Palmitic Acid Analogs Exhibit Nanomolar Binding Affinity for the HIV-1 CD4 Receptor and Nanomolar Inhibition of gp120-to-CD4 Fusion

Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA.
PLoS ONE (Impact Factor: 3.23). 08/2010; 5(8):e12168. DOI: 10.1371/journal.pone.0012168
Source: PubMed


We recently reported that palmitic acid (PA) is a novel and efficient CD4 fusion inhibitor to HIV-1 entry and infection. In the present report, based on in silico modeling of the novel CD4 pocket that binds PA, we describe discovery of highly potent PA analogs with increased CD4 receptor binding affinities (K(d)) and gp120-to-CD4 inhibition constants (K(i)). The PA analogs were selected to satisfy Lipinski's rule of drug-likeness, increased solubility, and to avoid potential cytotoxicity.
PA analog 2-bromopalmitate (2-BP) was most efficacious with K(d) approximately 74 nM and K(i) approximately 122 nM, ascorbyl palmitate (6-AP) exhibited slightly higher K(d) approximately 140 nM and K(i) approximately 354 nM, and sucrose palmitate (SP) was least efficacious binding to CD4 with K(d) approximately 364 nM and inhibiting gp120-to-CD4 binding with K(i) approximately 1486 nM. Importantly, PA and its analogs specifically bound to the CD4 receptor with the one to one stoichiometry.
Considering observed differences between K(i) and K(d) values indicates clear and rational direction for improving inhibition efficacy to HIV-1 entry and infection. Taken together this report introduces a novel class of natural small molecules fusion inhibitors with nanomolar efficacy of CD4 receptor binding and inhibition of HIV-1 entry.

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Available from: Alexander Shekhtman, Nov 23, 2015
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    • "We demonstrated specificity of PA-to-CD4 receptor binding by NMR saturation transfer spectroscopy (STD-NMR) [3], and the inhibition of HIV entry by CD4-to-gp120 competition ELISA experiments [5]. Utilizing in silico molecular modeling involving a combination of binding assay data, alpha site analysis and docking/scoring approaches, we have identified a novel druggable cavity on the CD4 receptor that binds both PA and 2-BP and inhibits gp120-to-CD4 binding, thus blocking HIV entry [4]. Considering that the CD4 glycoprotein is the obligatory HIV receptor regardless of HIV coreceptor usage, the PA and 2-BP represent small chemical entity (SCE) molecule binding to the specified CD4 cavity that explains the observed entry inhibition of both X4- and R5-tropic HIV [3], [4]. "
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    ABSTRACT: AIDS is a global pandemic that has seen the development of novel and effective treatments to improve the quality of life of those infected and reduction of spread of the disease. Palmitic Acid (PA), which we identified and isolated from Sargassum fusiforme, is a naturally occurring fatty acid that specifically inhibits HIV entry by binding to a novel pocket on the CD4 receptor. We also identified a structural analogue, 2-bromopalmitate (2-BP), as a more effective HIV entry inhibitor with a 20-fold increase in efficacy. We have used the structure-activity relationship (SAR) of 2-BP as a platform to identify new small chemical molecules that fit into the various identified active sites in an effort to identify more potent CD4 entry inhibitors. To validate further drug development, we tested the PA and 2-BP scaffold molecules for genotoxic potential. The FDA and International Conference on Harmonisation (ICH) recommends using a standardized 3-test battery for testing compound genotoxicity consisting of the bacterial reverse mutation assay, mouse lymphoma assay, and rat micronucleus assay. PA and 2-BP and their metabolites tested negative in all three genotoxicty tests. 2-BP is the first derivative of PA to undergo pre-clinical screening, which will enable us to now test multiple simultaneous small chemical structures based on activity in scaffold modeling across the dimension of pre-clinical testing to enable transition to human testing.
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    • "We reported that palmitic acid is a specific CD4 fusion inhibitor of both X4 and R5 HIV-1 entry, which also efficiently inhibited virus-to-cell and cell-to-cell fusion, and it did not internalize CD4 receptor or perturb lipid rafts [6]. PA bound to the CD4 receptor specifically, with dissociation constant (Kd) of ∼1.5 µM, and this binding was via PA's hydrophobic methyl and methelene groups located away from the carboxyl end, which functions by blocking efficient pgp120-to-CD4 attachment and fusion [6], [7]. We also showed that PA occupies a novel hydrophobic cavity on the CD4 receptor that is constrained by amino acids Phe52-to-Leu70 [7], which encompass residues that have been previously identified as a region critical for gp120 binding [8], [9]. "
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