Disclosed are purine nucleoside compounds that are selective to A.sub.3 adenosine receptors and are useful for the treatment of cancer and inflammatory diseases. The compounds are shown by the following general formula (I), including isomers thereof: wherein X is sulfur or oxygen; R.sub.1 is hydrogen, alkyl, benzyl, halobenzyl, or phenylalkyl; R.sub.2 is hydrogen, halogen, alkoxy, alkenyl, alkynyl, alkylthio, or thio; R.sub.3 and R.sub.3' are hydrogen, hydroxyalkyl, alkoxycarbonyl, or alkylaminocabonyl, whereas R.sub.3 and R.sub.3' do not have identical substituents simultaneously; and R.sub.4 is hydrogen or alkyl. Also disclosed are a pharmaceutical composition comprising a compound of formula (I), an isomer, or its pharmacologically acceptable salt as an active ingredient and a method for preventing or treating various diseases, state, or condition, including asthma, inflammation, cerebral ischemia, heart diseases, and cancer. 1