Mall cytokine, secreted locally, is expressed in some tissues, including major homing organs such as lung and bone marrow in breast cancer [31,44]. The relevance of the presence of disseminated tumor cells in the bone marrow is extensively discussed for various tumors [45]. Its relevance for esophageal Lixisenatide carcinoma has been indicated [27] but not yet been determined. Our results suggest an important role of CXCR4, a possible regulation of HER2 though inhibition of the CXCR4 pathway and a subsequent regulation 1676428 of local tumor progression and metastatic homing of esophageal carcinoma.Role of CXCR4- and HER2-receptor expressionWhile the inhibition of the HER2 receptor through the monoclonal antibody trastuzumab leads to reduction of primary tumor growth as well as significant reduction of metastases to lymph nodes, liver and lung. Inhibition of the CXCR4 receptor reduces metastases compared to the non-treated group in our experiments and leads to an over-expression 15481974 of HER2 in the primary tumor and even greater expression in the metastases. CXCR4-inhibition also seems to lower CXCR4-expression in metastases compared to the untreated group. The reduction of metastases strengthens the assumption that CXCR4 is indeed involved in metastastic homing in esophageal carcinoma. The combined inhibition of HER2 and CXCR4 leads to further reduction for primary tumor growth. Metastases throughout havea higher HER2-expression level than the primary tumor, suggesting that in metastatic disease HER2 expression is of even greater importance. In an SIS 3 site orthotopic model of HER2-positive esophageal carcinoma we have previously shown the significantly positive impact of inhibition of HER2 on primary tumor and on metastases [25]. The present findings support the theory of a strong linkage of two structurally unrelated membrane receptors, HER2 and CXCR4, and thus a functional role of CXCR4 in HER2-positive esophageal carcinoma, which has not been previously described. A similar functional linkage has only been previously established for breast cancer [26]. The group of Li et al. could show that, reciprocally to our findings, HER2 enhances CXCR4 expression, and that increased CXCR4 expression is necessary for HER2mediated invasion. Furthermore they demonstrated a significant correlation of HER2 and CXCR4 in breast cancer patients, which resulted in a significant worse prognosis. If assuming that HER2 upregulates the expression of CXCR4 [26], this might even suggest that through inhibition of CXCR4, HER2 in rebound is upregulated to again increase CXCR4. Multiple regulatory mechanisms can be responsible for a functional linkage of the structurally-unrelated receptor cascades of CXCR4 and HER2. It is however known that the parallel activation and transactivation of the ERK/MAPK signalling complex through G-coupled protein receptors, such as CXCR4, and receptor tyrosine 
kinases, such as HER2, exists. Although the detailed mechanisms of this phenomenon remain unclear, this multi-track signalling is known to lead to proliferation, invasion and migration, finally resulting in tumor progression [46]. Although these coherences have only been previously described for breast cancer [26], our data might further strengthen the theory that HER2-enhanced invasion, migration, adhesion and metastasis is dependent on the upregulation of CXCR4 in esophageal carcinoma. However, further functional analysis will be necessary to investigate the interaction of CXCR4 and HER2 pathways in esophag.Mall cytokine, secreted locally, is expressed in some tissues, including major homing organs such as lung and bone marrow in breast cancer [31,44]. The relevance of the presence of disseminated tumor cells in the bone marrow is extensively discussed for various tumors [45]. Its relevance for esophageal carcinoma has been indicated [27] but not yet been determined. Our results suggest an important role of CXCR4, a possible regulation of HER2 though inhibition of the CXCR4 pathway and a subsequent regulation 1676428 of local tumor progression and metastatic homing of esophageal carcinoma.Role of CXCR4- and HER2-receptor expressionWhile the inhibition of the HER2 receptor through the monoclonal antibody trastuzumab leads to reduction of primary tumor growth as well as significant reduction of metastases to lymph nodes, liver and lung. Inhibition of the CXCR4 receptor reduces metastases compared to the non-treated group in our experiments and leads to an over-expression 15481974 of HER2 in the primary tumor and even greater expression in the metastases. CXCR4-inhibition also seems to lower CXCR4-expression in metastases compared to the untreated group. The reduction of metastases strengthens the assumption that CXCR4 is indeed involved in metastastic homing in esophageal carcinoma. The combined inhibition of HER2 and CXCR4 leads to further reduction for primary tumor growth. Metastases throughout havea higher HER2-expression level than the primary tumor, suggesting that in metastatic disease HER2 expression is of even greater importance. In an orthotopic model of HER2-positive esophageal carcinoma we have previously shown the significantly positive impact of inhibition of HER2 on primary tumor and on metastases [25]. The present findings support the theory of a strong linkage of two structurally unrelated membrane receptors, HER2 and CXCR4, and thus a functional role of CXCR4 in HER2-positive esophageal carcinoma, which has not been previously described. A similar functional linkage has only been previously established for breast cancer [26]. The group of Li et al. could show that, reciprocally to our findings, HER2 enhances CXCR4 expression, and that increased CXCR4 expression is necessary for HER2mediated invasion. Furthermore they demonstrated a significant correlation of HER2 and CXCR4 in breast cancer patients, which resulted in a significant worse prognosis. If assuming that HER2 upregulates the expression of CXCR4 [26], this might even suggest that through inhibition of CXCR4, HER2 in rebound is upregulated to again increase CXCR4. Multiple regulatory mechanisms can be responsible for a functional linkage of the structurally-unrelated receptor 
cascades of CXCR4 and HER2. It is however known that the parallel activation and transactivation of the ERK/MAPK signalling complex through G-coupled protein receptors, such as CXCR4, and receptor tyrosine kinases, such as HER2, exists. Although the detailed mechanisms of this phenomenon remain unclear, this multi-track signalling is known to lead to proliferation, invasion and migration, finally resulting in tumor progression [46]. Although these coherences have only been previously described for breast cancer [26], our data might further strengthen the theory that HER2-enhanced invasion, migration, adhesion and metastasis is dependent on the upregulation of CXCR4 in esophageal carcinoma. However, further functional analysis will be necessary to investigate the interaction of CXCR4 and HER2 pathways in esophag.
