Abstract S6-8: Hedgehog Ligand Overexpression Predicts Poor Outcome in Breast Cancer and Is a Potential Therapeutic Target for Metastatic Disease

Abstract

Abstract Background: The Hh signalling pathway plays an important role in a number of malignancies, and accumulating data suggest it contributes significantly to the development and progression of breast cancer. However, there is scant data regarding the clinical significance of its dysregulation in breast cancer and its functional effects in breast cancer models. Methods: We investigated the clinical significance of the expression of Hh pathway components using immunohistochemistry in a well-characterised cohort of 279 patients with invasive ductal carcinoma (IDC) to determine its prognostic significance. A murine mammary cancer allograft model based on the M6 cell line, derived from the C3/SV40T transgenic mouse was used to determine the effects of Shh overexpression on tumour growth in vitro and in vivo. Finally, the therapeutic potential of Hh blockade using the monoclonal antibody 5E1 was also explored in two mouse mammary carcinoma models; the M6 allograft model and the highly metastatic 4T1 cell line in immunocompetent Balb/C mice. Results: High Hh ligand expression was observed in 34% of IDC and was associated with increased risk of breast cancer recurrence (HR 1.95, p=0.0004) and breast cancer specific death (HR 2.3, p=0.0002). High Hh expression was also associated with the basal-like subtype (p=0.004). Overexpression of Hh ligand in M6 cells transplanted to fat pads of immunodeficient mice resulted in a 4 fold increase in tumor volume (p= 0.006) and was associated with upregulation of the canonical Hh target genes Gli1 and HHIP. However, Shh promoted peritumoral lymphatic invasion in 4/5 mice compared to only 1/5 in the vector control group and was associated with a significantly shorter time to the development of metastatic disease (p=0.0004). M6 cells overexpressing Hh ligand showed no change in proliferation, self renewal or migration in vitro, suggesting a requirement for stromal interaction in Hh-dependent tumor promotion. Finally, we found that the enhanced tumor growth conferred by Hh ligand overexpression could be blocked by administration of a neutralizing antibody to Hh ligand. Furthermore, using a metastatic mammary carcinoma isograft model (4T1) that endogenously expresses Hh ligand, we demonstrate that Hh blockade resulted in smaller lung metastatic deposits (p=0.045). Conclusions: We found that high Hh ligand is associated with a poor prognosis in IDC. Overexpression of Hh ligand promotes murine mammary tumor growth, which requires stromal interaction, as well as lymphatic vessel invasion. Finally, we demonstrate that blockade of the Hh ligand is a potential therapy in metastatic breast carcinoma. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr S6-8.