Modulation of Δ9-tetrahydrocannabinol-induced MCF-7 breast cancer cell growth by cyclooxygenase and aromatase

Δ9-Tetrahydrocannabinol (Δ9-THC), a major constituent of marijuana, has been shown to stimulate the growth of MCF-7 breast cancer cells through cannabinoid receptor-independent signaling [Takeda, S., Yamaori, S., Motoya, E., Matsunaga, T., Kimura, T., Yamamoto, I., Watanabe, K., 2008. Δ9-Tetrahydrocannabinol enhances MCF-7 cell proliferation via cannabinoid receptor-independent signaling. Toxicology 245, 141–146]. Although the growth of MCF-7 cells is known to be stimulated by 17β-estradiol (E2), the interaction of Δ9-THC and E2 in MCF-7 cell growth is not fully clarified so far. In the present study, by using E2-sensitive MCF-7 cells that have expressed cyclooxygenase-2 (COX-2) and cytochrome P450 19 (aromatase), we studied whether or not COX-2 and aromatase are involved in Δ9-THC-mediated MCF-7 cell proliferation. It was shown that Δ9-THC-induced MCF-7 cell growth was inhibited by COX-2 inhibitors and was stimulated by arachidonic acid (a COX substrate). However, the growth of MCF-7 cells induced by Δ9-THC was not stimulated by PGE2, and the expression of aromatase was not affected by COX-2 inhibitors, arachidonic acid, and PGE2, suggesting that there is a disconnection between COX-2 (PGE2) and aromatase in Δ9-THC-mediated MCF-7 cell proliferation. On the other hand, Δ9-THC-induced MCF-7 cell growth was elevated by two kinds of aromatase inhibitors. Taken together with the evidence that Δ9-THC-induced MCF-7 cell proliferation was interfered with testosterone (an aromatase substrate) and exogenously provided E2, it is suggested that (1) the growth stimulatory effects of Δ9-THC are mediated by the product(s) of COX-2 except for PGE2, (2) the action of Δ9-THC is modulated by E2, and (3) COX-2 and aromatase are individually engaged in the proliferation of MCF-7 cells induced by Δ9-THC.