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In vitro activity data were also presented in this poster. These data demonstrated how the structural design elements of SPI-256 present a high genetic barrier to the emergence of resistant strains of HIV. Additionally, the unique structural properties of SPI-256 explain its high potency when tested against a panel of 50 viral strains in a PhenoSense (TM) assay. In this analysis, SPI-256 achieved potency levels 4- to 50-fold higher than currently approved front-line protease inhibitors when tested in wild-type HIV strains.
SPI-256 also exhibited an excellent resistance profile against multi-drug resistant (MDR) isolates. In an analysis of 11 "worst case scenario" MDR isolates (defined as 6 primary PI mutations and FC>50), SPI-256 retained low nanomolar activity against most MDR isolates and mean IC50 at least an order of magnitude lower than that for atazanavir, lopinavir, amprenavir, tipranavir and other reference PIs and was better than or comparable with darunavir.
Furthermore, an additional analysis demonstrated that SPI-256 possesses a high barrier to resistance. Through in vitro resistance selection experiments, when scientists at Sequoia attempted to propagate HIV in the presence of SPI-256, the drug posed a markedly higher barrier to developing resistance than atazanavir and lopinavir. Resistance to SPI-256 required the accumulation of multiple primary protease mutations.
"There is a compelling need for new protease inhibitors that potently
subdue prevalent strains of HIV and which impede the development of new
multi-drug resistant strains, without conferring toxicity," said John
Erickson, PhD, cofounder and
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