Summary activity statement /

ML267 (SID 124398570; CID 53257126) significantly improves the state of the art for the field of PPTase biology, and provides a first in class compound for the Sfp-subtype denotation of this enzyme class. With regard to potency at the directed target, we find that ML267 shows a 5-fold increase over Wyeth Compound 16, displaying an IC50 in the primary screen of 290 nM, with additional coverage of AcpS-PPTase at a potency of 6.93 μM. Furthermore, even greater improvements were seen in MIC experiments, where ML267 a remarkable 38-fold improvement in potency in the common laboratory strain B. subtilis 168, a result that was further enhanced in the genetically modified test strain B. subtilis HM489, whose viability is solely dependent upon an active Sfp gene product. With respect to MIC activity in human pathogens, we observed noteworthy inhibition of Gram positive representative strains of S. aureus, with an 18-fold increase over Wyeth compound 16 in a methicillin resistant strain, with an observed MIC of 3.4 μg/mL. In an act of further attentiveness, this activity was confirmed by an external contract laboratory specializing in anti-infective screening, a result we found particularly motivating. Testing in both Gram negative and fungal pathogens showed that our spectrum of activity was not enveloping with regard to microbial life, a result that is considered acceptable at this stage of an anti-infective discovery campaign (Payne 2007). While these organisms are expected to also depend on PPTase activity for viability, this limited scope of activity may be the result of genetic variability between PPTase loci, the reduced penetrability of the Gram-negative outer membrane (a formidable barrier) (Hancock 1997), or increased efflux capacities in fungal pathogens (Cannon 2009). The in vitro antimicrobial profile of ML267, provides the research community with a unique tool that may be leveraged to 1.) evaluate the role of Sfp-PPTase in bacterial cell viability, 2.) determine the potential of Sfp-PPTase as a drug target in the case of Gram positive bacterial infections, and 3.) assess the role that polyketide, nonribosomal peptide, and fatty acid synthases play in virulence biology. The favorable potency observed against CAMRSA in in vitro antimicrobial studies, coupled to the favorable in vitro and in vivo ADME and PK properties provide a glimmer of hope that a new class of antibiotic compounds acting through novel mechanism of action may soon be within reach.