Function- and interaction-based discovery of negative allosteric modulators of the A2A Receptor

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Project Summary Immune checkpoints are critical for maintaining immune homeostasis. They prevent overactivation of the immune response. However, aberrant activation of immune checkpoints pathways in certain cancers reduces anti-tumor immunity allowing tumors to proliferate. Therapies targeting immune checkpoints CTLA4, PD-1 and PDL-1 have been successful in treating a wide variety of refractory cancers. However, their efficacy is limited to a small percentage of patients highlighting the need for targeting additional immune checkpoint pathways. In this regard, the blockade of adenosine-adenosine A2A receptor (A2AR) immune checkpoint activation with high-affinity antagonists has shown promise in preclinical studies. As antagonists block adenosine-A2AR immune checkpoint globally, adverse events are anticipated. In contrast, negative allosteric modulators (NAM) conceivably block the activation of adenosine-A2AR immune checkpoint only at tumor sites where adenosine levels are elevated. We envision that blocking the adenosine-A2AR immune checkpoint activation with NAMs is disease-site specific and thus a more directed approach to enhance anti-tumor immunity. We have demonstrated previously that adenosine-A2AR immune checkpoint is amenable to positive allosteric modulation through synthetic small molecules. However, negative allosteric modulation of the adenosine-A2AR immune checkpoint has not been reported. To test our notion, we have designed and synthesized a library of over 300 compounds potentially containing adensoine-A2AR NAMs. In this proposal, we will identify A2AR NAMs utilizing in vitro screening paradigms established in our laboratory. Aim 1: Identify NAMs of the adenosine-A2AR immune checkpoint. (a) The compound library will be screened in a cell- based cAMP assay utilizing CHO cells stably expressing the A2AR. NAMs will be identified on the basis of adenosine-mediated inhibition of cAMP production. (b) NAMs will be confirmed in a radiolabeled agonist binding assay utilizing CHO-A2AR membranes. A reduction in the binding affinity of the A2AR selective agonist CGS 21680 is indicative of NAMs. Aim 2: Identify NAMs with best immune-enhancing activity and A2AR selectivity. (a) NAMs will be screened for their ability to reverse the adenosine-A2AR- mediated inhibition of IFN-g production by a-CD3/CD28-stimulated CD8+ T cells. (b) NAMs with the best immune enhancing activity will be evaluated for A1R, A2BR and A3R activity in cell-based cAMP assays utilizing cell lines stably expressing the receptors. If successful, this will be the first identification of NAMs of the adenosine-A2AR immune checkpoint and demonstration of a novel approach targeting the same.