Drug Metabolism and Disposition : the Biological Fate of Chemicals

Lung cancer is the leading cause of cancer deaths worldwide. We found that the cytochrome P450 isoform CYP4F11 is significantly overexpressed in patients with lung squamous cell carcinoma. CYP4F11 is a fatty acid w-hydroxylase and catalyzes the production of the lipid mediator 20-hydroxyeicosatetraenoic acid (20-HETE) from arachidonic acid. 20-HETE promotes cell proliferation and migration in cancer. An inhibition of 20-HETE-generating cytochrome P450 enzymes has been implicated as novel cancer therapy for more than a decade...

Our recent study revealed that SLC49A4, known as disrupted in renal carcinoma 2, is a H+ -coupled lysosomal exporter for pyridoxine (vitamin B6), a cationic compound, and involved in the regulation of its lysosomal and cellular levels. We here examined a possibility that this transporter might also transport cationic amphiphilic drugs (CADs) that are known to undergo lysosomal trapping, using pyrilamine, an H1 -antagonist, as a model CAD and the COS-7 cell line as a model cell system for transient introduction of human SLC49A4 and a recombinant SLC49A4 protein (SLC49A4-AA), in which the N-terminal dileucine motif involved in lysosomal localization was removed by replacing with dialanine for redirected localization to the plasma membrane...

Stiripentol (STP), an antiepileptic agent, causes drug-drug interactions by inhibiting cytochrome P450 (P450) enzymes. STP contains a methylenedioxyphenyl (MDP) group, which could form inhibitory metabolic intermediate complexes (MICs) with P450. The present study examined the possible time-dependent inhibition of CYP1A2 via MIC formation by STP and structurally related MDP compounds such as isosafrole. Time-dependent inhibition was observed in human liver microsomes for CYP1A2, but not CYP3A4. Spectral analysis of the liver microsomes from CYP1A-induced rats incubated with STP and NADPH revealed a Soret peak at approximately 455 nm, which was largely eliminated by potassium ferricyanide...

Our understanding of the fundamental molecular mechanisms of APAP hepatotoxicity began in 1973-1974 when investigators at the US National Institutes of Health published seminal studies demonstrating conversion of APAP to a reactive metabolite that depletes glutathione and binds to proteins in the liver in mice after overdose. Since then, additional groundbreaking experiments have demonstrated critical roles for mitochondrial damage, oxidative stress, nuclear DNA fragmentation, and necrotic cell death too. Over the years, some investigators have also attempted to translate these mechanisms to humans using human specimens from APAP overdose patients...

Cytochrome P450 family 1 subfamily A member 2 (CYP1A2), performs an indispensable role in metabolism of both exogenous and endogenous substances. What is more, CYP1A2 functions in human diseases by regulating homeostasis of cholesterol. Despite the emergence of gene-editing animal models, genetically humanized animals that overcome species differences for further exploring the role of CYP1A2 in drug metabolism and human diseases have not yet been constructed. In this study, we inserted human CYP1A2 cDNA into the rat Cyp1a2 gene by using CRISPR/Cas9 technology...

A STING (stimulator of interferon genes) agonist GSK3996915 under investigation in early discovery for hepatitis B was orally dosed to a mouse model for understanding the parent drug distribution in liver, the target organ. MALDI imaging mass spectrometry (IMS) was used to quantify the distribution of GSK3996915 in liver collected from mice administered a single oral dose at 90 mg/kg. GSK3996915 was detected with a zonal distribution localized in the portal triad and highly concentrated in the main bile ducts, indicating clearance through biliary excretion...

Atomoxetine is a cytochrome P450 (P450) 2D6 probe substrate and an approved medicine for attention-deficit/hyperactivity disorder. In this humanized-liver mouse study, interactions between atomoxetine and the P450 2D6 probe drug paroxetine were observed. Human physiologically based pharmacokinetic (PBPK) models were established by scaling up humanized-liver mouse data obtained in the absence or presence of paroxetine. These models could explain the drug monitoring results of atomoxetine and its primary 4-hydroxylated and N -demethylated metabolites in Japanese children aged 8-14 years and could be used to help establish the correct dosage and for the evaluation of clinical outcomes...

Physiologically-based pharmacokinetic (PBPK) modeling has become the established method for predicting human pharmacokinetics (PK) and drug-drug interactions (DDI). The number of drugs cleared by non-CYP enzyme metabolism has increased steadily and to date, there is no consolidated overview of PBPK modeling for drugs cleared by non-CYP enzymes. This review aims to describe the state-of-the-art for PBPK modeling for drugs cleared via non-CYP enzymes, to identify successful strategies, to describe gaps and to provide suggestion to overcome them...

Emvododstat is a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of COVID-19 and acute myeloid leukemia. Since the metabolism and pharmacokinetics of emvododstat in humans is time‑dependent, a repeat dose study design using a combination of microtracer radioactivity and high radioactivity doses was employed to evaluate the metabolism and excretion of emvododstat near steady state. Seven healthy male subjects each received 16 mg/0.3 µCi 14 C-emvododstat daily oral doses for 6 days followed by a 16 mg/100 µCi high radioactivity oral dose on Day 7...

Scientists from Canadian institutions have a rich history of making interesting and important contributions to the journal Drug Metabolism and Disposition (DMD) over the past 51 years. A goal of this minireview is to highlight these contributions and pay tribute to many of the scientists at Canadian institutions that have aided in the evolution of the discipline through their DMD publications. We conducted a geographical and research sectoral analysis of the temporal trends of DMD publications originating from Canadian sources...

In the early '70s, Dr B. B. Brodie, Head of the LCP, NHI, NIH, initiated a program to elucidate the mechanism of hepatic necrosis induced in rats by bromobenzene. These studies showed a crucial role for its 3,4-epoxide intermediate, known in part, to collapse to 4-bromophenol. To examine a possible contribution of this phenol to tissue toxicity, some rats were co-administered a high dose of acetaminophen to suppress phenolic clearance by glucuronidation and sulfation. Subsequent examination of liver slices showed that the acetaminophen-only control rats had extensive centrilobular liver necrosis...

Although the mention of cytochrome P450 (P450, CYP) inhibition usually brings to mind unwanted variability in pharmacokinetics, in several cases P450s are good targets for inhibition. These P450s are essential but in certain disease states it is desirable to reduce the concentrations of their products. Most of the attention to date has been with human P450s 5A1, 11A1, 11B1, 11B2, 17A1, 19A1, and 51A1. In some of those cases, there are multiple drugs in us, e.g., exemestane, letrozole, and anastrozole with P450 19A1, the steroid aromatase target in breast cancer...

Cytochrome P450 4F2 (CYP4F2) is an enzyme that is involved in the metabolism of arachidonic acid (AA), vitamin E and K (VK), and xenobiotics including drugs. CYP4F2*3 polymorphism (rs2108622; c.1297G>A; p.Val433Met) has been associated with hypertension, ischemic stroke, and variation in the effectiveness of the anticoagulant drug warfarin. In this study, we characterized wild-type CYP4F2 and 28 CYP4F2 variants, including a Val433Met substitution, detected in 8,380 Japanese subjects. The CYP4F2 variants were heterologously expressed in 293FT cells to measure the concentrations of CYP4F2 variant holoenzymes using carbon monoxide-reduced difference spectroscopy, where the wild type and 18 holoenzyme variants showed a peak at 450 nm...

PURPOSE: To investigate the value of drug exposure and host germline genetic factors in predicting apatinib (APA)-related toxicities. METHOD: In this prospective study, plasma APA concentrations were quantified using liquid chromatography with tandem mass spectrometry, and 57 germline mutations were genotyped in 126 advanced solid tumor patients receiving 250mg daily APA, a vascular endothelial growth factor receptor II inhibitor. The correlation between drug exposure, genetic factors, and the toxicity profile was analyzed...

Drug metabolizing enzymes and transporters (DMETs) are key regulators of pharmacokinetics (PK), efficacy and toxicity of therapeutics. Over the past two decades, significant advancements in in vitro methodologies, targeted proteomics, in vitro-to-in vivo extrapolation (IVIVE) methods and integrated computational approaches such as physiologically based pharmacokinetic (PBPK) modeling have unequivocally contributed to improving our ability to quantitatively predict the role of DMETs in ADME (absorption, distribution, metabolism, and excretion) and drug-drug interactions (DDIs)...

Reduced enzyme activity in hepatocellular carcinoma (HCC) and poor targeting limit the application of enzyme-activating prodrugs, which is also detrimental to the effective treatment of HCC. Here, we investigated whether accelerated blood clearance (ABC) phenomenon occurs in HCC models following repeated injections of PEGylated liposomes (PEG-L), thus inducing prodrugs accumulation and activation in the liver and exerting highly effective and low-toxicity therapeutic effects on HCC. Firstly, PEGylated liposomal cyclophosphamide (PEG-CP-L) was prepared by solvent injection and characterized...

Cytochrome P450s CYP3A5 and CYP3A4 exhibit differential plasticity that underlies differences in drug metabolism and drug-drug interactions. To extend previous studies, CYP3A4 and CYP3A5 were co-crystallized with clotrimazole, a compact ligand that binds to the heme iron in catalytic center of the active site. Binding studies indicate that clotrimazole exhibits tight binding to CYP3A5 with a Kd of<0.01 µM like that of CYP3A4. A single clotrimazole is bound to the heme iron in CYP3A4 that triggers expansion of active site cavity that reflects a loss of aromatic interactions between phenylalanine sidechains in the distal active site and increased conformational entropy for the F-F' connector due to reorientation of Phe-304 to accommodate clotrimazole...

Cerebrotein hydrolysate-1 (CH-1), a mixture of small peptides, polypeptides and various amino acids derived from porcine brain, has been widely used in the treatment of cerebral injury. However, the bioactive composition and pharmacokinetics of CH-1 are still unexplored due to their complex constitutes and extremely low concentrations in vivo Herein, NanoLC-Orbitrap-Fusion-Lumos-Tribrid-MS/MS was firstly used to qualitatively analyze the components of CH-1. A total of 1347 peptides were identified, of which 43 peptides were characterized by high MS intensity and identification accuracy...

Underestimation of AO-mediated clearance by current in vitro assays leads to uncertainty in human dose projections, thereby reducing the likelihood of success in drug development. In the present study we first evaluated the current drug development practices for AO substrates. Next, the overall predictive performance of in vitro-in vivo extrapolation (IVIVE) of unbound hepatic intrinsic clearance (CLint,u ) and unbound hepatic intrinsic clearance by AO (CLint,u,AO ) was assessed using a comprehensive literature database of in vitro (human cytosol/ S9/ hepatocytes) and in vivo (iv/oral) data collated for 22 AO substrates (total of 100 datapoints from multiple studies)...

Pharmaceutical companies subject all new molecular entities to a series of in vitro metabolic characterizations that guide the selection and/or design of compounds predicted to have favourable pharmacokinetic properties in humans. Current drug metabolism research is based on liver tissue predominantly obtained from people of European origin with limited access to tissue from people of African origin. Given the inter-individual and inter-population genomic variability in genes encoding drug metabolizing enzymes, efficacy and safety of some drugs are poorly predicted for African populations...