Cyclin dependent kinase inhibitors 2A and 2B loss drive pancreatic ductal adenocarcinoma liver metastasis

Introduction: Pancreatic Ductal Adenocarcinoma (PDAC) metastasizes mostly to the liver. A critical step of metastasis formation is the ability of cancer cells to colonize in foreign microenvironment. Yet, no genomic driver of liver metastasis (LM) in PDAC was identified. To identify mutations that prone PDAC cells to colonize in the liver and decipher mechanisms enabling the process.

Material and method: NGS of 312 cancer-related genes in 1741 PDAC primary and 1765 metastasis samples at different sites was conducted by FoundationOne. Proliferation, migration and invasion were assessed using methylene-blue, transwell, and wound-healing assays. Three-dimensional PDAC spheres were generated using InSphero assay. Mouse primary hepatocyte-conditioned media (PH-CM) was generated.

Results and discussion: FoundationOne database showed increased prevalence of frameshift mutations, resulting in deletion, in cyclin dependent kinase inhibitors 2A/2B (CDKN2A/B) in PDAC LM relative to primary tumor and other metastatic sites. High mRNA and protein levels of CDKN2A/B were noted in WT-CDKN2A/B COLO-357 cells while no expression was detected in mutated-CDKN2A/B MIA-PaCa-2 and PANC-1 cells. Overexpression of these genes in mutated-CDKN2A/B cells inhibited their proliferation while co-silencing in WT-CDKN2A/B COLO-357 increased proliferation and aggressive phenotype. The ability of CDKN2A/B loss to promote LM was examined. Overexpressing CDKN2A/B in mutated cells inhibited their proliferation in PH-CM compared to control. Whereas co-silencing of CDKN2A/B in WT COLO-357 cells increased proliferation and sphere formation in PH-CM compared to control.

Conclusion: This data indicate, for the first time, unique genomic profile of liver PDAC metastasis and indicate loss of p15 and p16 as promoting liver metastases.