In particular, hCA isoforms II and IX (tumor-associated) were more susceptible to inhibition by the synthesized derivatives, with K<sub>I</sub>s in the range of 2.6-598.2 nM for hCA II, and of 16.1-321 nM for hCA IX.
In contrast, GPR109A is a tumor suppressor, and decreased synthesis of β-hydroxybutyrate as its agonist suppresses signaling via this receptor, thus attenuating the tumor-suppressing function of GPR109A.
Interesting inhibitory activities were observed against all these isoforms. hCA I, an isoform involved in several eye diseases was inhibited moderately with K<sub>I</sub>s in the range of 191.8-904.2 nM, hCA II, an antiglaucoma drug target was highly inhibited by the new sulfonamides, with K<sub>I</sub>s in the range of 0.75-8.8 nM. hCA IX, a tumor-associated isoform involved in cancer progression and metastatic spread was potently inhibited by the new sulfonamides, with K<sub>I</sub>s in the range of 2.3-87.3 nM, whereas hCA XII, and antiglaucoma and anticancer drug target, was inhibited with K<sub>I</sub>s in the range of 6.1-71.8 nM.
Overall, our data indicate that GPR109A acts as a tumor suppressor in colon cancer, and the host immune system might use IFNγ to counteract DNA methylation-mediated GPR109A silencing as a mechanism to suppress tumor development.
In addition, deletion of Gpr109a in mice increased tumor incidence and triggered early onset of mammary tumorigenesis with increased lung metastasis in MMTV-Neu mouse model of spontaneous breast cancer.