Acute and Chronic Effects of Rifampin on Letermovir Suggest Transporter Inhibition and Induction Contribute to Letermovir Pharmacokinetics

Assessing Pleiotropic Effects of a Mixed-Mode Perpetrator Drug, Rifampicin, by Multiple Endogenous Biomarkers in Dogs

Rifampicin (RIF) is a mixed-mode perpetrator that produces pleiotropic effects on liver cytochrome P450 enzymes and drug transporters. To assess the complex drug-drug interaction liabilities of RIF in vivo, a known probe substrate, midazolam (MDZ), along with multiple endogenous biomarkers were simultaneously monitored in beagle dogs before and after a 7-day treatment period by RIF at 20 mg/kg per day. Confirmed by the reduced MDZ plasma exposure and elevated 4β-hydroxycholesterol (4β-HC, biomarker of CYP3A activities) level, CYP3A was significantly induced after repeated RIF doses, and such induction persisted for 3 days after cessation of the RIF administration. On the other hand, increased plasma levels of coproporphyrin (CP)-I and III [biomarkers of organic anion transporting polypeptides 1b (Oatp1b) activities] were observed after the first dose of RIF. Plasma CPs started to decline as RIF exposure decreased, and they returned to baseline 3 days after cessation of the RIF administration. The data suggested the acute (inhibitory) and chronic (inductive) effects of RIF on Oatp1b and CYP3A enzymes, respectively, and a 3-day washout period is deemed adequate to remove superimposed Oatp1b inhibition from CYP3A induction. In addition, apparent self-induction of RIF was observed as its terminal half-life was significantly altered after multiple doses. Overall, our investigation illustrated the need for appropriate timing of modulator dosing to differentiate between transporter inhibition and enzyme induction. As further indicated by the CP data, induction of Oatp1b activities was not likely after repeated RIF administration. SIGNIFICANCE STATEMENT: This investigation demonstrated the utility of endogenous biomarkers towards complex drug-drug interactions by rifampicin (RIF) and successfully determined the optimal timing to differentiate between transporter inhibition and enzyme induction. Based on experimental evidence, Oatp1b induction following repeated RIF administration was unlikely, and apparent self-induction of RIF elimination was observed.

Various effects of repeated rifampin dosing on coproporphyrin levels in humans

In recent years, the identification of endogenous substrates as biomarkers became an uprising topic. Particularly coproporphyrins (CPs), byproducts of heme biosynthesis, are intensely investigated as biomarkers for predicting interactions with the organic anion transporting polypeptide (OATP) 1B transporters. In the context of drug-drug interactions, several preclinical and clinical studies assessed the effect of the OATP1B-index inhibitor rifampin on CPI levels. However, rifampin is not only a "perpetrator" drug of transporters but is also known for its interaction with the nuclear receptor pregnane X receptor (PXR) leading to the efficient induction of PXR-target genes. These include hemoproteins like cytochrome P450 enzymes but also the δ-aminolevulinate synthase 1, which is the rate-limiting enzyme in heme biosynthesis. In this study, we showed that quantification of CPs in clinical serum samples was possible after long-term storage at -20°C. We quantified CPI, CPIII, and heme levels in clinical serum samples (at selected timepoints) that originated from a trial investigating the interaction potential of repeated rifampin administration in 12 healthy participants. In samples collected at the assumed time to maximum concentration of rifampin, higher CP levels were observed compared to baseline. Increased levels persisted even 14 h after discontinuation of rifampin. No impact on heme serum levels was observed. We found a correlation between CP isomers at baseline and at 14 h after rifampin intake. In summary, we show that multiple doses of rifampin affect CP levels. However, besides inhibition of hepatic OATP function there is evidence for an interaction with CP levels beyond the transporter level.

Effects of rifampicin on porphyrin metabolism in healthy volunteers

Pregnane X receptor (PXR) is known to stimulate haem synthesis, but detailed knowledge on the effects of PXR activation on porphyrin metabolism in humans is lacking. We utilized a randomized, crossover, open (blinded laboratory) and placebo-controlled trial with 600-mg rifampicin or placebo dosed for a week to investigate the effects of PXR activation on erythrocyte, plasma, faecal and urine porphyrins. Sixteen healthy volunteers participated on the trial, but the number of volunteers for blood and urine porphyrin analyses was 15 while the number of samples for faecal analyses was 14. Rifampicin increased urine pentaporphyrin concentration 3.7-fold (mean 1.80 ± 0.6 vs. 6.73 ± 4.4 nmol/L, p = 0.003) in comparison with placebo. Urine coproporphyrin I increased 23% (p = 0.036). Faecal protoporphyrin IX decreased (mean 31.6 ± 23.5 vs. 19.2 ± 27.8 nmol/g, p = 0.023). The number of blood erythrocytes was slightly elevated, and plasma bilirubin, catabolic metabolite of haem, was decreased. In conclusion, rifampicin dosing elevated the excretion of certain urinary porphyrin metabolites and decreased faecal protoporphyrin IX excretion. As urine pentaporphyrin and coproporphyrin I are not precursors in haem biosynthesis, increased excretion may serve as a hepatoprotective shunt when haem synthesis or porphyrin levels are increased.

Characterization of endogenous markers of hepatic function in patients receiving itraconazole treatment for prophylaxis of deep mycosis

BACKGROUND

Long-term use of itraconazole (ITZ) is associated with a risk of inducing hepatotoxicity. This study aimed to evaluate the associations of plasma concentrations of ITZ and its hydroxylated metabolite (OH-ITZ) with endogenous markers of hepatic function.

METHODS

Thirty six patients treated with oral ITZ solution for prophylaxis of deep mycosis were enrolled. Plasma concentrations of ITZ and OH-ITZ were determined on the 14th day or later after administration of ITZ. Their associations with endogenous marker levels of hepatic function including plasma coproporphyrin (CP)-I and OATP1B1 genotypes were assessed.

RESULTS

The serum level of total bilirubin (T-Bil) was moderately correlated with the plasma concentration of total ITZ (tITZ) and OH-ITZ (tOH-ITZ). T-Bil elevation above 0.3 mg/dL was observed in 19% of patients, although statistically significant difference was not identified. The plasma concentration of tITZ had no correlation with other endogenous markers levels including AST, ALT, albumin, and plasma CP-I. The serum AST and plasma CP-I levels were correlated with the plasma concentration of free OH-ITZ (fOH-ITZ). T-Bil and plasma CP-I, a marker of OATP1B1 activity, were not correlated with each other, and neither was associated with the OATP1B1 genotypes.

CONCLUSIONS

Plasma ITZ and OH-ITZ had a positive association with T-Bil. The patients with a higher fOH-ITZ level had lower OATP1B1 activity on the basis of plasma CP-I level. ITZ and OH-ITZ have the potential to slightly increase endogenous marker levels of hepatic function, although most likely by different mechanisms.

Characterizing complex and competing drug-drug interactions between the antiviral regimen of glecaprevir and pibrentasvir with rifampin or carbamazepine

The fixed-dose combination of the direct acting antivirals glecaprevir (GLE) and pibrentasvir (PIB) is an oral, once-daily treatment for all six major genotypes of chronic hepatitis C virus infection. A single and multiple-dose rifampin study (N = 12) and a carbamazepine study (N = 12) were conducted in healthy subjects to evaluate the effects of CYP3A/P-gp induction and OATP inhibition on the pharmacokinetics of GLE and PIB. In study 1, GLE 300 mg + PIB 120 mg was administered as a single dose either alone, after single and multiple daily doses of rifampin 600 mg, or 24 h after the last rifampin dose. In study 2, GLE 300 mg + PIB 120 mg was administered as a single dose either alone or after multiple doses of carbamazepine 200 mg. Relative to GLE + PIB alone, exposure of GLE was significantly increased by the first co-administered rifampin dose due to OATP inhibition, significantly decreased 24 h after the last rifampin dose due to CYP3A/P-gp induction, and slightly increased when co-administered with steady-state rifampin due to a combination of inhibition and induction forces. Exposure of PIB was not affected when co-administered with the first rifampin dose but was significantly decreased with steady-state rifampin co-administration, or 24 h after the last rifampin dose due to P-gp induction. Carbamazepine significantly decreased GLE and PIB exposure, mainly attributed to P-gp induction. The regimens tested were generally well-tolerated by the subjects and no new safety issues were identified.

Cluster Gauss-Newton method analyses of PBPK model parameter combinations of coproporphyrin-I based on OATP1B-mediated rifampicin interaction studies

Coproporphyrin I (CP-I) is an endogenous biomarker supporting the prediction of drug-drug interactions (DDIs) involving hepatic organic anion transporting polypeptide 1B (OATP1B). We previously constructed a physiologically-based pharmacokinetic (PBPK) model for CP-I using clinical DDI data with an OATP1B inhibitor, rifampicin (RIF). In this study, PBPK model parameters for CP-I were estimated using the cluster Gauss-Newton method (CGNM), an algorithm used to find multiple approximate solutions for nonlinear least-squares problems. Eight unknown parameters including the hepatic overall intrinsic clearance (CL_int,all ), the rate of biosynthesis (v_syn ), and the OATP1B inhibition constant of RIF(K_i,u,OATP ) were estimated by fitting to the observed CP-I blood concentrations in two different clinical studies involving changing the RIF dose. Multiple parameter combinations were obtained by CGNM that could well capture the clinical data. Among those, CL_int,all , K_i,u,OATP , and v_syn were sensitive parameters. The obtained K_i,u,OATP for CP-I was 5.0- and 2.8-fold lower than that obtained for statins, confirming our previous findings describing substrate-dependent K_i,u,OATP values. In conclusion, CGNM analyses of PBPK model parameter combinations enables estimation of the three essential parameters for CP-I to capture the DDI profiles, even if the other parameters remain unidentified. The CGNM also clarified the importance of appropriate combinations of other unidentified parameters to enable capture of the CP-I concentration time course under the influence of RIF. The described CGNM approach may also support the construction of robust PBPK models for additional transporter biomarkers beyond CP-I.

Reimagining the Framework Supporting the Static Analysis of Transporter Drug Interaction Risk; Integrated Use of Biomarkers to Generate Pan‐Transporter Inhibition Signatures

Solute carrier (SLC) transporters present as the loci of important drug-drug interactions (DDIs). Therefore, sponsors generate in vitro half-maximal inhibitory concentration (IC₅₀ ) data and apply regulatory agency-guided "static" methods to assess DDI risk and the need for a formal clinical DDI study. Because such methods are conservative and high false-positive rates are likely (e.g., DDI study triggered when liver SLC R value ≥ 1.04 and renal SLC maximal unbound plasma (C_max,u )/IC₅₀ ratio ≥ 0.02), investigators have attempted to deploy plasma- and urine-based SLC biomarkers in phase I studies to de-risk DDI and obviate the need for drug probe-based studies. In this regard, it was possible to generate in-house in vitro SLC IC₅₀ data for various clinically (biomarker)-qualified perpetrator drugs, under standard assay conditions, and then estimate "% inhibition" for each SLC and relate it empirically to published clinical biomarker data (area under the plasma concentration vs. time curve (AUC) ratio (AUCR, AUC_inhibitor /AUC_reference ) and % decrease in renal clearance (ΔCL_renal )). After such a "calibration" exercise, it was determined that only compounds with high R values (> 1.5) and C_max,u /IC₅₀ ratios (> 0.5) are likely to significantly modulate liver (AUCR > 1.25) and renal (ΔCL_renal  > 25%) biomarkers and evoke DDI risk. The % inhibition approach supports integration of liver and renal SLC data and allows one to generate pan-SLC inhibition signatures for different test perpetrators (e.g., SLC % inhibition ranking). In turn, such signatures can guide the selection of the most appropriate individual (or combinations of) biomarkers for testing in phase I studies.

Utilizing Endogenous Biomarkers to Derisk Assessment of Transporter Mediated Drug-Drug Interactions: A Scientific Perspective

Comprehensive characterization of transporter mediated drug-drug interactions (DDIs) is important to formulate clinical management strategies and ensure the safe and effective use of concomitantly administered drugs. The potential of a drug to inhibit transporters is predicted by comparing the ratio of the relevant concentration (depending on the transporter) and the half maximum inhibitory concentration (IC₅₀ ) to a pre-defined "cut off" value. If the ratio is greater than the cut off value, modeling approaches such as Physiologically Based Pharmacokinetic (PBPK) Modeling or a clinical DDI trial may be recommended. Because false positive (in vitro data suggests the potential for a DDI, whereas no significant DDI is observed in vivo) and false negative (in vitro data does not suggest the potential for a DDI, whereas significant DDI is observed in vivo) outcomes have been observed, there is interest in exploring additional approaches to facilitate prediction of transporter mediated DDIs. The idea of assessing changes in the concentration of endogenous biomarkers (which are substrates of clinically relevant transporters) to gain insight on the potential for a drug to inhibit transporter activity has received widespread attention. This brief report describes how endogenous biomarkers may help to expand the DDI assessment toolkit, highlights some current knowledge gaps, and outlines a conceptual framework that may complement the current paradigm of predicting the potential for transporter mediated DDIs. This article is protected by copyright. All rights reserved.

Pharmacokinetics, Safety, and Tolerability of Letermovir Following Single- and Multiple-Dose Administration in Healthy Japanese Subjects

Letermovir is a human cytomegalovirus terminase inhibitor for the prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant recipients. The pharmacokinetics, safety, and tolerability of letermovir were assessed in healthy Japanese subjects in 2 phase 1 trials: trial 1-single ascending oral doses (240, 480, and 720 mg) and intravenous (IV) doses (240, 480, and 960 mg), and trial 2-multiple oral doses (240 and 480 mg once daily for 7 days). Following administration of oral single and multiple doses, letermovir was absorbed with a median time to maximum plasma concentration of 2 to 4 hours, and concentrations declined in a biphasic manner with a terminal half-life of ≈10 to 13 hours. The post absorption plasma concentration-time profile of letermovir following oral administration was similar to the profile observed with IV dosing. There was minimal accumulation with multiple-dose administration. Letermovir exposure in healthy Japanese subjects was ≈1.5- to 2.5-fold higher than that observed in non-Japanese subjects. Based on the population pharmacokinetic analysis, weight differences primarily accounted for the higher exposures observed in Asians. Letermovir was generally well tolerated following oral and IV administration to healthy Japanese subjects.