Introduction: Fusion between cancer and myeloid cells contributes to malignant progression of cancer. Radiation has been shown to increase fusion hybrids during tissue regeneration. We would like to evaluate the mechanisms of radiation on enhancing cell fusion between pancreatic cancer cells and macrophages, and the contribution of fusion hybrids to pancreatic cancer progression. Materials and Methods: To demonstrate physical contact of cancer cells and macrophages contributing to progression of pancreatic cancer, we used trans-well and soft agar assays to measure the migratory and tumorigenic ability of cancer cells. The phenotypes after radiation exposure would also be studied. For dual fluorescence method to quantify fusion hybrids, we established stable clones of Panc-1-EGFP and THP-1-DsRed/U937-DsRed. For cre-loxP system, Pan-1 or Pan02 cells were stably transfected with cre-recombinase; Raw cells, U937 or THP-1 were stably transfected with pLV-CMV-LoxP-DsRed-LoxP-eGFP plasmid. Flow-cytometry and fluorescence microscopy were used to detect fusion hybrids. Tomato mice (B6.129-Cg-Gt(ROSA)26Sortm4(ACTB-tdTomato,-EGFP)Luo/JNarl ) were subcutaneously implanted with Pan02-cre cells. Mock or local radiation was given one week later. Tumor tissues were collected and evaluated at various time-points to measure fusion hybrids. KC mice (Pdx-1Cre KrasG12D ) of 10-12 week-old were given whole body irradiation (WBI) and bone marrow transplantation (BMT) from tomato mice. The pancreas tissues were collected at 24-30 week-old mice and evaluated for fusion hybrids and pancreatic malignancy. Results: Comparing with indirect coculture or cultured within conditioned medium of macrophages, pancreatic cancer cells cultured directly with macrophages revealed further enhanced ability of migration and colony formation. Similar observations were noted after exposure to radiation. These results suggested that physical contact between cancer cells and macrophages provided opportunities for malignant progression of pancreatic cancer. Using dual fluorescence and cre-loxP technique, we demonstrated in vitro that radiation might increase fusion hybrids. The tumor tissues from tomato mice showed increasing fusion hybrids expressing green fluorescence 2-6 weeks later. The frequency of fusion hybrids increased after local radiation. KC mice after WBI and BMT from tomato mice showed increased frequency of pancreatic cancer and fusion hybrids within pancreas at 24-30 weeks old. Conclusions: We demonstrated in vitro and in vivo that radiation enhanced fusion between pancreatic cancer cells and macrophages. Tumor-macrophage fusion hybrids correlated with enhanced clonogenic, migratory ability and radiation resistance of pancreatic cancer. Our results suggest that blocking fusion machinery or depleting macrophages might ameliorate pancreatic cancer progression.
Date:
2018-01
Relation:
Molecular Cancer Therapeutics. 2018 Jan;17(1, Suppl.):A209.
