A study of the molecular mechanism of binding kinetics and long residence times of human CCR5 receptor small molecule allosteric ligands.

BACKGROUND AND PURPOSE: The human CCR5 receptor is a co-receptor for HIV-1 infection and a target for anti-viral therapy. A greater understanding of the binding kinetics of small molecule allosteric ligand interactions with CCR5 will lead to a better understanding of the binding process and may help discover new molecules that avoid resistance. EXPERIMENTAL APPROACH: Using [(3) H] maraviroc as a radioligand, a number of different binding protocols were employed in conjunction with simulations to determine rate constants, kinetic mechanism and mutant kinetic fingerprints for wild-type and mutant human CCR5 with maraviroc, aplaviroc and vicriviroc. KEY RESULTS: Kinetic characterization of maraviroc binding to the wild-type CCR5 was consistent with a two-step kinetic mechanism that involved an initial receptor-ligand complex (RA), which transitioned to a more stable complex, R'A, with at least a 13-fold increase in affinity. The dissociation rate from R'A, k-2 , was 1.2 × 10(-3) min(-1) . The maraviroc time-dependent transition was influenced by F85L, W86A, Y108A, I198A and Y251A mutations of CCR5. CONCLUSIONS AND IMPLICATIONS: The interaction between maraviroc and CCR5 proceeded according to a multi-step kinetic mechanism, whereby initial mass action binding and later reorganizations of the initial maraviroc-receptor complex lead to a complex with longer residence time. Site-directed mutagenesis identified a kinetic fingerprint of residues that affected the binding kinetics, leading to the conclusion that allosteric ligand binding to CCR5 involved the rearrangement of the binding site in a manner specific to each allosteric ligand.

Evaluation of amide replacements in CCR5 antagonists as a means to increase intrinsic permeability. Part 2: SAR optimization and pharmacokinetic profile of a homologous azacyle series.

Replacement of a secondary amide with a piperidine or azetidine moiety in a series of CCR5 antagonists led to the discovery of compounds with increased intrinsic permeability. This effort led to the identification of a potent CCR5 antagonist which exhibited an improved in vivo pharmacokinetic profile.

Exploration of a new series of CCR5 antagonists: multi-dimensional optimization of a sub-series containing N-substituted pyrazoles.

The introduction of N-substituted pyrazoles in a new series of CCR5 antagonists was shown to substantially increase antiviral activity.

Synthesis, SAR and evaluation of [1,4']-bipiperidinyl-4-yl-imidazolidin-2-one derivatives as novel CCR5 antagonists.

Elaboration of our previously disclosed spiropiperidine template led to the development of a series of novel CCR5 antagonists. Results of SAR exploration and preliminary lead characterization are described.

Novel hexahydropyrrolo[3,4-c]pyrrole CCR5 antagonists.

Starting with a high-throughput screening lead, a novel series of CCR5 antagonists was developed utilizing an information-based approach. Improvement of pharmacokinetic properties for the series was pursued by SAR exploration of the lead template. The synthesis, SAR and biological profiles of the series are described.

Evaluation of a 3-amino-8-azabicyclo[3.2.1]octane replacement in the CCR5 antagonist maraviroc.

The bicyclic 5-amino-3-azabicyclo[3.3.0]octanes were shown to be effective replacements for the 3-amino-8-azabicyclo[3.2.1]octane found in the CCR5 antagonist maraviroc.

Evaluation of a 4-aminopiperidine replacement in several series of CCR5 antagonists.

The bicyclic 5-amino-3-azabicyclo[3.3.0]octanes were shown to be effective replacements for the conformationally restricted 4-aminopiperidine ring found in several series of CCR5 antagonists.

Novel CCR5 antagonists for the treatment of HIV infection: a review of compounds patented in 2006 - 2008.

IMPORTANCE OF THE FIELD: The HIV/AIDS epidemic and the resultant therapeutic efforts have continued to evolve over the last several years. The continued challenges in vaccine development, the growing longevity of the patient population and the emergence of resistant strains to current highly active antiretroviral therapy necessitate the development of new, effective therapeutics which target novel mechanism of actions. CCR5, a member of the GPCR superfamily, plays a key role as a co-receptor during the HIV viral entry process. The utility of CCR5 antagonists in the clinical setting has been validated, culminating in the launch of maraviroc (Selzentry by Pfizer (New York, NY, USA) in 2007. AREAS COVERED IN THIS REVIEW: This review covers patent applications for small-molecule CCR5 selective antagonists published between 2006 and 2008 and related literature, with a focus on the treatment of HIV infection. WHAT THE READER WILL GAIN: The reader will gain information on patent literature from 2006 to 2008 on CCR5 antagonists for the treatment of HIV infection. TAKE HOME MESSAGE: A variety of new chemotypes have emerged over this period. These efforts support the potential to develop the next generation of CCR5 antagonists for the treatment of HIV with improved potency, tolerability and convenience.

Spiropiperidine CCR5 antagonists.

A novel series of CCR5 antagonists has been identified, utilizing leads from high-throughput screening which were further modified based on insights from competitor molecules. Lead optimization was pursued by balancing opposing trends of metabolic stability and potency. Selective and potent analogs with good pharmacokinetic properties were successfully developed.

Discovery of a potent, selective and orally bioavailable 3,9-diazaspiro[5.5]undeca-2-one CCR5 antagonist.

Replacement of the cyclic carbamate in our previously disclosed 1-oxa-3,9-diazaspiro[5.5]undecan-2-one template led to the discovery of two novel series of 3,9-diazaspiro[5.5]undecane and undeca-2-one CCR5 antagonists. The synthesis, SAR, and antiviral activities of these two series are described. One compound (32) was found to have attractive combination of antiviral potency, selectivity, and pharmacokinetic profile. The asymmetric synthesis of 32 was also accomplished and both enantiomers were equally potent.