One promising derivative is F365 (QPX9003), which was designed inspired by polymyxin lipopeptides, but with key modifications that resulted in a significantly improved therapeutic index . The design of QPX9003 benefited from detailed structural models of the interaction between polymyxin B and LPS , allowing to identify modificationtolerant sites within the polymyxin scaffold. For example, the lipid tail of polymyxin was identified as a site that could be modified without compromising its essential binding interactions with LPS, as long as the hydrophobicity of the tail was maintained.