Abstract 808: Endocrine resistance: The influence of stromal-epithelial interaction on intracrine pathways of oestrogen synthesis

Abstract

Abstract Resistance to endocrine therapy, both de novo and acquired, poses a significant clinical challenge. Two primary pathways, the aromatase and steroid sulphatase (STS) pathways, exist for the production of estrogenic steroids from androstenedione and DHEAS, respectively. Numerous studies have demonstrated an upregulation of these pathways in breast tumour tissue compared to normal breast tissue. Therapies targeting oestrogenic pathways form the mainstay of the pharmacological approach to breast cancer treatment. The SERM, Tamoxifen, and aromatase inhibitors (AI) such as Letrozole, have shown substantial clinical benefit in hormone-dependent breast cancer patients. Additionally, to date one STS inhibitor has entered clinical trials. Despite this success, a proportion of hormone-receptor positive patients do not respond to hormone therapy with 40% of patients who initially show a response to Tamoxifen relapsing. As little is known about the influence of the tumour microenvironment, particularly stromal-fibroblasts, on these pathways in the development of endocrine resistance, we have examined the influence of stromal-epithelial interactions on the expression of enzymes of steroidogenesis in endocrine resistant cells. Wild type and tamoxifen-resistant MCF-7 breast cancer cells (MCF-7wt and MCF-7TamR, respectively) were indirectly co-cultured with primary fibroblasts derived from breast tumour and reduction mammoplasty samples, using 0.4μm 6-well inserts. Expression levels of 17α-hydroxysteroid dehydrogenase types 1 (17α-HSD1) and 2, (17α-HSD2), aromatase, oestrogen receptor ≤ (ERα) and β, progesterone receptor, steroid sulphatase (STS), and steroid sulphotransferase were assessed basally and in co-culture using RT-PCR. Significantly higher basal expression of STS (p<0.001), aromatase (p=0.012) and 17α-HSD2 (p=0.032) was seen in fibroblast versus epithelial lines. On co-culture a 2.5 - 5 fold up-regulation of aromatase expression was seen in MCF-7wt and MCF-7TamR (p=0.009, p=0.046 respectively). The expression of STS (p=0.150, p=0.05) and 17α-HSD1 (p=0.001, p=0.071) was also increased. Epithelial lines showed a significant down-regulation in ERα on co-culture. Both malignant and normal fibroblast lines demonstrated up-regulation of aromatase expression on co-culture (p=0.037). These data suggest that stromal-fibroblasts make a significant contribution to the tumour hormonal environment through both expression and modulation of the pathways associated with intracrine oestrogen production. The differential effect of cell-type combinations implicates these interactions in both oestrogen sensitivity and insensitivity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 808. doi:1538-7445.AM2012-808