Our previous study has shown that gossypol (GOS) exhibited the potent cytotoxic effect via apoptosis induction against human colorectal carcinoma cells; however, the role of cyclooxygenase 2 (COX-2)/prostaglandin E2 on GOS-induced apoptosis is still unknown. In the present study, 12-O-tetradecanoylphorbol-13-acetate (TPA) addition significantly inhibited GOS-induced apoptosis in human colorectal carcinoma cells COLO205 in according with inducing COX-2 protein/PGE2 production. TPA inhibition of GOS-induced apoptosis was blocked by adding protein kinase C (PKC) inhibitors including ST, GF, and H7, characterized by an occurrence of cleaved caspase 3 proteins and a decrease in COX-2 protein/PGE2 production in COLO205 cells. Addition of COX activity inhibitors including NS398, aspirin (AS), diclofenac (DI), and indomethacin (IN) suppressed TPA protection of GOS-induced apoptosis with decreased PGE2 production in COLO205 cells. Application of PGE2, but not it analogues PGD2, PGJ2, and PGF2, protected COLO205 cells from GOS-induced DNA ladders, and the EP1 receptor agonist 17PT-PGE2 mimicked the protection by PGE2, whereas the selective EP2 receptor agonist butaprostol (BUT), EP3 receptor agonist sulprostol (SUL), and EP4 receptor agonist PGE1 alcohol (PGE1) showed no significant effect on GOS-induced apoptosis in COLO205 cells. PGE2 protection of GOS-induced apoptosis was reversed by adding a selective EP1 receptor antagonist SC-19220. Furthermore, GOS had less apoptotic effect on HT-29 colorectal carcinoma cells which expressed higher level of endogenous COX-2 protein than COLO205 cells, and decreased COX-2 protein level via COX-2 siRNA significantly elevated GOS-induced cell death in HT-29 cells. COLO205-T cells were established through sustained TPA incubation of COLO205 cells, and COLO205-T cells showed a lower sensitivity to GOS-induced cell death with increased COX-2 (not Bcl-2 and Mcl-1) protein than parental COLO-205 cells. A decrease in COX-2 protein expression in COLO205-T cells by COX-2 siRNA transfection enhanced GOS-induced cell death by MTT assay. The notion of COX-2/PGE2 activation against GOS-induced apoptosis in colon carcinoma cells was demonstrated, and combination of GOS and COX-2 inhibitors to treat colon carcinoma reserved clinical potential for further investigation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C34.