serine ß-Lactamase-Producing Enterobacterales.

Coadministration of ß-lactam and ß-lactamase inhibitor (BLI) is one of the well-established therapeutic measures for bacterial infections caused by ß-lactam-resistant Gram-negative bacteria, whereas we have only two options for orally active BLI, clavulanic acid and sulbactam. Furthermore, these BLIs are losing their clinical usefulness because of the spread of new ß-lactamases, including extended-spectrum ß-lactamases (ESBLs) belonging to class A ß-lactamases, class C and D ß-lactamases, and carbapenemases, which are hardly or not inhibited by these classical BLIs. From the viewpoints of medical cost and burden of healthcare personnel, oral therapy offers many advantages. In our search for novel diazabicyclooctane (DBO) BLIs possessing a thio-functional group at the C2 position, we discovered a 2-sulfinyl-DBO derivative (2), which restores the antibacterial activities of an orally available third-generation cephalosporin, ceftibuten (CTB), against various serine ß-lactamase-producing strains including carbapenem-resistant Enterobacteriaceae (CRE). It can be orally absorbed via the ester prodrug modification and exhibits in vivo efficacy in a combination with CTB.

Human mass balance, metabolism, and cytochrome P450 phenotyping of lusutrombopag.

The human mass balance of lusutrombopag, an orally bioavailable thrombopoietin (TPO) receptor agonist, was characterised in seven healthy male subjects after a single oral dose of [14C]-lusutrombopag (2 mg, 100 µCi) in solution. Lusutrombopag was the main component in plasma, accounting for 56% of plasma radioactivity AUC0-∞. In plasma, the half-life of radioactivity (70.7 h) was longer than that of lusutrombopag (25.7 h), suggesting the presence of long circulating metabolites. The main excretion pathway of lusutorombopag was feces, with a radioactivity recovery of approximately 83% within 336 h post-dose. M6 (lusutrombopag-O-propanol or lusutrombopag-O-acetic acid) and M7 (lusutrombopag-O-ethane-1,2-diol) were also identified as main components in feces, accounting for at most 17.9%, and 16.9% of the dose, respectively, and were ß-oxidation related metabolites. Our in vitro metabolism study of lusutrombopag indicated that ß-oxidation was a subsequent metabolism of ω-oxidation and CYP4 enzymes, including CYP4A11, were the major isozymes contributing to ω-oxidation. In conclusion, lusutrombopag is primarily eliminated via ω-oxidation and excreted in the feces, where CYP4 enzymes play an important role.

Introduction of a Thio Functional Group to Diazabicyclooctane: An Effective Modification to Potentiate the Activity of ß-Lactams against Gram-Negative Bacteria Producing Class A, C, and D Serine ß-Lactamases.

By the emergence and worldwide spread of multi-drug-resistant Gram-negative bacteria, there have been growing demands for efficacious drugs to cure these resistant infections. The key mechanism for resistance to ß-lactam antibiotics is the production of ß-lactamases, which hydrolyze and deactivate ß-lactams. Diazabicyclooctane (DBO) analogs play an important role as one of the new classes of ß-lactamase inhibitors (BLIs), and several compounds such as avibactam (AVI) have been approved by the FDA, along with many derivatives under clinical or preclinical development. Although these compounds have a similar amide substituent at the C2 position, we have recently reported the synthesis of novel DBO analogs which possess a thio functional group. This structural modification enhances the ability to restore the antimicrobial activities of cefixime (CMF) against pathogens producing classes A, C, and D serine ß-lactamases compared with AVI and expands the structural tolerance at the six position. Furthermore, some of these analogs showed intrinsic microbial activities based on multipenicillin binding protein (PBP) inhibition. This is the unique feature which has never been observed in DBOs. One of our DBOs had a pharmacokinetic profile comparable to that of other DBOs. These results indicate that the introduction of a thio functional group into DBO is a novel and effective modification to discover a clinically useful new BLI.

Generation of intestinal organoids derived from human pluripotent stem cells for drug testing.

Drug absorption via the intestinal tissue is modulated by membrane permeability and metabolism in intestinal epithelial cells (IECs). In drug discovery research, using human IECs to evaluate membrane permeability and metabolic stability can offer very useful information when exploring for drug candidate compounds that have good bioavailability and when trying to predict the fraction absorbed and intestinal availability in humans. Here, we evaluated the pharmacokinetic functions of human IECs differentiated from human induced pluripotent stem cells (hiPSCs) in 3D cultures. As human IECs differentiated in 3D cultures form intestinal organoids and spheroids (herein termed organoids), their morphology makes it difficult to evaluate their pharmacokinetic functions. Therefore, we dissociated intestinal organoids into single cells and attempted to purify human IECs. We found that hiPSC-derived IECs (hiPSC-IECs) expressed the epithelial cell adhesion molecule (EpCAM) and could be highly purified by sorting EpCAM+ cells. The hiPSC-IEC monolayer showed a high TEER value (approximately 350 Ω × cm2). In addition, hiPSC-IECs oxidatively metabolized terfenadine (CYP3A and CYP2J2 substrate) and midazolam (CYP3A substrate). These results indicated that hiPSC-IECs form tight-junction and have cytochrome P450 enzymatic activities. In conclusion, we developed a novel application of hiPSC-derived intestinal organoids for drug testing.

Trifluoromethyl Dihydrothiazine-Based ß-Secretase (BACE1) Inhibitors with Robust Central ß-Amyloid Reduction and Minimal Covalent Binding Burden.

The ß-site amyloid precursor protein cleaving enzyme 1 (BACE1, also known as ß-secretase) is a promising target for the treatment of Alzheimer's disease. A pKa lowering approach over the initial leads was adopted to mitigate hERG inhibition and P-gp efflux, leading to the design of 6-CF3 dihydrothiazine 8 (N-(3-((4S,6S)-2-amino-4-methyl-6-(trifluoromethyl)-5,6-dihydro-4H-1,3-thiazin-4-yl)-4-fluorophenyl)-5-cyanopicolinamide). Optimization of 8 led to the discovery of 15 (N-(3-((4S,6S)-2-amino-4-methyl-6-(trifluoromethyl)-5,6-dihydro-4H-1,3-thiazin-4-yl)-4-fluorophenyl)-5-(fluoromethoxy)pyrazine-2-carboxamide) with an excellent balance of potency, hERG inhibition, P-gp efflux, and metabolic stability. Oral administration of 8 elicited robust Aß reduction in dog even at 0.16 mg/kg. Reflecting the reduced hERG inhibitory activity, no QTc prolongation was observed at high doses. The potential for reactive metabolite formation of 15 was realized in a nucleophile trapping assay using [14 C]-KCN in human liver microsomes. Utilizing covalent binding (CVB) in human hepatocytes and the maximum projected human dosage, the daily CVB burden of 15 was calculated to be at an acceptable value of below 1 mg/day. However, hepatotoxicity was observed when 15 was subjected to a two-week tolerance study in dog, which prevented further evaluation of this compound.

Isolation and characterization of an anti-insect ß-toxin from the venom of the scorpion Isometrus maculatus.

Im-3 was isolated from the venom of the scorpion Isometrus maculatus through several steps of HPLC fractionation based on the insect paralytic activity. Injecting Im-3 into crickets induced paralysis, but no toxicity was apparent in mice after an intracerebroventricular injection. Im-3 shares sequence similarity to scorpion ß-toxins that specifically affect insect sodium channels.

Isolation and characterization of a novel non-selective ß-toxin from the venom of the scorpion Isometrus maculatus.

Scorpion venom is composed of a number of peptides, many of which show neurotoxicity. The Isometrus maculatus scorpion, belonging to the Buthidae family, is found in many tropical regions, including the southern islands of Japan, but there have been no reports on the isolation of toxins from its venom affecting sodium channels. We isolated in this study a novel toxin, Im-2, from the I. maculatus venom. Im-2 induced paralysis in crickets after injecting 20 µg/g of body weight. Im-2 also induced lethality in mice after an intracerebroventricular injection, indicating that Im-2 had non-selective toxicity between insects and mammals. Im-2 consists of 68 amino acids cross-linked by 4 disulfide bonds, and has sequence similarity to scorpion ß-toxins that have been reported to affect the sodium channels of both insects and mammals. The toxic symptoms caused by Im-2 suggest that it acted on the nervous system and shared the action mechanism(s) with sequence-homologous ß-toxins.

Solution structure of a short-chain insecticidal toxin LaIT1 from the venom of scorpion Liocheles australasiae.

The solution structure of an insecticidal toxin LaIT1, a 36-residue peptide with a unique amino-acid sequence and two disulfide bonds, isolated from the venom of the scorpion Liocheles australasiae was determined by heteronuclear NMR spectroscopy. Structural similarity search showed that LaIT1 exhibits an inhibitory cystine knot (ICK)-like fold, which usually contains three or more disulfide bonds. Mutational analysis has revealed that two Arg residues of LaIT1, Arg(13) and Arg(15), play significant roles in insecticidal activity.