Background/aim: Pancreatic stellate cells are involved in fibrosis of pancreatic cancer termed desmoplasia, which may contribute to both pancreatic cancer growth and metastasis, as well as to drug resistance. A better understanding of pancreatic cancer-cell interactions with stellate cells is therefore critical to our ability to develop effective anti-metastatic therapeutics for pancreatic cancer.

Materials and methods: The human pancreatic cancer cell line XPA-1 was engineered to express green fluorescent protein (GFP) in the nucleus and red fluorescent protein (RFP) in the cytoplasm. Pancreatic stellate cells were engineered to express RFP. The pancreatic cancer cells and stellate cells were co-cultured and their interaction was imaged in vitro. The pancreatic cancer cells and stellate cells were then co-injected in the spleen of transgenic cyan fluorescent protein (CFP) nude mice and imaged in liver, lung and diaphragm metastasis.

Results: The interaction of the pancreatic cancer cells expressing GFP in the nucleus and RFP in the cytoplasm and stellate cells expressing RFP was first imaged in vitro. The intimate relationship between the two cell types could be seen. Three hours after splenic co-injection, dual-color pancreatic cancer cells and pancreatic stellate cells were found distributed in the host liver. By 28 days after splenic co-injection of the pancreatic cancer and stellate cells, liver metastases were observed in host CFP nude mice. Metastases were also observed in the lung and diaphragm. Stellate cells were observed along with the pancreatic cancer cells at all metastatic sites suggesting that stellate cells may be necessary for metastasis. With high-resolution intravital imaging afforded by the Olympus FV1000 confocal microscope, the interaction of the dual-colored pancreatic cancer cells and the RFP-expressing pancreatic stellate cells could be clearly imaged in the liver and other metastases, further suggesting that stellate cells participate in metastasis formation.

Conclusion: Pancreatic cancer cells and stellate stem cells form a very close relationship and accompany each other to distant metastatic sties. Our hypothesis is that pancreatic stellate cells form a niche for metastasis of pancreatic cancer.