FIGURE 2.

Hydrolysis-resistant 8-pCPT-modified cAMP analogs as well as 8-pCPT-modified adenosine analogs inhibited [³H]thymidine incorporation (incorp.) into the DNA in PC12 cells, whereas 8-Br-cAMP/8-Br-adenosine did not. PC12 cells were incubated with 10 μm (A and D) or the indicated concentration (B and C) of Sp-8-pCPT-2′-O-methyl-cAMPS, Sp-8-pCPT-cAMPS, 8-pCPT-ado, 8-pCPT-2′-O-methyl-ado, 8-Br-cAMP, or 8-Br-ado for the indicated time (A) or for 48 h (B–D). Then, [³H]thymidine incorporation into the cellular DNA was determined as described in the legend for Fig. 1. Values are means ± S.D. (error bars) of three independent determinations. Asterisks indicate a significant difference between cAMP analog-treated and vehicle-treated cells.