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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 (IC 50 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., Competing Interests: Declaration of competing interest The author declares no conflict of interest., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Introduction: HIV eradication is not feasible and lifelong treatment is warranted to manage HIV infection. In this scenario, the advent of single-tablet, once-daily, fixed-dose co-formulations is important for reducing pill burden and maximize long-term drug adherence. Cobicistat-boosted darunavir along with emtricitabine and tenofovir alafenamide co-formulation (DRV/c/FTC/TAF or the trade name Symtuza®) is the first marketed protease inhibitor-based fixed-dose combination regimen for the treatment of HIV infection. It was approved in late 2017 by the European Medical Agency both for naïve patients and treatment-experienced patients with viral suppression. Areas covered: PubMed, ClinicalTrials.gov and presentations at scientific meetings were searched with the terms 'darunavir/cobicistat' and 'tenofovir alafenamide and emtricitabine' for clinical trials either conducted to date or ongoing as well as a review of abstracts from major HIV/AIDS and infectious diseases conferences from 2015 to up to date. Expert opinion: DRV/c/FTC/TAF is a novel unique antiretroviral drug co-formulation that exhibits a convenient dosing, satisfactory safety profile, and high antiviral efficacy, even in patients harboring viruses with resistance to antivirals other than darunavir in the short-midterm. It represents the first fixed-dose combination therapy including a protease inhibitor given as one single pill once daily for drug-naïve patients and as second-line antiretroviral therapy.

Rilpivirine (RPV), dolutegravir (DTG) and elvitegravir (EVG) are the latest antiretroviral drugs approved for treatment of HIV infection. Currently, poor information is currently available concerning their pharmacokinetic and pharmacodynamic properties, thus making the use of therapeutic drug monitoring for these drugs not useful. This lack of information is partially due to the absence of an high-throughput method for their simultaneous quantification together with other antiretroviral drugs. In this work, we describe the development and validation of a new UPLC-MS/MS method to quantify these drugs, together with other fourteen antiretroviral agents, in human plasma. One hundred microliters of plasma samples were added with internal standard (6,7-Dimethyl- 2,3-di(2-pyridyl) quinoxaline), underwent a simple protein precipitation with methanol:acetonitrile (50:50v/v) followed by sample dilution with water. Chromatographic separation was performed on a Acquity ® UPLC HSS T3 column (150mm x 2.1mm I.D) with a particle size of 1.8μm and compounds were detected with a tandem mass detector, monitoring two ion transitions for each drugs. The mean recovery of RPV, DTG and EVG were 101%, 87% and 112.3% respectively. Accuracy and precision inter/intra-day were below 15% for all drugs, in accordance to Food and Drug Administration guidelines requirements. The UPLC-MS/MS method reported here could be used routinely to monitor plasma concentrations of antiviral drugs, including RPV, DTG and EVG., (Copyright © 2017. Published by Elsevier B.V.)