Pharmacologic Activation of STING in the Bladder Induces Potent Antitumor Immunity in Non-Muscle Invasive Murine Bladder Cancer.

Stimulator of interferon genes (STING) is an innate immune receptor activated by natural or synthetic agonists to elicit antitumoral immune response via type I IFNs and other inflammatory cytokines. Bacillus Calmette-Guerin (BCG) is the standard of care as intravesical therapy for patients with high-risk non-muscle invasive bladder cancer (NMIBC). There are limited options available for patients with NMIBC who developed BCG unresponsiveness. In this study, we characterized in vitro and in vivo antitumor effects of E7766, a macrocyle-bridged STING agonist, via intravesical instillation in two syngeneic orthotopic murine NMIBC tumor models resistant to therapeutic doses of BCG and anti-PD-1 agents. E7766 bound to recombinant STING protein with a Kd value of 40 nmol/L and induced IFNß expression in primary human peripheral blood mononuclear cells harboring any of seven major STING genotypes with EC50 values of 0.15 to 0.79 µmol/L. Intravesical E7766 was efficacious in both NMIBC models with induction of effective immunologic memory in the treated animals. Pharmacologic activation of the STING pathway in the bladder resulted in IFN pathway activation, infiltration of T cells and natural killer (NK) cells, dendritic cell activation, and antigen presentation in bladder epithelium, leading to the antitumor activity and immunity. In addition, measurements of the pharmacodynamic markers, Ifnß1 and CXCL10, in bladder, urine, and plasma, and of STING pathway intactness in cancer cells, supported this mode of action. Taken together, our studies reveal an antitumor immune effect of pharmacologic activation of the STING pathway in bladder epithelium and thus provide a rationale for subsequent clinical studies in patients with NMIBC.

Prediction of Transporter-Mediated Drug-Drug Interactions and Phenotyping of Hepatobiliary Transporters Involved in the Clearance of E7766, a Novel Macrocycle-Bridged Dinucleotide.

E7766 represents a novel class of macrocycle-bridged dinucleotides and is under clinical development for immuno-oncology. In this report, we identified mechanism of systemic clearance E7766 and investigated the hepatobiliary transporters involved in the disposition of E7766 and potential drug interactions of E7766 as a victim of organic anion-transporting polypeptide (OATP) inhibitors. In bile-duct cannulated rats and dogs, E7766 was mainly excreted unchanged in bile (>80%) and to a lesser extent in urine (<20%). Sandwich-cultured human hepatocytes (SCHHs), transfected cells, and vesicles were used to phenotype the hepatobiliary transporters involved in the clearance of E7766. SCHH data showed temperature-dependent uptake of E7766 followed by active biliary secretion. In vitro transport assays using transfected cells and membrane vesicles confirmed that E7766 was a substrate of OATP1B1, OATP1B3, and multidrug resistance-associated protein 2. Phenotyping studies suggested predominant contribution of OATP1B3 over OATP1B1 in the hepatic uptake of E7766. Studies in OATP1B1/1B3 humanized mice showed that plasma exposure of E7766 increased 4.5-fold when coadministered with Rifampicin. Physiologically based pharmacokinetic models built upon two independent bottom-up approaches predicted elevation of E7766 plasma exposure when administered with Rifampicin, a clinical OATP inhibitor. In conclusion, we demonstrate that OATP-mediated hepatic uptake is the major contributor to the clearance of E7766, and inhibition of OATP1B may increase its systemic exposure. Predominant contribution of OATP1B3 in the hepatic uptake of E7766 was observed, suggesting polymorphisms in OATP1B1 would be unlikely to cause variability in the exposure of E7766. SIGNIFICANCE STATEMENT: Understanding the clearance mechanisms of new chemical entities is critical to predicting human pharmacokinetics and drug interactions. A physiologically based pharmacokinetic model that incorporated parameters from mechanistic in vitro and in vivo experiments was used to predict pharmacokinetics and drug interactions of E7766, a novel dinucleotide drug. The findings highlighted here may shed a light on the pharmacokinetic profile and transporter-mediated drug interaction propensity of other dinucleotide drugs.

Physiologically-Based Pharmacokinetic Modeling in Renal and Hepatic Impairment Populations: A Pharmaceutical Industry Perspective.

The predictive performance of physiologically-based pharmacokinetics (PBPK) models for pharmacokinetics (PK) in renal impairment (RI) and hepatic impairment (HI) populations was evaluated using clinical data from 29 compounds with 106 organ impairment study arms were collected from 19 member companies of the International Consortium for Innovation and Quality in Pharmaceutical Development. Fifty RI and 56 HI study arms with varying degrees of organ insufficiency along with control populations were evaluated. For RI, the area under the curve (AUC) ratios of RI to healthy control were predicted within twofold of the observed ratios for > 90% (N = 47/50 arms). For HI, > 70% (N = 43/56 arms) of the hepatically impaired to healthy control AUC ratios were predicted within twofold. Inaccuracies, typically overestimation of AUC ratios, occurred more in moderate and severe HI. PBPK predictions can help determine the need and timing of organ impairment study. It may be suitable for predicting the impact of RI on PK of drugs predominantly cleared by metabolism with varying contribution of renal clearance. PBPK modeling may be used to support mild impairment study waivers or clinical study design.

First-in-human study of the PARP/tankyrase inhibitor E7449 in patients with advanced solid tumours and evaluation of a novel drug-response predictor.

BACKGROUND: This phase 1 study examined the safety, maximum-tolerated dose (MTD) and antitumour activity of E7449, a novel PARP 1/2 and tankyrase 1/2 inhibitor. METHODS: E7449 was orally administered once daily in 28-day cycles to patients with advanced solid tumours (50-800-mg doses). Archival tumour samples from consenting patients were evaluated for the expression of 414 genes in a biomarker panel (2X-121 drug-response predictor [DRP]) found to be predictive of the response to E7449 in cell lines. RESULTS: Forty-one patients were enrolled (13 pancreatic, 5 ovarian, 4 each with breast, lung or colorectal cancer and 11 with other tumour types). The most common grade ≥3 treatment-related adverse event was fatigue (n = 7, 17.1%). Five patients experienced a dose-limiting toxicity (fatigue, n = 4, 800 mg; anaphylaxis, n = 1, 600 mg) for an MTD of 600 mg. E7449 exhibited antitumour activity in solid tumours, including 2 partial responses (PRs), and stable disease (SD) in 13 patients, which was durable (>23 weeks) for 8 patients. In 13 patients, the 2X-121 DRP identified those achieving PR and durable SD. E7449 showed good tolerability, promising antitumour activity and significant concentration-dependent PARP inhibition following 50-800-mg oral dosing. CONCLUSION: The results support further clinical investigation of E7449 and its associated biomarker 2X-121 DRP. CLINICAL TRIAL REGISTRATION: www.ClinicalTrials.gov code: NCT01618136.

Physiologically-Based Pharmacokinetic Models for Evaluating Membrane Transporter Mediated Drug-Drug Interactions: Current Capabilities, Case Studies, Future Opportunities, and Recommendations.

Physiologically-based pharmacokinetic (PBPK) modeling has been extensively used to quantitatively translate in vitro data and evaluate temporal effects from drug-drug interactions (DDIs), arising due to reversible enzyme and transporter inhibition, irreversible time-dependent inhibition, enzyme induction, and/or suppression. PBPK modeling has now gained reasonable acceptance with the regulatory authorities for the cytochrome-P450-mediated DDIs and is routinely used. However, the application of PBPK for transporter-mediated DDIs (tDDI) in drug development is relatively uncommon. Because the predictive performance of PBPK models for tDDI is not well established, here, we represent and discuss examples of PBPK analyses included in regulatory submission (the US Food and Drug Administration (FDA), the European Medicines Agency (EMA), and the Pharmaceuticals and Medical Devices Agency (PMDA)) across various tDDIs. The goal of this collaborative effort (involving scientists representing 17 pharmaceutical companies in the Consortium and from academia) is to reflect on the use of current databases and models to address tDDIs. This challenges the common perceptions on applications of PBPK for tDDIs and further delves into the requirements to improve such PBPK predictions. This review provides a reflection on the current trends in PBPK modeling for tDDIs and provides a framework to promote continuous use, verification, and improvement in industrialization of the transporter PBPK modeling.

Celecoxib is a substrate of CYP2D6: Impact on celecoxib metabolism in individuals with CYP2C9*3 variants.

Celecoxib was characterized as a substrate of human cytochrome P450 (CYP) 2D6 in vitro. In recombinant CYP2D6, celecoxib hydroxylation showed atypical substrate inhibition kinetics with apparent Km, Ki, and Vmax of 67.2 µM, 12.6 µM, and 1.33 µM/min, respectively. In human liver microsomes (HLMs), a concentration-dependent inhibition of celecoxib hydroxylation by quinidine was observed after CYP2C9 and CYP3A4 were inhibited. In individual HLMs with variable CYP2D6 activities, a significant correlation was observed between celecoxib hydroxylation and CYP2D6-selective dextromethorphan O-demethylation when CYP2C9 and CYP3A4 activities were suppressed (r = 0.97, P < 0.0001). Molecular modeling showed two predominant docking modes of celecoxib with CYP2D6, resulting in either a substrate or an inhibitor. A second allosteric binding antechamber, which stabilized the inhibition mode, was revealed. Modeling results were consistent with the observed substrate inhibition kinetics. Using HLMs from individual donors, the relative contribution of CYP2D6 to celecoxib metabolism was found to be highly variable and dependent on CYP2C9 genotypes, ranging from no contribution in extensive metabolizers with CYP2C9*1*1 genotype to approximately 30% in slow metabolizers with allelic variants CYP2C9*1*3 and CYP2C9*3*3. These results demonstrate that celecoxib may become a potential victim of CYP2D6-associated drug-drug interactions, particularly in individuals with reduced CYP2C9 activity.

Application of Micropatterned Cocultured Hepatocytes to Evaluate the Inductive Potential and Degradation Rate of Major Xenobiotic Metabolizing Enzymes.

Long-term coculture models of hepatocytes are promising tools to study drug transport, clearance, and hepatoxicity. In this report we compare the basal expression of drug disposition genes and the inductive response of prototypical inducers (rifampin, phenobarbital, phenytoin) in hepatocyte two-dimensional monocultures and the long-term coculture model (HepatoPac). All the inducers used in the study increased the expression and activity of CYP3A4, CYP2B6 and CYP2C enzymes in the HepatoPac cultures. The coculture model showed a consistent and higher induction of CYP2C enzymes compared with the monocultures. The EC50 of rifampin for CYP3A4 and CYP2C9 was up to 10-fold lower in HepatoPac than the monocultures. The EC50 of rifampin calculated from the clinical drug interaction studies correlated well with the EC50 observed in the HepatoPac cultures. Owing to the long-term stability of the HepatoPac cultures, we were able to directly measure a half-life (t1/2) for both CYP3A4 and CYP2B6 using the depletion kinetics of mRNA and functional activity. The t1/2 for CYP3A4 mRNA was 26 hours and that for the functional protein was 49 hours. The t1/2 of CYP2B6 was 38 hours (mRNA) and 68 hours (activity), which is longer than CYP3A4 and shows the differential turnover of these two proteins. This is the first study to our knowledge to report the turnover rate of CYP2B6 in human hepatocytes. The data presented here demonstrate that the HepatoPac cultures have the potential to be used in long-term culture to mimic complex clinical scenarios.

Single B-cell deconvolution of peanut-specific antibody responses in allergic patients.

BACKGROUND: The frequencies, cellular phenotypes, epitope specificity, and clonal diversity of allergen-specific B cells in patients with food allergy are not fully understood but are of major pathogenic and therapeutic significance. OBJECTIVE: We sought to characterize peanut allergen-specific B-cell populations and the sequences and binding activities of their antibodies before and during immunotherapy. METHODS: B cells binding fluorescently labeled Ara h 1 or Ara h 2 were phenotyped and isolated by means of flow cytometric sorting from 18 patients at baseline and 13 patients during therapy. Fifty-seven mAbs derived from allergen-binding single B cells were evaluated by using ELISA, Western blotting, and peptide epitope mapping. Deep sequencing of the B-cell repertoires identified additional members of the allergen-specific B-cell clones. RESULTS: Median allergen-binding B-cell frequencies were 0.0097% (Ara h 1) or 0.029% (Ara h 2) of B cells in baseline blood from allergic patients and approximately 3-fold higher during immunotherapy. Five of 57 allergen-specific cells belonged to clones containing IgE-expressing members. Almost all allergen-specific antibodies were mutated, and binding to both conformational and linear allergen epitopes was detected. Increasing somatic mutation of IgG4 members of a clone was seen in immunotherapy, whereas IgE mutation levels in the clone did not increase. CONCLUSION: Most peanut allergen-binding B cells isolated by means of antigen-specific flow sorting express mutated and isotype-switched antibodies. Immunotherapy increases their frequency in the blood, and even narrowly defined allergen epitopes are recognized by numerous distinct B-cell clones in a patient. The results also suggest that oral immunotherapy can stimulate somatic mutation of allergen-specific IgG4.

Discovery and Characterization of a Water-Soluble Prodrug of a Dual Inhibitor of Bacterial DNA Gyrase and Topoisomerase IV.

Benzimidazole 1 is the lead compound resulting from an antibacterial program targeting dual inhibitors of bacterial DNA gyrase and topoisomerase IV. With the goal of improving key drug-like properties, namely, the solubility and the formulability of 1, an effort to identify prodrugs was undertaken. This has led to the discovery of a phosphate ester prodrug 2. This prodrug is rapidly cleaved to the parent drug molecule upon both oral and intravenous administration. The prodrug achieved equivalent exposure of 1 compared to dosing the parent in multiple species. The prodrug 2 has improved aqueous solubility, simplifying both intravenous and oral formulation.

B-cell repertoire responses to varicella-zoster vaccination in human identical twins.

Adaptive immune responses in humans rely on somatic genetic rearrangements of Ig and T-cell receptor loci to generate diverse antigen receptors. It is unclear to what extent an individual's genetic background affects the characteristics of the antibody repertoire used in responding to vaccination or infection. We studied the B-cell repertoires and clonal expansions in response to attenuated varicella-zoster vaccination in four pairs of adult identical twins and found that the global antibody repertoires of twin pair members showed high similarity in antibody heavy chain V, D, and J gene segment use, and in the length and features of the complementarity-determining region 3, a major determinant of antigen binding. These twin similarities were most pronounced in the IgM-expressing B-cell pools, but were seen to a lesser extent in IgG-expressing B cells. In addition, the degree of antibody somatic mutation accumulated in the B-cell repertoire was highly correlated within twin pair members. Twin pair members had greater numbers of shared convergent antibody sequences, including mutated sequences, suggesting similarity among memory B-cell clonal lineages. Despite these similarities in the memory repertoire, the B-cell clones used in acute responses to ZOSTAVAX vaccination were largely unique to each individual. Taken together, these results suggest that the overall B-cell repertoire is significantly shaped by the underlying germ-line genome, but that stochastic or individual-specific effects dominate the selection of clones in response to an acute antigenic stimulus.

Second-generation antibacterial benzimidazole ureas: discovery of a preclinical candidate with reduced metabolic liability.

Compound 3 is a potent aminobenzimidazole urea with broad-spectrum Gram-positive antibacterial activity resulting from dual inhibition of bacterial gyrase (GyrB) and topoisomerase IV (ParE), and it demonstrates efficacy in rodent models of bacterial infection. Preclinical in vitro and in vivo studies showed that compound 3 covalently labels liver proteins, presumably via formation of a reactive metabolite, and hence presented a potential safety liability. The urea moiety in compound 3 was identified as being potentially responsible for reactive metabolite formation, but its replacement resulted in loss of antibacterial activity and/or oral exposure due to poor physicochemical parameters. To identify second-generation aminobenzimidazole ureas devoid of reactive metabolite formation potential, we implemented a metabolic shift strategy, which focused on shifting metabolism away from the urea moiety by introducing metabolic soft spots elsewhere in the molecule. Aminobenzimidazole urea 34, identified through this strategy, exhibits similar antibacterial activity as that of 3 and did not label liver proteins in vivo, indicating reduced/no potential for reactive metabolite formation.

Convergent antibody signatures in human dengue.

Dengue is the most prevalent mosquito-borne viral disease in humans, and the lack of early prognostics, vaccines, and therapeutics contributes to immense disease burden. To identify patterns that could be used for sequence-based monitoring of the antibody response to dengue, we examined antibody heavy-chain gene rearrangements in longitudinal peripheral blood samples from 60 dengue patients. Comparing signatures between acute dengue, postrecovery, and healthy samples, we found increased expansion of B cell clones in acute dengue patients, with higher overall clonality in secondary infection. Additionally, we observed consistent antibody sequence features in acute dengue in the highly variable major antigen-binding determinant, complementarity-determining region 3 (CDR3), with specific CDR3 sequences highly enriched in acute samples compared to postrecovery, healthy, or non-dengue samples. Dengue thus provides a striking example of a human viral infection where convergent immune signatures can be identified in multiple individuals. Such signatures could facilitate surveillance of immunological memory in communities.

Polyproline fold-In imparting kinetic stability to an alkaline serine endopeptidase.

Polyproline II (PPII) fold, an unusual structural element was detected in the serine protease from Nocardiopsis sp. NCIM 5124 (NprotI) based on far UV circular dichroism spectrum, structural transitions of the enzyme in presence of GdnHCl and a distinct isodichroic point in chemical and thermal denaturation. The functional activity and conformational transitions of the enzyme were studied under various denaturing conditions. Enzymatic activity of NprotI was stable in the vicinity of GdnHCl upto 6.0M concentration, organic solvents viz. methanol, ethanol, propanol (all 90% v/v), acetonitrile (75% v/v) and proteases such as trypsin, chymotrypsin and proteinase K (NprotI:protease 10:1). NprotI seems to be a kinetically stable protease with a high energy barrier between folded and unfolded states. Also, an enhancement in the activity of the enzyme was observed in 1M GdnHCl upto 8h, in organic solvents (75% v/v) for 72h and in presence of proteolytic enzymes. The polyproline fold remained unaltered or became more prominent under the above mentioned conditions. However, it diminished gradually during thermal denaturation above 60°C. Thermal transition studies by differential scanning calorimetry (DSC) showed scan rate dependence as well as irreversibility of denaturation, the properties characteristic of kinetically stable proteins. This is the first report of PPII helix being the global conformation of a non structural protein, an alkaline serine protease, from a microbial source, imparting kinetic stability to the protein.

Complex drug interactions of HIV protease inhibitors 2: in vivo induction and in vitro to in vivo correlation of induction of cytochrome P450 1A2, 2B6, and 2C9 by ritonavir or nelfinavir.

Drug-drug interactions (DDIs) with the HIV protease inhibitors (PIs) are complex, paradoxical (e.g., ritonavir/alprazolam), and involve multiple mechanisms. As part of a larger study to better understand these DDIs and to devise a framework for in vitro to in vivo prediction of these DDIs, we determined the inductive effect of ∼2 weeks of administration of two prototypic PIs, nelfinavir (NFV), ritonavir (RTV), and rifampin (RIF; induction positive control) on the cytochrome P450 enzymes CYP1A2, CYP2B6, CYP2C9, and CYP2D6 and the inductive or inductive plus inhibitory effect of NFV, RTV, or RIF on CYP3A and P-glycoprotein in healthy human volunteers. Statistically significant induction of CYP1A2 (2.1-, 2.9-, and 2.2-fold), CYP2B6 (1.8-, 2.4-, and 4-fold), and CYP2C9 (1.3-, 1.8-, and 2.6-fold) was observed after NFV, RTV, or RIF treatment, respectively (as expected, CYP2D6 was not induced). Moreover, we accurately predicted the in vivo induction of these enzymes by quantifying their induction by the PIs in human hepatocytes and by using RIF as an in vitro to in vivo scalar. On the basis of the modest in vivo induction of CYP1A2, CYP2B6, or CYP2C9, the in vivo paradoxical DDIs with the PIs are likely explained by mechanisms other than induction of these enzymes such as induction of other metabolic enzymes, transporters, or both.

A comparison of the roles of peroxisome proliferator-activated receptor and retinoic acid receptor on CYP26 regulation.

The cytochrome P450 26 family is believed to be responsible for all-trans-retinoic acid (atRA) metabolism and elimination in the human fetus and adults. CYP26A1 and CYP26B1 mRNA is expressed in a tissue-specific manner, and mice in which the CPY26 isoform has been knocked out show distinct malformations and lethality. The aim of this study was to determine differences in CYP26A1 and CYP26B1 regulation and expression. Analysis of CYP26A1 and CYP26B1 expression in a panel of 57 human livers showed CYP26A1 to be the major CYP26 isoform present in the liver, and its expression to be subject to large interindividual variability between donors. CYP26A1 and retinoic acid receptor (RAR) beta were found to be greatly inducible by atRA in HepG2 cells, whereas CYP26B1, RARalpha, and RARgamma were induced to a much lesser extent. Based on treatments with RAR isoform-selective ligands, RARalpha is the major isoform responsible for CYP26A1 and RARbeta induction in HepG2 cells. Classic cytochrome P450 inducers did not affect CYP26 transcription, whereas the peroxisome proliferator-activated receptor (PPAR) gamma agonists pioglitazone and rosiglitazone up-regulated CYP26B1 transcription by as much as 209- +/- 80-fold and CYP26A1 by 10-fold. RARbeta was also up-regulated by pioglitazone and rosiglitazone. CYP26B1 induction by PPARgamma agonists was abolished by the irreversible PPARgamma antagonist 2-chloro-5-nitrobenzanilide (GW9662), whereas RARbeta and CYP26A1 induction was unaffected by GW9662. Overall, the results of this study suggest that CYP26B1 and CYP26A1 are regulated by different nuclear receptors, resulting in tissue-specific expression patterns. The fact that drugs can alter the expression of CYP26 enzymes may have toxicological and therapeutic importance.

Expression and functional characterization of cytochrome P450 26A1, a retinoic acid hydroxylase.

Retinoic acid (RA) is a critical signaling molecule that performs multiple functions required to maintain cellular viability. It is also used in the treatment of some cancers. Enzymes in the CYP26 family are thought to be responsible for the elimination of RA, and CYP26A1 appears to serve the most critical functions in this family. In spite of its importance, CYP26A1 has neither been heterologously expressed nor characterized kinetically. We expressed the rCYP26A1 in baculovirus-infected insect cells and purified the hexahistidine tagged protein to homogeneity. Heme incorporation was determined by carbon monoxide difference spectrum and a type 1 spectrum was observed with RA binding to CYP26A1. We found that RA is a tight binding ligand of CYP26A1 with low nM binding affinity. CYP26A1 oxidized RA efficiently (depletion K(m) 9.4+/-3.3nM and V(max) 11.3+/-4.3pmolesmin(-1)pmoleP450(-1)) when supplemented with P450 oxidoreductase and NADPH but was independent of cytochrome b5. 4-Hydroxy-RA (4-OH-RA) was the major metabolite produced by rCYP26A1 but two other primary products were also formed. 4-OH-RA was further metabolized by CYP26A1 to more polar metabolites and this sequential metabolism of RA occurred in part without 4-OH-RA leaving the active site of CYP26A1. The high efficiency of CYP26A1 in eliminating both RA and its potentially active metabolites supports the major role of this enzyme in regulating RA clearance in vivo. These results provide a biochemical framework for CYP26A1 function and offer insight into the role of CYP26A1 as a drug target as well as in fetal development and cell cycle regulation.

Age-dependent kinetics and metabolism of dichloroacetate: possible relevance to toxicity.

Dichloroacetate (DCA) is an investigational drug for certain metabolic diseases. It is biotransformed principally by the zeta-1 family isoform of glutathione transferase (GSTz1), also known as maleylacetoacetate isomerase (MAAI), which catalyzes the penultimate step in tyrosine catabolism. DCA causes a reversible peripheral neuropathy in several species, including humans. However, recent clinical trials indicate that adults are considerably more susceptible to this adverse effect than children. We evaluated the kinetics and biotransformation of DCA and its effects on tyrosine metabolism in nine patients treated for 6 months with 25 mg/kg/day and in rats treated for 5 days with 50 mg/kg/day. We also measured the activity and expression of hepatic GSTz1/MAAI. Chronic administration of DCA causes a striking age-dependent decrease in its plasma clearance and an increase in its plasma half-life in patients and rats. Urinary excretion of unchanged DCA in rats increases with age, whereas oxalate, an end product of DCA metabolism, shows the opposite trend. Low concentrations of monochloroacetate (MCA), which is known to be neurotoxic, increase as a function of age in the urine of dosed rats. MCA was detectable in plasma only of older animals. Hepatic GSTz1/MAAI-specific activity was inhibited equally by DCA treatment among all age groups, whereas plasma and urinary levels of maleylacetone, a natural substrate for this enzyme, increased with age. We conclude that age is an important variable in the in vivo metabolism and elimination of DCA and that it may account, in part, for the neurotoxicity of this compound in humans and other species.

Cytochrome P450 enzymes and transporters induced by anti-human immunodeficiency virus protease inhibitors in human hepatocytes: implications for predicting clinical drug interactions.

Although many of the clinically significant drug interactions of the anti-human immunodeficiency virus (HIV) protease inhibitors (PIs) can be explained by their propensity to inactivate CYP3A enzymes, paradoxically these drugs cause (or lack) interactions with CYP3A substrates that cannot be explained by this mechanism (e.g., alprazolam). To better understand these paradoxical interactions (or lack thereof), we determined the cytochromes P450 and transporters induced by various concentrations (0-25 microM) of two PIs, ritonavir and nelfinavir, and rifampin (positive control) in primary human hepatocytes. At 10 microM, ritonavir and nelfinavir suppressed CYP3A4 activity but induced its transcripts and protein expression (19- and 12- and 12- and 6-fold, respectively; a >2-fold change over control was interpreted as induction). At 10 microM, rifampin induced CYP3A4 transcripts, CYP3A protein, and activity by 23-, 12-, and 13-fold, respectively. The induction by rifampin of CYP3A activity was significantly correlated with its induction of CYP3A4 transcripts (r = 0.96, p < 0.05) and CYP3A protein (r = 0.89, p < 0.05). All three drugs (10 microM) induced CYP2B6 activity by 2- to 4-fold, CYP2C8 and 2C9 activity by 2- to 4-fold and the transcripts of CYP2B6, 2C8, and 2C9 by >3-, 5-, and 3-fold, respectively. CYP2C19 and 1A2 activity and transcripts were modestly induced (2-fold), whereas, as expected, CYP2D6 was not induced by any of the drugs. Of the transporters studied, protease inhibitors moderately induced multidrug resistance 1 (ABCB1) and multidrug resistance-associated protein (ABCC1) transcripts but had no or minimal effect on the transcripts of breast cancer resistance protein (ABCG2), organic anion-transporting peptide (OATP) 1B1 (SLCO1B1), or OATP1B3 (SLCO1B3). On the basis of these data, we concluded that many of the paradoxical drug interactions (or lack thereof) with the PIs are metabolismrather than transporter-based and are due to induction of CYP2B6 and 2C enzymes.

In vitro LC-MS cocktail assays to simultaneously determine human cytochrome P450 activities.

Using liquid chromatography-mass spectrometry (LC-MS), two sensitive cocktail assays were developed, one to simultaneously determine activities of the cytochrome P450 enzymes, CYP1A2 (phenacitin), 2B6 (bupropion), 2C8 (amodiaquine) and 2C19 (omperazole), and the other to determine simultaneously activities of CYP3A4/5 (testosterone), 2C9 (tolbutamide) and 2D6 (dextromethorphan). These cocktail assays are sensitive, require only a small amount of microsomal protein, employ selective and high turnover CYP substrates and do not require post-incubation extraction. In each of these cocktails, no interactions were observed between the substrates. Combining the two cocktails into a single cocktail resulted in significant inhibition of CYP2D6 by amiodiaquine. These assays were used successfully to determine induction of CYP enzymes in microsomes isolated from human hepatocytes treated (72 h) with or without the prototypic inducer, rifampin.