The effect of
9-deazaadenosine (
c9Ado) on cell lethality and the synthesis of
nucleic acids was investigated in human colon
carcinoma cell line HT-29.
c9Ado produced a rapid threshold-exponential reduction in colony formation as measured by a soft
agar clonogenic assay. This effect was evident after either a 2- or 24-hr exposure interval, and was produced over a very narrow concentration range of
drug. Following 2 hr of
drug exposure at concentrations producing a 1- to 3-log reduction in cell viability,
DNA and
RNA syntheses were inhibited 20% and
protein synthesis was inhibited 35-50%. The latter effect became quite pronounced in comparison to
nucleic acid synthesis 4 hr after
drug treatment. Long treatment intervals (24 hr) with concentrations of
c9Ado producing similar effects on cell viability resulted in 15-35% inhibition of
RNA synthesis, 80-85% inhibition of
DNA synthesis, and 60-70% inhibition of
protein synthesis. None of these metabolic effects could be accounted for by changes in ribonucleoside
triphosphate levels despite the considerable formation of
c9ATP. Measurements of the incorporation of [3H]
c9Ado into total cellular
nucleic acids indicated that the labeling of
RNA was 40-80% greater than that of
DNA. Polysomal
poly(A)RNA contained 300% more [3H]
c9Ado than non-
poly(A)RNA after 2 hr of
drug exposure and 50% more [3H]
c9Ado following 24 hr of treatment. There was no evidence of
DNA strand breakage by incorporated
c9Ado. Analysis of nascent
protein synthesis in
drug-treated cells revealed that this process was inhibited in concert with polysome breakdown. These results suggest that the rapidity by which cell lethality is produced by
c9Ado may be related to inhibition of translation via its incorporation into
RNA.