LAUSR

Introduction: Clear cell carcinoma of the ovary (CCC) is the 2nd most common ovarian cancer and is histologically and clinically distinct from other subtypes. Late stage CCC have a worse prognosis than other ovarian cancer histotypes as they are inherently resistant to the standard platinum/taxane chemotherapy. Deep endometriosis of the ovary, known as endometrioma or chocolate cyst, is the most common precursor for CCC. However, how transformation from endometriosis to CCC and, in particular, the important role of the hypoxic and ROS-rich microenvironment of endometriotic cysts are not well understood. As the molecular mechanisms pertinent to the genesis and progression of CCC are largely unknown, there are few, if any, therapeutic strategies for patients with advanced stage disease. Identifying factors that shape the development, progression and metastasis of CCC which can be targeted therapeutically could have tremendous potential to improve outcomes in this disease. Our recent findings identified cystathionine gamma-lyase (CTH), a key enzyme in the transsulfuration pathway, as a marker of Mullerian tract derived ciliated cells and CCC of both the ovary and uterus regardless of which mutations are present. Also, CTH is highly expressed both in CCC and the endometriosis adjacent to this cancer. Whether and how the transsulfuration pathway, notably CTH, enables CCC to adapt to the hostile microenvironment of an endometriotic cyst and ultimately to promote metastasis remain unanswered. Methods: We generated CTH knockout (KO) cells using CRISPR/Cas9. We assessed effects of CTH loss in vitro -under ambient and stress conditions- and in vivo on cell viability, cell proliferation, ROS levels, migration, invasion, and metastasis. Further, we used an organoid model system to assess the impact of CTH loss in primary endometrial cells on organoid growth and response to stress conditions including exposure to endometriotic cyst contents. Results: Our in-vitro, in-vivo data as well as data derived from the organoid modelling system show that CTH is critical for adaptive response to hypoxia. Further, it underpins the growth of CCC cells in-vitro and the growth of CTH in a mouse model of CCC. These data highly indicate that expression of the transsulfuration pathway enzyme CTH enables cells to survive in endometriotic cysts then upon transformation both marks CCC and potentiates tumor progression and metastasis. Conclusion: Targeting CTH in CCC and potentially other cancers might represent a novel and impactful therapeutic approach. Citation Format: Amal M. El-Naggar, Yuchen Ding, Genny Trigo-Gonzalez, Lucy Li, Shary Chen, Busra Turgu, Forouh Kalantari, Rodrigo Vallejos, Kiran Parmar, Cindy Shen, Gian Luca Negri, Paul Yong, Gregg Morin, David G. Huntsman. On the verge of metastasis: CTH defines a cell-state-dependent adaptive response to microenvironmental stresses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2482.