Interactive effects of sesame seed and tamoxifen on estrogen dependent breast cancer in athymic nude mice

Flaxseed (FS), the richest source of mammalian lignan precursor protects against breast cancer and increases the effectiveness of the breast cancer drug tamoxifen (TAM). Ingestion of sesame seed (SS) produces mammalian lignans comparable to FS but there is limited data on its anticancer potential. This study determined in an ovariectomized athymic nude mouse model, the interactive effects of SS and TAM on estrogen (E2) responsive breast cancer (MCF‐7) in the presence of high or low E2 levels. In study 1, mice (with low E2 to mimic post‐menopausal condition) with established MCF‐7 tumors were fed a basal diet and treated for 7 weeks as follows: 1) no treatment (–E2 control); 2) 10% SS; 3) TAM implant; 4) 10% SS + TAM; 5) E2 implant (+E2 control). Study 2 was similar to study 1 except that apart from the –E2 control, all groups received an E2 implant to mimic high E2 levels in pre‐menopausal women. Palpable tumor size was monitored weekly. Final tumor area, weight, cell proliferation, and apoptosis were also measured. In study 1, SS regressed tumor size similar to the –E2 control, while TAM and SS + TAM did not, resulting in larger tumors than –E2 control (P<0.05). In study 2, while SS did not, TAM regressed tumors to a final size that was 56% (p<0.05) of + E2 control. However, when SS was combined with TAM, TAM's inhibitory effect was negated resulting in tumors that did not differ in size from +E2 control. Unlike apoptosis, tumor cell proliferation related positively to palpable tumor area (p<0.05, r=0.52). In summary, 10% SS did not exert a protective effect nor strengthen the effect of TAM in MCF‐7 tumors, in part due to its effects on cell proliferation. Supported by NSERC