Potentiation by 2'-deoxycoformycin of the inhibitory effect of xylosyladenine on nuclear RNA synthesis in L1210 cells in vitro

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The effect of the adenosine deaminase inhibitor, 2'-deoxycoformycin (dCF), on the inhibitory effect of 9-β- d-xylofuranosyladenine (XA) on nuclear RNA synthesis was examined in L1210 cells in vitro. Pretreatment of cells for 15 min with a 100 per cent inhibitory dose (1 × 10 −6 M) of dCF resulted in approximately a 3- to 8-fold reduction in the 50 per cent inhibitory dose ( id 50) of XA for [ 3H]uridine and [ 3H]thymidine incorporation into RNA and DNA respectively. The id 50 for XA for RNA synthesis vs DNA synthesis was 5-fold lower in the absence of dCF and 20-fold lower in the presence of dCF, indicating the greater sensitivity of RNA synthesis to this inhibitor. Fractionation of nuclear RNA into rRNA, non-poly(A) heterogeneous RNA and poly(A)heterogeneous RNA revealed the latter species of RNA to be less sensitive to XA in the absence of dCF; however, in the presence of dCF, all three species of nuclear RNA showed similar sensitivities. Nuclear polyadenylic acid synthesis was among the most sensitive RNA fractions to XA, and was also inhibited to a greater degree by pretreatment of cells with dCF. These results indicate that XA is potentiated markedly by inhibition of adenosine deaminase, and that deamination serves as a major catabolic route for this drug.