PURINE NUCLEOSIDE PHOSPHORYLASE INHIBITORS - BIOCHEMICAL AND PHARMACOLOGICAL STUDIES WITH 9-BENZYL-9-DEAZAGUANINE AND RELATED-COMPOUNDS

Certain derivatives of 9-deazaguanine that contain arylmethyl, heteroa rylmethyl or cycloalkylmethyl groups at the 9-position are potent inhi bitors of purine nucleoside phosphorylase (PNP, E.C. 2.4.2.1). To dete rmine whether these agents can produce metabolically significant inhib ition of PNP in cells and in animals, the authors performed pharmacolo gical studies with a representative member of the series, 9-benzyl-9-d eazaguanine (BzDAG). BzDAG was a potent inhibitor of PNP from calf spl een (K(i) = 12 nM). It was also an effective inhibitor of PNP in cells and in animals as shown by the findings that it 1) inhibited the conv ersion of inosine to nucleotides in L1210 cells in culture at concentr ations that had little effect on the utilization of hypoxanthine; 2) p otentiated the toxicity of deoxyguanosine to CCRF-CEM cells in culture ; 3) increased the pools of deoxy GTP in CCRF-CEM, Molt-3 and Molt-4 c ells that had been treated with deoxyguanosine; 4) prevented the toxic ity of 6-thioguanosine to HEP-2 cells in culture; 5) increased the pla sma levels of endogenous inosine in rats; and 6) increased the plasma levels of 2',3'-dideoxyinosine in rats that had received BzDAG and did eoxyinosine in combination. Pharmacokinetic analysis of BzDAG in the r at showed it to be 48% orally bioavailable (at a dose of 5 mg/kg). Abo ut 95% of BzDAG was protein bound. After i.v. administration of BzDAG (5 mg/kg), more than 50% of the erythrocyte PNP was inhibited for 40 m in. These results indicate that the 9-substituted-9-deazaguanines are potent orally active PNP inhibitors and are therefore of potential cli nical interest as immunosuppressive and anti-inflammatory agents.