.

Physiologically-based pharmacokinetic (PBPK) modeling is a mechanistic dynamic modeling approach that can be used to predict or retrospectively describe changes in drug exposure due to drug-drug interactions. With advancements in commercially available PBPK software, PBPK DDI modeling has become a mainstream approach from early drug discovery through to late stage drug development and is often utilized to support regulatory packages for new drug applications. This minireview will briefly describe the approaches to predicting DDI utilizing PBPK and static modeling approaches, the basic model structures and features inherent to PBPK DDI models and key examples where PBPK DDI models have been used to describe complex DDI mechanisms.

The Importance of Tracking "Missing" Metabolites: How and Why?

Technologies currently employed to find and identify drug metabolites in complex biological matrices generally yield results that offer a comprehensive picture of the drug metabolite profile. However, drug metabolites can be missed or are captured only late in the drug development process. This could be due to a variety of factors, such as metabolism that results in partial loss of the molecule, covalent bonding to macromolecules, the drug being metabolized in specific human tissues, or poor ionization in a mass spectrometer.

Cytochrome P450 and Other Drug-Metabolizing Enzymes As Therapeutic Targets.

Cytochrome P450 and other families of drug-metabolizing enzymes are commonly thought of and studied for their ability to metabolize xenobiotics and other foreign entities as they are eliminated from the body. Equally as important, however, is the homeostatic role that many of these enzymes play in maintaining the proper levels of endogenous signaling molecules such as lipids, steroids, and eicosanoids as well as their ability to modulate protein-protein interactions involved in downstream signaling cascades. Throughout the years, many of these endogenous ligands or protein partners of drug-metabolizing enzymes have been associated with a wide range of disease states from cancer to various cardiovascular, neurologic, or inflammatory diseases, prompting an interest in whether modulation of drug-metabolizing enzyme activity could have a subsequent pharmacological impact or lessening of disease severity.

Modulation of Ligand-Gated Glycine Receptors Via Functional Monoclonal Antibodies.

Ion channels are targets of considerable therapeutic interest to address a wide variety of neurologic indications, including pain perception. Current pharmacological strategies have focused mostly on small molecule approaches that can be limited by selectivity requirements within members of a channel family or superfamily. Therapeutic antibodies have been proposed, designed, and characterized to alleviate this selectivity limitation; however, there are no Food and Drug Administration-approved therapeutic antibody-based drugs targeting ion channels on the market to date.

Discovery of pyridyl urea sulfonamide inhibitors of Na1.7.

Na1.7 is an actively pursued, genetically validated, target for pain. Recently reported quinolinone sulfonamide inhibitors displayed promising selectivity profiles as well as efficacy in preclinical pain models; however, concerns about off-target liabilities associated with this series resulted in an effort to reduce the lipophilicity of these compounds.

Pharmacokinetic and Drug Metabolism Properties of Novel Therapeutic Modalities.

The discovery and development of novel pharmaceutical therapies is rapidly transitioning from a small molecule-dominated focus to a more balanced portfolio consisting of small molecules, monoclonal antibodies, engineered proteins (modified endogenous proteins, bispecific antibodies, and fusion proteins), oligonucleotides, and gene-based therapies. This commentary, and the special issue as a whole, aims to highlight these emerging modalities and the efforts underway to better understand their unique pharmacokinetic and absorption, disposition, metabolism, and excretion (ADME) properties. The articles highlighted herein can be broadly grouped into those focusing on the ADME properties of novel therapeutics, those exploring targeted-delivery strategies, and finally, those discussing oligonucleotide therapies.

Use of Cryopreserved Hepatocytes as Part of an Integrated Strategy to Characterize In Vivo Clearance for Peptide-Antibody Conjugate Inhibitors of Nav1.7 in Preclinical Species.

The identification of nonopioid alternatives to treat chronic pain has received a great deal of interest in recent years. Recently, the engineering of a series of Nav1.7 inhibitory peptide-antibody conjugates has been reported, and herein, the preclinical efforts to identify novel approaches to characterize the pharmacokinetic properties of the peptide conjugates are described.

Engineering Na1.7 Inhibitory JzTx-V Peptides with a Potency and Basicity Profile Suitable for Antibody Conjugation To Enhance Pharmacokinetics.

Drug discovery research on new pain targets with human genetic validation, including the voltage-gated sodium channel Na1.7, is being pursued to address the unmet medical need with respect to chronic pain and the rising opioid epidemic. As part of early research efforts on this front, we have previously developed Na1.

1,2,4-Triazolsulfone: A novel isosteric replacement of acylsulfonamides in the context of Na1.7 inhibition.

Recently, the identification of several classes of aryl sulfonamides and acyl sulfonamides that potently inhibit Na1.7 and demonstrate high levels of selectivity over other Na isoforms have been reported. The fully ionizable nature of these inhibitors has been shown to be an important part of the pharmacophore for the observed potency and isoform selectivity.

Polymorphic Human Sulfotransferase 2A1 Mediates the Formation of 25-Hydroxyvitamin D-3--Sulfate, a Major Circulating Vitamin D Metabolite in Humans.

Metabolism of 25-hydroxyvitamin D (25OHD) plays a central role in regulating the biologic effects of vitamin D in the body. Although cytochrome P450-dependent hydroxylation of 25OHD has been extensively investigated, limited information is available on the conjugation of 25OHD In this study, we report that 25OHD is selectively conjugated to 25OHD-3--sulfate by human sulfotransferase 2A1 (SULT2A1) and that the liver is a primary site of metabolite formation. At a low (50 nM) concentration of 25OHD, 25OHD-3--sulfate was the most abundant metabolite, with an intrinsic clearance approximately 8-fold higher than the next most efficient metabolic route.

Discovery of a biarylamide series of potent, state-dependent Na1.7 inhibitors.

The Na1.7 ion channel has garnered considerable attention as a target for the treatment of pain. Herein we detail the discovery and structure-activity relationships of a novel series of biaryl amides.

Correction to "Sulfonamides as Selective Na1.7 Inhibitors: Optimizing Potency and Pharmacokinetics to Enable Target Engagement".

[This corrects the article DOI: 10.1021/acsmedchemlett.6b00243.

Sulfonamides as Selective Na1.7 Inhibitors: Optimizing Potency, Pharmacokinetics, and Metabolic Properties to Obtain Atropisomeric Quinolinone (AM-0466) that Affords Robust in Vivo Activity.

Because of its strong genetic validation, Na1.7 has attracted significant interest as a target for the treatment of pain. We have previously reported on a number of structurally distinct bicyclic heteroarylsulfonamides as Na1.

Sulfonamides as Selective Na1.7 Inhibitors: Optimizing Potency and Pharmacokinetics While Mitigating Metabolic Liabilities.

Several reports have recently emerged regarding the identification of heteroarylsulfonamides as Na1.7 inhibitors that demonstrate high levels of selectivity over other Na isoforms. The optimization of a series of internal Na1.

Sulfonamides as Selective Na1.7 Inhibitors: Optimizing Potency and Pharmacokinetics to Enable in Vivo Target Engagement.

Human genetic evidence has identified the voltage-gated sodium channel Na1.7 as an attractive target for the treatment of pain. We initially identified naphthalene sulfonamide as a potent and selective inhibitor of Na1.

Comparison of the ligand binding site of CYP2C8 with CYP26A1 and CYP26B1: a structural basis for the identification of new inhibitors of the retinoic acid hydroxylases.

The CYP26s are responsible for metabolizing retinoic acid and play an important role in maintaining homeostatic levels of retinoic acid. Given the ability of CYP2C8 to metabolize retinoic acid, we evaluated the potential for CYP2C8 inhibitors to also inhibit CYP26. In vitro assays were used to evaluate the inhibition potencies of CYP2C8 inhibitors against CYP26A1 and CYP26B1.

Discovery and in Vivo Evaluation of the Potent and Selective PI3Kδ Inhibitors 2-((1S)-1-((6-Amino-5-cyano-4-pyrimidinyl)amino)ethyl)-6-fluoro-N-methyl-3-(2-pyridinyl)-4-quinolinecarboxamide (AM-0687) and 2-((1S)-1-((6-Amino-5-cyano-4-pyrimidinyl)amino)ethyl)-5-fluoro-N-methyl-3-(2-pyridinyl)-4-quinolinecarboxamide (AM-1430).

Optimization of the potency and pharmacokinetic profile of 2,3,4-trisubstituted quinoline, 4, led to the discovery of two potent, selective, and orally bioavailable PI3Kδ inhibitors, 6a (AM-0687) and 7 (AM-1430). On the basis of their improved profile, these analogs were selected for in vivo pharmacodynamic (PD) and efficacy experiments in animal models of inflammation. The in vivo PD studies, which were carried out in a mouse pAKT inhibition animal model, confirmed the observed potency of 6a and 7 in biochemical and cellular assays.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics.

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes.

"Target-Site" Drug Metabolism and Transport.

The recent symposium on "Target-Site" Drug Metabolism and Transport that was sponsored by the American Society for Pharmacology and Experimental Therapeutics at the 2014 Experimental Biology meeting in San Diego is summarized in this report. Emerging evidence has demonstrated that drug-metabolizing enzyme and transporter activity at the site of therapeutic action can affect the efficacy, safety, and metabolic properties of a given drug, with potential outcomes including altered dosing regimens, stricter exclusion criteria, or even the failure of a new chemical entity in clinical trials. Drug metabolism within the brain, for example, can contribute to metabolic activation of therapeutic drugs such as codeine as well as the elimination of potential neurotoxins in the brain.

Induction of CYP26A1 by metabolites of retinoic acid: evidence that CYP26A1 is an important enzyme in the elimination of active retinoids.

All-trans-retinoic acid (atRA), the active metabolite of vitamin A, induces gene transcription via binding to nuclear retinoic acid receptors (RARs). The primary hydroxylated metabolites formed from atRA by CYP26A1, and the subsequent metabolite 4-oxo-atRA, bind to RARs and potentially have biologic activity. Hence, CYP26A1, the main atRA hydroxylase, may function either to deplete bioactive retinoids or to form active metabolites.

Characterization of the active site properties of CYP4F12.

Cytochrome P450 4F12 is a drug-metabolizing enzyme that is primarily expressed in the liver, kidney, colon, small intestine, and heart. The properties of CYP4F12 that may impart an increased catalytic selectivity (decreased promiscuity) were explored through in vitro metabolite elucidation, kinetic isotope effect experiments, and computational modeling of the CYP4F12 active site. By using astemizole as a probe substrate for CYP4F12 and CYP3A4, it was observed that although CYP4F12 favored astemizole O-demethylation as the primary route of metabolism, CYP3A4 was capable of metabolizing astemizole at multiple sites on the molecule.

Evaluation of UGT protein interactions in human hepatocytes: effect of siRNA down regulation of UGT1A9 and UGT2B7 on propofol glucuronidation in human hepatocytes.

Previous experiments performed in recombinant systems have suggested that protein-protein interactions occur between the UGTs and may play a significant role in modulating enzyme activity. However, evidence of UGT protein-protein interactions either in vivo or in more physiologically relevant in vitro systems has yet to be demonstrated. In this study, we examined oligomerization and its ability to affect glucuronidation in plated human hepatocytes.