Abstract B69: Noninvasive tumor tracking and characterization of stage-specific immunity in a syngeneic mouse model of ovarian cancer

Abstract Ovarian cancers are the most lethal gynecologic malignancy, with high levels of relapse and acquired chemoresistance. Immunity clearly plays a role in ovarian tumor growth, but the inability to accurately correlate progression with stage-specific changes in immunity—both over time and in response to therapy—has hampered our understanding of antitumor immune responses. There is a clear need for improved methods to accurately model and monitor ovarian cancer progression and study its interplay with immunity in vivo. We have generated and characterized an ovarian cancer mouse model allowing noninvasive, real-time tumor imaging with stage-specific tracking of progression over time. Using CRISPR, we integrated the near infra-red phytochrome iRFP720 into the ROSA26 locus of ID8 mouse ovarian cancer cells, and intrabursally implanted these into syngeneic C57BL/6 mice. Noninvasive fluorescence imaging was correlated with post-mortem tumor deposition, and immune populations were assessed at each stage to link immune status with disease progression. Finally, we tested whether this model could be used to monitor therapeutic responses in vivo in real time. Fluorescence imaging accurately identified four distinct stages of cancer progression; (i) primary tumor establishment and growth over 3 weeks; (ii) initial dissemination; (iii) development and expansion of multiple metastases; and (iv) end-stage accumulation of peritoneal ascites. These observations were validated post-mortem. Weight and circumference increase, the standard parameters for tumor burden, did not occur until extensive disease dissemination (week 8), demonstrating their inadequacy for early tumor monitoring. There were no significant differences in immune populations between wild-type and iRFP+ tumor-bearing mice by flow cytometry, indicating iRFP expression by itself does not alter immune profiles. Tumor progression, by contrast, was clearly correlated with decreased frequencies of T-helper 1 (Th1) cells, increased Th2 cells, and a stage-specific decrease in Teff:Treg cell ratios in the peritoneal cavity. Treatment with paclitaxel reduced the tumor volume detected by fluorescence, with tumor recurrence over time. Moreover, paclitaxel depleted peritoneal CD8+ Teff cells, dendritic cells and Th1 cells. Our data demonstrate the effective use of noninvasive fluorescence imaging to discretely stage and quantify ovarian tumor progression, and to correlate therapeutic responses in real time. Moreover, the model mimics the progression of human disease, despite lacking genetic equivalence to human ovarian cancer, and hence has utility for the stage-specific analysis of immune-mediated function. Citation Format: Amy L. Wilson, Kirsty L. Wilson, Maree Bilandzic, Laura R. Moffitt, Magdalena Plebanski, Andrew N. Stephens. Noninvasive tumor tracking and characterization of stage-specific immunity in a syngeneic mouse model of ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B69.