ALDH expression marks pancreatic cancer cells that have stem cell and mesenchymal features. The enhanced clonogenic growth and migratory properties of ALDH-positive pancreatic cancer cells suggest that they play a key role in the development of metastatic disease that negatively affects the overall survival of patients with pancreatic adenocarcinoma.

Background Pancreatic cancer is a near uniformly lethal disease and a better understanding of the molecular basis of this malignancy may lead to improved therapeutics. The Axl receptor tyrosine kinase is implicated in cellular transformation and tumor progression, although its role in pancreatic cancer has not been previously documented. Results Axl labeling was present in 54 of 99 (55%), and was absent in 45 of 99 (45%) cases, respectively. Axl expression in pancreatic cancer was significantly associated with lymph node metastases (p < 0.01), and a shorter median survival (12 versus 18 months, p < 0.01), than in tumors with negative labeling. Stable knockdown of Axl resulted in significant reduction in cell viability (p < 0.001), anchorage independent growth (p = 0.0031), as well as attenuation of migratory (p < 0.001) and invasive properties (p < 0.005), compared to vector-transfected cells. Profound inhibition of p42/p44 MAP kinase and PI-3kinase/Akt effector pathways was observed in MIAPaCa-2 cells with loss of Axl function. The reduction in invasion and migration upon Axl knockdown was mirrored by a decrease in the amounts of activated (GTP-bound) GTPase proteins Rho and Rac, significant downregulation in transcript levels of the epithelial mesenchymal transition (EMT)-associated transcription factors slug, snail and twist, and significant decrease in matrix metalloproteinase MMP-9 mRNA levels. Materials The immunohistochemical expression of Axl protein was assessed in a panel of 99 archival pancreatic cancers. Endogenous Axl expression was stably downregulated by lentiviral short hairpin shRNA directed against AXL mRNA in MIAPaCa-2 cells, and the effects on cell viability, anchorage independent growth, invasion, migration and intracellular effector pathways was assessed, by comparing to lentiviral vector-transfected cells. Conclusion Expression of Axl tyrosine kinase in pancreatic cancers confers an adverse prognostic influence, and represents a new therapeutic target in this malignancy.

Recent evidence suggests that blockade of aberrant Hedgehog signaling can be exploited as a therapeutic strategy for pancreatic cancer. Our previous studies using the prototype Hedgehog small-molecule antagonist cyclopamine had shown the striking inhibition of systemic metastases on Hedgehog blockade in spontaneously metastatic orthotopic xenograft models.