Interaction of CYP3A4 with the inhibitor cobicistat: Structural and mechanistic insights and comparison with ritonavir.

Cobicistat is a derivative of ritonavir marketed as a pharmacoenhancer for anti-HIV therapy. This study investigated the interaction of cobicistat with the target protein, drug-metabolizing cytochrome P450 3A4 (CYP3A4), at the molecular level using spectral, kinetic, functional, and structural approaches. It was found that, similar to ritonavir, cobicistat directly coordinates to the heme via the thiazole nitrogen but its affinity and the binding rate are 2-fold lower: 0.030 µM and 0.72 s-1, respectively. The newly determined 2.5 Å crystal structure of cobicistat-bound CYP3A4 suggests that these changes arise from the inability of cobicistat to H-bond to the active site S119 and establish multiple stabilizing contacts with the F-F' connecting fragment, which becomes disordered upon steric clashing with the bulky morpholine moiety. Nonetheless, cobicistat inhibits recombinant CYP3A4 as potently as ritonavir (IC50 of 0.24 µM vs 0.22 µM, respectively) due to strong ligation to the heme and formation of extensive hydrophobic/aromatic interactions via the phenyl side-groups. To get insights into the inhibitory mechanism, the K257 residue, known to be solely and irreversibly modified by the reactive ritonavir metabolite, was substituted with alanine. Neither this nor control K266A mutation changed the extent of time-dependent inhibition of CYP3A4 by cobicistat and ritonavir, suggesting the existence of alternative inactivation mechanism(s). More importantly, K257 was found to be functionally important and contributed to CYP3A4 allosterism, possibly by modulating protein-ligand interactions through conformational dynamics.

Cannabidiol Inhibits In Vitro Human Liver Microsomal Metabolism of Remdesivir.

Introduction: The year 2020 began with the world being flounced with a wave of novel coronavirus (severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2]) disease, named COVID-19. Based on promising pre-clinical and clinical data, remdesivir (RDV) was the first drug to receive FDA approval and so far, it is the most common therapy for treatment of SARS-CoV-2/MERS-CoV. However, following intravenous administration, RDV metabolizes majorly by human liver carboxylesterase 1 (CES1) and marginally by the CYP3A4 enzyme in merely less than an hour. Its resultant active metabolite is a hydrophilic nucleoside with very limited accumulation within lung tissues. Therefore, there is a need to investigate strategies to overcome such premature metabolism issues and improve the antiviral efficacy of RDV at the target site. Objective: Considering the major CES1-mediated metabolism of RDV on systemic administration, we intend to explore the remarkable CES1 plus CYP3A4 inhibitory activity of cannabidiol (CBD) against in vitro microsomal metabolism of RDV to indicate its therapeutic potential as an adjuvant to RDV in the treatment and management of COVID-19. Methods: We investigated the in vitro human liver microsomal metabolism of RDV in the presence of two potential CES1 inhibitors-CBD and nelfinavir, and two standard CYP3A4 inhibitors-ritonavir (RITO) and cyclosporin A. The microsomal metabolism assay was further validated by using a well-characterized CYP3A4-selective substrate, midazolam (MDZ), in the presence of CBD and RITO. Results: Our findings depicted that RDV was rapidly and completely metabolized by human liver microsomes within 60 min. Coincubation with CBD substantially reduced microsomal metabolism of RDV and prolonged its in vitro half-life from 8.93 to 31.07 min. CBD showed significantly higher inhibition of RDV compared with known CES1 and CYP3A4 inhibitors. Inhibition of MDZ metabolism by CBD and RITO further validated the assay. Conclusions: The current study strongly suggests that CBD significantly inhibits human liver microsomal metabolism of RDV and extends its in vitro half-life. Thus, concomitant administration of CBD with RDV intravenous injection could be a promising strategy to prevent premature metabolism in COVID-19 patients.

Direct and Sequential Bioactivation of Pemigatinib to Reactive Iminium Ion Intermediates Culminates in Mechanism-Based Inactivation of Cytochrome P450 3A.

We recently established the mechanism-based inactivation (MBI) of cytochrome P450 3A (CYP3A) by the fibroblast growth factor receptor (FGFR) inhibitors erdafitinib and infigratinib. Serendipitously, our preliminary data have also revealed that pemigatinib (PEM), another clinically approved FGFR1-3 inhibitor, similarly elicited time-dependent inhibition of CYP3A. This was rather unexpected, as it was previously purported that PEM did not pose any metabolism-dependent liabilities due to the absence of glutathione-related conjugates in metabolic profiling experiments conducted in human liver microsomes. Here, we confirmed that PEM inhibited both CYP3A isoforms in a time-, concentration-, and cofactor-dependent manner consistent with MBI, with inactivator concentration at half-maximum rate constant, maximum inactivation rate constant, and partition ratio of 8.69 and 11.95 µM, 0.108 and 0.042 min-1, and approximately 44 and approximately 47 for CYP3A4 and CYP3A5, respectively. Although the rate of inactivation was diminished by coincubation with an alternative substrate or direct inhibitor of CYP3A, the inclusion of nucleophilic trapping agents afforded no such protection. Furthermore, the lack of catalytic activity recovery following dialysis and oxidation with potassium ferricyanide coupled with the absence of a spectrally resolvable peak in the Soret region collectively implied that the underlying mechanism of inactivation was not elicited via the formation of pseudo-irreversible metabolite-intermediate complexes. Finally, utilizing cyanide trapping and high-resolution mass spectrometry, we illuminated the direct and sequential oxidative bioactivation of PEM and its major O-desmethylated metabolite at its distal morpholine moiety to reactive iminium ion hard electrophilic species that could covalently inactivate CYP3A via MBI. SIGNIFICANCE STATEMENT: This study reports for the first time the covalent MBI of CYP3A by PEM and deciphered its bioactivation pathway involving the metabolic activation of PEM and its major O-desmethylated metabolite to reactive iminium ion intermediates. Following which, a unique covalent docking methodology was harnessed to unravel the structural and molecular determinants underpinning its inactivation. Findings from this study lay the foundation for future investigation of clinically relevant drug-drug interactions between PEM and concomitant substrates of CYP3A.

Arylacetamide deacetylase knockout mice are sensitive to ketoconazole-induced hepatotoxicity and adrenal insufficiency.

Orally administered ketoconazole may rarely induce liver injury and adrenal insufficiency. A metabolite formed by arylacetamide deacetylase (AADAC)-mediated hydrolysis has been observed in cellulo studies, and it is relevant to ketoconazole-induced cytotoxicity. This study tried to examine the significance of AADAC in ketoconazole-induced toxicity in vivo using Aadac knockout mice. Oral administration of 150 mg/kg ketoconazole resulted in the area under the plasma concentration-time curve values of ketoconazole and N-deacetylketoconazole, a hydrolyzed metabolite of ketoconazole, in Aadac knockout mice being significantly higher and lower than those in wild-type mice, respectively. With the administration of ketoconazole (300 mg/kg/day) for 7 days, Aadac knockout mice showed higher mortality (100%) than wild-type mice (42.9%), and they also showed significantly higher plasma alanine transaminase and lower corticosterone levels, thus representing liver injury and steroidogenesis inhibition, respectively. It was suggested that a higher plasma ketoconazole concentration likely accounts for the inhibition of the synthesis of corticosterone, which has anti-inflammatory effects, in the adrenal gland in Aadac KO mice. In Aadac knockout mice, hepatic mRNA levels of immune- and inflammation-related factors were increased by the administration of 300 mg/kg ketoconazole, and the increase was restored by the replenishment of corticosterone (40 mg/kg, s.c.) along with recoveries of plasma alanine transaminase levels. In conclusion, Aadac defects exacerbate ketoconazole-induced liver injury by inhibiting glucocorticoid synthesis and enhancing the inflammatory response. This in vivo study revealed that the hydrolysis of ketoconazole by AADAC can mitigate ketoconazole-induced toxicities.

Novel Bruton's Tyrosine Kinase inhibitor remibrutinib: Drug-drug interaction potential as a victim of CYP3A4 inhibitors based on clinical data and PBPK modeling.

Remibrutinib, a novel oral Bruton's Tyrosine Kinase inhibitor (BTKi) is highly selective for BTK, potentially mitigating the side effects of other BTKis. Enzyme phenotyping identified CYP3A4 to be the predominant elimination pathway of remibrutinib. The impact of concomitant treatment with CYP3A4 inhibitors, grapefruit juice and ritonavir (RTV), was investigated in this study in combination with an intravenous microtracer approach. Pharmacokinetic (PK) parameters, including the fraction absorbed, the fractions escaping intestinal and hepatic first-pass metabolism, the absolute bioavailability, systemic clearance, volume of distribution at steady-state, and the fraction metabolized via CYP3A4 were evaluated. Oral remibrutinib exposure increased in the presence of RTV 4.27-fold, suggesting that remibrutinib is not a sensitive CYP3A4 substrate. The rich PK dataset supported the building of a robust physiologically-based pharmacokinetic (PBPK) model, which well-described the therapeutic dose range of 25-100 mg. Simulations of untested scenarios revealed an absence of drug-drug interaction (DDI) risk between remibrutinib and the weak CYP3A4 inhibitor fluvoxamine (area under the concentration-time curve ratio [AUCR] <1.25), and a moderate effect with the CYP3A4 inhibitor erythromycin (AUCR: 2.71). Predictions with the moderate and strong CYP3A4 inducers efavirenz and rifampicin, suggested a distinct remibrutinib exposure decrease of 64% and 89%. Oral bioavailability of remibrutinib was 34%. The inclusion of an intravenous microtracer allowed the determination of all relevant remibrutinib PK parameters, which facilitated construction of the PBPK model. This will provide guidance on the selection or restriction of comedications and prediction of DDI risks.

Cytotoxicity evaluation and metabolism of hepatotoxicity components of Euodiae Fructus in L02 cells.

Euodiae Fructus (EF), the dried unripe scented fruit of Euodia rutaecarpa (Juss.) Benth., was reported to show anti-hypertensive, antitumor, and anti-obesity effects. The main alkaloids of EF were reported as the reason for toxicity of EF by metabolic activation majority through CYP3A. Up till the present moment, the cytotoxicity mechanisms of EF have not yet to be fully clarified. For the purposes of this article, the influence of CYP3A inducer and inhibitor on cytotoxicity of EF and metabolism in L02 cells of five alkaloids related to toxicity of EF were evaluated. The results indicated that CYP3A inducer aggravated the toxicity and CYP3A inhibitor alleviated the toxicity. UPLC-Q-Exactive-MS was used for the identification of five alkaloids of EF in L02 cells. A total of 13 metabolites were detected in L02 cells. In general, five alkaloids were widely metabolized in L02 cells such as oxygenation, demethylation, dehydrogenation, and etc. In addition, oxygenation was the main metabolic pathway. It was inferred that the toxicity of EF was closely related to the CYP3A and the metabolic intermediate might be one of the reasons for the toxicity of EF. Hence, the choice of optimal dose might be critical to avoid the adverse reactions owing to combination of EF and CYP3A inducer.

Analyzing Potential Intestinal Transporter Drug-Drug Interactions: Reevaluating Ticagrelor Interaction Studies.

PURPOSE: Previous studies evaluating ticagrelor drug-drug interactions have not differentiated intestinal versus systemic mechanisms, which we do here. METHODS: Using recently published methodologies from our laboratory to differentiate metabolic- from transporter-mediated drug-drug interactions, a critical evaluation of five published ticagrelor drug-drug interactions was carried out to investigate the purported clinical significance of enzymes and transporters in ticagrelor disposition. RESULTS: The suggested CYP3A4 inhibitors, ketoconazole and diltiazem, displayed unchanged mean absorption time (MAT) and time of maximum concentration (Tmax) values as was expected, i.e., the interactions were mainly mediated by metabolic enzymes. The potential CYP3A4/P-gp inhibitor cyclosporine also showed an unchanged MAT value. Further analysis assuming there was no P-gp effect suggested that the increased AUC and unchanged t1/2 for ticagrelor after cyclosporine administration were attributed to the inhibition of intestinal CYP3A4 rather than P-gp. Rifampin, an inducer of CYP3As after multiple dosing, unexpectedly showed decreased MAT and Tmax values, which cannot be completely explained. In contrast, grapefruit juice, an intestinal CYP3A/P-gp/OATP inhibitor, significantly increased MAT and Tmax values for ticagrelor, which may be due to activation of P-gp or inhibition of OATPs expressed in intestine. CONCLUSIONS: This study provides new insight into the role of transporter pathways in ticagrelor intestinal absorption by examining potential MAT and Tmax changes mediated by drug-drug interactions.

Physiologically-Based Pharmacokinetic Modelling of Entrectinib Parent and Active Metabolite to Support Regulatory Decision-Making.

BACKGROUND AND OBJECTIVE: Entrectinib is a selective inhibitor of ROS1/TRK/ALK kinases, recently approved for oncology indications. Entrectinib is predominantly cleared by cytochrome P450 (CYP) 3A4, and modulation of CYP3A enzyme activity profoundly alters the pharmacokinetics of both entrectinib and its active metabolite M5. We describe development of a combined physiologically based pharmacokinetic (PBPK) model for entrectinib and M5 to support dosing recommendations when entrectinib is co-administered with CYP3A4 inhibitors or inducers. METHODS: A PBPK model was established in Simcyp® Simulator. The initial model based on in vitro-in vivo extrapolation was refined using sensitivity analysis and non-linear mixed effects modeling to optimize parameter estimates and to improve model fit to data from a clinical drug-drug interaction study with the strong CYP3A4 inhibitor, itraconazole. The model was subsequently qualified against clinical data, and the final qualified model used to simulate the effects of moderate to strong CYP3A4 inhibitors and inducers on entrectinib and M5 pharmacokinetics. RESULTS: The final model showed good predictive performance for entrectinib and M5, meeting commonly used predictive performance acceptance criteria in each case. The model predicted that co-administration of various moderate CYP3A4 inhibitors (verapamil, erythromycin, clarithromycin, fluconazole, and diltiazem) would result in an average increase in entrectinib exposure between 2.2- and 3.1-fold, with corresponding average increases for M5 of approximately 2-fold. Co-administration of moderate CYP3A4 inducers (efavirenz, carbamazepine, phenytoin) was predicted to result in an average decrease in entrectinib exposure between 45 and 79%, with corresponding average decreases for M5 of approximately 50%. CONCLUSIONS: The model simulations were used to derive dosing recommendations for co-administering entrectinib with CYP3A4 inhibitors or inducers. PBPK modeling has been used in lieu of clinical studies to enable regulatory decision-making.

Single- and multiple-dose pharmacokinetics, potential for CYP3A inhibition, and food effect in patients with cancer and healthy subjects receiving ipatasertib.

PURPOSE: To examine the single- and multiple-dose pharmacokinetics (PK), CYP3A inhibition potential of ipatasertib, and effect of food on PK of ipatasertib in patients with refractory solid tumors and a dedicated food effect assessment in healthy subjects. METHODS: The Phase I dose-escalation study enrolled patients with solid tumors in a standard 3 + 3 design with a 1 week washout after the first dose, followed by once-daily dosing on a 3-week-on/1-week-off schedule. In the expansion cohort, the effect of ipatasertib on CYP3A substrate (midazolam) was assessed by examining the change in midazolam exposure when dosed in the absence and presence of steady-state ipatasertib at 600 mg. The effect of food on ipatasertib PK was studied with ipatasertib administered in fed or fasted state (6 patients from Phase I patient study and 18 healthy subjects from the dedicated food effect study). RESULTS: Ipatasertib was generally well tolerated at doses up to 600 mg given daily for 21 days. Ipatasertib showed rapid absorption (tmax, 0.5-3 h), was dose-proportional over a range of 200-800 mg, had a median half-life (range) of 45.0 h (27.8-66.9 h), and had approximately two-fold accumulation following once-daily dosing. Midazolam exposure (AUC0-∞) increased by 2.2-fold in the presence of ipatasertib. PK was comparable in subjects administered ipatasertib in a fed or fasted state. CONCLUSION: Ipatasertib exhibited rapid absorption and was dose-proportional over a broad dose range. Ipatasertib appeared to be a moderate CYP3A inhibitor when administered at 600 mg and could be administered with or without food in clinical studies. TRAIL REGISTRATION: NCT01090960 (registered March 23, 2010); NCT02536391 (registered August 31, 2015).

Differential Reversible and Irreversible Interactions between Benzbromarone and Human Cytochrome P450s 3A4 and 3A5.

Mounting evidence has revealed that despite the high degree of sequence homology between cytochrome P450 3A isoforms (i.e., CYP3A4 and CYP3A5), they have the propensities to exhibit vastly different irreversible and reversible interactions with a single substrate. We have previously established that benzbromarone (BBR), a potent uricosuric agent used in the management of gout, irreversibly inhibits CYP3A4 via mechanism-based inactivation (MBI). However, it remains unelucidated if CYP3A5-its highly homologous counterpart-is susceptible to inactivation by BBR. Using three structurally distinct probe substrates, we consistently demonstrated that MBI was not elicited in CYP3A5 by BBR. Our in silico covalent docking models and molecular dynamics simulations suggested that disparities in the susceptibilities toward MBI could be attributed to the specific effects of BBR covalent adducts on the F-F' loop. Serendipitously, we also discovered that BBR reversibly activated CYP3A5-mediated rivaroxaban hydroxylation wherein apparent V max increased and K m decreased with increasing BBR concentration. Fitting data to the two-site model yielded interaction factors α and ß of 0.44 and 5.88, respectively, thereby confirming heterotropic activation of CYP3A5 by BBR. Furthermore, heteroactivation was suppressed by the CYP3A inhibitor ketoconazole in a concentration-dependent manner and decreased with increasing preincubation time, implying that activation was incited via binding of parent BBR molecule within the enzymatic active site. Finally, noncovalent docking revealed that CYP3A5 can more favorably accommodate both BBR and rivaroxaban in concert as compared with CYP3A4, which further substantiated our experimental observations. SIGNIFICANCE STATEMENT: Although it has been previously demonstrated that benzbromarone (BBR) inactivates CYP3A4, it remains uninterrogated whether it also elicits mechanism-based inactivation in CYP3A5, which shares ∼85% sequence similarity with CYP3A4. This study reported that BBR exhibited differential irreversible and reversible interactions with both CYP3A isoforms and further unraveled the molecular determinants underpinning their diverging interactions. These data offer important insight into differential kinetic behavior of CYP3A4 and CYP3A5, which potentially contributes to interindividual variabilities in drug disposition.

Plausible drug interaction between cyclophosphamide and voriconazole via inhibition of CYP2B6.

The inhibitory activities of eight cytochrome P450 (CYP) isoenzymes for representative or suspected inhibitors of CYPs, including pesticides, were evaluated simultaneously using an in vitro cocktail incubation method to demonstrate the importance of systematic evaluation of CYP inhibitory risks in drug interaction (DI). Potent inhibition of CYP2B6 was noticeable for some azoles, including voriconazole. When voriconazole and cyclophosphamide were co-administered in mice, cyclophosphamide-induced alopecia and leukopenia were significantly suppressed by approximately 50% with increased blood concentrations of cyclophosphamide. The formation of an active metabolite of cyclophosphamide was suppressed effectively by voriconazole in the mouse liver microsomes. Surveys of adverse event reporting databases in Japan (JADER) and the U.S. (FAERS) showed that the proportional reporting ratios of neutropenia, hemorrhagic cystitis, and alopecia for cyclophosphamide, which is principally activated by CYP2B6 in humans, were mostly reduced, or tended to be reduced when azoles, including voriconazole, were prescribed in combination. It is highly likely that DIs between cyclophosphamide and azoles occur in the clinical setting. This study also suggests that more proper consideration of CYP2B6-mediated DIs is warranted. The combination of the in vitro cocktail method and a survey of adverse event reporting databases was a useful method to comprehensively detect pharmacokinetic DIs.

Tertiary Oxidation of Deoxycholate Is Predictive of CYP3A Activity in Dogs.

Deoxycholic acid (DCA, 3α, 12α-dihydroxy-5ß-cholan-24-oic acid) is the major circulating secondary bile acid, which is synthesized by gut flora in the lower gut and selectively oxidized by CYP3A into tertiary metabolites, including 1ß,3α,12α-trihydroxy-5ß-cholan-24-oic acid (DCA-1ß-ol) and 3α,5ß,12α-trihydroxy-5ß-cholan-24-oic acid (DCA-5ß-ol) in humans. Since DCA has the similar exogenous nature and disposition mechanisms as xenobiotics, this work aimed to investigate whether the tertiary oxidations of DCA are predictive of in vivo CYP3A activities in beagle dogs. In vitro metabolism of midazolam (MDZ) and DCA in recombinant canine CYP1A1, 1A2, 2B11, 2C21, 2C41, 2D15, 3A12, and 3A26 enzymes clarified that CYP3A12 was primarily responsible for either the oxidation elimination of MDZ or the regioselective oxidation metabolism of DCA into DCA-1ß-ol and DCA-5ß-ol in dog liver microsomes. Six male dogs completed the CYP3A intervention studies including phases of baseline, inhibition (ketoconazole treatments), recovery, and induction (rifampicin treatments). The oral MDZ clearance after a single dose was determined on the last day of the baseline, inhibition, and induction phases, and subjected to correlation analysis with the tertiary oxidation ratios of DCA detected in serum and urine samples. The results confirmed that the predosing serum ratios of DCA oxidation, DCA-5ß-ol/DCA, and DCA-1ß-ol/DCA were significantly and positively correlated both intraindividually and interindividually with oral MDZ clearance. It was therefore concluded that the tertiary oxidation of DCA is predictive of CYP3A activity in beagle dogs. Clinical transitional studies following the preclinical evidence are promising to provide novel biomarkers of the enterohepatic CYP3A activities. SIGNIFICANCE STATEMENT: Drug development, clinical pharmacology, and therapeutics are under insistent demands of endogenous CYP3A biomarkers that avoid unnecessary drug exposure and invasive sampling. This work has provided the first proof-of-concept preclinical evidence that the CYP3A catalyzed tertiary oxidation of deoxycholate, the major circulating secondary bile acid synthesized in the lower gut by bacteria, may be developed as novel in vivo biomarkers of the enterohepatic CYP3A activities.

Dose adjustment of venetoclax when co-administered with posaconazole: clinical drug-drug interaction predictions using a PBPK approach.

PURPOSE: Venetoclax, a targeted anticancer agent approved for the treatment of chronic lymphocytic leukemia and acute myeloid leukemia, is a substrate of cytochrome P450 (CYP) 3A enzyme (CYP3A4). Posaconazole, commonly used to prevent invasive fungal infections in neutropenic patients with hematological malignancies, potently inhibits CYP3A4. The purpose of this evaluation was to predict venetoclax exposures following co-administration of posaconazole at doses not previously studied clinically. METHODS: Two physiologically based pharmacokinetic (PBPK) models were developed for posaconazole based on published parameters, one for an oral suspension and another for delayed released tablets. Parameter optimization, guided by sensitivity analyses, was conducted such that the models could replicate clinical exposures of posaconazole and drug-drug interactions with sensitive CYP3A substrates including venetoclax. The clinically verified posaconazole PBPK models were then utilized to predict DDI with a previously published venetoclax PBPK model at clinically relevant dosing scenarios. RESULTS: The posaconazole PBPK models predicted posaconazole exposure and DDI related fold changes with acceptable prediction errors for both posaconazole formulations. The model predicted exposures of venetoclax, when co-administered with a 300 mg QD dose of delayed release tablets of posaconazole, were in concordance with observed data. Increasing the posaconazole dose to 500 mg QD increased venetoclax exposures by about 12% relative to 300 mg QD, which were still within the venetoclax safe exposure range. CONCLUSIONS: The posaconazole PBPK models were developed and clinically verified. Predictions using the robust PBPK model confirmed the venetoclax label recommendation of 70 mg in the presence of posaconazole at doses up to 500 mg QD.

The relationship between stereochemical and both, pharmacological and ADME-Tox, properties of the potent hydantoin 5-HT7R antagonist MF-8.

This study concerns synthesis and evaluation of pharmacodynamic and pharmacokinetic profile for all four stereoisomers of MF-8 (5-(4-fluorophenyl)-3-(2-hydroxy-3-(4-(2-methoxyphenyl)piperazin-1-yl)propyl)-5-methylimidazolidine-2,4-dione), the previously described, highly potent 5-HT7R ligand with antidepressant activity on mice. The combination of DFT calculations of 1H NMR chemical shifts with docking and dynamic simulations, in comparison to experimental screening results, provided prediction of the configuration for one of two present stereogenic centers. The experimental data for stereoisomers (MF-8A-MF-8D) confirmed the significant impact of stereochemistry on both, 5-HT7R affinity and antagonistic action, with Ki and Kb values in the range of 3-366 nM and 0.024-99 µM, respectively. We also indicated the stereochemistry-dependent influence of the tested compounds on P-glycoprotein efflux, absorption in Caco-2 model, metabolic pathway as well as CYP3A4 and CYP2C9 activities.

The utility of CYP3A activity endogenous markers for evaluating drug-drug interaction between sildenafil and CYP3A inhibitors in healthy subjects.

Cytochrome P450 (CYP) 3A-related drug-drug interaction (DDI) studies are needed during drug development to determine clinical interaction effects. We aimed to evaluate DDI between sildenafil and two CYP3A inhibitors, clarithromycin and itraconazole, regarding the changes in pharmacokinetics and endogenous markers. An open-label, one-sequence, one-period, two-treatment parallel study was conducted in 32 healthy Korean subjects. Each of 16 subjects were randomly assigned to the clarithromycin and itraconazole groups. Both groups received a single dose of sildenafil 25 mg as a control, and either clarithromycin 250 mg or itraconazole 100 mg was administered four times to inhibit CYP3A activity. Pharmacokinetics of sildenafil showed the similar magnitude of inhibitory effects of the two inhibitors on total CYP3A activity; both inhibitors similarly increased systemic exposure of sildenafil by 2-fold. Urinary 6ß-OH-cortisone/cortisone and plasma 4ß-OH-cholesterol were significantly decreased after clarithromycin administration but not after itraconazole. A significant correlation between sildenafil CL/F and metabolic markers of CYP3A activity was observed after clarithromycin administration. We confirmed that sildenafil has moderate pharmacokinetic interaction with clarithromycin and itraconazole. Endogenous markers well reflected the CYP3A inhibition of clarithromycin, suggesting possible utility in DDI study with moderate to strong CYP3A inhibition; however, there are limitations in predicting intestinal CYP3A mediated DDI.

A current review of the safety of cystic fibrosis transmembrane conductance regulator modulators.

WHAT IS KNOWN AND OBJECTIVE: Treatment with cystic fibrosis transmembrane conductance regulator (CFTR) modulators has led to improved clinical outcomes and an increase in lifespans of cystic fibrosis (CF) patients. As CF patients continue to live longer, they are at risk for developing adverse drug reactions associated with polypharmacy and CFTR modulators. COMMENT: The authors aim to describe safety concerns of the current combination CFTR modulators, based upon a literature review, including notable safety concerns and recommendations for drug-drug interactions. WHAT IS NEW AND CONCLUSION: Cystic fibrosis transmembrane conductance regulator agents are generally well tolerated with low discontinuation rates when compared to placebo. Elevations in liver enzymes and drug-drug interactions are the most notable safety concerns. Additionally, lumacaftor/ivacaftor has shown more respiratory-related adverse events and drug-drug interactions compared to elexacaftor/tezacaftor/ivacaftor and tezacaftor/ivacaftor. Postmarketing studies are needed to determine long-term safety concerns.

Structure-Property Relationships and Machine Learning Models for Addressing CYP3A4-Mediated Victim Drug-Drug Interaction Risk in Drug Discovery.

Among the FDA-approved small molecule drugs (2005-2016) that are primarily metabolized by cytochrome P450 (CYP), 64% are primarily metabolized by CYP3A4. As the proportion of an individual drug's fraction metabolized through CYP3A4 increases, the risk for the drug to be a victim of an interaction with CYP3A4 inhibitors or inducers increases. Therefore, it is important to assess the extent of involvement of individual CYP enzymes in the overall clearance for a scaffold early in discovery and mitigate the CYP3A4-mediated victim-drug-drug interaction (DDI) risk, if warranted by the desired clinical profile of the drug. To mitigate the CYP3A4-mediated victim DDI risk in discovery, we analyzed the physicochemical properties of the CYP3A4 substrates and found that molecular weight was the property that provided the best separation of the CYP3A4 substrates from other CYP substrates. In addition, neutral and basic compounds with MW ≥ 360 g/mol tend to be primarily metabolized by CYP3A4, whereas acidic compounds with MW < 360 g/mol are most likely to be primarily metabolized by other CYP enzymes. We then developed Support Vector Machine based on fingerprints (SVM-FP) and Deep-Learning (DL) models to predict if a molecule will be primarily metabolized by CYP3A4. Our models were trained on 2306 compounds, which is the largest training set among published models for this endpoint. Both models showed positive predictive values (PPV) > 80% in predicting a CYP3A4 substrate on a prospective testing set. Given the high PPV of the models, project teams can confidently deprioritize compounds predicted to be CYP3A4 substrates to avoid the potential liability of CYP3A4 victim DDI. Teams can then focus time and resources on synthesizing compounds that are predicted to have a lower dependency on CYP3A4 metabolism and confirm that experimentally. Through such iterative in silico-in vitro learning circles, drug discovery teams can decide if metabolism through non-CYP3A4 pathways could be achieved in the SAR of a chemical series to mitigate the CYP3A4 victim DDI risk.

FDA approved drugs with pharmacotherapeutic potential for SARS-CoV-2 (COVID-19) therapy.

In December 2019, a novel SARS-CoV-2 coronavirus emerged, causing an outbreak of life-threatening pneumonia in the Hubei province, China, and has now spread worldwide, causing a pandemic. The urgent need to control the disease, combined with the lack of specific and effective treatment modalities, call for the use of FDA-approved agents that have shown efficacy against similar pathogens. Chloroquine, remdesivir, lopinavir/ritonavir or ribavirin have all been successful in inhibiting SARS-CoV-2 in vitro. The initial results of a number of clinical trials involving various protocols of administration of chloroquine or hydroxychloroquine mostly point towards their beneficial effect. However, they may not be effective in cases with persistently high viremia, while results on ivermectin (another antiparasitic agent) are not yet available. Interestingly, azithromycin, a macrolide antibiotic in combination with hydroxychloroquine, might yield clinical benefit as an adjunctive. The results of clinical trials point to the potential clinical efficacy of antivirals, especially remdesivir (GS-5734), lopinavir/ritonavir, and favipiravir. Other therapeutic options that are being explored involve meplazumab, tocilizumab, and interferon type 1. We discuss a number of other drugs that are currently in clinical trials, whose results are not yet available, and in various instances we enrich such efficacy analysis by invoking historic data on the treatment of SARS, MERS, influenza, or in vitro studies. Meanwhile, scientists worldwide are seeking to discover novel drugs that take advantage of the molecular structure of the virus, its intracellular life cycle that probably elucidates unfolded-protein response, as well as its mechanism of surface binding and cell invasion, like angiotensin converting enzymes-, HR1, and metalloproteinase inhibitors.

Nitrogen-Walk Approach to Explore Bioisosteric Replacements in a Series of Potent A2B Adenosine Receptor Antagonists.

A systematic exploration of bioisosteric replacements for furan and thiophene cores in a series of potent A2BAR antagonists has been carried out using the nitrogen-walk approach. A collection of 42 novel alkyl 4-substituted-2-methyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carboxylates, which contain 18 different pentagonal heterocyclic frameworks at position 4, was synthesized and evaluated. This study enabled the identification of new ligands that combine remarkable affinity (Ki < 30 nM) and exquisite selectivity. The structure-activity relationship (SAR) trends identified were substantiated by a molecular modeling study, based on a receptor-driven docking model and including a systematic free energy perturbation (FEP) study. Preliminary evaluation of the CYP3A4 and CYP2D6 inhibitory activity in optimized ligands evidenced weak and negligible activity, respectively. The stereospecific interaction between hA2BAR and the eutomer of the most attractive novel antagonist (S)-18g (Ki = 3.66 nM) was validated.