The adenosine A2a receptor (A2aR) plays a critical role in controlling inflammation. Endogenous adenosine is elevated at inflamed sites, where it engages the A2aR to down-regulate the inflammatory response and limit tissue damage. While activation of the A2aR with synthetic orthosteric agonists attenuates inflammation in animal models of disease, this therapeutic approach is limited by adverse effects due to unintended activation of the A2aR outside the target tissue. The current research is designed to explore an alternative approach: the targeted enhancement of the A2aR via positive allosteric modulation, which is expected to have a focused effect at disease sites where endogenous adenosine is elevated. The goal of this proposal is to demonstrate that the A2aR is amenable to positive allosteric modulation, and that such modulation will mount a discernible anti-inflammatory response. These studies will make use of a recently identified positive allosteric modulator of the A2aR, AEA061, as well as human and mouse primary cells and an engineered cell line (CHO-hA2aR) stably expressing the human A2aR (hA2aR).
Specific Aim 1 is to demonstrate that the A2aR is amenable to positive allosteric modulation. First, to determine whether the increased cAMP production upon positive allosteric modulation of the A2aR in CHO-hA2aR cells is a direct consequence of A2aR activation, AEA061-induced A2aR-dependent Gas activation will be measured by quantifying GTPg35S incorporation into the Gas subunit. Second, to investigate whether functional enhancement of the A2aR by AEA061 is due to altered orthosteric agonist binding kinetics, equilibrium-binding experiments will be performed to evaluate the adenosine affinity and Bmax at the hA2aR in the presence and absence of AEA061. Third, to examine allosteric modulator-mediated pathway-biased signaling, we will compare the effect of AEA061 on Gas-driven cAMP and Gaq/11-driven inositol phosphate production in CHO-hA2bR cells.
Specific Aim 2 is to determine whether positive allosteric modulation of the A2aR alters inflammatory cytokine and chemokine production/release in vitro and in vivo. To evaluate the in vitro effects of positive allosteric modulation, cytokine productio by LPS-stimulated human and mouse monocytes will be quantified in the presence and absence of AEA061. To assess in vivo effects, plasma inflammatory cytokine and chemokine levels of LPS-challenged control and A2aR-deficient mice with and without AEA061 treatment will be determined. Additional in vivo studies will assess the influence of positive allosteric modulation on disease progression in a rodent model of chronic inflammatory arthritis. If successful, we will have validated that increasing A2aR responsiveness to endogenous adenosine with the administration of a positive allosteric modulator, that has no intrinsic abilityto activate the A2aR, is an effective strategy to reduce progression of disease characterized by inflammation.
Inflammation is a natural consequence of a response to injury and is auto-regulated by the body's natural control mechanisms. Chronic persistent inflammation is an abnormal accompaniment of many disease processes that when left unchecked by naturally occurring control systems leads to organ dysfunction. The focus of the current research proposal is to identify, understand and provide a means of therapeutic exploitation of a previously unrecognized component of a key natural pathway that self-regulates inflammation.