WHICH COMPONENT OF FLAXSEED, WITH OR WITHOUT TAMOXIFEN, IS MORE EFFECTIVE IN REDUCING HUMAN TUMOR GROWTH?

Lilian U. Thompson, Jasdeep Saggar, Jian-Min Chen, Paul Corey, Sandra Sacco

Department of Nutritional Sciences, Faculty of Medicine

University of Toronto, Toronto, Ontario, Canada M5S 3E2

ABSTRACT

`           Our previous studies have shown that flaxseed (FS), an oilseed rich in the phytoestrogen lignan (secoisolariciresinol diglycoside; SDG) and n-3 fatty acid α-linolenic acid-rich oil (FO), can inhibit the growth of established estrogen receptor positive (ER+) human breast tumors (MCF-7) in ovariectomized athymic mice and in postmenopausal breast cancer patients, and increase the effectiveness of the cancer drug tamoxifen (TAM).  The objectives of this study were (a) to elucidate which major component of FS (SDG or FO) is more responsible for this effect, with or without TAM, and its potential mechanism(s) of action, (b) to determine whether, at the same level present in FS, the SDG–rich FS hull (FH) is just as effective as the pure SDG, and (c) to determine whether sesame seed (SS), another high mammalian lignan- producing oilseed, has the same cancer protective effect as FS. The study used ovariectomized athymic mice with established ER+ human breast tumors (MCF-7) treated for 8 weeks with the different diets, with or without TAM implant.  Results showed that both SDG and FO components of FS have tumor reducing effect, with SDG more effective without TAM, and FO more effective with TAM. Combining SDG and FO reduced each other’s effects. Their effect is due to reduction in cell proliferation and decrease in apoptosis. The potential mechanisms involve the modulation of the ER- and growth factor- signaling pathways. FH and SDG have similar effects.  SS did not exert the same tumor reducing effect as FS indicating that not all high mammalian lignan- producing foods have similar effects.