Characterization of an Intraperitoneal Ovarian Cancer Xenograft Model in Nude Rats Using Noninvasive MicroPET Imaging

MicroPET is a noninvasive imaging modality that can potentially track tumor development in nude rats using the radiotracer fluorine 18-fluorodeoxyglucose ((18)F-FDG). Our goal was to determine whether microPET, as opposed to more invasive techniques, could be used to noninvasively monitor the development of ovarian cancer in the peritoneal cavity of nude rats for monitoring treatment response in future studies. Female nude rats were inoculated intraperitoneally with 36 million NIH:OVCAR-3 cells. Imaging was carried out at 2, 4, 6, or 8 weeks postinoculation. Each rat was fasted overnight and intravenously injected with 11.1 MBq (300 microCi) of (18)F-FDG in 0.2 mL of saline. Thirty minutes following injection, the rats were placed in the microPET and scanned for 30 min. After imaging, rats were euthanized for ascites and tissue collection for biodistribution and histopathologic correlation. Standard uptake values (SUVs) of (18)F-FDG within the peritoneal cavity were also calculated from regions of interest analysis of the microPET images. MicroPET images showed diffuse increased uptake of (18)F-FDG throughout the peritoneal cavity of tumor rats (mean SUV=4.64) compared with control rats (mean SUV=1.03). Ascites gathered from tumor-bearing rats had increased (18)F-FDG uptake as opposed to the peritoneal fluid collected from control rats. Biodistribution data revealed that the percent injected dose per gram (% ID/g) was significantly higher in tumor-bearing rats (6.29%) than in control rats (0.59%) in the peritoneal lymph nodes. Pathology verified that these lymph nodes were more reactive in tumor-bearing rats. By 6 weeks, some rats developed solid masses within the peritoneum, which could be detected on microPET images and confirmed as tumor by histopathology. (18)F-FDG uptake in these tumors at necropsy was 2.83% ID/g. These results correlate with previous invasive laparoscopic studies of the same tumor model and demonstrate that microPET using (18)F-FDG is a promising noninvasive tool to localize and follow tumor growth in an intraperitoneal ovarian cancer model.