Drug Metabolism and Pharmacokinetics

Conversion from Twice-Daily Prograf ® to Once-Daily Advagraf ® in Multi-ethnic Asian Adult Renal Transplant Recipients With or Without Concomitant Use of Diltiazem: Impact of CYP3A5 and MDR1 Genetic Polymorphisms on Tacrolimus Exposure Abstract Background and Objectives Tacrolimus is the mainstay of immunosuppression in renal transplantation. Given that once-daily administration improves patient compliance, 1:1 dose conversion from twice-daily Prograf® to once-daily Advagraf® is recommended. Although cytochrome P450 (CYP) 3A5 and multi-drug resistance 1 (MDR1) polymorphisms influence tacrolimus concentrations, it is unknown if these impact on conversion. This study investigated the change in the pharmacokinetics of tacrolimus after conversion from Prograf® to Advagraf® and examined the impact of CYP3A5 and MDR1 C3435T polymorphisms on those pharmacokinetics. Methods A prospective open-label pharmacokinetic study of 1:1 conversion from Prograf® to Advagraf® with or without diltiazem was conducted on 26 stable renal transplant recipients. Blood samples were collected over 24 h during each phase, tacrolimus concentrations were assayed, and noncompartmental pharmacokinetic analysis was performed. All participants were genotyped for CYP3A5*3 and MDR1 C3435T. Results After conversion, without diltiazem, the area under the concentration–time curve at steady state from 0 to 24 h after dose administration (AUCss, 0–24) was significantly reduced [median 224 (range 172–366) vs. 184 (104–347) ng·h/mL, p = 0.006, n = 26]. A decrease in tacrolimus exposure (median 21%) was only evident among CYP3A5 expressors [227 (172–366) vs. 180 (104–347) ng·h/mL, p = 0.014, n = 18], not among non-expressors [215 (197–290) vs. 217 (129–281) ng·h/mL, p = 0.263, n = 8]. In contrast, among CYP3A5 expressors receiving diltiazem, AUCss, 0–24 did not change significantly upon conversion [229 (170–296) vs. 221 (123–342) ng·h/mL, p = 0.575, n = 10]. An independent effect was not evident for MDR1 C3435T polymorphism. Conclusion The high prevalence of CYP3A5 polymorphism among Asians may lead to a significant reduction in tacrolimus exposure with 1:1 dose conversion of Prograf® to Advagraf®. These results advocate for CYP3A5 determination prior to conversion, and suggest that 1:1.25 conversion should be used for CYP3A5 expressors and 1:1 conversion for other patients.

Glucuronidation of d -Luciferin In Vitro: Isoform Selectivity and Kinetics Characterization Abstract Background d-luciferin is one of the most commonly used substrates in bioluminescence imaging for real-time monitoring of sophisticated biological processes in models of human biology or disease in vitro and in vivo. d-luciferin is rapidly cleared from blood circulation after being exogenously delivered in vivo and the presence of phenolic groups indicates that glucuronide conjugation is a possible metabolic pathway for the compound. Objectives This study aimed to characterize the glucuronidation pathway of d-luciferin in human liver microsomes (HLM) and human intestine microsomes (HIM). Methods HLM and HIM were employed to catalyze the glucuronidation of d-luciferin in vitro. The activity of recombinant uridine-diphospho-glucuronosyltransferase (UGT) isoforms towards d-luciferin glucuronidation was screened. Chemical inhibition assay and kinetic analysis was combined to determine the UGT isoforms responsible for the formation of d-luciferin glucuronide in HLM and HIM. Results d-luciferin could be catalyzed to form one mono-glucuronide which was characterized as 6′-O-glucuronide in HLM and HIM. UGT1A1, 1A3, 1A6, 1A8, 1A9 and 1A10 participated in the formation of d-luciferin glucuronide, with UGT1A1 exhibiting the highest catalytic activity. Both chemical inhibition assays and kinetic analysis showed that UGT1A1 and UGT1A3 played important roles in d-luciferin-6′-O-glucuronidation in HLM and HIM, with UGT1A6 also giving a non-negligible contribution to this biotransformation in HLM. Conclusions UGT1A1, UGT1A3 and UGT1A6 were responsible for 6′-O-glucuronidation of d-luciferin in HLM, while UGT1A1 and UGT1A3 were the major contributors to this biotransformation in HIM.

Effect of Gender on the Pharmacokinetics of ON 123300, A Dual Inhibitor of ARK5 and CDK4/6 for the Treatment of Cancer, in Rats Abstract Background and Objectives ON 123300, a small molecule dual inhibitor of the c-MYC activated kinases ARK5 and CDK4/6, is being developed as a novel drug candidate for the treatment of cancer. The objective of this research was to evaluate gender differences in the in vitro metabolism and in vivo systemic exposure of ON 123300 in rats. Methods In vitro metabolism experiments (n = 2/group) were performed in rat liver microsomes from male and female donors. ON 123300 bislactate (final concentration 10 µM) was incubated with 0.5 mg/mL microsomes, and samples (100 µL) were withdrawn at specified incubation times over a period of 60 min, and immediately quenched and centrifuged. The supernatant was analyzed for ON 123300 and its metabolites by HPLC. ON 123300 (bislactate salt) pharmacokinetics were evaluated following intravenous (i.v.) (30 s infusion, 5 and 10 mg/kg) or oral administration (25 and 100 mg/kg) to male and female Sprague–Dawley rats (250–300 g). Following dosing, blood samples were collected over a time period up to 24 h. ON 123300 plasma concentrations were measured by LC–MS/MS. Pharmacokinetic parameters were estimated by non-compartmental analysis. Plasma and microsomal binding of ON 123300 and blood:plasma ratio were also determined. Results ON 123300 displayed more rapid microsomal degradation in vitro in males compared to females, as reflected in intrinsic clearance (181 vs 53.1 µL/min/mg). This translated into a significantly higher exposure of ON 123300 following oral administration to female rats, with the area under the curve (AUC) increasing nearly 3-fold (5617 ± 1914 ng·h/mL) compared to males (AUC = 1965 ± 749 ng·h/mL). This gender effect was less pronounced following i.v. dosing, where the AUC was ~ 2-fold higher in females. Based on these results, the higher plasma exposure observed in females can be primarily attributed to reductions in both hepatic clearance and presystemic metabolism compared to males. Conclusions This investigation demonstrated a significantly lower metabolism of ON 123300 in female rats, which resulted in high systemic exposure. Additional testing is warranted to assess the potential clinical implications of these findings.

Enhancing Curcumin Oral Bioavailability Through Nanoformulations Abstract Curcumin is a promising therapeutic agent that exhibits manifold therapeutic activities. However, it is challenging to study curcumin as it exhibits poor aqueous solubility and low permeability and it is a substrate for P-glycoprotein (P-gp). It is readily metabolized in the body, but many active metabolites of curcumin have been identified that could also be exploited for therapy. Strategies for the oral bioenhancement of curcumin to leverage the potential of curcumin as a therapeutic molecule are discussed here in light of these challenges. A brief discussion of conventional bioenhancement strategies using cyclodextrin complexes, solid dispersions, and solid self-emulsifying drug delivery systems is given. However, the major focus of this review is the application of nano-based approaches to the bioenhancement of curcumin. A description of the main advantages of nanosystems is followed by a detailed review of various nanosystems of curcumin, including nanosuspensions and various carrier-based nanosystems. Each nanosystem considered here is first briefly introduced, and then studies of the nanosystem containing curcumin are discussed. Lipid-based systems including liposomes and solid lipid nanoparticles, microemulsions, self-microemulsifying drug-delivery systems, nanoemulsions, and polymeric nanoparticles—which are widely explored—are dealt with in detail. Other miscellaneous systems discussed include inorganic nanoparticles, micelles, solid nanodispersions, phytosomes, and dendrimers. The possibility of using intact nanoparticles to achieve the targeted oral delivery of curcumin and thus harness the benefits of this wonder nutraceutical is an exciting prospect.

A Gallbladder-Based Enterohepatic Circulation Model for Pharmacokinetic Studies Abstract Background and Objectives Strategies for modeling the enterohepatic circulation (EHC) process reported in the literature vary; however, gallbladder-based models currently provide the best physiological representation of the process. Regardless, the addition of a gallbladder to the model does not fully depict the physiology of EHC. A more physiological gallbladder-based EHC model is needed. This model should take into account a physiological representation of the bile secretion, gallbladder filling and emptying, the duration of gallbladder emptying, and irregular mealtimes. Considering all of these factors, the objectives of the present analysis were to propose a gallbladder-based EHC model and then to use that model to perform sensitivity analyses evaluating the effect of the extent of EHC on the pharmacokinetic profile and noncompartmental analysis (NCA) calculations. Methods A gallbladder-based model that describes the EHC process was developed and used to perform determinant simulations assuming various degrees of EHC. Next, these simulations were compared to evaluate the effect of the EHC on the pharmacokinetic profiles of orally administered drugs. The influence of the EHC process on the NCA calculations was determined while assuming two sampling schemes that differed in the times at which sampling was performed in relation to meal times. Results The presence of EHC results in nonlinearity in the system and changes the pharmacokinetic profile, affecting the maximum concentration (Cmax), time to Cmax (Tmax), and half-life estimates. Comparison of the results obtained using the two sampling schemes for a drug undergoing various degrees of EHC demonstrated a significant influence of the selected sampling times on the NCA estimations. Bias in the NCA calculations was also dependent on the sampling times used. Conclusion Caution should be taken when designing clinical studies for drugs that undergo EHC. It may be essential to consider the timing of meals when planning pharmacokinetic studies and defining sampling times. The period over which samples are taken needs to be extended as compared to that traditionally used with other drugs. Future studies that attempt to identify the best sampling strategies in the presence of EHC are needed.

Influence of Obesity and Type 2 Diabetes Mellitus on the Pharmacokinetics of Tramadol After Single Oral Dose Administration Abstract Background and Objectives The number of overweight, obese and diabetic patients is constantly increasing. Metabolic disorders may affect the pharmacokinetics of drugs, e.g., by altering the activity of cytochrome P450 (CYP) isoenzymes. Tramadol is a commonly used analgesic metabolised mainly via CYP2D6 to its active metabolite, O-desmethyltramadol. The aim of the study was to assess the influence of overweight, obesity and type 2 diabetes mellitus on tramadol and O-desmethyltramadol pharmacokinetics. Methods All patients received a single oral dose (100 mg) of tramadol. The plasma concentrations of tramadol and O-desmethyltramadol were measured with the validated high-performance liquid chromatography method with fluorescence detection. The pharmacokinetic parameters of tramadol and O-desmethyltramadol were calculated by non-compartmental methods. Results After nephrectomy, the patients were divided into four groups—a control group (n = 12, mean [SD] age 61 [14] years, body mass index (BMI) 22 [2] kg/m2, CLcr (creatinine clearance) 74 [30] mL/min); an overweight group (n = 15, mean [SD] age 63 [11] years, BMI 27 [1] kg/m2, CLcr 81 [35] mL/min); an obese group (n = 12, mean [SD] age 57 [8] years, BMI 33 [4] kg/m2, CLcr 113 [51] mL/min); and an obese and diabetic group (n = 9, mean [SD] age 64 [10] years, BMI 33 [4] kg/m2, CLcr 87 [35] mL/min). Apart from the time to first occurrence of maximal concentration (tmax), there were no significant differences in the pharmacokinetic parameters of tramadol and O-desmethyltramadol among the groups. Moreover, there were no significant differences in the O-desmethyltramadol/tramadol ratios among the four groups of patients after nephrectomy. Conclusions No significant differences were found in the pharmacokinetics of tramadol and O-desmethyltramadol, indicating that the opioid can be administered to overweight, obese and diabetic patients without dosage adjustment.

Clinical Pharmacokinetics of a Lipid-Based Formulation of Risperidone, VAL401: Analysis of a Single Dose in an Open-Label Trial of Late-Stage Cancer Patients Abstract Background and Objectives A clinical trial was conducted to measure and analyse the pharmacokinetic parameters of a lipid formulation of risperidone, VAL401. The VAL401 formulation is designed to repurpose risperidone from an antipsychotic to an adenocarcinoma treatment, with the lipid formulation altering the cellular uptake of risperidone, thus enabling anticancer biology to be exhibited in preclinical testing. Methods This first human trial of VAL401 measured the concentrations of risperidone and its primary metabolite, 9-hydroxyrisperidone, in the blood of patients after treatment with a single 2-mg dose of VAL401. Results The trial provided information on differences in the pharmacokinetic profile of risperidone in VAL401 that may be caused by the formulation and/or the nature of the cancer patient population. VAL401 provided the following key pharmacokinetic parameters for the risperidone plasma concentration after a single 2-mg dose of VAL401, with results normalised to a dosage of 1 mg for comparison with literature values: Tmax, 2 h; Cmax, 8 ng/ml; half-life, 3.5 h; area under the plasma concentration–time curve from time zero to infinity (AUC0–∞), 58.2 ng h2/mL. Conclusions Further comparisons of the pharmacokinetic parameters of risperidone and 9-hydroxyrisperidone in plasma of patients administered VAL401 and the corresponding parameters obtained from published data for conventionally formulated risperidone provide evidence for altered biological processing of VAL401 as compared to risperidone. The absolute values obtained provide support for future studies of VAL401 as a cancer treatment, as the Cmaxdemonstrates sufficient exposure to reach the concentrations seen during preclinical anticancer testing, yet the overall exposure to the active moiety supports the use of the safety and tolerability data from conventional risperidone during future clinical trials.

Comparison of the Pharmacokinetic Profiles of Ceftriaxone Used Alone and Combined with Danhong Injection in Old Rats Abstract Background and Objectives Danhong injection is the most commonly prescribed adjuvant drug applied for the treatment of cardiovascular and cerebrovascular diseases in China. Ceftriaxone is usually prescribed along with Danhong injection to elderly patients with complications. However, the pharmacokinetic interactions between these two medications have not been investigated. The aim of this study was to investigate whether Danhong injection influences the pharmacokinetic profile of ceftriaxone in old rats when these two medications are used in combination. Methods The animal experiment protocol was designed according to the clinical data. Ten-month-old male Sprague–Dawley (SD) rats were dosed with ceftriaxone through intravenous administration for 1 or 7 days in the presence or absence of Danhong injection. The combinations were divided into 1-day, 7-day, and 14-day combined-treatment groups in which Danhong injection was administered for 1, 7, or 14 days and ceftriaxone was given for 1, 7, or 7 days, respectively. The plasma concentration of ceftriaxone was determined by ultrahigh performance liquid chromatography coupled with triple-quadrupole mass spectrometry (UHPLC–TQ–MS) on a BEH C18 column with a mobile phase consisting of acetonitrile and 0.4% formic acid–water. The chromatographic method was validated and found to be simple, rapid, and stable. Results Danhong injection significantly increased the plasma clearance of and decreased systemic exposure to ceftriaxone. In the 1-day combined-treatment group, the plasma clearance of ceftriaxone increased by 52.69%, and the area under the concentration–time curve (AUC) of ceftriaxone was decreased by 32.54% (P < 0.01). In the 7-day combined-treatment group, the rate of plasma clearance increased by 52.49% and the area under the concentration–time curve decreased by 31.15% (P < 0.01). For the 14-day combined-treatment group, the plasma clearance of ceftriaxone increased by 26.73%, and the area under the concentration–time curve decreased by 21.44% (P < 0.05). Conclusions In old male rats, systemic exposure to ceftriaxone decreased when used concomitantly with Danhong injection, which may be because Danhong injection increased the plasma clearance of ceftriaxone. Further investigations should be carried out to clarify the mechanism for the influence of Danhong injection on the pharmacokinetics of ceftriaxone.

Population Pharmacokinetic Modelling of Pyrazinamide and Pyrazinoic Acid in Patients with Multi-Drug Resistant Tuberculosis Abstract Background and Objectives Pyrazinamide, a drug used in the regimen for the treatment of drug-sensitive tuberculosis, is also used for the treatment of multidrug-resistant tuberculosis (MDR-TB). We aimed to describe the population pharmacokinetics of pyrazinamide and its major metabolite, pyrazinoic acid, in patients with MDR-TB and characterise the effects of demographic variables. Methods This was a non-randomised clinical study involving 51 adult patients admitted for the intensive phase of MDR-TB treatment. Blood samples were collected at pre-dose and at 0.5, 1, 1.5, 2, 3, 4, 8, 16 and 24 h after drug administration. Plasma concentrations of pyrazinamide and pyrazinoic acid were analysed using a validated LC–MS/MS method. Nonlinear mixed-effects modelling using Monolix 2018R1 software was employed to estimate population pharmacokinetic parameters. Results A one-compartment pharmacokinetic model with transit compartment absorption process and first-order elimination best described the pyrazinamide and pyrazinoic acid concentration–time data. The estimated population pharmacokinetic parameters were 0.7 h, 3.38 h−1, 57.1 l, 4.37 L/h and 10.5 L/h for mean transit time, absorption rate constant, apparent distribution volume for pyrazinamide, and apparent clearance for pyrazinamide and pyrazinoic acid (CLm/F), respectively. These parameters were not affected by patient age, HIV status or sex. The parameter variability in CLm/F was the highest (83.5%), while the rest of the parameters ranged from 16.2 to 58%. Conclusions The developed population pharmacokinetic model adequately described the disposition of pyrazinamide and pyrazinoic acid and can be useful for dose determination of pyrazinamide in patients with MDR-TB.

Advanced In Vitro HepaRG Culture Systems for Xenobiotic Metabolism and Toxicity Characterization Abstract Several HepaRG three-dimensional (3D) in vitro model systems have been developed to improve the predictability of xenobiotic metabolism and toxicity. In this review, we present a detailed summary and critique of the performance of various HepaRG 3D models compared to the conventional 2D monolayer culture. HepaRG 3D models can be broadly categorized into (1) scaffold-free, (2) scaffold-based, and (3) bioartificial liver (BAL) models. With respect to the scaffold-free configurations, the hanging drop model closely mimics the normal physiological function and metabolic profile of the liver. The micromold model is suitable for high-throughput multiplexed assays and exhibits higher accuracy when predicting drug-induced liver toxicity risk in both acute and chronic culture. Scaffold- and BAL-based models also present improved precision and accuracy for hepatotoxic drug screening in addition to allowing improved model control to closely mimic physiological assay conditions. Overall, all 3D HepaRG models exhibit improved cellular function, metabolic activity, and toxicity screening ability compared to the conventional 2D monolayer culture. These improvements reported in 3D models may be due to a higher degree of differentiation and cell polarity. Nevertheless, the expression and functions of various phase II, phase III, and nuclear receptors need to be further characterized in these 3D models.