Pre-clinical studies to repurpose FDA-approved adenosine A2A receptor antagonists for lethal rickettsial infection - Abstract Rickettsial infections caused by obligately intracellular bacteria of the genus Rickettsia (R) are notoriously difficult to clinically diagnose early because of their nonspecific flu-like signs and symptoms. The delays lead to missed treatment windows that result in severe morbidity and mortality. It is forecasted that global climate change will lead to more widespread distribution of rickettsioses. It is crucial to develop therapeutics for severe infections, particularly for clinically delayed diagnosed cases. We reported cAMP-signaling plays a critical role during fatal rickettsioses. The adenosine receptors are a class of transmembrane receptors that can stimulate intracellular cAMP accumulation. The FDA approved A2AR antagonist istradefylline (Istra) for treatment of Parkinson’s disease in 2019. During project R21AI137785, we examined efficacies of Istra in mouse models of lethal R australis and R conorii infections. We observed that, similar to Doxy, initiating daily treatment with Istra up to 48 hrs post-infection (p.i.) conferred protection against lethality in mice. However, no protection was observed when Istra or Doxy was administered individually when treatments begin at 72 hrs p.i. We found that treatments beginning at 72 hrs p.i. using combinations of Doxy and Istra exhibit protection. Mechanistic studies suggest that the inhibition of A2AR enhances the host's innate immune response, resulting in improved bacterial clearance. Our central hypothesis is that A2AR signaling dampens anti-R immunity, and targeting A2AR with FDA- or FDA- Investigational New Drug (IND)-approved drugs may provide a potential avenue for novel therapeutics against severe R infections. During this multiple-PI project, we will perform a mechanistic study to determine the role of A2AR in R infection (Aim 1); utilize cost- and effort-effective approaches to identify lead candidates among FDA/IND-approved A2AR antagonists for therapeutics against R infection using immune signature analyses, single living cells, ex vivo assays, and prioritization and selection based on the overall drug properties including absorption, distribution, metabolism, excretion and toxicity (ADMET) profiles from the FDA database (Aim 2) before moving to in vivo efficacy studies to evaluate the therapeutic efficacy of the optimized lead candidate, solely or combined with Doxy, for the treatment of lethal rickettsial infection at later timepoints (Aim 3). The proposed research is based on more than a decade of extensive studies of the cAMP signaling in R infections immunology, and medicinal chemistry performed in our laboratories and demonstrated in the joint publications of the MPIs, the co-I, and consultants, and directly builds on a number of ongoing or recently completed clinical trials targeting A2AR. Success will save huge amounts of time and resources and lead to the identification of a new class of therapeutics for fatal rickettsiosis and potentially for other bacterial infections given that the reported evidence suggests deletion of A2AR protects animals from polymicrobial sepsis.
