Biochemical studies on cytidine deaminase and adenosine deaminase

Rhodium(II) acetate has been found to inhibit cytidine deaminase and deoxycytidine kinase in Swiss albino and BDF[lowered 1] mouse, respectively, in vitro. The phosphorylation of ara-C in L1210/S cells in vivo was slightly increased by this compound. A portion of the synergistic effect of ara-C and rhodium(II) acetate in the treatment of L1210/S cells bearing mice may partly be due to this slight increase in phosphorylation of ara-C observed. DHMPR (1,6-dihydro-6-hydroxymethylpurine riboside) has been found to decrease the deamination of ara-A in L1210/S cells in vitro. This compound has not shown any effects on phosphorylation and deamination of ara-A in L1210/S cells in vitro and in vivo, respectively. The loss of the inhibitory activity of DHMPR against adenosine deaminase in vivo suggests the breakdown of this compound in the in vivo environment. The compound 21 -deoxycoformycin has been found to be a potent inhibitor of adenosine deaminase partially purified from BDF[lowered 1] mouse brain. The mouse injected with this compound intraperitoneally showed about 68% inhibition of brain adenosine deaminase within 15 minutes after the injection and the inhibition lasted more than 24 hours. Combination therapy of ara-A and 2'-deoxycoformycin in BDF[lowered 1] mice bearing CNS L1210/S tumor showed a significant increase in the life span of these mice.