Abstract PO018: PAX8 represents a potential novel therapeutic target in copy number high uterine serous carcinoma

Purpose: Assess the suitability of PAX8 as a therapeutic target in copy number (CNV)-high uterine cancers. Methods: Patterns of gene expression and somatic mutations were evaluated across 97 specimens of uterine cancers characterized by the National Institute of Health’s Clinical Proteomics Tumor Analysis Consortium. Three established USC cell lines (ARK1, ARK2, ARK4) were transfected with small interfering RNAs (siRNAs) targeting PAX8 or a non-targeting siRNA control. Proliferation and apoptosis were evaluated using MTS and Caspase 3/7 assays, respectively. Migration and invasion were evaluated using Boyden chamber assays. PAX8 expression was evaluated using semi-quantitative rtPCR and Western blot. Statistical significance was evaluated using two-tailed t-tests. Results: Our analyses revealed that PAX8 is highly expressed in a subset of uterine cancers and correlates with advanced clinical stage, serous histology and inactivating TP53 mutations. In vitro, knockdown of PAX8 expression resulted in significantly decreased rates of proliferation and apoptosis when compared to cells transfected with non-targeting controls. Decreased proliferation was seen most profoundly at the 72- and 96-hour time points. Enforced reductions in PAX8 expression also decreased rates of tumor migration and invasion. Invasion was significantly decreased in ARK1 (p = 0.05). Migration was significantly decreased in ARK2 (p = 0.002), and the decrease in invasion approached statistical significance (p=0.07). In ARK4, both migration (p = 0.02) and invasion (p = 0.02) were significantly decreased. Knockdown of PAX8 was confirmed using rtPCR for all in vitro experiments. Conclusion: High levels of PAX8 expression are a key feature of a CNV-high uterine cancers that drive tumor proliferation, invasion and migration. These results indicate that PAX8 overexpression contributes to the aggressive clinical behavior of these cancers. They also establish that agents targeting PAX8 activity or expression could ultimately prove to be effective therapeutically. Citation Format: Susan H. Read, Matthew L. Anderson, Thomas J. Rutherford, Venkata A. Jonnalagadda, Yongchao Dou, Bing Zhang. PAX8 represents a potential novel therapeutic target in copy number high uterine serous carcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO018.