Disposition and metabolism of [14C]lemborexant,a novel dual orexin receptor antagonist,in rats and monkeys

1. The disposition and metabolism of lemborexant, a novel dual orexin receptor antagonist currently under development as a therapeutic agent for insomnia disorder, were evaluated after a single oral administration of [¹⁴C]lemborexant in Sprague-Dawley rats (10?mg/kg) and cynomolgus monkeys (3?mg/kg).

2. In both species, [¹⁴C]lemborexant was rapidly absorbed: radioactivity concentration in blood peaked at 0.83–1.8?h, and decreased with elimination half-life of 110?h. The radioactivity administered was excreted primarily into faeces, with relatively little excreted into urine.

3. Lemborexant was not detected in bile, urine or faeces, indicating that lemborexant administered orally was completely absorbed from the gastrointestinal tract and that the main elimination pathway was metabolism in both species.

4. In rats, lemborexant was found to be minor in plasma (≤5.2% of total radioactivity), and M9 (hydroxylated form) was the major circulating metabolite. In monkeys, the major circulating components were lemborexant, M4 (N-oxide metabolite), M13 (di-oxidised form), M14 (di-oxidised form) and M16 (glucuronide of mono-oxidised form).

5. In both species, lemborexant was metabolised to various metabolites by multiple pathways, the primary of which was oxidation of the dimethylpyrimidine or fluorophenyl moiety.

     

Characterization of in vitro and in vivo metabolism of leelamine using liquid chromatography-tandem mass spectrometry

1. Leelamine is a diterpene compound found in the bark of pine trees and has garnered considerable interest owing to its potent anticancer properties. The aim of the present study was to investigate the metabolic profile of leelamine in human liver microsomes (HLMs) and mice using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

2. We found that leelamine undergoes only Phase I metabolism, which generates one metabolite that is mono-hydroxylated at the C9 carbon of the octahydrophenanthrene ring (M1) both in vitro and in vivo. The structure and metabolic pathway of M1 were determined from the MSⁿ fragmentation obtained by collision-induced dissociation using LC-MS/MS in HLMs.

3. Cytochrome p450 (CYP) 2D6 was found to be the dominant CYP enzyme involved in the biotransformation of leelamine to its hydroxylated metabolite, whereas CYP2C19, CYP1A1, and CYP3A4 contributed to some extent.

4. Moreover, we identified only one metabolite M1, in the urine, but none in the feces. In conclusion, leelamine was metabolized to a mono-hydroxyl metabolite by CYP2D6 and mainly excreted in the urine.

     

Comprehensive preclinical pharmacokinetic evaluations of trastuzumab deruxtecan (DS-8201a), a HER2-targeting antibody-drug conjugate,in cynomolgus monkeys

1. Trastuzumab deruxtecan (DS-8201a) is an antibody-drug conjugate (ADC) composed of a monoclonal antibody targeting human epidermal growth factor receptor 2 (HER2) conjugated to a topoisomerase I inhibitor (DXd) at a drug-to-antibody ratio (DAR) of 7-8. Here, we examined the pharmacokinetic (PK) profiles of DS-8201a and DXd in cynomolgus monkeys, a cross-reactive species.

2. Following intravenous (iv) administration of DS-8201a, the linker was stable in plasma, and systemic DXd exposure was low. DXd was rapidly cleared following iv dosing. Biodistribution studies revealed that intact DS-8201a was present mostly in the blood without tissue-specific retention. The major pathway of excretion for DXd was the faecal route following iv administration of radiolabelled DS-8201a. The only detectable metabolite in the urine and faeces was unmetabolized DXd. DXd is a substrate of organic anion transporting polypeptides, P-gp, and breast cancer resistance protein.

3. In conclusion, the stable linker in circulation and the high clearance of DXd upon release resulted in the low systemic exposure to DXd. Furthermore, the minimal tissue-specific retention and rapid excretion of DXd into faeces as its unmetabolized form with potentially limited impact on drug???drug interaction as a victim were also critical elements of the PK profile of DS-8201a.

     

Investigation of disposition for TAK-448, a synthetic peptide of kisspeptin analog,in rats and dogs using the radiolabeled TAK-448 suitable for pharmacokinetic study

1. Disposition of 2-(N-acetyl-d-tyrosyl-trans-4-hydroxy-l-prolyl-l-asparaginyl-l-threonyl-l-phenylalanyl) hydrazinocarbonyl-L-leucyl-N^ω-methyl-l-arginyl-l-tryptophanamide monoacetate (TAK-448, RVT-602), a synthetic kisspeptin analog, was investigated after parenteral dosing of radiolabeled TAK-448 ([d-Tyr-¹⁴C]TAK-448) to rats and dogs, and it was confirmed if the radiolabeling position at d-Tyr was eligible for assessment of in vivo disposition.

2. Dosed radioactivity was rapidly and well absorbed after subcutaneous administration and an appreciable amount of unchanged TAK-448 (TAK-448F) and a hydrolyzed metabolite, M-I, were detected in the plasma of rats and dogs.

3. After intravenous administration of [d-Tyr-¹⁴C]TAK-448 to rats, the radioactivity widely distributed to tissues with relatively higher concentrations in kidney and urinary bladder.

4. The radioactivity was decreased rapidly from the tissues.

5. After subcutaneous administration of [d-Tyr-¹⁴C]TAK-448 to rats and dogs, the dosed radioactivity was almost completely recovered by 48 and 72?h in rats and dogs, respectively, and most of the radioactivity was excreted in urine after extensive metabolism in the two species.

6. These results suggest that TAK-448 has an acceptable pharmacokinetic profile for clinical evaluation and development, and demonstrate that the synthesized [D-Tyr-¹⁴C]TAK-448 used in this study represents a favorable labeling position to evaluate disposition properties of this compound.

     

Absorption,disposition and metabolic pathway of amiselimod (MT-1303) in healthy volunteers in a mass balance study

1. The absorption, metabolism and excretion of MT-1303 were investigated in healthy male subjects after a single oral dose of 0.4?mg [14C]-MT-1303 (ClinicalTrials.gov NCT02293967).

2. The MT-1303 concentration in the plasma reached a maximum at 12?h after administration. Thereafter, the concentration declined with a half-life of 451?h. At the final assessment on Day 57, 91.16% of the administered radioactivity was excreted, and the cumulative excretion in the urine and faeces was 35.32% and 55.84%, respectively.

3. The most abundant metabolite in plasma was MT-1303-P, which accounted for 42.6% of the area under the plasma concentration–time curve (AUC) of the total radioactivity. The major component excreted in urine was Human Urine (HU)4 (3066434), accounting for 28.1% of radioactivity in the sample (4.05% of the dose), whereas MT-1303 was a major component in the faeces, accounting for 89.8% of radioactivity in the sample (25.49% of the dose) up to 240?h after administration.

4. This study indicates that multiple metabolic pathways are involved in the elimination of MT-1303 from the human body and the excretion of MT-1303 and MT-1303-P via the kidney is low. Therefore, MT-1303 is unlikely to cause conspicuous drug interactions or alter pharmacokinetics in patients with renal impairment.

     

Human urinary concentrations of monoisononyl phthalate estimated using physiologically based pharmacokinetic modeling and experimental pharmacokinetics in humanized-liver mice orally administered with diisononyl phthalate

1. Diisononyl phthalate (DINP) used as a plasticizer is a mixture of compounds consisting of isononyl esters of phthalic acid. There are concerns about the bioaccumulation of such esters in humans. A [phenyl-U-¹⁴C]DINP mixture was synthesized and orally administered (50?mg/kg body weight) to control and humanized-liver mice and their pharmacokinetics were determined.

2. Monoisononyl phthalate (MINP, a primary metabolite of DINP), oxidized MINP (isomers with hydroxy, carbonyl, and carboxy functional groups), and their glucuronides were detected in plasma from control and humanized-liver mice. Biphasic plasma concentration–time curves of MINP and its glucuronide were seen in control mice. In contrast, no such biphasic relationship was seen in humanized-liver mice, in which MINP and oxidized MINP were extensively excreted in the urine within 48?h.

3. Animal biomonitoring equivalents of MINP and oxidized MINP from humanized-liver mice studies were scaled to human equivalents using known species allometric scaling factors with a simple physiologically based pharmacokinetic (PBPK) model.

4. Estimated urinary oxidized MINP concentrations in humans were roughly consistent with reported concentrations of MINP (with a different side chain). The simplified PBPK model could estimate human urinary concentrations of MINP after ingestion of DINP and was capable of both forward and reverse dosimetry.

     

Disposition and metabolism of the G protein-coupled receptor 40 agonist TAK-875 (fasiglifam) in rats,dogs, and humans

1. The absorption, distribution, metabolism, and excretion of fasiglifam were investigated in rats, dogs, and humans.

2. The absolute oral bioavailability of fasiglifam was high in all species (>76.0%).

3. After oral administration of [¹⁴C]fasiglifam, the administered radioactivity was quantitatively recovered and the major route of excretion of radioactivity was via feces in all species.

4. Fasiglifam was a major component in the plasma and feces in all species. Its oxidative metabolite (M-I) was observed as a minor metabolite in rat and human plasma (<10% of plasma radioactivity). In human plasma, hydroxylated fasiglifam (T-1676427), the glucuronide of fasiglifam (fasiglifam-G), and the glucuronide of M-I were detected as additional minor metabolites (<2% of plasma radioactivity). None of these metabolites were specific to humans. Fasiglifam-G was the major component in the rat and dog bile.

5. In vitro cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) reaction phenotyping indicated that oxidation (to form M-I and T-1676427) and glucuronidation of fasiglifam are mainly mediated by CYP3A4/5 and UGT1A3, respectively.

6. Fasiglifam and fasiglifam-G are substrates of BCRP and Mrp2/MRP2, respectively.

7. Glucuronidation of fasiglifam-G was found to be the predominant elimination pathway of fasiglifam in all species tested, including humans.

     

Absorption,disposition, metabolism and excretion of [14C]mizagliflozin,a novel selective SGLT1 inhibitor,in rats

1. The pharmacokinetic and metabolite profiles of mizagliflozin, a novel selective sodium glucose co-transporter 1 inhibitor designed to act only in the intestine, were investigated in rats.

2. Mizagliflozin administrated intravenously (0.3?mg/kg) and orally (3?mg/kg) declined with a short half-life (0.23 and 1.14?h, respectively). The absolute bioavailability was only 0.02%. Following intravenous administration of [^14?C]mizagliflozin (0.3?mg/kg), radioactivity in plasma was also rapidly declined. Up to 24?h after oral administration of [^14?C]mizagliflozin (1?mg/kg), radioactivity was recovered in the faeces (98.4%) and in the urine (0.8%). No remarkable accumulation of radioactivity in tissues was observed using tissue dissection technique and whole body autoradiography.

3. Orally dosed [^14?C]mizagliflozin was mostly metabolised to its aglycone, KP232, in the intestine. In the plasma, KP232 and its glucuronide were predominant. KP232 glucuronide was also prominent in the bile and was recovered as KP232 in the faeces possibly because of the deconjugation by gut microflora. Mizagliflozin was observed neither in the urine nor the faeces.

4. These findings suggest that orally administered mizagliflozin is poorly absorbed, contributing to low systemic exposure; if absorbed, mizagliflozin is rapidly cleared from circulation.

     

Disposition of tris(4-chlorophenyl)methanol and tris(4-chlorophenyl)methane in male and female Harlan Sprague Dawley rats and B6C3F1/N mice following oral and intravenous administration

1. Tris(4-chlorophenyl)methane (TCPME) and tris(4-chlorophenyl)methanol (TCPMOH) have been detected in various biota and human tissues.

2. The current studies were undertaken to investigate the disposition and metabolism of TCPME and TCPMOH in rats and mice.

3. [¹⁴C]TCPME was well absorbed (≥66%) in male rats and mice following a single oral administration of 1, 10, or 100?mg/kg. The excretion of [¹⁴C]TCPME-derived radioactivity in urine (≤2.5%) and feces (≤18%) was low. The administered dose was retained in tissues (≥?64%) with adipose containing the highest concentrations. The metabolism of TCPME was minimal. The disposition and metabolism of [¹⁴C]TCPME in females was similar to males.

4. The time to reach maximum concentration was ≤7?h, the plasma elimination half-life was ≥31?h, and the bioavailability was ≥82% following a 10?mg/kg oral dose of [¹⁴C]TCPME in male rats and mice.

5. The disposition of [¹⁴C]TCPMOH was similar to that of [¹⁴C]TCPME.

6. Following an intravenous administration of [¹⁴C]TCPME or [¹⁴C]TCPMOH in male rats and mice, the pattern of disposition was similar to that of oral administration.

7. In conclusion, both TCPME and TCPMOH are readily absorbed and highly bioavailable following a single oral administration pointing to importance of assessing the toxicity of these chemicals.

     

Development of simultaneous quantification method of loteprednol etabonate (LE) and its acidic metabolites,and analysis of LE metabolism in rat

1. Loteprednol etabonate (LE) is a soft corticosteroid with two labile ester bonds at 17α- and 17β-positions. Its corticosteroidal activity disappears upon hydrolysis of either ester bond. Hydrolysis of both ester bonds produces the inactive metabolite, Δ¹-cortienic acid (Δ¹-CA).

2. The simple high-performance liquid chromatography method using acetic acid gradient was developed for the simultaneous determination of LE and its acidic metabolites.

3. LE was hydrolyzed in rat plasma with a half-life of 9?min. However, LE hydrolysis was undetectable in rat liver and intestine. LE hydrolysis in rat plasma was completely inhibited by paraoxon and bis(p-nitrophenyl) phosphate, thus identifying carboxylesterase as the LE hydrolase. Rat plasma carboxylesterase had a K_m of 6.7?μM for LE.

4. In contrast to the disappearance rate of LE in rat plasma, the formation rate of 17α-monoester and Δ¹-CA was markedly low, and a main hydrolysate of LE was not detected in rat plasma.

5. The metabolism of LE proceeded via different pathways in human and rat plasma. LE was slowly hydrolyzed by paraoxonase in human plasma to 17α-monoester with a half-life of 12?h, but by carboxylesterase in rat plasma to yield undetectable products, presumed to include the unstable 17β-monoester.

     

UPLC-MS,HPLC-radiometric,and NMR-spectroscopic studies on the metabolic fate of 3-fluoro-[U-14C]-aniline in the bile-cannulated rat

1. A study of the rates and routes of excretion of 3-fluoro-[U-¹⁴C]aniline following intraperitoneal administration to male bile-cannulated rats by liquid scintillation counting (LSC) gave a total recovery of ～ 90% in the 48?h following dosing, with the majority of the dose being excreted in the urine during the first 24?h (～ 49%).

2. The total recovery as determined by ¹⁹F-nuclear magnetic resonance (¹⁹F-NMR) was ～ 49%, with the majority of the dose excreted in the first 24?h (～ 41%). The comparatively low recovery in comparison to that obtained from LSC was due to matrix effects in bile and a contribution from metabolic defluorination.

3. High-performance liquid chromatography with radiometric profiling of urine and bile revealed a complex pattern of metabolites with the bulk of the dose excreted as a single peak.

4. Ultra-performance liquid chromatography-orthogonal acceleration time of flight mass spectrometry profiling also showed a complex pattern of metabolites, detecting ～ 21 metabolites of 3-fluoroaniline (3-FA) with six of these detected only in urine and four solely in bile.

5. ¹⁹F-NMR revealed the presence of the parent compound and 15 metabolites in urine collected during the first 24?h after -dosing. The matrix effects of bile on ¹⁹F-NMR spectroscopy made metabolite profiling impractical for this biofluid.

6. The major metabolite of 3-FA was identified as 2-fluoro-4-acetamidophenol-sulfate.

     

Preclinical assessment of the ADME,efficacy and drug-drug interaction potential of a novel NAMPT inhibitor

1. GNE-617 (N-(4-((3,5-difluorophenyl)sulfonyl)benzyl)imidazo[1,2-a]pyridine-6-carboxamide) is a potent, selective nicotinamide phosphoribosyltransferase (NAMPT) inhibitor being explored as a potential treatment for human cancers.

2. Plasma clearance was low in monkeys and dogs (9.14?mL min^?1?kg^?1 and 4.62?mL min^?1?kg^?1, respectively) and moderate in mice and rats (36.4?mL min^?1?kg^?1 and 19.3?mL min^?1?kg^?1, respectively). Oral bioavailability in mice, rats, monkeys and dogs was 29.7, 33.9, 29.4 and 65.2%, respectively.

3. Allometric scaling predicted a low clearance of 3.3?mL min^?1?kg^?1 and a volume of distribution of 1.3?L kg^?1 in human.

4. Efficacy (57% tumor growth inhibition) in Colo-205 CRC tumor xenograft mice was observed at an oral dose of 15?mg/kg BID (AUC?=?10.4?µM h).

5. Plasma protein binding was moderately high. GNE-617 was stable to moderately stable in vitro. Main human metabolites identified in human hepatocytes were formed primarily by CYP3A4/5. Transporter studies suggested that GNE-617 is likely a substrate for MDR1 but not for BCRP.

6. Simcyp^® simulations suggested a low (CYP2C9 and CYP2C8) or moderate (CYP3A4/5) potential for drug-drug interactions. The potential for autoinhibition was low.

7. Overall, GNE-617 exhibited acceptable preclinical properties and projected human PK and dose estimates.

     

In vitro and in vivo pharmacokinetic characterization of mavacamten,a first-in-class small molecule allosteric modulator of beta cardiac myosin

1. Mavacamten is a small molecule modulator of cardiac myosin designed as an orally administered drug for the treatment of patients with hypertrophic cardiomyopathy. The current study objectives were to assess the preclinical pharmacokinetics of mavacamten for the prediction of human dosing and to establish the potential need for clinical pharmacokinetic studies characterizing drug–drug interaction potential.

2. Mavacamten does not inhibit CYP enzymes, but at high concentrations relative to anticipated therapeutic concentrations induces CYP2B6 and CYP3A4 enzymes in vitro. Mavacamten showed high permeability and low efflux transport across Caco-2 cell membranes. In human hepatocytes, mavacamten was not a substrate for drug transporters OATP, OCT and NTCP. Mavacamten was determined to have minimal drug–drug interaction risk.

3. In vitro mavacamten metabolite profiles included phase I- and phase II-mediated metabolism cross-species. Major pathways included aromatic hydroxylation (M1), aliphatic hydroxylation (M2); N-dealkylation (M6), and glucuronidation of the M1-metabolite (M4). Reaction phenotyping revealed CYPs 2C19 and 3A4/3A5 predominating.

4. Mavacamten demonstrated low clearance, high volume of distribution, long terminal elimination half-life and excellent oral bioavailability cross-species.

5. Simple four-species allometric scaling led to predicted plasma clearance, volume of distribution and half-life of 0.51?mL/min/kg, 9.5?L/kg and 9?days, respectively, in human.

     

Impact of collagen-induced arthritis on the pharmacokinetic disposition of voriconazole,a widely used antifungal agent: in vitro and in vivo investigations in DBA/1J mice

1. Pharmacokinetics of voriconazole, an anti-fungal agent, was determined in collagen-induced arthritic (CIA) and healthy DBA/1J mice. CIA was confirmed in DBA/1J mice by clinical scoring and histological analysis.

2. In vivo oral pharmacokinetic study (3?mg/kg) and in vitro stability assessment in liver microsomes were performed in CIA vs. healthy DBA/1J mice. Additionally, hepatic portal vein cannulated (HPVC) CIA and healthy mice were used to clarify the role of gut first-pass effect. Voriconazole/N-oxide metabolite was measured in plasma and in vitro samples using liquid chromatography tandem-mass spectrometry method.

3. Voriconazole exposure was reduced in CIA by 27% as compared to healthy mice. Formation of voriconazole N-oxide was higher in CIA mice as evidenced by higher molar C_max ratio (i.e. metabolite/parent) of 2.08 vs. 1.66 in healthy mice. Because voriconazole was stable in microsomes, involvement of presystemic gut metabolism was suspected for decreased voriconazole exposure and formation of higher molar ratio of metabolite. HPVC work revealed higher formation of voriconazole N-oxide in CIA relative to healthy mice resulting in C_max/AUC ratios of 0.41/0.54 and 0.08/0.17, respectively, confirming first-pass effect.

4. The findings may have implications in the clinical therapy of arthritis patients who are concomitantly given voriconazole for the management of fungal infections.

     

Metabolism and disposition of lesinurad,a uric acid reabsorption inhibitor,in humans

1. The objectives of this study were to determine the absolute bioavailability of lesinurad and to characterized its disposition in humans.

2. The oral bioavailability assessment was performed using a clinical design of simultaneous dosing of a therapeutic oral dose of lesinurad with an intravenous infusion of [¹⁴C]lesinurad microdose. The bioavailability of lesinurad was determined to be 100%.

3. The disposition of lesinurad in humans involves hepatic oxidation and renal elimination following administration of oral [¹⁴C]lesinurad dose.

4. Metabolism of lesinurad occurred post-systemically with low circulating levels of metabolites <3% of total radioactivity as 74.2% of total radioactivity was attributed to lesinurad.

5. In vitro metabolism studies identified CYP2C9 as the predominant isoform, and summation of metabolites indicated that it was responsible for ～50% of metabolism.

     

Intestinal phase-II metabolism of quercetin in HT29 cells, 3D human intestinal tissues and in healthy volunteers: a qualitative comparison using LC-IMS-MS and LC-HRMS

1. Flavonoids are a large class of dietary molecules, among which quercetin is the most ubiquitous, which undergo an extensive intestinal phase-II metabolism. We compared the in vivo metabolism of quercetin in healthy volunteers with two in vitro models, HT29 cells and 3?D human intestinal tissues. Supernatants of the in vitro experiments and the human intestinal fluids (HIF) were analyzed by LC-IMS-MS and LC-HRMS in a qualitative way.

2. Quercetin glucuronides, sulfates and their methyl conjugates were detected in all three systems. The metabolic profiles were found to be different, both in terms of the metabolites produced and their relative proportions. In particular, quercetin sulfates were almost absent in supernatants from HT29 cells incubations while they were a major metabolite in HIF and also found in 3?D intestinal tissues incubations.

3. IMS provided structural information as well as a third dimension of characterization, while HRMS brought increased sensitivity and MS/MS confirmation. HT29 cells are a useful tool to generate phase-II metabolites but do not represent the in vivo situation. 3?D intestinal tissues appear as a more relevant tool to study the intestinal phase-II metabolism of flavonoids.

     

Model-based pharmacokinetic and pharmacodynamic analysis for acute effects of a small molecule inhibitor of diacylglycerol acyltransferase-1 in the TallyHo/JngJ polygenic mouse

1. The purpose of this study was to evaluate the acute effect of a small molecule inhibitor of DGAT-1 on triglycerides (TG) and cholesterol in polygenic type 2 diabetic TallyHo/JngJ (TH) mice. PF-04620110, a potent and selective DGAT-1 inhibitor, was used as a model compound in this study and which was administered to TH and ICR mice.

2. The concentration of the model compound that produced 50% of maximum lowering of TG level (IC₅₀) in TH mice was not significantly different from that in ICR mice, when estimated using the model-based pharmacokinetic and pharmacodynamic assay, a two-compartmental model and an indirect response model.

3. The clearance of the inhibitor in TH mice was fivefold higher than that in ICR mice, suggesting significantly altered pharmacokinetics. Moreover, the in vitro metabolic elimination kinetic parameters (k_e,met), determined using liver microsomes from TH and ICR mice were 1.24?±?0.14 and 0.174?±?0.116?min^?1, respectively.

4. Thus, we report that the differences in the acute effects of the small molecule DAGT-1 inhibitor between TH mice and ICR mice can be attributed to altered pharmacokinetics caused by an altered metabolic rate for the compound in TH mice.

     

Distribution and metabolism of 14C-sulfoquinovosylacylpropanediol (14C-SQAP) after a single intravenous administration in tumor-bearing mice

1. Sulfoquinovosylacylpropanediol (SQAP) is a novel potent radiosensitizer that inhibits angiogenesis in vivo and results in increased oxigenation and reduced tumor volume. We investigated the distribution, metabolism, and excretion of SQAP in male KSN-nude mice transplanted with a human pulmonary carcinoma, Lu65.

2. For the metabolism analysis, a 2?mg (2.98?MBq)/kg of [glucose-U-¹⁴C]-SQAP (CP-3839) was intravenously injected. The injected SQAP was decomposed into a stearic acid and a sulfoquinovosylpropanediol (SQP) in the body.

3. The degradation was relatively slow in the carcinoma tissue.1,3-propanediol[1-¹⁴C]-SQAP (CP-3635) was administered through intravenous injection of a 1?mg (3.48?MBq)/kg dose followed by whole body autoradiography of the mice.

4. The autoradiography analysis demonstrated that SQAP rapidly distributed throughout the whole body and then quickly decreased within 4 hours except the tumor and excretion organs such as liver, kidney.

5. Retention of SQAP was longer in tumor parts than in other tissues, as indicated by higher levels of radioactivity at 4 hours. The radioactivity around the tumor had also completely disappeared within 72 hours.

     

Minor contribution of CYP3A5 to the metabolism of hepatitis C protease inhibitor paritaprevir in vitro

1. Paritaprevir (PTV) is a non-structural protein 3/4A protease inhibitor developed for the treatment of hepatitis C disease as a fixed dose combination of ombitasvir (OBV) and ritonavir (RTV) with or without dasabuvir.

2. The aim of this study was to evaluate the effects of cytochrome P450 (CYP) 3A5 on in vitro PTV metabolism using human recombinant CYP3A4, CYP3A5 (rCYP3A4, rCYP3A5) and human liver microsomes (HLMs) genotyped as either CYP3A5*1/*1, CYP3A5*1/*3 or CYP3A5*3/*3.

3. The intrinsic clearance (CL_int, V_max/K_m) for the production of a metabolite from PTV in rCYP3A4 was 1.5 times higher than that in rCYP3A5. The PTV metabolism in CYP3A5*1/*1 and CYP3A5*1/*3 HLMs expressing CYP3A5 was comparable to that in CYP3A5*3/*3 HLMs, which lack CYP3A5.

4. CYP3A4 expression level was significantly correlated with PTV disappearance rate and metabolite formation. In contrast, there was no such correlation found for CYP3A5 expression level.

5. This study represents that the major CYP isoform involved in PTV metabolism is CYP3A4, with CYP3A5 having a minor role in PTV metabolism. The findings of the present study may provide foundational information on PTV metabolism, and may further support dosing practices in HCV-infected patients prescribed PTV-based therapy.