The HIV-1 Env gp120 Inner Domain Shapes the Phe43 Cavity and the CD4 Binding Site.

The HIV-1 envelope glycoproteins (Env) undergo conformational changes upon interaction of the gp120 exterior glycoprotein with the CD4 receptor. The gp120 inner domain topological layers facilitate the transition of Env to the CD4-bound conformation. CD4 engages gp120 by introducing its phenylalanine 43 (Phe43) in a cavity ("the Phe43 cavity") located at the interface between the inner and outer gp120 domains. Small CD4-mimetic compounds (CD4mc) can bind within the Phe43 cavity and trigger conformational changes similar to those induced by CD4. Crystal structures of CD4mc in complex with a modified CRF01_AE gp120 core revealed the importance of these gp120 inner domain layers in stabilizing the Phe43 cavity and shaping the CD4 binding site. Our studies reveal a complex interplay between the gp120 inner domain and the Phe43 cavity and generate useful information for the development of more-potent CD4mc.IMPORTANCE The Phe43 cavity of HIV-1 envelope glycoproteins (Env) is an attractive druggable target. New promising compounds, including small CD4 mimetics (CD4mc), were shown to insert deeply into this cavity. Here, we identify a new network of residues that helps to shape this highly conserved CD4 binding pocket and characterize the structural determinants responsible for Env sensitivity to small CD4 mimetics.

Optimization of Small Molecules That Sensitize HIV-1 Infected Cells to Antibody-Dependent Cellular Cytotoxicity.

With approximately 37 million people living with HIV worldwide and an estimated 2 million new infections reported each year, the need to derive novel strategies aimed at eradicating HIV-1 infection remains a critical worldwide challenge. One potential strategy would involve eliminating infected cells via antibody-dependent cellular cytotoxicity (ADCC). HIV-1 has evolved sophisticated mechanisms to conceal epitopes located in its envelope glycoprotein (Env) that are recognized by ADCC-mediating antibodies present in sera from HIV-1 infected individuals. Our aim is to circumvent this evasion via the development of small molecules that expose relevant anti-Env epitopes and sensitize HIV-1 infected cells to ADCC. Rapid elaboration of an initial screening hit using parallel synthesis and structure-based optimization has led to the development of potent small molecules that elicit this humoral response. Efforts to increase the ADCC activity of this class of small molecules with the aim of increasing their therapeutic potential was based on our recent cocrystal structures with gp120 core.

A New Family of Small-Molecule CD4-Mimetic Compounds Contacts Highly Conserved Aspartic Acid 368 of HIV-1 gp120 and Mediates Antibody-Dependent Cellular Cytotoxicity.

The HIV-1 envelope glycoprotein (Env) trimer mediates virus entry into cells. The "closed" conformation of Env is resistant to nonneutralizing antibodies (nnAbs). These antibodies mostly recognize occluded epitopes that can be exposed upon binding of CD4 or small-molecule CD4 mimetics (CD4mc). Here, we describe a new family of small molecules that expose Env to nnAbs and sensitize infected cells to antibody-dependent cellular cytotoxicity (ADCC). These compounds have a limited capacity to inhibit virus infection directly but are able to sensitize viral particles to neutralization by otherwise nonneutralizing antibodies. Structural analysis shows that some analogs of this family of CD4mc engage the gp120 Phe43 cavity by contacting the highly conserved D368 residue, making them attractive scaffolds for drug development.IMPORTANCE HIV-1 has evolved multiple strategies to avoid humoral responses. One efficient mechanism is to keep its envelope glycoprotein (Env) in its "closed" conformation. Here, we report on a new family of small molecules that are able to "open up" Env, thus exposing vulnerable epitopes. This new family of molecules binds in the Phe43 cavity and contacts the highly conserved D368 residue. The structural and biological attributes of molecules of this family make them good candidates for drug development.

TMEDA-derived biscationic amphiphiles: An economical preparation of potent antibacterial agents.

Bis-alkylated derivatives of N,N,N',N'-tetramethylethylenediamine (TMEDA) represent a well-known class of versatile biscationic amphiphiles, owing to their low cost and ease of preparation. Asymmetric TMEDA derivatives, however, have been studied significantly less, particularly in regards to their antimicrobial properties. We have thus prepared a series of 36 mono- and bis-alkylated TMEDA derivatives to evaluate their inhibition of bacterial growth. This series of compounds showed low micromolar activity against a panel of four bacteria. Optimal inhibition was observed when the biscationic amphiphiles possessed modest asymmetry and were composed of between 20 and 24 total carbon atoms in the side chains. These amphiphiles were prepared in a simple two-step procedure, utilizing inexpensive materials and atom-economical reactions, making them practical for further development.

The antibacterial activity of 4,4'-bipyridinium amphiphiles with conventional, bicephalic and gemini architectures.

Dialkyl 4,4'-bipyridinium compounds are widely employed for their useful redox properties, and are commonly known as viologens due to their intense coloration upon reduction. Despite their prevalence and amphiphilic nature, the antibacterial activity of these compounds remains largely unreported. We have thus prepared a series of mono- and bis-alkylated analogs of 4,4'-bipyridine to investigate structure-activity relationships in their inhibition of a battery of Gram positive and Gram negative bacteria. The prepared cationic compounds were conventional (one cationic head, one non-polar tail), bicephalic (two heads, one tail), or gemini (two heads, two tails) in their amphiphilic structure. Additionally, an isomeric series of six bis-alkylated compounds ranging from symmetric (PQ-11,11) to highly asymmetric (PQ-20,2) were prepared. Four themes of bioactivity emerged: (1) the most bioactive compounds were gemini in structure; (2) 22 carbons in the alkyl chains, with little to modest asymmetry, led to optimal activity; (3) bicephalic compounds were generally comparable to conventional amphiphiles, though only about 12 carbons in the alkyl chains were solubilized in water by each cationic nitrogen; (4) the effects of counterion identity were not evident between chlorides and bromides; however, the presence of the iodide counterion inhibited dissolution in all compounds tested. Three isomeric compounds with little to no asymmetry in tail length, PQ-11,11, PQ-12,10, and PQ-14,8, prepared as the bromide salts, showed comparable and highly potent activity, with MIC levels around 2 µM against 3 of 4 bacteria tested. The simple (one- to two-step) syntheses of potent antimicrobials portend well for future optimization.