Background:  In 2003, we identified the cellular protein, LEDGF/p75, as a strong binding partner of HIV-1 integrase (IN) in eukaryotic cells. We have since established a thorough validation procedure for novel HIV co-factors. Implementation of our validation scheme corroborated LEDGF/p75 as an important co-factor of HIV integration and validated the virus-host interaction as a potential drug target for antiviral therapy.

Methods:  The resolved X-ray structure of IN-core complexed with the IBD of LEDGF/p75 revealed a well defined interphase suggesting that small molecule protein-protein interaction inhibitors (SMPPII) might be capable of disrupting the interaction. We have now applied rational drug design to identify small molecules potentially binding to the interaction site. For in vitro hit identification, we developed a high throughput Alphascreen assay monitoring the LEDGF/p75 HIV-1 Integrase interaction. Antiviral activity and cytotoxicity of initial hits from in vitro screening were evaluated in cell culture in the MT4/MTT HIV replication system.

Results:  We have rationally designed a series of 2-(quinolin-3-yl)acetic acid derivatives that act as potent inhibitors of the LEDGF/p75-integrase interaction and HIV-1 replication at micromolar concentration by blocking the integration step. A 1.84 Å resolution co-crystal structure corroborates the binding of the inhibitor in the LEDGF/p75 binding pocket of integrase. The lack of cross-resistance with 2 clinical integrase inhibitors (Raltegravir and Elvitegravir) defines the 2-(quinolin-3-yl)acetic acid derivatives as the first genuine allosteric HIV-1 integrase inhibitors.

Conclusion:  Our work demonstrates the feasibility of rational design of small molecules inhibiting the protein-protein interaction between a viral protein and a cellular host factor. The discovery of the 2-(quinolin-3-yl)acetic acid derivatives as the first selective SMPPII inhibiting the LEDGF/p75-IN interaction and HIV replication provides the ultimate proof for the crucial role of the co-factor in HIV replication. The antiviral profiling, as well as their ADMEDTox profile, demonstrates a potential for antiviral therapy.