Disclosed are A3 adenosine receptor antagonists and/or partial agonists of formula (I): wherein R1 to R5 are as described herein, as well as pharmaceutical compositions thereof and methods of use thereof. The antagonists or partial agonists find use in treating a number of diseases including cancer, glaucoma, inflammatory diseases, asthma, stroke, myocardial infarction, allergic reactions, rhinitis, poison ivy induced responses, urticaria, scleroderma, arthritis, brain arteriole diameter constriction, bronchoconstriction, and myocardial ischemia, as well as in preventing cardiac ischemia. Also disclosed are radiolabeled compounds of formula (I) and the use thereof in diagnostic imaging of tissues and organs.