Effect of cyclooxygenase-2 (COX-2) inhibitors on prostate cancer cell proliferation

Background: The tricyclic cyclooxygenase-2 (COX-2) inhibitors celecoxib and rofecoxib exhibit different magnitudes of antiproliferative activity against the human prostate cancer cell lines LNCaP and PC-3. We investigated the correlation between the COX-2 inhibitory potencies, antiproliferative activities and the nature of the central ring sytem of novel tricyclic COX-2 inhibitors belonging to the diarylcycloalkyl and diatylheterocyclic classes possessing a central 3-membered cyclopropyl (1 and 2), a 5-membered isoxazoline (3), an isoxazole (4) or 2-(5H)furanone (5), and a 6-membered pyran-2-one (6a-c) ring system. Materials and Methods: Novel tricyclics were synthesized and evaluated in vitro for their COX-1/COX-2 inhibitory activities and their abilities to inhibit cell proliferation in prostate (AT3B-1, PC-3 and LNCaP) and breast (MCF-7) cancer cell lines. A molecular modeling study was carried out to characterize the electronic nature of the central ring systems of the novel tricyclic COX-2 inhibitors. Results: The isoxazoline (3), which exhibited excellent COX-2 inhibitory potency and selectivity, showed growth inhibition in all the cell lines tested with IC50 values of 349 muM (AT3B-1), 378 muM (PC-3), 100 muM (LNCaP) and 200 pM (MCF-7), respectively. The rofecoxib analog (5) and 6-membered pyran-2-ones (6a-c) showed weak inhibition (MCF-7, AT3-B-1 and PC-3) inspite of possessing good COX-2 inhibitory potencies and selectivities. Conclusion: This study demonstrates that the antiproliferative activity profiles exhibited by the novel tricyclic COX-2 inhibitors is dependent on the electronic nature of the central ring system and is independent of their COX-2 inhibitory potencies and selectivities. Accordingly, the 2,3-dimethyl-5-(4-methylsulfonylphenyl)-4-phenyl-4-isoxazoline (3), which possesses an electron rich central 5-membered isoxazole ring, could serve as a lead compound to develop novel drugs to treat prostate cancer.