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Maraviroc – a CCR5 Antagonist for the Treatment of HIV-1 Infection

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Maraviroc – a CCR5 Antagonist for the Treatment of HIV-1 Infection View metadata, citation and similar papers at core.ac.uk brought to you by CORE OPINION ARTICLE published:provided 05 June by 2015 Frontiers - Publisher Connector doi: 10.3389/fimmu.2015.00277 Maraviroc – a CCR5 antagonist for the treatment of HIV-1 infection Elna Van Der Ryst* The Research Network, Sandwich, UK *Correspondence: [email protected] Edited by: Bernhard Moser, Cardiff University, UK Reviewed by: Guido Poli, Vita-Salute San Raffaele University, Italy Keywords: HIV, CCR5 antagonist, HIV-1 RNA, tropism, antiretroviral drug Despite the dramatic decline in human (5,6). This, together with the fact that challenges to address in the design of the immunodeficiency virus type 1 (HIV-1)- members of the G protein-coupled recep- clinical program, in addition to demon- related morbidity and mortality following tor superfamily are often tractable to devel- strating safety and efficacy. The first of the discovery of the protease inhibitors and opment of potent, selective, and orally these was that no commercially available, the advent of combination highly active bioavailable drugs (7), led to the initia- clinically validated assay to identify patients antiretroviral (ARV) therapy in the mid- tion of CCR5 ligand discovery programs infected with R5 HIV-1 existed. This was 1990s, many patients were still failing ther- by multiple groups, including a team from critical, as MVC is active only against R5 apy due to resistance and/or intolerability Pfizer Global Research and Development HIV-1 strains (7). Secondly, in spite of (1). It was clear that more ARVs acting on based at the Sandwich laboratories in the the apparently healthy phenotype of indi- different steps in the virus lifecycle, active United Kingdom. viduals with CCR5D32 (5, 6), concerns against resistant viruses, and better toler- Maraviroc (UK-427,857, MVC) was dis- remained regarding the safety of long-term ated were needed. The demonstration of covered through high-throughput screen- exposure to CCR5 antagonists, as blocking the key role of the chemokine receptors ing of the Pfizer compound library using of CCR5 may be different from congen- CCR5 and CXCR4 in HIV-1 entry sparked a chemokine radioligand-binding assay. ital absence of the CCR5 receptor, where interest in this process as a new ARV tar- The most promising compound from the immune system has matured in the get (2,3). CCR5 is the co-receptor for the screening process was optimized for absence of CCR5 and compensatory mech- the majority of HIV-1 strains, and these potency against the receptor, antiviral anisms may have developed. Finally, in viruses are termed CCR5 tropic (R5). Virus activity, pharmacokinetic characteristics, HIV-1 infected individuals, the incidence strains that use CXCR4 are called CXCR4- and selectivity against human cellular tar- of CXCR4-using HIV-1 strains increases tropic (X4), while strains that can use both gets through a large medicinal chemistry with disease progression and decrease in receptors are dual-tropic (4). Virus from effort in which almost 1000 molecules were CD4 cell counts (9),although no causal link a patient can often contain mixtures of characterized (7). MVC binds in the trans- between CXCR4-using virus and CD4-cell R5, X4, and dual-tropic strains, collectively membrane pocket of CCR5 and is a slow- depletion has been demonstrated. This has called CXCR4-using. offset functional antagonist that prevents led to concerns that selective pressure from The key role of CCR5 in HIV-1 entry, internalization (7, 8). It has potent antivi- a CCR5 antagonist may drive the virus pop- coupled with the demonstration that indi- ral activity against a wide-range of HIV-1 ulation to use CXCR4 and result in CD4 cell viduals who were homozygous for a 32 isolates (7). Together with its excellent pre- decline. base pair deletion in the CCR5 gene clinical safety profile and acceptable phar- Phase 1 single and multiple dose stud- (CCR5D32), and subsequently do not macokinetics, this resulted in it being nom- ies in healthy volunteers, conducted in express functional CCR5, were highly pro- inated as a clinical candidate in December 2001 and the first half of 2002, demon- tected from infection with R5 HIV-1, 2000 (7). strated that MVC was safe and well- focused attention on CCR5 as an attrac- It was always clear that the clinical devel- tolerated in multiple doses up to 300 mg tive target (5). Although some studies opment of CCR5 antagonists would be twice a day (BID), had a pharmacoki- have demonstrated subtle effects of the challenging, as these would be the first netic profile compatible with once daily CCR5D32 mutation on immune function, host-targeted ARV drugs and we were (QD) or BID oral dosing, could be com- such as decreased inflammatory scores in therefore venturing into uncharted terri- bined with other ARVs, and that doses of hepatitis C-infected individuals and recov- tory. In order to pre-empt key issues, a ≥100 mg BID resulted in exposure above ery from hepatitis B in heterozygotes; while clinical development team was established the geometric mean antiviral IC90 in vitro homozygotes are more susceptible to tick- very soon after the start of the discovery (7, 10). To demonstrate proof of phar- borne encephalitis and severe West Nile program and I was recruited to lead the macology, CCR5 receptor saturation was virus disease, these individuals suffer lit- early development team, joining Pfizer in measured using a bespoke ex vivo MIP- tle apparent adverse effects on their health February 1999. We identified several key 1b internalization assay. Dose-dependent www.frontiersin.org June 2015 | Volume 6 | Article 277 | 1 Van Der Ryst CCR5 antagonist to treat HIV-1 saturation was demonstrated, with doses of ≥25 mg QD resulting in near maxi- mum saturation levels, raising the inter- esting possibility that MVC could be effi- cacious in doses as low as 25 mg QD. Receptor saturation remained high for sev- eral days after dosing was discontinued, reflecting slow offset from the receptor in vivo (11). We were both excited and encouraged by the phase 1 data and rapidly moved on to a phase 2a proof of concept program. HIV-1 infected patients were screened for the presence of R5 virus only, using a novel phenotypic tropism assay (Trofile®, Mono- gram Biosciences,South San Francisco,CA, USA), and received MVC as monotherapy for 10 days (12). CCR5 receptor satura- tion was measured in this study to evaluate the possibility of using this as a biomarker for efficacy and in therapeutic monitoring. The keenly awaited data lived up to our expectations and demonstrated that doses of ≥100 mg BID resulted in mean maxi- mum HIV-1 RNA reductions of >1.5log10 (Figure 1A), with all patients, excluding one patient with X4 virus who has been erroneously included, achieving an HIV- 1 RNA reduction of at least 1log10 (12). This gave us confidence that the assay cor- rectly identified patients likely to respond FIGURE 1 | Maraviroc proof of concept and phase 3 efficacy results. (A) Mean maximum change to MVC. HIV-1 RNA nadir occurred 1– from baseline in HIV-1 RNA in patients receiving MVC monotherapy. Based on phase 1 data and 5 days after the last dose of MVC, consis- modeling and simulation, doses ranging from 25 mg QD to 300 mg BID (including 150 mg BID fed and fasted) were selected. HIV-1 RNA, safety, and MVC pharmacokinetics were evaluated (12). tent with prolonged receptor saturation as (B) MOTIVATE 1 and 2 – proportion of patients achieving HIV-1 RNA <50 copies/mL at week 48. HIV-1 demonstrated in the phase 1 studies (12). infected patients with R5 HIV-1 and triple class experience and/or resistance were randomized to For all doses except 25 mg QD receptor receive MVC QD or BID, or placebo, in combination with an optimized background antiretroviral regimen saturation of >80% was observed through- (OBT). P < 0.001 (13, 14). out the dosing period. However, there was no correlation between viral load reduc- tion and degree of receptor saturation. likely efficacious dose of MVC in combina- This was a massive undertaking, with The most likely explanation for this is tion with other ARVs. We were therefore 4794 patients screened at more than 200 that very high levels of receptor saturation able to move straight to phase 3 effi- sites in the USA, Canada, Europe, Aus- is required for antiviral efficacy and the cacy studies evaluating MVC at 300 mg (or tralia, South Africa, Mexico, and Argentina. inherent variability of the assay does not equivalent, depending on co-administered Two other small molecule CCR5 antago- allow differentiation to that degree (11,12). drugs) QD and BID, without the need to do nists (aplaviroc and vicriviroc) were also The phase 2a data generated excitement stand-alone phase 2b dose-ranging studies, being evaluated in phase 2b studies at this throughout the company and we were keen thereby significantly shortening the devel- time (17, 18). In addition to the usual to progress the clinical development pro- opment timeline. In late 2004, we initi- challenges of managing large clinical stud- gram as quickly as possible as there was ated four large studies; MOTIVATE 1 and ies, we were thrown two curveballs, the a high medical need for new ARVs to 2 in treatment-experienced patients with first of these were the discontinuation of treat patients with no or limited treatment R5 HIV-1 (13, 14), MERIT (a phase 3 aplaviroc due to idiosyncratic hepatotoxic- options. The extensive phase 1 program study with a phase 2b roll-in) in treatment- ity. There was speculation that this could (including multiple drug-drug interaction naïve patients with R5 HIV-1 (15), and be a class effect of CCR5 antagonists as studies) and wide dose range evaluated study A4001029, a phase 2b safety study CCR5 knockout mice are more suscepti- in the phase 2a proof of concept stud- in treatment-experienced patients with ble concanavalin-A mediated hepatoxicity ies,together with modeling and simulation, non-CCR5 tropic virus (CXCR4-using or (17).
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