Combined inhibitory effect of formestane and herceptin on a subpopulation of CD44+/CD24low breast cancer cells

Abstract

In breast cancer, stromal cells surrounding cancer epithelial cells can influence phenotype by producing paracrine factors. Among many mediators of epithelial-stromal interactions, aromatase activity is perhaps one of the best studied. Clinical data suggest that estrogen-independent signaling leads to increased proliferation even during therapy with aromatase inhibitors (AIs). Molecular mechanism of crosstalk between the estrogen receptor (ER) and the epidermal growth factor receptor (HER) family have been implicated in resistance to endocrine therapy, but this interaction is unclear. The ability of aromatase to induce estradiol biosynthesis provides a molecular rationale to combine agents that target aromatase activity and the HER pathway. We targeted stromal-epithelial interactions using formestane, which exerts antiaromatase activity, combined with the monoclonal anti-HER2 antibody herceptin, in a subpopulation of CD44+/CD24low cells sorted from epithelial-mesenchymal co-cultures of breast cancer tissues. The growth inhibition was respectively 16% (P < 0.01) in the response to herceptin, 25% to formestane (P < 0.01), and 50% (P < 0.001) with the combination of the two drugs, suggesting that herceptin cooperates with formestane-induced inhibition of aromatase and this effect could be mediated through HER family receptors. In cells which expressed ERa, formestane/herceptin combination suppressed the mRNA expression of aromatase and HER2 and decreased cyclin D1 expression. These results show that combination therapies involving AIs and anti-HER2 can be efficacious for the treatment of cancer in experimental models and suggest that subtyping breast tumors gives useful information about response to treatment. (Cancer Sci 2010; 101: 1661-1669 T umor phenotype is influenced by genetic and epigenetic alterations, tumor stroma, and the systemic environment, which lead to a complex mixture of factors that represent the tumor microenvironment.(1) Estrogens play a critical role in the development of breast cancer. Six enzymes catalyze the conversion of cholesterol to biologically active 17-b-estradiol (E2). The aromatase enzyme catalyzes the final and key step of estrogen biosynthesis, that is the conversion of C19 steroids to estrogens. In premenopausal women, most plasma estrogen is synthesized in the ovaries and a small proportion (<10%) derives from peripheral synthesis by aromatase, which is present in subcutaneous fat. As a woman ages, the breast's epithelial tissue is gradually replaced by adipocytes. In postmenopausal women, estrogens are synthesized by peripheral aromatization from androgens and peripheral aromatase activity increases with age.(2) Most patients with breast cancer are postmenopausal women and 75% of them have estrogen-dependent tumors defined by estrogen receptor (ER) positivity.(3,4) As estrogens synthesized locally or peripherally by aromatase are able to induce mitogenic signals, the ER has long represented the target for endocrine therapies that aim to block the action of estrogen on tumor ce...

Epigenetic downregulation of HER2 during EMT leads to tumor resistance to HER2-targeted therapies in breast cancer

“…Basal breast cancer cell line JIMT-1 which is HER2-positive, trastuzumab-refractory, ER-negative, and Vimentin-positive is a best cell model to explain the link between HER2, EMT and trastuzumab resistance. De novo resistance of JIMT-1 cells to trastuzumab can be explained by the emergence of trastuzumab-resistance BCSCs due to the dynamic interaction between HER2 and EMT [19,[38][39][40][41][42][43]. The subpopulation of CD44+/CD24-BCSC in the early culture of the JIMT-1 cell line is reported around 10%.…”

HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance

“…Basal BC cell line JIMT-1 cells are HER2+, trastuzumab-refractory, ER−, and Vimentin+. The de novo resistance of JIMT-1 cell to trastuzumab can be explained by the emergence of trastuzumab-resistance BCSCs due to the dynamic interaction between HER2 and EMT [98,99,100,101,102,103,104]. JIMT-1 cell line is composed of approximately 10% CD44+/CD24− BCSC.…”

“…Treatment of CD44+/CD24− BCSCs derived from breast tumor tissues with formestane, an aromatase inhibitor, results in a 16% ( p < 0.01) decrease in cell proliferation in response to single-agent trastuzumab and 50% decrease ( p < 0.001) in response to combined trastuzumab and formestane treatment. The combined treatment also inhibits the expression of EGFR, HER2, Aromatase and Cyclin D1 in CD44+/CD24− cells, which suggests that targeting HER2 by trastuzumab may inhibit the growth of CD44+/CD24− BCSCs through the inhibition of cell cycle progression [101]. Some other reports suggest that preferential killing of the putative CD44+/CD24− BCSCs might be sufficient to overcome primary resistance to trastuzumab.…”

Issues of banking breast cancer cells to generate mammospheres

“…Studies to determine the effects of freeze and thaw on mammospheres derived from the MCF7 breast cancer cell line demonstrate that cryopreservation does not affect cellular proliferation and function but increases the rate of senescence mediated pathway (Karimi-Busheri et al 2010). Comparison of plates, media and supplements used to mammospheres formation from single cell suspension of tumor cells are reported on Table 1 (Dontu et al 2003;Ponti et al 2005;Fillmore and Kuperwasser 2008;Mani et al 2008;Klopp et al 2010;Cavaliere et al 2010). Widely used protocols of Dontu et al (2003) and Ponti et al (2005) are reported to be successful to propagate cancer stem cells on low or ultra low attachment surface of 6 or 24-well plates with cell dilutions ranging from 1 to 1,000 cells/mL.…”