Simultaneous blockade of the downstream effects mediated by both receptor subtypes with a dual inhibitor has the potential to reverse adenosine-mediated suppression of tumor immune surveillance as either a single-agent treatment or in combination with other immunotherapy agents such as anti-PD-1/PD-L1 monoclonal antibodies. This publication describes the discovery and optimization of a novel series of potent and selective dual A2AR/A2BR antagonists, resulting in compound 46 (MK-1088) being identified for progression to human clinical studies.