Elevated Src kinase activity attenuates Tamoxifen response in vitro and is associated with poor prognosis clinically.

Activated Src kinase may contribute to the progression and spread of breast cancers and recent in vitro evidence suggests a role for Src in acquired endocrine resistance. The purpose of this study was to investigate whether modulation of Src activity in endocrine-sensitive and endocrine-resistant breast cancer cells directly affected their phenotype and sensitivity to 4-hydroxy Tamoxifen (tamoxifen) and to determine whether Src activity in breast cancer tissue affected patient outcome. Expression of constitutively active Src in ER-positive, endocrine-sensitive MCF7 breast cancer cells resulted in the development of an aggressive phenotype, akin to that previously observed in cell models of Tamoxifen resistance, and, significantly, attenuated their response to tamoxifen. Conversely, expression of dominant negative-Src in tamoxifen-resistant MCF7 cells resensitized them to tamoxifen. An exploratory immunohistochemical study of an archival primary breast tumor series (n = 75) with parallel clinicopathological data and in normal breast tissues (n = 19) revealed higher levels of activated Src in the cytoplasm (p < 0.01) and lower levels of nuclear Src (p < 0.01) in tumor tissue compared with normal tissue. Whereas elevated levels of activated-Src in the cytoplasm of tumors was significantly associated with reduced survival in ER+ patients (p = 0.031), elevated levels of activated Src within the nucleus appeared to associate with an improved hormonal response. Together these data are further suggestive of a role for Src in breast cancer where it may alter response to endocrine therapy.

The emerging role of the LIV-1 subfamily of zinc transporters in breast cancer.

Zinc transporter LIV-1 (SLC39A6) is estrogen regulated and present in increased amounts in estrogen receptor-positive breast cancer as well as in tumors that spread to the lymph nodes. The LIV-1 subfamily of ZIP zinc transporters consists of nine human sequences that share considerable homology across transmembrane domains. Many of these sequences have been shown to transport zinc and/or other ions across cell membranes. Increasingly, studies have implicated members of the LIV-1 transporter subfamily in a variety of diseases. We review these studies and report our own investigations of the role in breast cancer of the nine LIV-1 zinc transporters. We have documented the response of these transporters to estrogen and antiestrogens, and also their presence in our models of resistance to antiestrogens. Resistance to antiestrogen drugs such as tamoxifen and fulvestrant often occurs in advanced breast cancer. In these models we observed differential expression of individual LIV-1 family members, which may be related to their observed variable tissue expression. We were unable detect ZIP4, which is known to be expressed in the intestine. HKE4/SLC39A7 had elevated expression in both antiestrogen-resistant cell lines, and ZIP8 had elevated expression in fulvestrant-resistant cells. In addition, we investigated the expression of the nine LIV-1 family members in a clinical breast cancer series. Although a number of different LIV-1 family members showed some association with growth factor receptors, LIV-1 was solely associated with estrogen receptor and a variety of growth factors commonly associated with clinical breast cancer. HKE4, however, did show an association with the marker of cell proliferation Ki67 the spread of breast cancer to lymph nodes.

Determination of the isoflavonoids genistein and daidzein in biological samples by gas chromatography-mass spectrometry.

BACKGROUND: The marked differences in the incidences of both breast and prostate cancer between the East and the West have been attributed to habitual diet. Traditionally, Japanese and Far Eastern people in general consume large quantities of soya and soya-derived foodstuffs. Diphenolic soya phytoestrogens have weak oestrogenic and anti-oestrogenic properties and have been implicated in preventing or limiting the early processes associated with breast and prostate carcinogenesis. METHODS: We have developed a gas chromatography-mass spectrometry procedure that is suitable for measurement of the phytoestrogens daidzein and genistein in serum, urine and tissue samples. RESULTS: In serum samples of Japanese subjects mean (standard deviation) concentrations of daidzein [men, 281 (375.5) nmol/L; women, 246 (369.4) nmol/L] and genistein (men, 493 (604.4) nmol/L; women, 502 (717.6) nmol/L] were approximately 15 times higher than the mean levels achieved in British men [daidzein, 18.2 (20.4) nmol/L; genistein, 34.1 (27.2) nmol/L] and women [daidzein, 13.5 (11.6) nmol/L; genistein, 30.1 (31.2) nmol/L]. In pharmacokinetic studies of British subjects, maximum levels of daidzein and genistein were achieved within 6-8 h after the consumption of a cereal bar containing 20 mg of soya isoflavonoids; these levels were very similar to the mean levels achieved in normal Japanese subjects. Unlike serum, the mean daidzein concentration in urine from British subjects was higher than the mean genistein concentration (1.66 and 0.72 micromol per 24 h, respectively); following soy supplementation, urinary isoflavonoid levels were increased at least 10-fold. CONCLUSIONS: Serum daidzein and genistein concentrations are lower in British subjects than in Japanese subjects; this may be due to dietary differences.