Cyclic Phosphatidic Acid Stimulates cAMP Production and Inhibits Growth in Human Colon Cancer Cells

Colon cancer is a malignancy that develops in colon and rectal tissues. The prognosis for metastatic colon cancer remains poor, and novel therapeutic options are required to reduce colon cancer mortality. Recently, intracellular cAMP levels have been suggested to influence the behavior of cancer cells. Intriguingly, cyclic phosphatidic acid (cPA) and its structural analogs inhibit growth in many cancer cell lines, and our previous work has suggested that cPA increases cAMP production. Phosphodiesterase (PDE) type 3 isoforms PDE3A and PDE3B are expressed mainly in cardiovascular tissue and adipose tissue, respectively. Moreover, increase in intracellular cAMP levels has been associated with the inhibition of growth in colon cancer cells. These findings suggest that cPA could be used in colon cancer therapy. In this study, we found that cPA inhibited the growth of HT-29 cells, which express high levels of PDE3B, but not the growth of DLD-1 cells, which express low levels of PDE3B. Furthermore, cPA inhibited the phosphorylation of Akt in HT-29 cells in a dose-dependent fashion. Our results suggest that PDE3B expression and intracellular cAMP levels are correlated with the proliferation of colon cancer cells. These findings demonstrate for the first time that cPA may serve as a useful a molecule in targeted therapy for colon cancer.