Abstract

Most patients with ductal adenocarcinoma of the pancreas (PDAC) have an ominous prognosis mainly due to early cell dissemination. PDAC cells constitute a difficult target due to a complex genomic landscape rendering a dynamic heterogeneity. However, in order to establish metastases, these cells depend on finding proper niches in target organs. Destabilizing the metastatic ecosystem through relevant, and more stable, molecular targets on niche-forming cells, has the potential to prevent further metastatic progression. In an orthotopic xenograft mouse model with L3.6pl cells, a human PDAC cell line, the mouse-specific blockade of exon-v6 containing isoforms of CD44, thus not targeting cancer cells, nearly abolished metastases. In mice orthotopically implanted with syngeneic FC1245 cells (KPC-mouse-derived), we found hematopoietic (CD45+/CD11b+) cell clusters in the liver that were significantly higher in number and size than in control mice, 14 days after cancer cell implantation or sham surgery respectively. Cells that formed these clusters invariably expressed CD44 and a high proportion also expressed hematopoietic stem/progenitor cell markers as SCA-1 and c-kit, not expressed in Kupffer cells scattered in its surroundings. In bone marrow derived cells (BMDCs) isolated from the same tumor-bearing mice, we found an upregulation of CD44 and a splicing switch towards a CD44v6-v10 isoform, together with an increased proportion of SCA-1+/c-kit+ immature cells. These cells also upregulated CXCR4, VLA4 and MMP9, significantly increasing their chemotaxis towards CXCL12 in transwell assays and adhesion to VCAM-1 coated plates, as compared to naïve BMDCs, underscoring a tumor-factor-induced mobilizing phenotype. Interestingly, the number of migrating and adhering cells in these assays, were significantly decreased by incubation with CD44-blocking antibodies. We are currently assessing the impact of CD44 or CD44v6 knock-out, specifically in the bone marrow, for premetastatic niche and metastasis formation in vivo, at different time-points during primary tumor development and its spontaneous metastasis, in our orthotopic syngeneic model.