A study of the pharmacokinetics, safety, and efficacy of bictegravir/emtricitabine/tenofovir alafenamide in virologically suppressed pregnant women with HIV.

OBJECTIVE: The objective of this study was to assess the pharmacokinetics, safety, and efficacy and confirm the dose of once-daily bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF; B/F/TAF) during pregnancy. DESIGN: An open-label, multicenter, single-arm, phase 1b study (NCT03960645) was conducted in 33 virologically suppressed pregnant women with HIV-1. METHODS: Participants received B/F/TAF (50/200/25 mg) from the second or third trimester through ∼16 weeks postpartum. Steady-state maternal plasma pharmacokinetic samples were collected at the second and third trimesters and 6 and 12 weeks postpartum for BIC, FTC, and TAF. Neonates ( n  = 29) were followed from birth to 4-8 weeks with sparse washout pharmacokinetic sampling for BIC and TAF. The proportion of participants with HIV-1 RNA less than 50 copies/ml at delivery (missing = excluded) was evaluated. RESULTS: Mean areas under the concentration-time curve over the dosing interval (AUC tau ) for BIC, FTC, and TAF were lower during pregnancy versus postpartum but were closer to AUC tau values for nonpregnant adults with HIV reported in other studies. Geometric least-squares mean ratios for BIC, FTC, and TAF AUC tau during pregnancy versus postpartum ranged from 41 to 45%, 64 to 69% and 57 to 78%, respectively. Mean BIC trough concentrations during pregnancy were more than 6.5-fold greater than the protein-adjusted 95% effective concentration. In neonates, the median BIC half-life was 43 h. Virologic suppression was maintained in all adult participants throughout the study, with no virologic failure or treatment-emergent resistance to HIV-1, no discontinuations because of adverse events, and no perinatal transmission. CONCLUSION: Exposures to BIC, FTC, and TAF were lower during pregnancy than postpartum. However, mean BIC trough concentrations were maintained at levels indicative of efficacious exposure, and FTC/TAF data were concordant with published literature in this population. Pharmacokinetic and safety data, combined with maintenance of robust virologic suppression, suggest that once-daily B/F/TAF without dose adjustment is appropriate during pregnancy.

Plasma Protein Binding Determination for Unstable Ester Prodrugs: Remdesivir and Tenofovir Alafenamide.

Remdesivir (RDV) and tenofovir alafenamide (TAF) are prodrugs designed to be converted to their respective active metabolites. Plasma protein binding (PPB) determination of these prodrugs is important for patients with possible alteration of free fraction of the drugs due to plasma protein changes in renal impairment, hepatic impairment, or pregnancy. However, the prodrugs' instability in human plasma presents a challenge for accurate PPB determination. In this research work, two approaches were used in the method development and qualification for PPB assessment of RDV and TAF. For RDV, dichlorvos was used to inhibit esterase activity to stabilize the prodrug in plasma during equilibrium dialysis (ED). The impact of dichlorvos on protein binding was evaluated and determined to be insignificant by comparing the unbound fraction (fu) determined by the ED method with dichlorvos present and the fu determined by an ultrafiltration method without dichlorvos. In contrast to RDV, TAF degradation in plasma is ∼3-fold slower, and TAF stability cannot be improved by dichlorvos. Fit-for-purpose acceptance criteria for the TAF PPB method were chosen, and an ED method was developed based on these criteria. These two methods were then qualified and applied for PPB determinations in clinical studies.

Regional Proteomic Quantification of Clinically Relevant Non-Cytochrome P450 Enzymes along the Human Small Intestine.

Current challenges in accurately predicting intestinal metabolism arise from the complex nature of the intestine, leading to limited applicability of available in vitro tools as well as knowledge deficits in intestinal physiology, including enzyme abundance. In particular, information on regional enzyme abundance along the small intestine is lacking, especially for non-cytochrome P450 enzymes such as carboxylesterases (CESs), UDP-glucuronosyltransferases (UGTs), and sulfotransferases (SULTs). We used cryopreserved human intestinal mucosa samples from nine donors as an in vitro surrogate model for the small intestine and performed liquid chromatography tandem mass spectrometry-based quantitative proteomics for 17 non-cytochrome P450 enzymes using stable isotope-labeled peptides. Relative protein quantification was done by normalization with enterocyte marker proteins, i.e., villin-1, sucrase isomaltase, and fatty acid binding protein 2, and absolute protein quantification is reported as picomoles per milligram of protein. Activity assays in glucuronidations and sequential metabolisms were conducted to validate the proteomics findings. Relative or absolute quantifications are reported for CES1, CES2, five UGTs, and four SULTs along the small intestine: duodenum, jejunum, and ileum for six donors and in 10 segments along the entire small intestine (A-J) for three donors. Relative quantification using marker proteins may be beneficial in further controlling for technical variabilities. Absolute quantification data will allow for scaling factor generation and in vivo extrapolation of intestinal clearance using physiologically based pharmacokinetic modeling. SIGNIFICANCE STATEMENT: Current knowledge gaps exist in intestinal protein abundance of non-cytochrome P450 enzymes. Here, we employ quantitative proteomics to measure non-cytochrome P450 enzymes along the human small intestine in nine donors using cryopreserved human intestinal mucosa samples. Absolute and relative abundances reported here will allow better scaling of intestinal clearance.

Normalized Testosterone Glucuronide as a Potential Urinary Biomarker for Highly Variable UGT2B17 in Children 7-18 Years.

UDP-glucuronosyltransferase 2B17 (UGT2B17) is a highly variable androgen-metabolizing and drug-metabolizing enzyme. UGT2B17 exhibits a unique ontogeny profile characterized by a dramatic increase in hepatic protein expression from prepubertal age to adulthood. Age, sex, copy number variation (CNV), and single nucleotide polymorphisms only explain 26% of variability in protein expression, highlighting the need for a phenotypic biomarker for predicting interindividual variability in glucuronidation of UGT2B17 substrates. Here, we propose testosterone glucuronide (TG) normalized by androsterone glucuronide (TG/AG) as a urinary UGT2B17 biomarker, and examine the associations among urinary TG/AG and age, sex, and CNV. We performed targeted metabolomics of 12 androgen conjugates with liquid-chromatography tandem mass spectrometry in 63 pediatric subjects ages 7-18 years followed over 7 visits in 3 years. Consistent with the reported developmental trajectory of UGT2B17 protein expression, urinary TG/AG is significantly associated with age, sex, and CNV. In conclusion, TG/AG shows promise as a phenotypic urinary UGT2B17 biomarker.

Age- and Genotype-Dependent Variability in the Protein Abundance and Activity of Six Major Uridine Diphosphate-Glucuronosyltransferases in Human Liver.

The ontogeny of hepatic uridine diphosphate-glucuronosyltransferases (UGTs) was investigated by determining their protein abundance in human liver microsomes isolated from 136 pediatric (0-18 years) and 35 adult (age >18 years) donors using liquid chromatography / tandem mass spectrometry (LC-MS/MS) proteomics. Microsomal protein abundances of UGT1A1, UGT1A4, UGT1A6, UGT1A9, UGT2B7, and UGT2B15 increased by ∼8, 55, 35, 33, 8, and 3-fold from neonates to adults, respectively. The estimated age at which 50% of the adult protein abundance is observed for these UGT isoforms was between 2.6-10.3 years. Measured in vitro activity was generally consistent with the protein data. UGT1A1 protein abundance was associated with multiple single nucleotide polymorphisms exhibiting noticeable ontogeny-genotype interplay. UGT2B15 rs1902023 (*2) was associated with decreased protein activity without any change in protein abundance. Taken together, these data are invaluable to facilitate the prediction of drug disposition in children using physiologically based pharmacokinetic modeling as demonstrated here for zidovudine and morphine.

Targeted LC-MS/MS Proteomics-Based Strategy To Characterize in Vitro Models Used in Drug Metabolism and Transport Studies.

Subcellular fractionation of tissue homogenate provides enriched in vitro models (e.g., microsomes, cytosol, or membranes), which are routinely used in the drug metabolism or transporter activity and protein abundance studies. However, batch-to-batch or interlaboratory variability in the recovery, enrichment, and purity of the subcellular fractions can affect performance of in vitro models leading to inaccurate in vitro to in vivo extrapolation (IVIVE) of drug clearance. To evaluate the quality of subcellular fractions, we developed a simple, targeted, and sensitive LC-MS/MS proteomics-based strategy, which relies on determination of protein markers of various cellular organelles, i.e., plasma membrane, cytosol, nuclei, mitochondria, endoplasmic reticulum (ER), lysosomes, peroxisomes, cytoskeleton, and exosomes. Application of the quantitative proteomics method confirmed a significant effect of processing variables (i.e., homogenization method and centrifugation speed) on the recovery, enrichment, and purity of isolated proteins in microsomes and cytosol. Particularly, markers of endoplasmic reticulum lumen and mitochondrial lumen were enriched in the cytosolic fractions as a result of their release during homogenization. Similarly, the relative recovery and composition of the total membrane fraction isolated from cell vs tissue samples was quantitatively different and should be considered in IVIVE. Further, analysis of exosomes isolated from sandwich-cultured hepatocyte media showed the effect of culture duration on compositions of purified exosomes. Therefore, the quantitative proteomics-based strategy developed here can be applied for efficient and simultaneous determination of multiple protein markers of various cellular organelles when compared to antibody- or activity-based assays and can be used for quality control of subcellular fractionation procedures including in vitro model development for drug metabolism and transport studies.

Quantitative characterization of UDP-glucuronosyltransferase 2B17 in human liver and intestine and its role in testosterone first-pass metabolism.

Protein abundance and activity of UGT2B17, a highly variable drug- and androgen-metabolizing enzyme, were quantified in microsomes, S9 fractions, and primary cells isolated from human liver and intestine by validated LC-MS/MS methods. UGT2B17 protein abundance showed >160-fold variation (mean ±â€¯SD, 1.7 ±â€¯2.7 pmol/mg microsomal protein) in adult human liver microsomes (n = 26) and significant correlation (r2 = 0.77, p < 0.001) with testosterone glucuronide (TG) formation. Primary role of UGT2B17 in TG formation compared to UGT2B15 was confirmed by performing activity assays in UGT2B17 gene deletion samples and with a selective UGT2B17 inhibitor, imatinib. Human intestinal microsomes isolated from small intestine (n = 6) showed on average significantly higher protein abundance (7.4 ±â€¯6.6 pmol/mg microsomal protein, p = 0.016) compared to liver microsomes, with an increasing trend towards distal segments of the gastrointestinal (GI) tract. Commercially available pooled microsomes and S9 fractions confirmed greater abundance and activity of UGT2B17 in intestinal fractions compared to liver fractions. To further investigate the quantitative role of UGT2B17 in testosterone metabolism in whole cell system, a targeted metabolomics study was performed in hepatocytes (n = 5) and enterocytes (n = 16). TG was the second most abundant metabolite after androstenedione in both cell systems. Reasonable correlation between UGT2B17 abundance and activity were observed in enterocytes (r2 = 0.69, p = 0.003), but not in hepatocytes. These observational and mechanistic data will be useful in developing physiologically-based pharmacokinetic (PBPK) models for predicting highly-variable first-pass metabolism of testosterone and other UGT2B17 substrates.

Hepatic Abundance and Activity of Androgen- and Drug-Metabolizing Enzyme UGT2B17 Are Associated with Genotype, Age, and Sex.

The major objective of this study was to investigate the association of genetic and nongenetic factors with variability in protein abundance and in vitro activity of the androgen-metabolizing enzyme UGT2B17 in human liver microsomes (n = 455). UGT2B17 abundance was quantified by liquid chromatography-tandem mass spectrometry proteomics, and enzyme activity was determined by using testosterone and dihydrotestosterone as in vitro probe substrates. Genotyping or gene resequencing and mRNA expression were also evaluated. Multivariate analysis was used to test the association of UGT2B17 copy number variation, single nucleotide polymorphisms (SNPs), age, and sex with its mRNA expression, abundance, and activity. UGT2B17 gene copy number and SNPs (rs7436962, rs9996186, rs28374627, and rs4860305) were associated with gene expression, protein levels, and androgen glucuronidation rates in a gene dose-dependent manner. UGT2B17 protein (mean ± S.D. picomoles per milligram of microsomal protein) is sparsely expressed in children younger than 9 years (0.12 ± 0.24 years) but profoundly increases from age 9 years to adults (∼10-fold) with ∼2.6-fold greater abundance in males than in females (1.2 vs. 0.47). Association of androgen glucuronidation with UGT2B15 abundance was observed only in the low UGT2B17 expressers. These data can be used to predict variability in the metabolism of UGT2B17 substrates. Drug companies should include UGT2B17 in early phenotyping assays during drug discovery to avoid late clinical failures.