Elevated L1CAM expression in precursor lesions and primary and metastastic tissues of pancreatic ductal adenocarcinoma.

The promigratory molecule L1CAM is overexpressed in various tumors, often representing an unfavorable prognostic marker. Recently, we identified L1CAM expression in pancreatic ductal adenocarcinoma (PDAC) cells accounting for chemoresistance and increased cell migration. Thus, the present study aims at further elucidating the role of L1CAM in a larger cohort of PDAC specimens including precursor lesions and metastasis. L1CAM expression was determined by immunohistochemistry in tissues of 123 patients including tissues of 110 primary PDACs, 15 lymph node metastases and 14 liver metastases. The immunohistochemical analyses revealed L1CAM expression in 92.7% of primary PDACs, 80% of lymph node metastases and 100% of liver metastases. Furthermore, we have investigated PDAC precursors, pancreatic intraepithelial neoplasia (PanIN) lesions, revealing a significant increase of L1CAM expression with the PanIN grade (6.4 and 6.8% in PanIN 1A and B, 35% in PanIN 2 and 20% in PanIN 3). The elevated expression of L1CAM already found in PanINs points to a role of L1CAM quite early in tumorigenesis of PDAC. Furthermore, its broad expression in primary tumors as well as in metastases of PDAC patients provide a rationale to further explore the value of L1CAM as a therapeutic target in the treatment of this highly malignant tumor.

alpha5-integrin is crucial for L1CAM-mediated chemoresistance in pancreatic adenocarcinoma.

We recently showed that the adhesion molecule L1CAM (CD171) is overexpressed in pancreatic adenocarcinoma (PDAC) essentially contributing to chemoresistance of PDAC cells. In search of the mechanisms of this effect we now identified alpha5-integrin as the L1CAM ligand being essential for L1CAM-mediated chemoresistance of these highly malignant tumor cells. Thus, blockade or knock-down of alpha5-integrin in the L1CAM expressing PDAC cell lines PT45-P1res, Colo357 and Panc1 increased anti-cancer drug sensitivity. In line with the previously reported NO-dependent caspase inhibition resulting from L1CAM induced iNOS expression, the loss of chemoresistance upon alpha5-integrin inhibition was preceded by decreased iNOS expression and enhanced caspase-3/-7 activation. Accordingly, the loss of anti-cancer drug protection by alpha5-integrin inhibition could be overcome by administration of the NO-donor SNAP. Moreover, the gain of chemoresistance of parental PT45-P1 cells when transfected with L1CAM was abrogated by alpha5-integrin inhibition, whereas transfection of PT45-P1 cells with an integrin binding-deficient L1CAM mutant (L1mutRGE) did neither induce chemoresistance or iNOS expression nor conferred sensitivity to alpha5-integrin inhibition as seen upon transfection with wild-type L1CAM. Thus, mutational loss of the integrin binding site in the L1CAM molecule or the blockade of alpha5-integrin abolished the induction of iNOS expression and chemoresistance by L1CAM, indicating that both a functional L1CAM and alpha5-integrin are indispensable of L1CAM-induced drug resistance in PDAC cells.