Omega-3-Acid Ethyl Esters Block the Protumorigenic Effects of Obesity in Mouse Models of Postmenopausal Basal-like and Claudin-Low Breast Cancer

Abstract

Obesity induces chronic inflammation and is an established risk and progression factor for triple-negative breast cancers, including basal-like (BL) and claudin-low (CL) subtypes. We tested the effects of dietary supplementation with ethyl esters of the marine-derived anti-inflammatory omega-3 fatty acids eicosapentaenoic and docosahexaenoic acid (EPA+DHA; Lovaza) on growth of murine BL and CL mammary tumors. Female ovariectomized C57BL/6 mice were fed a control diet or a diet-induced obesity (DIO) diet with or without EPA+DHA (0.025%, resulting in blood levels of EPA and DHA comparable with women taking Lovaza 4 g/d) for 6 weeks. All mice were then orthotopically injected with Wnt-1 cells (a BL tumor cell suspension derived from MMTV-Wnt-1 transgenic mouse mammary tumors) or M-Wnt cells (a CL tumor cell line cloned from the Wnt-1 tumor cell suspension). Mice were killed when tumors were 1 cm in diameter. EPA+DHA supplementation did not significantly affect Wnt-1 or M-Wnt mammary tumor growth in normoweight control mice. However, EPA+DHA supplementation in DIO mice reduced growth of Wnt-1 and M-Wnt tumors; reduced leptin:adiponectin ratio and proinflammatory eicosanoids in the serum; improved insulin sensitivity; and decreased tumoral expression of COX-2 and phospho-p65. Thus, EPA+DHA supplementation in mouse models of postmenopausal BL and CL breast cancer offsets many of the protumorigenic effects of obesity. These preclinical findings, in combination with results from parallel biomarker studies in women, suggest that EPA+DHA supplementation may reduce the burden of BL and CL breast cancer in obese women.

Figure 1

EPA+DHA supplementation does not alter body composition, body weight or feed intake. A, body composition is assessed as the percentage of fat and lean tissue at 5 weeks, B, average body weight (1-6 weeks on diet) and C, average kcals consumed per day (1-6 weeks on diet); n=10 per group. Means ± SEM, statistically significant (P<0.05) differences are indicated by different letters.

Figure 2

The effect of diet regimens on serum hormones. A, Leptin, B, Adiponectin, C, Leptin:Adiponectin ratio, D, IGF-1, E, Glucose, F, GTT conducted at 6 weeks on diet, n=10 per group. Means ± SEM, statistically significant (P<0.05) differences are indicated by different letters.

Figure 3

The effect of a DIO regimen +/− EPA+DHA supplementation on tumor growth. A, in vivo M-Wnt (claudin—low) and Wnt-1 (basal-like) mammary tumor growth, n=10 per group. B, M-Wnt and Wnt-1 average ex vivo tumor weight, n=10 per group. C, representative photomicrographs of pathology and IHC staining of tumors for Ki-67 and bar graphs representing the Aperio image quantitation, scale bars indicate 100 μm, n=6 per group. Means ± SEM, statistically significant (P<0.05) differences are indicated by different letters.

Figure 4

The effect of a DIO regimen +/− EPA+DHA supplementation on IHC tumoral staining. A, representative photomicrographs of pathology and IHC staining of tumors for cleaved caspase-3, COX-2 and phospho-p65. B, bar graphs representing the Aperio image quantitation, scale bars indicate 100 μm, n=6 per group. Means ± SEM, statistically significant (P<0.05) differences are indicated by different letters.