Targeted and Non-targeted Microbubbles for Pediatric Applications - Project Summary
Staphylococcus is the most common cause of community- and hospital-acquired infective endocarditis
worldwide. Staphylococcal (S. aureus) endocarditis is a serious health problem in children and adults that
carries high morbidity and mortality. The incidence of this disease is increasing due to healthcare advances
with widespread use of intra-cardiac devices and prosthetic heart valves, and greater prevalence of valvular
heart disease. One of the key limitations with antibiotic therapy for S. aureus endocarditis is poor drug
penetration into the vegetation. The shear jets induced by ultrasound-mediated cavitation (UMC) of circulating
microbubbles (MBs) have been utilized to dissolve thrombi within vessels and the microvasculature. Fibrin
affords an attractive target for developing targeted MBs in the treatment of endocarditis with ultrasound, as the
conjugate binding permits MB adherence even in conditions of high shear stress. We propose to develop fibrin-
targeted MBs, and evaluate the effectiveness of fibrin-targeted MBs and UMC co-administered with systemic
vancomycin in the treatment of S. aureus aortic valve endocarditis. After production of bioconjugate and fibrin-
targeted MBs, we will evaluate MB binding to the fibrin target under conditions of variable shear stress. We
hypothesize that UMC of fibrin targeted MB will improve vancomycin activity against S. aureus by improving
antibiotic penetration into the vegetation, and promoting vegetation clearance. Furthermore, we hope to
demonstrate that the reductions in vegetation size by UMC may decrease complications including valvular
regurgitation, perivalvular extension and embolization, resulting in improved outcomes including survival. We
will examine this therapeutic approach in an established rabbit model of S. aureus endocarditis, randomized to
receive either transthoracic UMC application with systemic vancomycin co-administered with fibrin-targeted
MBs, versus vancomycin alone. Bacterial counts (colony forming units/ml) in the treated vegetation will be
quantified as the primary outcome variable. Residual bacterial counts in peripheral organs and brain as a result
of embolic phenomena will also be quantified. Secondary outcomes of serial vegetation size, valvular
regurgitation and five-day survival will be tested. Successful completion of this research could significantly
impact the clinical management of this life-threatening disease. Results of these studies will be used to
advance this non-invasive therapeutic strategy into an Investigational New Drug application.
