Cooperative action of tamoxifen and c-Src inhibition in preventing the growth of estrogen receptor–positive human breast cancer cells

Abstract

It has long been appreciated that estrogenic signaling contributes to breast cancer progression. c-Src is also required for a number of processes involved in tumor progression and metastasis. We have previously identified the K303R mutant estrogen receptor A (ERA) that confers hypersensitivity to low levels of estrogen. Because ERA and c-Src have been shown to interact in a number of different systems, we wanted to evaluate the role of c-Src kinase in estrogen-stimulated growth and survival of ERA-positive breast cancer cells. MCF-7 cells stably expressing the mutant receptor showed increased c-Src kinase activity and c-Src tyrosine phosphorylation when compared with wild-type ERA-expressing cells. A c-Src inhibitor, AZD0530, was used to analyze the biological effects of pharmacologically inhibiting c-Src kinase activity. MCF-7 cells showed an anchoragedependent growth IC 50 of 0.47 Mmol/L, which was increased 4-fold in the presence of estrogen. In contrast, cells stably expressing the mutant ERA had an elevated IC 50 that was only increased 1.4-fold by estrogen stimulation. The c-Src inhibitor effectively inhibited the anchorage-independent growth of both of these cells, and estrogen was able to reverse these effects. When cells were treated with suboptimal concentrations of c-Src inhibitor and tamoxifen, synergistic inhibition was observed, suggesting a cooperative interaction between c-Src and ERA. These data clearly show an important role for ERA and estrogen signaling in c-Src -mediated breast cancer cell growth and survival. Here, we show that c-Src inhibition is blocked by estrogen signaling; thus, the therapeutic use of c-Src inhibitors may require inhibition of ERA in estrogen-dependent breast cancer.

Dasatinib plus Capecitabine for Advanced Breast Cancer: Safety and Efficacy in Phase I Study CA180004

“…DCR was 53% for all evaluable patients and median PFS was 13 weeks, which was similar to the median PFS reported for capecitabine monotherapy in other studies (36,37). However, in post hoc subset analysis of patients with HRþ tumors, DCR was 78% and median PFS was 23.1 weeks; the suggestion of enhanced activity against HRþ tumors and bone metastases may be related to the role of Src kinase in HR signaling (14)(15)(16)(17) and inhibition by dasatinib on osteoclasts and on tumor resident in bone (9,26). Dasatinib has been studied in ABC in combination with paclitaxel (38) or with ixabepilone (39) and in combination with hormonal therapies for ERþ disease, including fulvestrant (40), exemestane (41), and letrozole (in progress, NCT00696072).…”

“…12) and Her2/neu (13) and via the estrogen receptor (ER; refs. 14, 15) and contribute to endocrine therapy resistance (16,17) as well as resistance to Her2 inhibition (18). Src kinase activity also plays a role in VEGF-induced angiogenesis and vascular permeability (19), VEGF production (20), and downstream VEGF signaling (21).…”

A Phase 2 Trial of Dasatinib in Patients with Advanced HER2-Positive and/or Hormone Receptor–Positive Breast Cancer

“…One setting of interest is treatment of patients with endocrine-resistant breast cancer. Multiple in vitro observations have shown increased SRC expression and activity in ERþ cell lines exposed to estrogen (26) and in those with tamoxifen resistance (27). Recent preclinical studies have shown a role for activated SRC in ER degradation, suggesting a potential mechanism in development of endocrine resistance (28).…”

“…Recent preclinical studies have shown a role for activated SRC in ER degradation, suggesting a potential mechanism in development of endocrine resistance (28). Preclinical studies combining SRC inhibitors with antiestrogens have shown synergistic antitumor activity (26,29,30). Trials of dasatinib combined with endocrine therapy in patients with HRþ MBC are underway using a better-tolerated once daily schedule of dasatinib.…”

Dual targeting of Src and ER prevents acquired antihormone resistance in breast cancer cells

“…Thus, the ability to inhibit Src activity, alongside targeting of the ER with anti-oestrogens, may enhance the anti-tumour activity seen with each agent alone. Indeed, two recent studies provide compelling evidence to support such a hypothesis, demonstrating the short-term effectiveness of such combinational treatments in preventing the growth of MCF7 cells [25,44]. However, it is currently unknown whether co-targeting both Src and the ER is effective in other ERpositive cell lines and whether such treatment regimens would be effective in circumventing the phenomena of acquired tamoxifen resistance that occurs following chronic exposure to this agent [8,45,46].…”