Figure 2
A: Levels of cAMP in xenograft tissues. (ELISA assays). Gemcitabine and GABA were equally effective in significantly reducing cAMP levels. Nicotine significantly reduced this effect of gemcitabine, a response reversed by simultaneous treatment with GABA. Baclofen alone significantly increased cAMP levels, diminished the effects of gemcitabine and enhanced the adverse effects of nicotine in gemcitabine treated animals. The differences among treatment groups were significant (P < 0.001 by Kruskal-Wallis ANOVA). Data are mean values and standard deviations of five randomly selected xenografts per treatment group. ★Significantly ( p < 0.01 by Mann–Whitney test) different from controls. ✖Significantly (p < 0.01 by Mann–Whitney test) different from gemcitabine alone. Significantly (p < 0.01 by Mann–Whitney test) different from treatment with gemcitabine plus nicotine. The inset shows representative Western blots from xenografts exemplifying downregulated receptor proteins of both GABA-B-Rs in the mice treated with baclofen alone while receptor proteins remained unchanged in the xenograft of mice treated with GABA alone. B: Levels of p-CREB in xenograft tissues. ELISA assays were used to determine the levels of p-CREB in xenograft tissues. The differences among treatment groups were significant (P < 0.0001 by Kruskal-Wallis ANOVA). Gemcitabine and GABA each significantly reduced p-CREB levels, an effect significantly enhanced by the combination of both agents. Nicotine completely blocked this anti-tumorigenic effect of gemcitabine, an effect reversed by GABA. Baclofen had adverse effects similar to nicotine on gemcitabine-induced p-CREB reduction while even significantly increasing p-CREB levels over those observed in controls when given as a single agent. Data are mean values and standard deviations of five randomly selected xenografts per treatment group. ★Significantly ( p < 0.01 by Mann–Whitney test) different from controls. ✖Significantly (p < 0.01 by Mann–Whitney test) different from gemcitabine alone. Significantly (p < 0.01 by Mann–Whitney test) different from treatment with gemcitabine plus nicotine.