Development of new antibody-fusion inhibitor conjugates to block HIV infection

National Institute Of Diabetes And Digestive And Kidney Diseases

Investigators

Abstract

Substantial scientific effort has been expended to develop tools and therapies to prevent infection by and transmission of HIV. Although these efforts have provided an impressive collection of therapies that diminish the pathogenicity caused by HIV, many unaddressed challenges remain, as evidenced by the enduring medical and societal impact of AIDS. One useful strategy to contain HIV spread within the body is the development of molecules that block the entry of HIV into its cellular reservoirs. So called fusion inhibitors (FIs) block the interaction of viral proteins (such GP120) with target proteins expressed on the mammalian cell surface (CD4/CXCR4/CCR5). Blockade is often achieved using polypeptides, ranging from medium-length synthetic peptides that bind and disable the viral fusion machinery to recombinantly expressed monoclonal antibodies that obstruct viral access to cellular protein receptors. FIs have been developed into approved therapeutics that target viral proteins (enfuvurtide-GP120) or host proteins (Ibalizumab-CD4). Such therapies are often applied when other regimens fail, underscoring their utility. Despite clinical application of FIs, these compounds suffer from drawbacks common to many types of HIV therapeutics. No drugs are effective against all strains of virus in all infected individuals, side effects can complicate or negate therapeutic benefit, and most inhibitors are susceptible to the development of mutants of virus that circumvent their mechanism of action. Many of these drawbacks can be addressed through simultaneous engagement of multiple mechanisms of inhibition of viral infection simultaneously. Further progress can be realized through directed delivery of inhibitors to biological sites where antiviral activity is most effective. Multivalent inhibitors that address more than one mechanism of viral infection in tandem or facilitate localized delivery offer the promise of improved efficacy, lower required doses and reduced side-effects, and increased barriers to the development of viral resistance. This project aims to develop a new approach for the generation of multivalent inhibitors of HIV infection using a combination of recombinant expression of single domain antibodies (nanobodies), chemical synthesis of polypeptide inhibitors of viral fusion, and enzymatic methods to create nanobody-based conjugates. The scheme, as described below, uses nanobodies in two complementary roles. Like conventional antibodies, nanobodies have been generated that bind to a variety of proteins found on the cell surface. In one role, nanobodies will be used for guided delivery of a linked anti-HIV cargo (peptides, other nanobodies) specifically to cell types that are known to be particularly susceptible to viral infection (CD4+ T cells). In an analogous role, the nanobodies that are used for delivery will also bind to cellular receptors that facilitate HIV infection (CD4, CXCR4) thereby offering a distinct mechanism of anti-HIV activity. Such Nb-peptide and Nb-Nb conjugates might facilitate improved potency (lower dosing and fewer side effects) and engagement of multiple mechanisms of antiviral activity (higher barriers to antiviral resistance).