No abstract

The Staphylococcus aureus MSCRAMM (microbial surface components recognizing adhesive matrix molecules) protein clumping factor A (ClfA) has been shown to be a critical virulence factor in several experimental models of infection. This report describes the generation, characterization, and in vivo evaluation of a murine monoclonal antibody (MAb) against ClfA. Flow cytometric analysis revealed that MAb 12-9 recognized ClfA protein expressed by all of the clinical S. aureus strains obtained from a variety of sources. In assays measuring whole-cell S. aureus binding to human fibrinogen, MAb 12-9 inhibited S. aureus binding by over 90% and displaced up to 35% of the previously adherent S. aureus bacteria. Furthermore, a single infusion of MAb 12-9 was protective against an intravenous challenge with a methicillin-resistant strain of S. aureus in a murine sepsis model (P < 0.0001). These data suggest that anti-ClfA MAb 12-9 should be further investigated as a novel immunotherapy for the treatment and prevention of life-threatening S. aureus infections.

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Hepatitis C virus infection constitutes a serious health problem in need of more effective therapies. Nucleoside analogues with improved exposure, efficacy, and selectivity are recognized as likely key components of future HCV therapy. 2'-C-Methylguanosine triphosphate has been known as a potent inhibitor of HCV RNA polymerase for some time, but the parent nucleoside is only moderately active due to poor intracellular phosphorylation. We herein report the application of phosphoramidate ProTide technology to bypass the rate-limiting initial phosphorylation of this nucleoside. Over 30 novel ProTides are reported, with variations in the aryl, ester, and amino acid regions. l-Alanine compounds are recognized as potent and selective inhibitors of HCV in replicon assay but lack rodent plasma stability despite considerable ester variation. Amino acid variation retaining the lead benzyl ester moiety gives an increase in rodent stability but at the cost of potency. Finally l-valine esters with ester variation lead to potent, stable compounds. Pharmacokinetic studies on these agents in the mouse reveal liver exposure to the bioactive triphosphate species following single oral dosing. Systemic exposure of the ProTide and parent nucleoside are low, indicating possible low toxicity in vivo, while liver concentrations of the active species may be predictive of efficacy in the clinic. This represents one of the most thorough cross-species studies of ProTides to date.

We report the humanization and characterization of monoclonal antibody (MAb) T1-2 or tefibazumab, a monoclonal antibody that recognizes clumping factor A expressed on the surface of Staphylococcus aureus. We demonstrate that the binding kinetics of MAb T1-2 is indistinguishable compared to that of its murine parent. Furthermore, MAb T1-2 is shown to enhance the opsonophagocytic uptake of ClfA-coated latex beads, protect against an intravenous challenge in a prophylactic model of rabbit infective endocarditis, and enhance the efficacy of vancomycin therapy in a therapeutic model of established infective endocarditis.