Selective inhibition of carbonic anhydrase IX decreases cell proliferation and induces ceramide-mediated apoptosis in human cancer cells

Recently, carbonic anhydrase (CA) inhibitors have been proposed as a potential new class of antitumor agents. The aim of this study was to evaluate the antitumor activity of three CA inhibitors, namely acetazolamide (AZ) and two newly synthesized aromatic sulfonamides with high affinity for CA IX, 2-(4-sulfamoylphenyl-amino)-4,6-dichloro-1,3,5-triazine (TR1) and 4-[3-(N,N-dimethylaminopropyl)thioreidophenylsulfonylaminoethyl]benzenesulfonamide (GA15), against human tumor cells. The effects of AZ, TR1, and GA15 on cell proliferation and apoptosis were evaluated in CA IX-positive HeLa and 786-O cells and CA IX-negative 786-O/von Hippel-Lindau (VHL) cells. We also investigated whether the potential antitumor activity of these molecules might be mediated by an increase in ceramide production. AZ, TR1, and GA15 could significantly reduce cell proliferation and induce apoptosis in HeLa and 786-O cells. Moreover, all three inhibitors could decrease intracellular pH (pH(i)) and increase ceramide production in the same cells. Treatment with the ceramide synthase inhibitor fumonisin B1 prevented the apoptotic effects of the three CA inhibitors. In all experiments, the effects of aromatic sulfonamides were more pronounced than those of AZ. The three inhibitors did not show any antitumor activity in CA IX-negative 786-O/VHL cells and failed to lower pH(i) or increase intracellular ceramide levels in the same cells. In conclusion, CA inhibition can decrease cell proliferation and induce apoptosis in human tumor cells. The ability of CA inhibitors to decrease pH(i) might trigger cell apoptosis through mediation of ceramide synthesis. Activation of this apoptotic cascade probably is mediated by inhibition of the CA IX isoform.