Increased beta1 integrin is associated with decreased survival in invasive breast cancer.

Aberrant microenvironments and loss of balance in cell-extracellular matrix signaling are associated with breast cancer invasion, metastasis, and resistance to therapy. We have recently shown that increased beta1 integrin signaling is involved in malignant progression and that inhibitory antibody to beta1 integrin leads to selective apoptosis and decreased proliferation in three-dimensional cultures and in xenograft models of breast cancer in vivo. To investigate the clinical importance of these findings, in the present study we examined the expression of beta1 integrin and extracellular beta1 integrin ligands fibronectin and laminin-1 in a cohort of 249 breast cancer patients who had a median follow-up of 8.4 years. Among the 149 scorable cases, the highest beta1 integrin intensity score (3+ versus 0-2+) was associated with significantly decreased 10-year overall survival of 48% versus 71% (P<0.03) and decreased disease-free survival of 50% versus 80% (P<0.05). Importantly, high fibronectin expression was associated with decreased overall and disease-free survival on univariate analysis (P<0.04) and beta1 integrin intensity score was significantly correlated with fibronectin expression (Kendall's tau-b=0.19; P=0.03). In a multivariate Cox proportional hazards model, beta1 integrin intensity score remained a significant independent predictor of overall survival [hazard ratio (HR), 1.69; 95% confidence interval (95% CI), 1.19-2.38; P<0.003] and disease-free survival (HR, 1.87; 95% CI, 1.21-2.88; P<0.005). These findings show that beta1 integrin expression has potential prognostic value in invasive breast cancer and that coexpression of fibronectin may help identify patients with more aggressive tumors who may benefit from targeted therapy.

Beta1 integrin inhibition dramatically enhances radiotherapy efficacy in human breast cancer xenografts.

Beta(1) integrin signaling has been shown to mediate cellular resistance to apoptosis after exposure to ionizing radiation (IR). Other signaling molecules that increase resistance include Akt, which promotes cell survival downstream of beta(1) integrin signaling. We previously showed that beta(1) integrin inhibitory antibodies (e.g., AIIB2) enhance apoptosis and decrease growth in human breast cancer cells in three-dimensional laminin-rich extracellular matrix (lrECM) cultures and in vivo. Here, we asked whether AIIB2 could synergize with IR to modify Akt-mediated IR resistance. We used three-dimensional lrECM cultures to test the optimal combination of AIIB2 with IR treatment of two breast cancer cell lines, MCF-7 and HMT3522-T4-2, as well as T4-2 myr-Akt breast cancer colonies or HMT3522-S-1, which form normal organotypic structures in three-dimensional lrECM. Colonies were assayed for apoptosis and beta(1) integrin/Akt signaling pathways were evaluated using Western blot. In addition, mice bearing MCF-7 xenografts were used to validate the findings in three-dimensional lrECM. We report that AIIB2 increased apoptosis optimally post-IR by down-regulating Akt in breast cancer colonies in three-dimensional lrECM. In vivo, addition of AIIB2 after IR significantly enhanced tumor growth inhibition and apoptosis compared with either treatment alone. Remarkably, the degree of tumor growth inhibition using AIIB2 plus 2 Gy radiation was similar to that of 8 Gy alone. We previously showed that AIIB2 had no discernible toxicity in mice; here, its addition allowed for a significant reduction in the IR dose that was necessary to achieve comparable growth inhibition and apoptosis in breast cancer xenografts in vivo.