Cell growth inhibitory effects of caulerpenyne, a sesquiterpenoid from the marine algae Caulerpa taxifolia.

Caulerpa taxifolia (Vahl) C. Agardh (Ulvophyceae, Caulerpales) is an algae of tropical origin that was accidentally introduced into the Mediterranean in 1984. Caulerpenyne (Cau) is the major metabolite present in Caulerpa taxifolia. This metabolite has previously been shown to be cytotoxic against cell lines in culture as in KB cells and fibroblasts from hamsters. Cau along with 6 other drugs representative of the major classes of anticancer products was tested against 8 cancer cell lines of human origin. Cau demonstrated growth-inhibitory effects in all cases with some variability between cell lines; this inter-cell variability was, however, less marked than that observed with the anticancer drug tested. Cells of colorectal cancer origin were the most sensitive to the presence of Cau with IC50 values of 6.1 and 7.7 microM. Increasing the duration of contact between Cau and the cells from 75 min to 29.5 hr did not improve the cytotoxic efficacy of this compound. When Cau was pre-incubated in the culture medium for from 7 to 83 min before being exposed to CAL 27 cells (head and neck cancer origin), there was a constant loss of cytostatic action of Cau as a function of Cau pre-incubation time. As the bovine serum albumin concentration increased in the culture medium, the concentration-response curves showed a constant shift towards the right, indicating a loss of cytostatic activity of Cau. In the presence of Cau, cells in culture clearly exhibited an early and marked shift into S phase followed by a blockade into the premitotic G2 M phase. Possible targets for CAU remain to be identified. Cau needs to be tested on tumor bearing animals to confirm this promising antiproliferative activity.