PURINE ENZYME PROFILE IN HUMAN COLON-CARCINOMA CELL-LINES AND DIFFERENTIAL SENSITIVITY TO DEOXYCOFORMYCIN AND 2'-DEOXYADENOSINE IN COMBINATION

Different cell lines, 2 from human colon carcinoma (LoVo and HT29) and 1 from Chinese hamster ovary (CHO K-1), were examined to assess the effect of deoxycoformycin (dCF), an inhibitor of adenosine deaminase (ADA), and 2'-deoxyadenosine (dAdo) on their growth. When used alone, neither dCF or dAdo were cytotoxic for the 3 cell lines, while their combination caused inhibition of cell growth, with the following sensitivity: CHO K-1 > LoVo > HT29. We studied the pattern of enzymatic activities involved in the metabolism of dAdo in the 3 cell lines. The phosphorylation of dAdo by adenosine kinase appears to play a central role in the toxicity of the deoxynucleoside in combination with dCF. In fact, CHO K-1 cells, which are the most sensitive, possess the highest level of this enzyme. Moreover, the cytotoxic effect was almost completely reversed in the 3 cell lines when inhibitors of adenosine kinase, such as 5'-amino-5'-deoxyadenosine and iodotubercidine, were added to the culture medium together with dCF and dAdo. In addition, baby hamster kidney (BHK) adenosine-kinase-deficient (AK(-)) cells were highly resistant to this treatment. Uptake inhibition of dAdo using dipyridamole also caused reversal of the toxicity. The AMP and deoxy AMP dephosphorylating activities, much lower in the CHO K-1 cells, also appear to play a central role in the toxicity of dAdo when adenosine deaminase is inhibited. However, our data suggest that other factors may modulate the toxic effect, such as S-adenosyl-homocysteine-hydrolase inhibition by dAdo at high concentrations. (C) 1995 Wiley-Liss, Inc.