Abstract 3847: Metastasizing host stromal cells potentiate colonization of metastatic tumors

Metastatic cancer cells only grow in the secondary sites with a permissive microenvironment. Here, we show that the metastatic cells can also carry their own “soil”, including activated fibroblasts from the primary site. Moreover, we found that these non-malignant carryover host-derived cells can potentiate metastatic cell colonization in the lungs and increase cancer's metastatic efficiency. Materials and Methods: Using the isolated renal perfusion model we were able to collect fragments shed by the primary tumor and assess their viability. Next, we adjusted the parabiosis model to transplant a 2 cm Actb-GFP+ skin graft onto a wild type mouse. Tumors were allowed to grow in the graft and metastasize to the lung. GFP+ cells carried over by the tumor to the lung in the lung were characterized using immunohistochemistry. In a spontaneous metastases model we used two lung tumor cell lines (LLC1 and LA-P0297) in combination with human carcinoma associated fibroblasts to study the modulation of the metastatic efficiency by stromal cells. Results: We show here that, in addition to single cells (81%), tumors shed fragments consisting of both tumor and host stromal cells. These heterogeneous fragments are more viable in the circulation compared to tumor cells alone (p < 0.05) and their stromal component proliferates in the metastic site for up to seven days. Next, we assessed the nature of these host stromal cells using immunohistochemistry and indentified 80% of them being of fibroblast origin. When we selectively depleted the host stromal cells in the tumor microenvironment the spontaneous formation of metastases was significantly reduced three weeks after the primary tumor resection as compared to control mice (p < 0.05). Also, in mice with metastases, survival was significantly decreased after co-implantation of CAFs with LLC1 compared to mice implanted with cancer cells alone. This effect could be reversed by selective depletion of the “circulating” CAFs after primary tumor removal (p < 0.01). Discussion: We found that tumor-associated stromal cells can escape primary tumors along with cancer cells, survive in blood circulation and in metastatic nodules. Pre-existence of a tissue-like structure in the form of heterotypic cell fragments may increase the viability of cancer cells in blood circulation and promote metastasis efficiency at the secondary site. How this mechanism contributes to the organo-tropism of certain metastatic tumors is not known. But demons