Inhibitory potential of tuberculosis drugs on ATP-binding cassette drug transporters

Assessing potential drug-drug interactions between clofazimine and other frequently used agents to treat drug-resistant tuberculosis

Clofazimine is included in drug regimens to treat rifampicin/drug-resistant tuberculosis (DR-TB), but there is little information about its interaction with other drugs in DR-TB regimens. We evaluated the pharmacokinetic interaction between clofazimine and isoniazid, linezolid, levofloxacin, and cycloserine, dosed as terizidone. Newly diagnosed adults with DR-TB at Klerksdorp/Tshepong Hospital, South Africa, were started on the then-standard treatment with clofazimine temporarily excluded for the initial 2 weeks. Pharmacokinetic sampling was done immediately before and 3 weeks after starting clofazimine, and drug concentrations were determined using validated liquid chromatography-tandem mass spectrometry assays. The data were interpreted with population pharmacokinetics in NONMEM v7.5.1 to explore the impact of clofazimine co-administration and other relevant covariates on the pharmacokinetics of isoniazid, linezolid, levofloxacin, and cycloserine. Clofazimine, isoniazid, linezolid, levofloxacin, and cycloserine data were available for 16, 27, 21, 21, and 6 participants, respectively. The median age and weight for the full cohort were 39 years and 52 kg, respectively. Clofazimine exposures were in the expected range, and its addition to the regimen did not significantly affect the pharmacokinetics of the other drugs except levofloxacin, for which it caused a 15% reduction in clearance. A posteriori power size calculations predicted that our sample sizes had 97%, 90%, and 87% power at P < 0.05 to detect a 30% change in clearance of isoniazid, linezolid, and cycloserine, respectively. Although clofazimine increased the area under the curve of levofloxacin by 19%, this is unlikely to be of great clinical significance, and the lack of interaction with other drugs tested is reassuring.

Overexpression of a membrane transport system MSMEG_1381 and MSMEG_1382 confers multidrug resistance in Mycobacterium smegmatis

Mycobacterium tuberculosis is a leading cause of human mortality worldwide, and the emergence of drug-resistant strains demands the discovery of new classes of antimycobacterial that can be employed in the therapeutic pipeline. Previously, a secondary metabolite, chrysomycin A, isolated from Streptomyces sp. OA161 displayed potent bactericidal activity against drug-resistant clinical isolates of M. tuberculosis and different species of mycobacteria. The antibiotic inhibits mycobacterial topoisomerase I and DNA gyrase, leading to bacterial death, but the mechanisms that could cause resistance to this antibiotic are currently unknown. To further understand the resistance mechanism, using M. smegmatis as a model, spontaneous resistance mutants were isolated and subjected to whole-genome sequencing. Mutation in a TetR family transcriptional regulator MSMEG_1380 was identified in the resistant isolates wherein the gene was adjacent to an operon encoding membrane proteins MSMEG_1381 and MSMEG_1382. Sequence analysis and modeling studies indicated that MSMEG_1381 and MSMEG_1382 are components of the Mmp family of efflux pumps and over-expression of either the operon or individual genes conferred resistance to chrysomycin A, isoniazid, and ethambutol. Our study highlights the role of membrane transporter proteins in conferring multiple drug resistance and the utility of recombinant strains overexpressing membrane transporters in the drug screening pipeline.

Pharmacokinetics and safety of first-line tuberculosis drugs rifampin, isoniazid, ethambutol, and pyrazinamide during pregnancy and postpartum: results from IMPAACT P1026s

Physiological changes during pregnancy may alter the pharmacokinetics (PK) of antituberculosis drugs. The International Maternal Pediatric Adolescent AIDS Clinical Trials Network P1026s was a multicenter, phase IV, observational, prospective PK and safety study of antiretroviral and antituberculosis drugs administered as part of clinical care in pregnant persons living with and without HIV. We assessed the effects of pregnancy on rifampin, isoniazid, ethambutol, and pyrazinamide PK in pregnant and postpartum (PP) persons without HIV treated for drug-susceptible tuberculosis disease. Daily antituberculosis treatment was prescribed following World Health Organization-recommended weight-band dosing guidelines. Steady-state 12-hour PK profiles of rifampin, isoniazid, ethambutol, and pyrazinamide were performed during second trimester (2T), third trimester (3T), and 2-8 of weeks PP. PK parameters were characterized using noncompartmental analysis, and comparisons were made using geometric mean ratios (GMRs) with 90% confidence intervals (CI). Twenty-seven participants were included: 11 African, 9 Asian, 3 Hispanic, and 4 mixed descent. PK data were available for 17, 21, and 14 participants in 2T, 3T, and PP, respectively. Rifampin and pyrazinamide AUC0-24 and C max in pregnancy were comparable to PP with the GMR between 0.80 and 1.25. Compared to PP, isoniazid AUC0-24 was 25% lower and C max was 23% lower in 3T. Ethambutol AUC0-24 was 39% lower in 3T but limited by a low PP sample size. In summary, isoniazid and ethambutol concentrations were lower during pregnancy compared to PP concentrations, while rifampin and pyrazinamide concentrations were similar. However, the median AUC0-24 for rifampin, isoniazid, and pyrazinamide met the therapeutic targets. The clinical impact of lower isoniazid and ethambutol exposure during pregnancy needs to be determined.

Mechanisms and Clinical Significance of Pharmacokinetic Drug Interactions Mediated by FDA and EMA-approved Hepatitis C Direct-Acting Antiviral Agents

The treatment of patients infected with the hepatitis C virus (HCV) has been revolutionised by the development of direct-acting antiviral agents (DAAs) that target specific HCV proteins involved in viral replication. The first DAAs were associated with clinical problems such as adverse drug reactions and pharmacokinetic drug-drug interactions (DDIs). Current FDA/EMA-approved treatments are combinations of DAAs that simultaneously target the HCV N5A-protein, the HCV N5B-polymerase and the HCV NS3/4A-protease. Adverse events and DDIs are less likely with these DAA combinations but several DDIs of potential clinical significance remain. Much of the available information on the interaction of DAAs with CYP drug-metabolising enzymes and influx and efflux transporters is contained in regulatory summaries and is focused on DDIs of likely clinical importance. Important DDIs perpetrated by current DAAs include increases in the pharmacokinetic exposure to statins and dabigatran. Some mechanistic information can be deduced. Although the free concentrations of DAAs in serum are very low, a number of these DDIs are likely mediated by the inhibition of systemic influx transporters, especially OATP1B1/1B3. Other DDIs may arise by DAA-mediated inhibition of intestinal efflux transporters, which increases the systemic concentrations of some coadministered drugs. Conversely, DAAs are victims of DDIs mediated by cyclosporin, ketoconazole, omeprazole and HIV antiretroviral drug combinations, especially when boosted by ritonavir and, to a lesser extent, cobicistat. In addition, concurrent administration of inducers, such as rifampicin, carbamazepine and efavirenz, decreases exposure to some DAAs. Drug-drug interactions that increase the accumulation of HCV N3/4A-protease inhibitors like grazoprevir may exacerbate hepatic injury in HCV patients.

Characterization of Clofazimine as a Potential Substrate of Drug Transporter

In this study, we explored clofazimine (CFZ) as a potential substrate of uptake and efflux transporters that might be involved in CFZ disposition, using transporter gene overexpressing cell lines in vitro. The intracellular concentrations of CFZ were significantly increased in the presence of selective inhibitors of P-gp and BCRP, which include verapamil, cyclosporine-A, PSC-833, quinidine, Ko143, and daunorubicin. In a bidirectional transport assay using transwell cultures of cell lines overexpressing P-gp and BCRP, the mean efflux ratios of CFZ were found to be 4.17 ± 0.63 and 3.37 ± 1.2, respectively. The K_m and maximum rate of uptake (V_max) were estimated to be 223.3 ± 14.73 μM and 548.8 ± 87.15 pmol/min/mg protein for P-gp and 381.9 ± 25.07 μM and 5.8 ± 1.22 pmol/min/mg protein for BCRP, respectively. Among the uptake transporters screened, the CFZ uptake rate was increased 1.93 and 3.09-fold in HEK293 cell lines overexpressing OAT1 and OAT3, respectively, compared to the control cell lines, but no significant uptake was observed in cell lines overexpressing OCT1, OCT2, OATP1B1, OATP1B3, OATP2B1, or NTCP. Both OAT1- and OAT3-mediated uptake was inhibited by the selective inhibitors diclofenac, probenecid, and butanesulfonic acid. The K_m and V_max values of CFZ were estimated to be 0.63 ± 0.15 μM and 8.23 ± 1.03 pmol/min/mg protein, respectively, for OAT1 and 0.47 ± 0.1 μM and 17.81 ± 2.19 pmol/min/mg protein, respectively, for OAT3. These findings suggest that CFZ is a novel substrate of BCRP, OAT1, and OAT3 and a known substrate of P-gp in vitro.

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

Critical discussion on drug efflux in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can withstand months of antibiotic treatment. An important goal of tuberculosis research is to shorten the treatment to reduce the burden on patients, increase adherence to the drug regimen and thereby slow down the spread of drug resistance. Inhibition of drug efflux pumps by small molecules has been advocated as a promising strategy to attack persistent Mtb and shorten therapy. Although mycobacterial drug efflux pumps have been broadly investigated, mechanistic studies are scarce. In this critical review, we shed light on drug efflux in its larger mechanistic context by considering the intricate interplay between membrane transporters annotated as drug efflux pumps, membrane energetics, efflux inhibitors and cell wall biosynthesis processes. We conclude that a great wealth of data on mycobacterial transporters is insufficient to distinguish by what mechanism they contribute to drug resistance. Recent studies suggest that some drug efflux pumps transport structural lipids of the mycobacterial cell wall and that the action of certain drug efflux inhibitors involves dissipation of the proton motive force, thereby draining the energy source of all active membrane transporters. We propose recommendations on the generation and interpretation of drug efflux data to reduce ambiguities and promote assigning novel roles to mycobacterial membrane transporters.

Prediction of Moxifloxacin Concentrations in Tuberculosis Patient Populations by Physiologically Based Pharmacokinetic Modeling

Moxifloxacin has an important role in the treatment of tuberculosis (TB). Unfortunately, coadministration with the cornerstone TB drug rifampicin results in suboptimal plasma exposure. We aimed to gain insight into the moxifloxacin pharmacokinetics and the interaction with rifampicin. Moreover, we provided a mechanistic framework to understand moxifloxacin pharmacokinetics. We developed a physiologically based pharmacokinetic model in Simcyp version 19, with available and newly generated in vitro and in vivo data, to estimate pharmacokinetic parameters of moxifloxacin alone and when administered with rifampicin. By combining these strategies, we illustrate that the role of P-glycoprotein in moxifloxacin transport is limited and implicate MRP2 as transporter of moxifloxacin-glucuronide followed by rapid hydrolysis in the gut. Simulations of multiple dose area under the plasma concentration-time curve (AUC) of moxifloxacin (400 mg once daily) with and without rifampicin (600 mg once daily) were in accordance with clinically observed data (predicted/observed [P/O] ratio of 0.87 and 0.80, respectively). Importantly, increasing the moxifloxacin dose to 600 mg restored the plasma exposure both in actual patients with TB as well as in our simulations. Furthermore, we extrapolated the single dose model to pediatric populations (P/O AUC ratios, 1.04-1.52) and the multiple dose model to children with TB (P/O AUC ratio, 1.51). In conclusion, our combined approach resulted in new insights into moxifloxacin pharmacokinetics and accurate simulations of moxifloxacin exposure with and without rifampicin. Finally, various knowledge gaps were identified, which may be considered as avenues for further physiologically based pharmacokinetic refinement.

Increased bactericidal activity but dose-limiting intolerability at 50 mg·kg-1 rifampicin

Background

Accumulating data indicate that higher rifampicin doses are more effective and shorten tuberculosis (TB) treatment duration. This study evaluated the safety, tolerability, pharmacokinetics, and 7- and 14-day early bactericidal activity (EBA) of increasing doses of rifampicin. Here we report the results of the final cohorts of PanACEA HIGHRIF1, a dose escalation study in treatment-naive adult smear-positive patients with TB.

Methods

Patients received, in consecutive cohorts, 40 or 50 mg·kg⁻¹ rifampicin once daily in monotherapy (day 1–7), supplemented with standard dose isoniazid, pyrazinamide and ethambutol between days 8 and 14.

Results

In the 40 mg·kg⁻¹ cohort (n=15), 13 patients experienced a total of 36 adverse events during monotherapy, resulting in one treatment discontinuation. In the 50 mg·kg⁻¹ cohort (n=17), all patients experienced adverse events during monotherapy, 93 in total; 11 patients withdrew or stopped study medication. Adverse events were mostly mild/moderate and tolerability rather than safety related, i.e. gastrointestinal disorders, pruritis, hyperbilirubinaemia and jaundice. There was a more than proportional increase in the rifampicin geometric mean area under the plasma concentration–time curve from time 0 to 12 h (AUC_0–24 h) for 50 mg·kg⁻¹ compared with 40 mg·kg⁻¹; 571 (range 320–995) versus 387 (range 201–847) mg·L⁻¹·h, while peak exposures saw proportional increases. Protein-unbound exposure after 50 mg·kg⁻¹ (11% (range 8–17%)) was comparable with lower rifampicin doses. Rifampicin exposures and bilirubin concentrations were correlated (Spearman's ρ=0.670 on day 3, p<0.001). EBA increased considerably with dose, with the highest seen after 50 mg·kg⁻¹: 14-day EBA −0.427 (95% CI −0.500– −0.355) log₁₀CFU·mL⁻¹·day⁻¹.

Conclusion

Although associated with an increased bactericidal effect, the 50 mg·kg⁻¹ dose was not well tolerated. Rifampicin at 40 mg·kg⁻¹ was well tolerated and therefore selected for evaluation in a phase IIc treatment-shortening trial.

While bactericidal activity continues to increase with dose, for the first time we identified dose-limiting intolerability for rifampicin dosed at 50 mg·kg⁻¹; 40 mg·kg⁻¹ seems the optimal tolerable dose for evaluation in TB treatment-shortening trialshttps://bit.ly/37dUIuB

Clofazimine as a Treatment for Multidrug-Resistant Tuberculosis: A Review

Multidrug-resistant tuberculosis (MDR-TB) is an infectious disease caused by Mycobacterium tuberculosis which is resistant to at least isoniazid and rifampicin. This disease is a worldwide threat and complicates the control of tuberculosis (TB). Long treatment duration, a combination of several drugs, and the adverse effects of these drugs are the factors that play a role in the poor outcomes of MDR-TB patients. There have been many studies with repurposed drugs to improve MDR-TB outcomes, including clofazimine. Clofazimine recently moved from group 5 to group B of drugs that are used to treat MDR-TB. This drug belongs to the riminophenazine class, which has lipophilic characteristics and was previously discovered to treat TB and approved for leprosy. This review discusses the role of clofazimine as a treatment component in patients with MDR-TB, and the drug’s properties. In addition, we discuss the efficacy, safety, and tolerability of clofazimine for treating MDR-TB. This study concludes that the clofazimine-containing regimen has better efficacy compared with the standard one and is also well-tolerated. Clofazimine has the potential to shorten the duration of MDR-TB treatment.

Clofazimine pharmacokinetics in patients with TB: dosing implications

BACKGROUND

Clofazimine is in widespread use as a key component of drug-resistant TB regimens, but the recommended dose is not evidence based. Pharmacokinetic data from relevant patient populations are needed to inform dose optimization.

OBJECTIVES

To determine clofazimine exposure, evaluate covariate effects on variability, and simulate exposures for different dosing strategies in South African TB patients.

PATIENTS AND METHODS

Clinical and pharmacokinetic data were obtained from participants with pulmonary TB enrolled in two studies with intensive and sparse sampling for up to 6 months. Plasma concentrations were measured by LC-MS/MS and interpreted with non-linear mixed-effects modelling. Body size descriptors and other potential covariates were tested on pharmacokinetic parameters. We simulated different dosing regimens to safely shorten time to average daily concentration above a putative target concentration of 0.25 mg/L.

RESULTS

We analysed 1570 clofazimine concentrations from 139 participants; 79 (57%) had drug-resistant TB and 54 (39%) were HIV infected. Clofazimine pharmacokinetics were well characterized by a three-compartment model. Clearance was 11.5 L/h and peripheral volume 10 500 L for a typical participant. Lower plasma exposures were observed in women during the first few months of treatment, explained by higher body fat fraction. Model-based simulations estimated that a loading dose of 200 mg daily for 2 weeks would achieve average daily concentrations above a target efficacy concentration 37 days earlier in a typical TB participant.

CONCLUSIONS

Clofazimine was widely distributed with a long elimination half-life. Disposition was strongly influenced by body fat content, with potential dosing implications for women with TB.

Influence of Single Nucleotide Polymorphisms on Rifampin Pharmacokinetics in Tuberculosis Patients

Rifampin (RF) is metabolized in the liver into an active metabolite 25-desacetylrifampin and excreted almost equally via biliary and renal routes. Various influx and efflux transporters influence RF disposition during hepatic uptake and biliary excretion. Evidence has also shown that Vitamin D deficiency (VDD) and Vitamin D receptor (VDR) polymorphisms are associated with tuberculosis (TB). Hence, genetic polymorphisms of metabolizing enzymes, drug transporters and/or their transcriptional regulators and VDR and its pathway regulators may affect the pharmacokinetics of RF. In this narrative review, we aim to identify literature that has explored the influence of single nucleotide polymorphisms (SNPs) of genes encoding drug transporters and their transcriptional regulators (SLCO1B1, ABCB1, PXR and CAR), metabolizing enzymes (CES1, CES2 and AADAC) and VDR and its pathway regulators (VDR, CYP27B1 and CYP24A1) on plasma RF concentrations in TB patients on antitubercular therapy. Available reports to date have shown that there is a lack of any association of ABCB1, PXR, CAR, CES1 and AADAC genetic variants with plasma concentrations of RF. Further evidence is required from a more comprehensive exploration of the association of SLCO1B1, CES2 and Vitamin D pathway gene variants with RF pharmacokinetics in distinct ethnic groups and a larger population to reach conclusive information.

Validation of Pharmacological Protocols for Targeted Inhibition of Canalicular MRP2 Activity in Hepatocytes Using [99mTc]mebrofenin Imaging in Rats

The multidrug resistance-associated protein 2 (MRP2) mediates the biliary excretion of drugs and metabolites. [^99mTc]mebrofenin may be employed as a probe for hepatic MRP2 activity because its biliary excretion is predominantly mediated by this transporter. As the liver uptake of [^99mTc]mebrofenin depends on organic anion-transporting polypeptide (OATP) activity, a safe protocol for targeted inhibition of hepatic MRP2 is needed to study the intrinsic role of each transporter system. Diltiazem (DTZ) and cyclosporin A (CsA) were first confirmed to be potent MRP2 inhibitors in vitro. Dynamic acquisitions were performed in rats (n = 5-6 per group) to assess the kinetics of [^99mTc]mebrofenin in the liver, intestine and heart-blood pool after increasing doses of inhibitors. Their impact on hepatic blood flow was assessed using Doppler ultrasound (n = 4). DTZ (s.c., 10 mg/kg) and low-dose CsA (i.v., 0.01 mg/kg) selectively decreased the transfer of [^99mTc]mebrofenin from the liver to the bile (k₃). Higher doses of DTZ and CsA did not further decrease k₃ but dose-dependently decreased the uptake (k₁) and backflux (k₂) rate constants between blood and liver. High dose of DTZ (i.v., 3 mg/kg) but not CsA (i.v., 5 mg/kg) significantly decreased the blood flow in the portal vein and hepatic artery. Targeted pharmacological inhibition of hepatic MRP2 activity can be achieved in vivo without impacting OATP activity and liver blood flow. Clinical studies are warranted to validate [^99mTc]mebrofenin in combination with low-dose CsA as a novel substrate/inhibitor pair to untangle the role of OATP and MRP2 activity in liver diseases.

Safety implications of combined antiretroviral and anti-tuberculosis drugs

Introduction: Antiretroviral and anti-tuberculosis (TB) drugs are often co-administered in people living with HIV (PLWH). Early initiation of antiretroviral therapy (ART) during TB treatment improves survival in patients with advanced HIV disease. However, safety concerns related to clinically significant changes in drug exposure resulting from drug-drug interactions, development of overlapping toxicities and specific challenges related to co-administration during pregnancy represent barriers to successful combined treatment for HIV and TB.Areas covered: Pharmacokinetic interactions of different classes of ART when combined with anti-TB drugs used for sensitive-, drug-resistant (DR) and latent TB are discussed. Overlapping drug toxicities, implications of immune reconstitution inflammatory syndrome (IRIS), safety in pregnancy and research gaps are also explored.Expert opinion: New antiretroviral and anti-tuberculosis drugs have been recently introduced and international guidelines updated. A number of effective molecules and clinical data are now available to build treatment regimens for PLWH with latent or active TB. Adopting a systematic approach that also takes into account the need for individualized variations based on the available evidence is the key to successfully integrate ART and TB treatment and improve treatment outcomes.

A Pharmacology Perspective of Simultaneous Tuberculosis and Hepatitis C Treatment

Tuberculosis (TB) and hepatitis C virus (HCV) infection are both major public health problems. Despite high rates of co-infection there is scarce literature addressing the convergence of the two diseases. One particularly unexplored area is the potential for simultaneous treatment of TB and HCV which would allow for leveraging an extensive global TB treatment infrastructure to help scale up HCV treatment. We review the drug metabolism of anti-TB and HCV drugs and the known and potential drug-drug interactions between recommended HCV regimens and individual anti-TB drugs. Rifampin is the only anti-TB drug to have been formally studied for potential drug interactions with anti-HCV direct-acting antivirals (DAAs) and existing data precludes these combinations. However, based on known pathways of drug metabolism and enzyme effects, the combination of HCV DAA regimens with all other anti-TB drugs may be feasible. Pharmacokinetic studies are needed next to help move co treatment regimens forward for clinical use among patients coinfected with TB and HCV.

Potential drug-drug interactions between antiretroviral therapy and treatment regimens for multi-drug resistant tuberculosis: Implications for HIV care of MDR-TB co-infected individuals

HIV-positive TB co-infected patients are at increased risk of multidrug-resistant (MDR)-TB compared to HIV-negative patients. Co-treatment of MDR-TB and HIV is common particularly in Sub-Saharan Africa where the co-morbidity is endemic. We discuss potential cellular metabolic pathway-mediated drug-drug interactions and the possible effect on HIV treatment outcomes of commonly prescribed antiretroviral therapy.

Rifampin Induces Expression of P-glycoprotein on the THP1 Cell-Derived Macrophages, Causing Decrease Intramacrophage Concentration of Prothionamide

Rifampin (RIF) has been widely used for the treatment of bacterial infections, including tuberculosis (TB). Treatment of drug-resistant TB is a global problem because of reduced drug efficacy. The present study determined the effect of RIF on MDR1 gene (P-glycoprotein, P-gp) expression in THP1 macrophages and analyzed the intracellular concentration of the anti-TB drug prothionamide in the presence of RIF. RIF treatment significantly induced MDR1 protein and mRNA levels in phorbol 12-myristate 13-acetate-stimulated THP1 macrophages (p < 0.001 and 0.01, respectively). The pregnane X receptor inhibitors resveratrol and ketoconazole significantly suppressed RIF-induced P-gp expression in THP1 macrophages (p < 0.05). RIF-treated THP1 macrophages also exhibited strong efflux of P-gp substrate, resulting in a reduced intracellular concentration of rhodamine-123 and prothionamide (p < 0.01 and 0.05, respectively). By contrast, the P-gp inhibitor cyclosporine A significantly increased intracellular concentration of rhodamine-123 and prothionamide (p < 0.001 and 0.05, respectively). The present results suggest that the usage of RIF together with P-gp-substrate drugs to treat TB may lead to deteriorated treatment efficacy because of the lower intracellular drug concentration. Further studies would be necessary to know the influence of RIF-induced P-gp induction on the treatment outcome of patients with TB.

Intensified antibiotic treatment of tuberculosis meningitis

INTRODUCTION

Meningitis is the most severe manifestation of tuberculosis, resulting in death or disability in over 50% of those affected, with even higher morbidity and mortality among patients with HIV or drug resistance. Antimicrobial treatment of Tuberculous meningitis (TBM) is similar to treatment of pulmonary tuberculosis, although some drugs show poor central nervous system penetration. Therefore, intensification of antibiotic treatment may improve TBM treatment outcomes. Areas covered: In this review, we address three main areas: available data for old and new anti-tuberculous agents; intensified treatment in specific patient groups like HIV co-infection, drug-resistance, and children; and optimal research strategies. Expert commentary: There is good evidence from preclinical, clinical, and modeling studies to support the use of high-dose rifampicin in TBM, likely to be at least 30 mg/kg. Higher dose isoniazid could be beneficial, especially in rapid acetylators. The role of other first and second line drugs is unclear, but observational data suggest that linezolid, which has good brain penetration, may be beneficial. We advocate the use of molecular pharmacological approaches, physiologically based pharmacokinetic modeling and pharmacokinetic-pharmacodynamic studies to define optimal regimens to be tested in clinical trials. Exciting data from recent studies hold promise for improved regimens and better clinical outcomes in future.

A new therapeutic combination for osteosarcoma: Gemcitabine and Clofazimine co-loaded liposomal formulation

Osteosarcoma is the most common cancer in bone. Drug resistance is a challenge of current treatments that needs to be improved with novel treatment strategies. In this research, a new dual drug delivery system was developed with Gemcitabine (GEM) and Clofazimine (CLF) co-loaded liposome formulations. GEM is a well-known anticancer agent and CLF is a leprostatic and anti-inflammatory drug recently recognized as effective on cancer. GEM and CLF co-loaded liposomal formulation was achieved with compartmentalization as hydrophilic GEM being in core and lipophilic CLF sequestering in lipid-bilayer. Liposomes had high encapsulation efficiency (above 90%, GEM and above 80%, CLF). CLF release was enhanced while GEM release was slowed down in co-loaded liposomes compared to single cases. GEM/CLF co-loaded liposomes significantly enhanced cytotoxicity than GEM or CLF loaded liposomes on osteosarcoma cell line. CLF and GEM had synergistic effect (CI < 1). Results of flow cytometry showed higher apoptotic cell ratio, caspase-3 activity, mitochondrial membrane depolarized cells' ratio for GEM/CLF co-loaded liposome treatments than other liposomes. Cytotoxicity of CLF on bone cancer cells and also its synergistic effect with GEM on osteosarcoma is reported for the first time with this study. CLF's loading with GEM into liposome was also a new approach for enhancement of anticancer effect on Saos-2 cells. Therefore, GEM/CLF co-loaded liposomal delivery system is proposed as a novel approach for treatment of osteosarcoma.

Effect of Rifampicin on the Distribution of [11C]Erlotinib to the Liver, a Translational PET Study in Humans and in Mice

Organic anion-transporting polypeptides (OATPs) mediate the uptake of various drugs from blood into the liver in the basolateral membrane of hepatocytes. Positron emission tomography (PET) is a potentially powerful tool to assess the activity of hepatic OATPs in vivo, but its utility critically depends on the availability of transporter-selective probe substrates. We have shown before that among the three OATPs expressed in hepatocytes (OATP1B1, OATP1B3, and OATP2B1), [¹¹C]erlotinib is selectively transported by OATP2B1. In contrast to OATP1B1 and OATP1B3, OATP2B1 has not been thoroughly explored yet, and no specific probe substrates are currently available. To assess if the prototypical OATP inhibitor rifampicin can inhibit liver uptake of [¹¹C]erlotinib in vivo, we performed [¹¹C]erlotinib PET scans in six healthy volunteers without and with intravenous pretreatment with rifampicin (600 mg). In addition, FVB mice underwent [¹¹C]erlotinib PET scans without and with concurrent intravenous infusion of high-dose rifampicin (100 mg/kg). Rifampicin caused a moderate reduction in the liver distribution of [¹¹C]erlotinib in humans, while a more pronounced effect of rifampicin was observed in mice, in which rifampicin plasma concentrations were higher than in humans. In vitro uptake experiments in an OATP2B1-overexpressing cell line indicated that rifampicin inhibited OATP2B1 transport of [¹¹C]erlotinib in a concentration-dependent manner with a half-maximum inhibitory concentration of 72.0 ± 1.4 μM. Our results suggest that rifampicin-inhibitable uptake transporter(s) contributed to the liver distribution of [¹¹C]erlotinib in humans and mice and that [¹¹C]erlotinib PET in combination with rifampicin may be used to measure the activity of this/these uptake transporter(s) in vivo. Furthermore, our data suggest that a standard clinical dose of rifampicin may exert in vivo a moderate inhibitory effect on hepatic OATP2B1.

Characterization of new, efficient Mycobacterium tuberculosis topoisomerase-I inhibitors and their interaction with human ABC multidrug transporters

Drug resistant tuberculosis (TB) is a major worldwide health problem. In addition to the bacterial mechanisms, human drug transporters limiting the cellular accumulation and the pharmacological disposition of drugs also influence the efficacy of treatment. Mycobacterium tuberculosis topoisomerase-I (MtTopo-I) is a promising target for antimicrobial treatment. In our previous work we have identified several hit compounds targeting the MtTopo-I by in silico docking. Here we expand the scope of the compounds around three scaffolds associated with potent MtTopo-I inhibition. In addition to measuring the effect of newly generated compounds on MtTopo-I activity, we characterized the compounds’ antimicrobial activity, toxicity in human cells, and interactions with human multidrug transporters. Some of the newly developed MtTopo-I inhibitors have strong antimicrobial activity and do not harm mammalian cells. Moreover, our studies revealed significant human ABC drug transporter interactions for several MtTopo-I compounds that may modify their ADME-Tox parameters and cellular effects. Promising new drug candidates may be selected based on these studies for further anti-TB drug development.

Impact of Clofazimine Dosing on Treatment Shortening of the First-Line Regimen in a Mouse Model of Tuberculosis

The antileprosy drug clofazimine was recently repurposed as part of a newly endorsed short-course regimen for multidrug-resistant tuberculosis. It also enables significant treatment shortening when added to the first-line regimen for drug-susceptible tuberculosis in a mouse model. However, clofazimine causes dose- and duration-dependent skin discoloration in patients, and the optimal clofazimine dosing strategy in the context of the first-line regimen is unknown. We utilized a well-established mouse model to systematically address the impacts of duration, dose, and companion drugs on the treatment-shortening activity of clofazimine in the first-line regimen. In all studies, the primary outcome was relapse-free cure (culture-negative lungs) 6 months after stopping treatment, and the secondary outcome was bactericidal activity, i.e., the decline in the lung bacterial burden during treatment. Our findings indicate that clofazimine activity is most potent when coadministered with first-line drugs continuously throughout treatment and that equivalent treatment-shortening results are obtained with half the dose commonly used in mice. However, our studies also suggest that clofazimine at low exposures may have negative impacts on treatment outcomes, an effect that was evident only after the first 3 months of treatment. These data provide a sound evidence base to inform clofazimine dosing strategies to optimize the antituberculosis effect while minimizing skin discoloration. The results also underscore the importance of conducting long-term studies to allow the full evaluation of drugs administered in combination over long durations.

Aconitum alkaloids, the major components of Aconitum species, affect expression of multidrug resistance-associated protein 2 and breast cancer resistance protein by activating the Nrf2-mediated signalling pathway

BACKGROUND

Aconitum alkaloids from Aconitum species are often used to treat arthritis and rheumatic diseases but have the drawback of high toxicity. Identifying their pharmacokinetic behaviour is important for the safe clinical application of Aconitum species. Efflux transporters (ETs), including P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP), have important functions in regulating the pharmacokinetic behaviours of drugs and in herb-herb or herb-drug interactions (HDIs). The Aconitum alkaloids regulate P-gp expression and function, but their effects on MRP2 and BCRP expression remain unknown.

PURPOSE

To determine the effects of three Aconitum alkaloids, aconitine (AC), benzoylaconine (BAC), and aconine, on MRP2 and BCRP.

METHODS

The levels of the protein and mRNA expression of MRP2 and BCRP in vivo and in vitro were measured via Western blotting and real-time PCR, respectively. Fluorescence signals of MRP2 and BCRP were detected via confocal fluorescence microscopy. A reporter assay using HepG2-C8 cells, which were generated by transfecting plasmids containing the antioxidant response element (ARE)-luciferin gene into HepG2 cells, was used to examine the ARE-luciferin activity. The transport activities of MRP2 and BCRP were tested via flow cytometry using substrate probes.

RESULTS

The Aconitum alkaloids significantly up-regulated MRP2 and BCRP expression, accompanied by a marked increase in nuclear factor E2-related factor-2 (Nrf2) expression in the jejunum, ileum, and colon of FVB mice, in the order AC < BAC < aconine. In the in vitro model, the Aconitum alkaloids increased MRP2 and BCRP expression in Caco-2 and LS174T cells, in the order AC < BAC < aconine. Additionally, these alkaloids promoted the translocation of Nrf2 from the cytoplasm to the nucleus and significantly increased ARE-luciferin activity in HepG2-C8 cells. Luteolin, a potent inhibitor of Nrf2, markedly prevented MRP2 and BCRP expression from being induced by the three Aconitum alkaloids. The efflux activity of MRP2 was also significantly increased in cells receiving the same treatment.

CONCLUSIONS

The tested Aconitum alkaloids significantly increased the expression of MRP2 and BCRP by activating the Nrf2-mediated signalling pathway and enhanced the efflux activity of MRP2. The potential for herb-herb interactions or HDIs exists when Aconitum species are co-administered with substrate drugs that are transported via MRP2 and BCRP. Therefore, the Aconitum alkaloids may be used as quality indicators for the herbs of Aconitum species.

Intestinal Farnesoid X Receptor Activation by Pharmacologic Inhibition of the Organic Solute Transporter α-β

BACKGROUND & AIMS

The organic solute transporter α-β (OSTα-OSTβ) mainly facilitates transport of bile acids across the basolateral membrane of ileal enterocytes. Therefore, inhibition of OSTα-OSTβ might have similar beneficial metabolic effects as intestine-specific agonists of the major nuclear receptor for bile acids, the farnesoid X receptor (FXR). However, no OSTα-OSTβ inhibitors have yet been identified.

METHODS

Here, we developed a screen to identify specific inhibitors of OSTα-OSTβ using a genetically encoded Förster Resonance Energy Transfer (FRET)-bile acid sensor that enables rapid visualization of bile acid efflux in living cells.

RESULTS

As proof of concept, we screened 1280 Food and Drug Administration-approved drugs of the Prestwick chemical library. Clofazimine was the most specific hit for OSTα-OSTβ and reduced transcellular transport of taurocholate across Madin-Darby canine kidney epithelial cell monolayers expressing apical sodium bile acid transporter and OSTα-OSTβ in a dose-dependent manner. Moreover, pharmacologic inhibition of OSTα-OSTβ also moderately increased intracellular taurocholate levels and increased activation of intestinal FXR target genes. Oral administration of clofazimine in mice (transiently) increased intestinal FXR target gene expression, confirming OSTα-OSTβ inhibition in vivo.

CONCLUSIONS

This study identifies clofazimine as an inhibitor of OSTα-OSTβ in vitro and in vivo, validates OSTα-OSTβ as a drug target to enhance intestinal bile acid signaling, and confirmed the applicability of the Förster Resonance Energy Transfer-bile acid sensor to screen for inhibitors of bile acid efflux pathways.

The Role of Efflux Pumps in Tuberculosis Treatment and Their Promise as a Target in Drug Development: Unraveling the Black Box

Insight into drug transport mechanisms is highly relevant to the efficacious treatment of tuberculosis (TB). Major problems in TB treatment are related to the transport of antituberculosis (anti-TB) drugs across human and mycobacterial membranes, affecting the concentrations of these drugs systemically and locally. Firstly, transporters located in the intestines, liver, and kidneys all determine the pharmacokinetics and pharmacodynamics of anti-TB drugs, with a high risk of drug-drug interactions in the setting of concurrent use of antimycobacterial, antiretroviral, and antidiabetic agents. Secondly, human efflux transporters limit the penetration of anti-TB drugs into the brain and cerebrospinal fluid, which is especially important in the treatment of TB meningitis. Finally, efflux transporters located in the macrophage and Mycobacterium tuberculosis cell membranes play a pivotal role in the emergence of phenotypic tolerance and drug resistance, respectively. We review the role of efflux transporters in TB drug disposition and evaluate the promise of efflux pump inhibition from a novel holistic perspective.

Investigation of Glycochenodeoxycholate Sulfate and Chenodeoxycholate Glucuronide as Surrogate Endogenous Probes for Drug Interaction Studies of OATP1B1 and OATP1B3 in Healthy Japanese Volunteers

PURPOSE

To assess the use of glycochenodeoxycholate-3-sulfate (GCDCA-S) and chenodeoxycholate 3- or 24-glucuronide (CDCA-3G or -24G) as surrogate endogenous substrates in the investigation of drug interactions involving OATP1B1 and OATP1B3.

METHODS

Uptake of GCDCA-S and CDCA-24G was examined in HEK293 cells transfected with cDNA for OATP1B1, OATP1B3, and NTCP and in cryopreserved human hepatocytes. Plasma concentrations of bile acids and their metabolites (GCDCA-S, CDCA-3G, and CDCA-24G) were determined by LC-MS/MS in eight healthy volunteers with or without administration of rifampicin (600 mg, po).

RESULTS

GCDCA-S and CDCA-24G were substrates for OATP1B1, OATP1B3, and NTCP. The uptake of [³H]atorvastatin, GCDCA-S, and CDCA-24G by human hepatocytes was significantly inhibited by both rifampicin and pioglitazone, whereas that of taurocholate was inhibited only by pioglitazone. Rifampicin elevated plasma concentrations of GCDCA-S more than those of other bile acids. The area under the plasma concentration-time curve for GCDCA-S was 20.3 times higher in rifampicin-treated samples. CDCA-24G could be detected only in plasma from the rifampicin-treatment phase, and CDCA-3G was undetectable in both phases.

CONCLUSIONS

We identified GCDCA-S and CDCA-24G as substrates of NTCP, OATP1B1, and OATP1B3. GCDCA-S is a surrogate endogenous probe for the assessment of drug interactions involving hepatic OATP1B1 and OATP1B3.

Pharmacokinetic Interaction of Rifampicin with Oral Versus Intravenous Anticancer Drugs: Challenges, Dilemmas and Paradoxical Effects Due to Multiple Mechanisms

Since many drugs are cytochrome P450 (CYP)-3A4 substrates, it has become common practice to assess drug-drug interaction (DDI) potential with a CYP3A4 inhibitor (ketoconazole) or inducer (rifampicin) in early drug development. Such an evaluation is relevant to anticancer drugs with metabolism governed by CYP3A4. DDIs with rifampicin are complex, involving other physiological mechanisms that may impact overall pharmacokinetics. Our objective was to study and delineate such mechanisms for oral versus intravenous anticancer drugs. We hypothesized that DDIs between anticancer drugs and rifampicin were primarily driven by CYP3A4 induction. This hypothesis was proven for the oral anticancer drugs; however, in some cases, other intrinsic mechanisms such as P-glycoprotein (Pgp)/UDP glucuronosyl transferase (UGT) induction and transporter inhibition may have played an important role alongside the induced CYP3A4 enzymes. The hypothesis that CYP3A4 induction would decrease drug exposure appeared paradoxical for intravenous romidepsin and-to a somewhat lesser extent-for cabazitaxel. In light of this dilemma in the interpretation of the pharmacokinetic data with rifampicin, several questions require further consideration. Given the complexity and paradoxical effects arising with DDIs with rifampicin, the continued preference for rifampicin as CYP3A4 inducer needs immediate re-appraisal.

Substrate and method dependent inhibition of three ABC-transporters (MDR1, BCRP, and MRP2)

Drug transport and drug-drug interactions (DDI) with human ABC transporters are generally investigated in mammalian cell lines or inverted membrane vesicles from insect cells (Sf9) overexpressing the transporter of interest. In this study, we instead used membrane vesicles from human embryonic kidney cells (HEK293) overexpressing wild type MDR1/Pgp (ABCB1), BCRP (ABCG2), and MRP2 (ABCC2) with the aim to study the concentration dependent inhibition of shared and prototypic probe substrates. We first investigated 15 substrates and identified estrone-17-beta-glucorinide (E17G) as shared substrate. Nine specific and general inhibitors were then studied using E17G and prototypic probe substrates. The results were compared with those previously obtained in Sf9 vesicles and cell lines of canine (MDCKII) and human (Saos-2) origin. For the majority of inhibitors, K_i values differed <10-fold between E17G and probe substrates. Significant differences in K_i values were observed for about one third of the inhibitors. The transport inhibition potencies in HEK293 vesicles were in good agreement with those obtained in Sf9 vesicles. Large differences were found in the inhibition potencies observed in the vesicular systems compared to the cellular systems. Nevertheless, the rank order correlations between the different experimental systems were generally good. Our study provides further information on substrate dependent inhibition of ABC-transporters, and suggests that simple ranking of compounds can be used as a tier one approach to bridge results obtained in different experimental systems.

Activity of moxifloxacin and linezolid against Mycobacterium tuberculosis in combination with potentiator drugs verapamil, timcodar, colistin and SQ109

Current treatment for tuberculosis (TB) is complicated by the emergence of multidrug resistant TB (MDR-TB). As a result, there is an urgent need for new powerful anti-TB regimens and novel strategies. In this study, we aimed to potentiate a moxifloxacin + linezolid backbone as treatment for MDR-TB with the efflux pump inhibitors verapamil and timcodar as well as with drugs that act on mycobacterial cell wall stability such as colistin and SQ109. Using a time-kill kinetics assay, the activities of moxifloxacin, linezolid, verapamil, timcodar, colistin and SQ109 as single drugs against Mycobacterium tuberculosis were evaluated. In addition, the activity of the moxifloxacin + linezolid backbone in combination with one of the potentiator drugs was assessed. As little as 0.125 mg/L moxifloxacin achieved 99% killing of M. tuberculosis after 6 days of exposure. Linezolid showed moderate killing but 99% killing was not achieved. Verapamil, timcodar and colistin only resulted in killing with the highest concentrations tested but 99% killing was not achieved. SQ109 resulted in complete elimination after 1 day of exposure to 256 mg/L and in 99% elimination after 6 days of exposure to 1 mg/L. Furthermore, colistin added to the moxifloxacin + linezolid backbone resulted in increased elimination, whereas verapamil, timcodar and SQ109 showed no added value to the backbone. This finding that colistin potentiates the activity of the moxifloxacin + linezolid backbone against M. tuberculosis suggests its potential role in further studies on the applicability of a moxifloxacin + linezolid treatment of MDR-TB.

Mechanisms of action and therapeutic efficacies of the lipophilic antimycobacterial agents clofazimine and bedaquiline

Drug-resistant (DR)-TB is the major challenge confronting the global TB control programme, necessitating treatment with second-line anti-TB drugs, often with limited therapeutic efficacy. This scenario has resulted in the inclusion of Group 5 antibiotics in various therapeutic regimens, two of which promise to impact significantly on the outcome of the therapy of DR-TB. These are the 're-purposed' riminophenazine, clofazimine, and the recently approved diarylquinoline, bedaquiline. Although they differ structurally, both of these lipophilic agents possess cationic amphiphilic properties that enable them to target and inactivate essential ion transporters in the outer membrane of Mycobacterium tuberculosis. In the case of bedaquiline, the primary target is the key respiratory chain enzyme F₁/F₀-ATPase, whereas clofazimine is less selective, apparently inhibiting several targets, which may underpin the extremely low level of resistance to this agent. This review is focused on similarities and differences between clofazimine and bedaquiline, specifically in respect of molecular mechanisms of antimycobacterial action, targeting of quiescent and metabolically active organisms, therapeutic efficacy in the clinical setting of DR-TB, resistance mechanisms, pharmacodynamics, pharmacokinetics and adverse events.

Inhibitory Potential of Antifungal Drugs on ATP-Binding Cassette Transporters P-Glycoprotein, MRP1 to MRP5, BCRP, and BSEP

Inhibition of ABC transporters is a common mechanism underlying drug-drug interactions (DDIs). We determined the inhibitory potential of antifungal drugs currently used for invasive fungal infections on ABC transporters P-glycoprotein (P-gp), MRP1 to MRP5, BCRP, and BSEP in vitro Membrane vesicles isolated from transporter-overexpressing HEK 293 cells were used to investigate the inhibitory potential of antifungal drugs (250 μM) on transport of model substrates. Concentration-inhibition curves were determined if transport inhibition was >60%. Fifty percent inhibitory concentrations (IC50s) for P-gp and BCRP were both 2 μM for itraconazole, 5 and 12 μM for hydroxyitraconazole, 3 and 6 μM for posaconazole, and 3 and 11 μM for isavuconazole, respectively. BSEP was strongly inhibited by itraconazole and hydroxyitraconazole (3 and 17 μM, respectively). Fluconazole and voriconazole did not inhibit any transport for >60%. Micafungin uniquely inhibited all transporters, with strong inhibition of MRP4 (4 μM). Anidulafungin and caspofungin showed strong inhibition of BCRP (7 and 6 μM, respectively). Amphotericin B only weakly inhibited BCRP-mediated transport (127 μM). Despite their wide range of DDIs, azole antifungals exhibit selective inhibition on efflux transporters. Although echinocandins display low potential for clinically relevant DDIs, they demonstrate potent in vitro inhibitory activity. This suggests that inhibition of ABC transporters plays a crucial role in the inexplicable (non-cytochrome P450-mediated) DDIs with antifungal drugs.