Abstract 3657: Identification of active metabolites of docosohexaenoic acid (DHA): A first step towards unraveling the fish oil/breast cancer conundrum.

The role of fish oil (FO) rich in omega-3 fatty acid (n-3FA) in breast cancer prevention remains controversial. Based on our data showing that a high n-3:n-6 ratio (≥10) is necessary to inhibit N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinogenesis (Zhu Z, et al., Cancer Prev Res 4(10):1675, 2011), we hypothesize that this chemopreventive effect of FO may be due to one of its components (e.g., Docosohexaenoic acid, DHA, 22:6) and/or to the production of Active DHA Metabolites (ADM) which may be present in small and variable amounts in FO preparations used in different preclinical studies. To test this hypothesis, we used LC-TOF/MS followed by tandem mass spectroscopy to quantify ADM in the plasma and mammary tumors of rats fed a 20% CO diet and administered either saline or one of two doses of DHA (1.5 ml/kg and 3.0 ml/kg) by gavage twice a week for 8 weeks following ip MNU injection (50 mg/kg) at 21 days of age. The lower dose of DHA was also given in combination with Tamoxifen (Tam) (0.6 ppm) to test the hypothesis that n-3FA may inhibit the development of antiestrogen resistant tumors. We observed that both doses of DHA similarly inhibited mammary carcinogenesis and that the combination of Tam and DHA was more effective than each of the individual agents. DHA administration caused a significant dose-dependent increase in the plasma levels of several ADM including 4-OH-DHA, 7-OH-DHA, 14-OH-DHA, and 17-OH-DHA. The levels of these ADM were ∼10-fold higher in the tumors of the rats given DHA compared to control, irrespective of the dose of DHA administered. The most abundant ADM in the tumors was 14-OH-DHA followed in order by 17-OH-DHA, 4-OH-DHA, and 7-OH-DHA. In order to compare the biological activity of these ADM to that of the parent compound, we tested in vitro their ability to induce PPARγ activation using a PPARγ reporter assay since PPARγ activation is considered to be a potential mechanism by which n-3FA exert their antitumor action. We observed that every ADM was more effective than DHA by at least 2-fold in inducing PPARγ activity with the following order of magnitude of the effect, 7-OH-DHA > 14-OH-DHA > 4-OH-DHA > 17-OH-DHA. In summary, our studies identify for the first time ADM which may be responsible for the chemopreventive effect of FO. This finding may have major translational significance since compounds with well-defined chemical structure given at optimal concentrations are likely to be more effective chemopreventive agents than FO which contains an inconsistent mixture of FA with varying biological activity. In addition, since DHA inhibits carcinogenesis in Tam-treated rats, these ADM may complement the effect of Tam by inhibiting the development of hormone independent tumors. This work is supported by grant KG081632 from Susan G. Komen for the Cure. Citation Format: Andrea Manni, John P. Richie, Neil Trushin, Bogdan Prokopczyk, A Patterson, John P. Vanden Heuvel, Sharlene Washington, Haifang Xu, Cesar Aliaga, Arunangshu Das, Krishne Gowda, Shantu Amin, Jason Liao, Henry Thompson, Karam El-Bayoumy. Identification of active metabolites of docosohexaenoic acid (DHA): A first step towards unraveling the fish oil/breast cancer conundrum. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3657. doi:10.1158/1538-7445.AM2013-3657