Combating Plague: Fighting a War on Two Fronts Through Vaccine Design and New Therapeutic Intervention
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Assumed by many to be a disease of the past, plague continues to be a globally prevalent disease, with thousands of cases estimated to occur annually. With no FDA-approved vaccine and therapeutics limited to antibiotics, there is an imperative need to develop new prophylactics as well as therapeutics against plague infection. Identification of new virulence factors of Y. pestis and understanding their role during the infection process is imperative in designing a better vaccine candidate. By using high-throughput signature-tagged mutagenic approach, we screened 5,088 mutants of Y. pestis CO92 to identify clones with impairment in dissemination to the spleen. In subsequent screens, 20/118 mutants exhibited attenuation when individually tested in a mouse model of bubonic plague. Upon sequencing, 3 of the attenuated mutants carried interruptions in genes encoding hypothetical type VI secretion system components. Through the generation of several T6SS associated gene deletion mutants, we have shown significant attenuation of the bacterium in pneumonic models of plague. Combinatorial deletions of T6SS associated genes resulted in further augmenting attenuation as well as providing protection against subsequent re-challenge with wild-type (WT) bacteria. For therapeutic development, traditional drug discovery is an inefficient and costly process; however, systematic screening of Food and Drug Administration (FDA)-approved therapeutics for other indications in humans offers a rapid alternative approach. Utilizing this approach, we screened a library of 780 FDA-approved drugs to identify molecules that rendered RAW 264.7 murine macrophages resistant to cytotoxicity induced by the highly virulent Yersinia pestis CO92 strain. Following in vitro screening, a total of 17 prioritized drugs were chosen for further evaluation in a murine model of pneumonic plague to delineate if in vitro efficacy could be translated in vivo. Three drugs, doxapram (DXP), amoxapine (AXPN), and trifluoperazine (TFP), increased animal survivability despite not exhibiting any direct bacteriostatic or bactericidal effect on Y. pestis in vitro and having no modulating effect on crucial Y. pestis virulence factors, suggesting that DXP, AXPN, and TFP may modulate host cell pathways necessary for disease pathogenesis. Taken together, these results provide potential new tools in the arsenal to combat plague infection.