Ovarian cancer is the 5th leading cancer killer amongst women, and mortality rates have remained largely unchanged over the past three decades. The current standard of care is cytoreductive surgery, which is the physical removal of tumor tissue from the abdominal cavity, followed by chemotherapy. Despite high rates of cancer recurrence, likely due to outgrowth of residual cancer cells or metastases remaining after treatment, the mechanisms of disease relapse are incompletely understood. Animal models that faithfully mimic human conditions are critical tools for gaining important insights into the biological underpinnings of disease, leading to the discovery of life-saving treatments for patients. Dr. Christopher Morse, former Gynecology Oncology Fellow at the University of Washington School of Medicine, teamed up with members of the Greenberg Lab in the Fred Hutch Clinical Research Division to develop a preclinical model that more closely recapitulates ovarian cancer relapse after surgical cytoreduction. In an article recently published in Gynecologic Oncology, the team presents a model that they hope will be useful for evaluating new therapies to prevent cancer recurrence following surgery.
Traditional preclinical models of metastatic ovarian cancer involve injections of large numbers of highly aggressive ovarian cancer cell lines directly into the intraperitoneal cavity of animals, followed soon thereafter by the initiation of therapy. While these systems do recapitulate many histological and molecular aspects of advanced human ovarian cancer, concerns remain about whether they faithfully model the biology of tumor cell dissemination from the primary lesion, and metastatic engraftment and outgrowth in clinical situations. To address this, Dr. Morse and colleagues developed a system for orthotopically injecting small numbers of tumor cells directly into the ovarian bursa, leading to the progressive development of primary and metastatic disease similar to that seen in humans. These cancers can be treated via cytoreductive surgery to extend animal survival, allowing for micro-metastatic outgrowth similar to clinical disease recurrence settings. “Whereas most ovarian cancer animal models create metastatic disease by injecting tumor cells directly into the abdominal cavity, we think this model may more faithfully recapitulate how metastatic disease develops in our patients, where the cancer starts in the ovary or fallopian tube and then spreads throughout the abdomen”, said Dr. Morse.
In order to track micro-metastatic disease, the group began by engineering the ID8 murine ovarian cancer cell line to express an enhanced luciferase construct, allowing for the detection of very small numbers of tumor cells by in vivo bioluminescence. They injected the modified tumor cells under the ovarian bursae of syngeneic recipient animals and tracked tumor progression via bioluminescent imaging of live animals at different time points after implantation. Primary disease was detectable 3 weeks later and, encouragingly, micro-metastatic disease could be visualized by 6-8 weeks post-injection. To determine the finer kinetics and tropism of metastatic seeding, they sacrificed animals at two-week intervals after ID8 tumor cell implantation and imaged individual organs. Primary tumors were detectable 2 weeks post-injection, followed 2 weeks later by micro-metastases found at various surfaces within the peritoneal cavity, including the diaphragm, spleen, stomach, and bowel, recapitulating patterns of metastatic spread observed in patients. Followed to later stages of disease, the mice developed overt metastases to numerous additional sites, including the peritoneum, liver, and contralateral ovary, eventually developing terminal ascites, reaching humane euthanasia criteria at approximately 29 weeks after tumor implantation.
Finally, to model clinical therapeutic intervention settings, the group tested the feasibility and impact of cytoreductive surgery in this system. All mice receiving the surgery exhibited evidence of pre-operative micro-metastatic disease, but no macroscopic metastases. The surgery was well tolerated in all cases, leading to significant extension of survival when performed at 6 weeks after disease initiation. However, metastatic disease and terminal ascites invariably emerged, mimicking clinical disease recurrence. “Very few preclinical animal models have investigated the role of surgery, which is such a cornerstone to how we treat ovarian cancer in humans, and this study reinforces the critical role of surgery in managing ovarian cancer,” said Dr. Morse.
These findings present a strategy for modeling ovarian cancer with improved relevance to clinical settings. Dr. Morse said, “This novel work allows us to not only create a model where the tumor develops and spreads from a primary site, but also to begin to explore and ask questions about the role that surgical cytoreduction has on the tumor microenvironment and response to potential treatments, including immunotherapy.” Importantly, the authors caution that human ovarian cancer presents in multiple distinct subtypes, some of which may not be adequately modeled by their ID8-based system. They posit that the approaches presented here may be adapted to different ovarian cancer cell lines to develop faithful models for other patient disease subtypes. “We were very excited to develop this model and to prove that these concepts work. Combining our ovarian cancer cell line with the enhanced luciferase construct allowed us to study small volume disease in an animal model. We hope to further study aspects of the tumor microenvironment in small volume metastatic disease, especially as we incorporate this model with novel immunotherapies that we are developing in the Greenberg lab.”
This work was supported by the National Institutes of Health, the Colleen's Dream Foundation, the OCRA Ann and Sol Schreiber Mentored Investigator Award, and Juno Therapeutics.
UW/Fred Hutch Cancer Consortium members Raphael Gottardo and Philip Greenberg contributed to this work.
Morse CB, Voillet V, Bates BM, Chiu EY, Garcia NM, Gottardo R, Greenberg PD, Anderson KG. Development of a clinically relevant ovarian cancer model incorporating surgical cytoreduction to evaluate treatment of micro-metastatic disease. Gynecol Oncol. 2020 Nov 20:S0090-8258(20)34117-2. doi: 10.1016/j.ygyno.2020.11.009. PMID: 33229044.