Formycin B-resistant mutants of Chinese hamster ovary cells: novel genetic and biochemical phenotype affecting adenosine kinase.

Abstract

The pyrazolopyrimidine ribosides formycin A and formycin B constitute an important class of nucleoside analogs (C-nucleosides) which, rather than having the usual C-N bond in the ribosidic linkage, are linked by a carbon-carbon bond (7,29). As a result of this structural modification, these antibiotics are hydrolytically stable and possess very useful biochemical and medicinal properties, including antivirus and anticancer (7,15,25,29). Earlier biochemical studies with these analogs have indicated that unlike formycin A and other adenosine analogs (e.g., toyocamycin and tubercidin), formycin B, which is an analog of inosine, is not phosphorylated in cells (31). However, formycin B has been reported to be a good inhibitor of human purine nucleoside phosphorylase (6,26,28)

Molecular Characterization of Chinese Hamster Cells Mutants Affected in Adenosine Kinase and Showing Novel Genetic and Biochemical Characteristics

“…The Toy R -4, DrToy R -18 and Fom R -4 mutants of CHO cells were also isolated and partially characterized in earlier work [24,32,34]. Of these Toy R -4 and DrToy R -18 mutants are highly resistant to both N- and C-Ado analogs.…”

Structure-Activity Studies on Mammalian Adenosine Kinase

“…Aliquots of 50 l were withdrawn at various times in the linear reaction range and added to 1 mL of ice-cold 100 mM lanthanum chloride to precipitate the phosphorylated product. The precipitate was collected, washed and radioactivity representing AMP formation was counted and analyzed as previously reported (17,31,33). Thermal inactivation was performed by incubating the enzyme samples at 45°C.…”

Adenosine kinase and ribokinase – the RK family of proteins

“…Another interesting kind of mutant affected in AK has been obtained in CHO cells by selecting in the presence of C-nucleosides formycin A and B [81]. These novel mutants (referred to as Class B) exhibit cross-resistance to, and are unable to phosphorylate, various C-adenosine analogues, while remaining sensitive and fully capable of phosphorylating N-adenosine analogues [84]. The genetic lesion in these mutants thus specifically prevents the phosphorylaCell.…”

“…65,2008 Review Article tion of C-adenosine analogues without any effect on N-adenosine analogues. What is also intriguing with the Class B mutants is that, although these cells are sensitive to N-nucleosides, no AK activity (using adenosine, a N-nucleoside) could be detected in their cell extracts [84]. Some other mutants affected in AK (Class C) show reduced phosphorylation and affinity of certain adenosine analogues to which they exhibit increased resistance [73].…”