Aromatase inhibitors (AI) are a standard-of-care treatment for postmenopausal, estrogen receptor-positive breast cancers. Although tumor recurrence on AI therapy occurs, the mechanisms underlying acquired resistance to AIs remain unknown. In this study, we examined a cohort of endocrine-treated breast cancer patients and used a cell line model of resistance to the AI letrozole. In patients treated with a first-line AI, hormone receptor switching between primary and resistant tumors was a common feature of disease recurrence. Resistant cells exhibited a switch from steroid-responsive growth to growth factor-responsive and endocrine-independent growth, which was accompanied by the development of a more migratory and disorganized phenotype. Both the resistant cells and tumors from AI-resistant patients showed high expression of the steroid receptor coactivator SRC-1. Direct interactions between SRC-1 and the transcription factor Ets2 regulated Myc and MMP9. SRC-1 was required for the aggressive and motile phenotype of AI-resistant cells. Interestingly, SRC-1 expression in primary and/or recurrent tumors was associated with a reduction in disease-free survival in treated patients. Moreover, there was a significant association between SRC-1 and Ets2 in the recurrent tissue compared with the matched primary tumor. Together, our findings elucidate a mechanism of AI-specific metastatic progression in which interactions between SRC-1 and Ets2 promote dedifferentiation and migration in hormone-dependent breast cancer. Cancer Res; 72(2); 548-59. Ó2011 AACR.

BackgroundCancer progression is influenced by genetic aberrations in the cancer cell population as well as by other factors including the microenvironment present within a tumour. Direct interactions between various cell types as well as cellular signalling via secreted cytokines can drive key tumourigenic properties associated with disease progression and treatment resistance. Also, cancer stem cell functions are influenced by the microenvironment. This challenging subset of cells has been linked to malignant properties. Within a screen, using in vivo like growth conditions, we identified progranulin as a highly secreted cytokine affecting cancer stem cells in breast cancer. This cytokine is known to play a role in numerous biological and tumour-related processes including therapy resistance in a range of cancer types.MethodsDifferent in vitro and in vivo relevant conditions were used to validate breast cancer stem cell expansion mediated by progranulin and its receptor sortilin. Small interfering ribonucleic acid (siRNA) and pharmacological inhibition of sortilin were used to elucidate the role of sortilin as a functional receptor during progranulin-induced breast cancer stem cell propagation, both in vitro and in vivo, using breast cancer xenograft models. In addition, single-cell gene expression profiling as well as a Sox2 reporter breast cancer cell line were used to validate the role of dedifferentiation mediated by progranulin.ResultsIn various in vivo-like screening assays, progranulin was identified as a potent cancer stem cell activator, highly secreted in ERα-negative breast cancer as well as in ERα-positive breast cancer under hypoxic adaptation. Progranulin exposure caused dedifferentiation as well as increased proliferation of the cancer stem cell pool, a process that was shown to be dependent on its receptor sortilin. Subcutaneous injections of progranulin or its active domain (GRN A) induced lung metastases in breast cancer xenograft models, supporting a major role for progranulin in cancer progression. Importantly, an orally bioavailable small molecule (AF38469) targeting sortilin, blocked GRN A-induced lung metastases and prevented cancer cell infiltration of the skin.ConclusionThe collective results suggest that sortilin targeting represents a potential novel breast cancer therapy approach inhibiting tumour progression driven by secretion and microenvironmental influences.Electronic supplementary materialThe online version of this article (10.1186/s13058-018-1060-5) contains supplementary material, which is available to authorized users.

It is well known that tumour cells are dependent on communication with the tumour microenvironment. Previously, it has been shown that hypoxia (HX) induces pronounced, diverse and direct effects on cancer stem cell ( CSC ) qualities in different breast cancer subtypes. Here, we describe the mechanism by which HX‐induced secretion influences the spreading of CSC s. Conditioned media (CM) from estrogen receptor ( ER )‐α‐positive hypoxic breast cancer cell cultures increased the fraction of CSC s compared to normal growth conditions, as determined using sets of CSC assays and model systems. In contrast, media from ER α‐negative hypoxic cell cultures instead decreased this key subpopulation of cancer cells. Further, there was a striking overrepresentation of JAK ‐ STAT ‐associated cytokines in both the ER α‐positive and ER α‐negative linked hypoxic responses as determined by a protein screen of the CM. JAK ‐ STAT inhibitors and knockdown experiments further supported the hypothesis that this pathway is critical for the CSC ‐activating and CSC ‐inactivating effects induced by hypoxic secretion. We also observed that the interleukin‐6‐ JAK 2‐ STAT 3 axis was specifically central for the ER α‐negative hypoxic behaviour. Our results underline the importance of considering breast cancer subtypes in treatments targeting JAK ‐ STAT or HX‐associated processes and indicate that HX is not only a confined tumour biological event, but also influences key tumour properties in widespread normoxic microenvironments.

BackgroundEndocrine therapy is standard treatment for estrogen receptor (ER)-positive breast cancer. However, its efficacy is limited by intrinsic and acquired resistance. Here the potential of S100β as a biomarker and inhibition of its signaling network as a therapeutic strategy in endocrine treated patients was investigated.MethodsThe expression of S100β in tissue and serum was assessed by immunohistochemistry and an enzyme-linked immunosorbent assay, respectively. The S100β signaling network was investigated in cell line models of endocrine resistance by western blot, PCR, immunoprecipitation, and chromatin-immunoprecipitation. Endocrine resistant xenografts and tumor explants from patients with resistant tumors were treated with endocrine therapy in the presence and absence of the p-Src kinase inhibitor, dasatinib.ResultsTissue and serum levels of S100β were found to predict poor disease-free survival in endocrine-treated patients (n = 509, HR 2.32, 95% CI is 1.58–3.40, p < 0.0001 and n = 187, HR 4.009, 95% CI is 1.66–9.68, p = 0.002, respectively). Moreover, elevated levels of serum S100β detected during routine surveillance over the patient treatment period significantly associated with subsequent clinically confirmed disease recurrence (p = 0.019). In vivo studies demonstrated that endocrine treatment induced transcriptional regulation of S100β which was successfully disrupted with tyrosine kinase inhibition. In endocrine resistant xenografts and tumor explants from patients with endocrine resistant breast cancer, combined endocrine and dasatinib treatment reduced tumor proliferation and down-regulated S100β protein expression in comparison to endocrine treatment alone.ConclusionsS100β has potential as a new surveillance tool for patients with ER-positive breast cancer to monitor ongoing response to endocrine therapy. Moreover, endocrine resistant breast cancer patients with elevated S100β may benefit from combined endocrine and tyrosine-kinase inhibitor treatment.Trial registrationClinicalTrials.gov, NCT01840293). Registered on 23 April 2013. Retrospectively registered.Electronic supplementary materialThe online version of this article (doi:10.1186/s12916-017-0836-2) contains supplementary material, which is available to authorized users.

Background:Cutaneous melanoma is an aggressive disease. S100beta is an established biomarker of disease progression; however, the mechanism of its regulation in melanoma is undefined.Methods:Expression of HOXC11 and SRC-1 was examined by immunohistochemistry and immunofluorescence. Molecular and cellular techniques were used to investigate regulation of S100beta, including, western blot, qPCR, ChIP and migration assays.Results:Expression levels of the transcription factor HOXC11 and its coactivator SRC-1 were significantly elevated in malignant melanoma in comparison with benign nevi (P<0.001 and P=0.017, respectively, n=80), and expression of HOXC11 and SRC-1 in the malignant tissue associated with each other (P<0.001). HOXC11 recruitment to the promoter of S100beta was observed in the primary melanoma cell line SKMel28. S100beta expression was found to be dependant on both HOXC11 and SRC-1. Treatment with the Src/Abl inhibitor, dasatinib, reduced HOXC11–SRC-1 interaction and prevented recruitment of HOXC11 to the S100beta promoter. Dasatinib inhibited both mRNA and protein levels of S100beta and reduced migration of the metastatic cell line MeWo.Conclusion:We have defined a signalling mechanism regulating S100beta in melanoma, which can be modulated by dasatinib. Profiling patients for expression of key markers of this network has the potential to increase the efficacy of dasatinib treatment.