In vivo-selected ID8 ovarian cancer cells display accelerated peritoneal metastasis accompanied with increased macrophage recruitment and M2 polarization

Ovarian cancer is the leading cause of gynecological cancer related death. The overall 5 year survival rate is only 29%. Over 85% of ovarian cancer patients present with advanced stage III or IV disease characterized by intraperitoneal metastasis when diagnosed. However, the process and mechanism of ovarian tumor metastasis remain poorly understood partially because of the lack of a mouse model which could recapitulate the development of metastatic lesion in an appropriate timeframe. In order to generate a convenient ovarian cancer model with accelerated peritoneal metastasis, we performed an in vivo selection study using ID8 ovarian cancer cells to establish a rapid metastasizing mouse ovarian cancer cell line, designated ID8-M. Syngeneic mice with intraperitoneal inoculation of ID8-M cells showed measurable ascites average 35 days after the inoculation and survived only an average of 52 days, while those inoculated with parental ID8 cells showed measurable ascites after 67 days and survived over 81 days. Further analysis showed that, compared with ID8 tumors, ID8-M tumors resulted in more macrophages in the ascites; and compared to ID8 cells, ID8-M cells were more potent to promote macrophages to acquire a M2 phenotype. A microarray analysis provided information to explain the accelerated metastatic phenotype of ID8-M cells. Parental ID8 cells were intraperitoneally injected into 8-week-old, female C57BL/6 mice. Twelve weeks after the inoculation, mice were sacrificed while the mice displayed abundant ascites. Hemorrhagic fluid was collected from the peritoneal cavity, then centrifuged and lysed with red blood cell lysis buffer to remove erythrocytes and supernatant. After filtered with 70-μm strainer, cells were re-suspended with complete medium and seeded in 35 mm plates at 37 °C in a humidified 5% CO2 atmosphere. Four days later, cell clones were picked and after several times of trypsinization and passage, we obtained a new cell line designated ID8-M. For microarray analysis, 3 samples of ID8-M cells and 3 samples of parental ID8 cells were used.