Evaluation of novel in vitro and in vivo models to characterize anti-Shigella therapeutic PK/PD relationships

PROJECT SUMMARY/ABSTRACT Enteric infection with Shigella spp. can lead to symptoms ranging from acute watery diarrhea to sudden, severe dysentery. Approximately 164,000 diarrheal deaths annually are attributed to Shigella (12.5% of total diarrheal deaths) with a disproportionate impact in low-middle income countries (LMIC). The impact in LMIC was recently illustrated by a reanalysis of the Global Enteric Multicenter Study (GEMS) which found that Shigella has the highest attributable fraction for diarrhea in children < 60 months. While recent studies have highlighted the burden of the disease, there has been a concurrent reduction in therapeutic options for the treatment of shigellosis as drug resistant strains increase in prevalence. In addition, increasing reports of drug resistant shigellosis cases in the men who has sex with men (MSM) community confirm that the impact isn't limited to LMIC. Moving forward, there are critical gaps in the development of new shigellosis treatments. The long-term goals of the proposed work are to establish a rigorous pre-clinical framework which can be used to identify repurposing opportunities or new chemical entities for the treatment of shigellosis. Our previous innovative studies on the gut localized pathogen Cryptosporidium demonstrated the importance of gastrointestinal drug exposure for in vivo anti-Cryptosporidium efficacy. The pharmacokinetic/ pharmacodynamic (PK/PD) relationship for anti-Cryptosporidium drugs was characterized with in vitro and in vivo models of cryptosporidiosis. Our central hypothesis for this proposal is that a similar approach with in vitro and in vivo models can be used to establish the relationship between drug exposure and in vivo efficacy for shigellosis treatments. However, while there currently is no "gold standard" for the treatment of cryptosporidiosis in humans, there are a set of approved antibacterials with variable clinical efficacy against shigellosis in humans. Towards our hypothesis, we have initiated the development of in vitro and in vivo models of Shigella infection which can be used to characterize the efficacy of anti-Shigella therapeutics. The exciting preliminary data from these models suggest that they can be used to identify PK/PD relationships for antibacterials used to treat shigellosis. This crucial information will assist in our understanding of why the efficacy of antibacterials differ in the clinic. We propose to evaluate the PK/PD relationship for antibacterials by undertaking the following three Specific Aims: (1) To characterize the anti-Shigella efficacy of antibacterials with a panel of in vitro models. (2) To investigate the in vivo efficacy and pharmacokinetics of antibacterials to treat shigellosis. (3) To identify associations between antibacterial in vitro efficacy, pharmacokinetics, and in vivo efficacy. Taken together, these studies will help us better understand the current treatments for shigellosis and will provide a series of methods to identify new treatment options. In addition, the results of the work will provide fundamental support for drug discovery in infectious disease, especially in the area of enteric infections.