Abstract 935: Co-clinical endometrial cancer (EC) patient-derived organoids (PDO) to assess functional effects of replication stress (RS)-targeting agents

Abstract Background: EC is the most commonly diagnosed gynecologic cancer in the US and has both rising incidence and mortality. Uterine serous cancer (USC) and uterine carcinosarcoma (UCS) are high grade ECs characterized by TP53 mutation and molecular alterations suggesting high replication stress (RS) and cell cycle dysregulation. These molecular alterations could engender sensitivity to RS-targeting strategies such as WEE1 inhibition. In a single arm phase 2 of 35 patients, the WEE1 inhibitor adavosertib demonstrated clinical activity in recurrent USC, with an overall response rate of 29.4%. To support the development of predictive biomarkers of sensitivity to RS targeting agents, we report on the establishment of co-clinical EC PDOs from pre- and on-treatment biopsies from patients with USC or UCS enrolled to a translational trial of adavosertib. Methods: Patients with USC or UCS consented for trial participation underwent pre- and on-treatment biopsies while receiving adavosertib monotherapy. Biopsies were dissociated and passaged as 3D organoid cultures in Matrigel in an optimized media. Established PDOs were seeded in 3D microfluidic devices, treated with adavosertib in a dose-dependent manner and assessed for viability after 6 days of treatment by dual labeling live/dead imaging. IC50 values were calculated using log(inhibitor) vs response - variable slope (four parameters) model in GraphPad Prism. To assess the effect of adavosertib on replication fork speed, DNA fiber assays were conducted with PDOs treated with adavosertib for 72 hours. Finally, FFPE blocks were created from PDOs for assessment of DNA damage repair biomarkers by IHC. Results: 19 biopsies were obtained from 11 participating patients. 6 biopsies did not yield sufficient tumor cells for PDO generation. From the remaining 13 samples, 5 PDOs were successfully established (3 USC and 2 UCS), with a higher success rate when 3 biopsy cores were received (3 of 4; 75%) compared to when 2 biopsy cores were received (2 of 9; 22 %). Dual labeling live/dead imaging of PDOs treated with adavosertib resulted in IC50 values ranging from 113nM to 856nM. DNA fiber assays revealed consistent decrease in fork speed with adavosertib exposure, consistent with the hypothesized effect of adavosertib in increasing RS in these cells. A dose dependent effect on replication fork speed was observed, with greater decreases in fork speed with increasing concentrations of adavosertib. Due to the limited number of samples and the number of PDOs generated from on-treatment as opposed to pre-treatment biopsies, clinical correlation between PDO adavosertib sensitivity and clinical activity was not formally assessed. IHC analysis of potential DNA damage biomarkers is ongoing. Conclusions: We describe the successful establishment of co-clinical EC PDOs for functional evaluation of sensitivity to RS targeting agents. Citation Format: Elena Ivanova, Aisha L. Saldanha, Shrabasti Roychoudhury, Bose Kochupurakkal, Ari P. Zlota, Clare E. Padrick, Ha V. Vo, Eli K. Greenberg, Hannah Sawyer, Carina Feeney, Courtney H. Qi, Swati Narayan, Jennifer D. Curtis, Nabihah Tayob, Marisa R. Nucci, Panagiotis Konstantinopoulos, Dipanjan Chowdhury, Geoffrey Shapiro, Cloud P. Paweletz, Ursula A. Matulonis, Joyce F. Liu. Co-clinical endometrial cancer (EC) patient-derived organoids (PDO) to assess functional effects of replication stress (RS)-targeting agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 935.