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High-grade serous ovarian cancer (HGSC) is the most lethal histotype of ovarian cancer and is highly prone to metastasis, with the majority of patients presenting at advanced stages of disease. There are few targeted treatment options for HGSC patients, especially for women with high metastatic tumor burdens. In order to identify potential genetic targets in metastatic disease, we characterized the genomic and transcriptomic alterations of metastatic tumors in HGSC patients. In this study, matched normal tissue, primary, and metastatic tumors from 23 HGSC short-term (ST) survivors (overall survival [OS] 5 years) underwent whole exome and RNA sequencing. We compared somatic mutations, copy number alternations, mutational burdens, differential expression, immune cell fractions, and gene fusion predictions between the primary and metastatic tumors of the ST and LT survival groups. We confirmed that tumors of LT survivors were more likely to have BRCA1 alterations and more copy-altered segments when compared to tumors of ST survivors. There was a higher percentage of shared variants between the primary and metastatic tumors for ST survivors compared to LT survivors. ST survivors also had a greater mutational burden and more predicted gene fusions than LT. We observed few differentially expressed genes between primary and metastatic tumors, but we did observe significant differences between the transcriptomes of LT and ST survivors' tumors. Overall, we observed that HGSC primary and metastatic tumors had similar genomic and transcriptomic landscapes, but we identified genetic characteristics specific to metastatic tumors that correlate with survival. Citation Format: Emilee N. Kotnik, Nicholas C. Spies, Tiandao Li, Matthew Inkman, Jin Zhang, Fernanda Martins-Rodrigues, Ian S. Hagemann, Carolyn K. McCourt, Premal H. Thaker, Andrea R. Hagemann, Matthew A. Powell, David G. Mutch, Christopher A. Maher, Christopher A. Miller, Katherine C. Fuh. Genetic characterization of metastasis and prognosis in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2202.

Background: Evidence suggests that inducing homologous recombination deficiency (HRD) can be a therapeutic target in endometrial cancer (EC). Given this, we determined whether AVB-500, an AXL inhibitor, could induce HRD measured by a reduction of RAD51 foci in response to DNA damage in a uterine serous cancer (USC). Methods: Baseline homologous recombination (HR) status was determined after inducing DNA damage by radiating USC cell lines (ARK1 and ARK4) with 10Gy radiation treatment (RT) and identifying RAD51 foci by immunofluorescence (IF). Both radiated and non-radiated cells were quantified in both cell lines. Cell lines were considered to be HR proficient if over 30% of the cells expressed RAD51 (>5 foci per cell). AVB-500 (Aravive Biologics, Houston, TX) was given prior to radiation after baseline HR status was established. IF was conducted using a Leica confocal microscope and foci were quantified using FociCounter. Results: Both ARK1 and ARK4, showed HR proficiency at baseline. After radiation, there was an increase in gamma-H2Ax indicative of DNA damage and an appropriate increase in RAD51 foci in response. However, when cells were treated with AVB-500 prior to radiation, there was a decrease in RAD51 foci when compared to radiation alone in both ARK1 (2.7 foci for AVB + RT vs 7.3 foci for RT only, p=0.0003) and ARK4 (6.3 foci for AVB + RT vs 13.0 foci for RT only, p=0.0054). Furthermore, after treatment with AVB-500 followed by RT, the proportion of ARK1 cells expressing RAD51 decreased to 21%, indicating HR deficiency. Conclusions: ARK1 and ARK4 are HR proficient at baseline. Pretreatment with AVB500 followed by RT led to a decrease in RAD51 foci suggestive of inducing HRD. Additional therapeutic and mechanistic experiments are ongoing. Citation Format: Michael D. Toboni, Barbara Blachut, Elena Lomonosova, Dineo Khabele, Lindsay Kuroki, Andrea Hagemann, Carolyn McCourt, Premal Thaker, David Mutch, Matthew Powell, Katherine Fuh. Inducing homologous recombination deficiency in uterine serous cancer (USC) using AVB-500, a receptor tyrosine kinase AXL inhibitor [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 PO002.

Objectives: We determined whether inhibition of GAS6/AXL with AVB-500 in combination with olaparib could improve response in HR-proficient (HRP) uterine serous cancer (USC). Methods: Two USC cell lines (ARK1 & ARK4) were radiated with 10Gy, and RAD51 foci were identified by immunofluorescence (IF). These were treated with AVB-500 (Aravive Biologics, Houston, TX) in combination with the poly ADP ribose polymerase (PARP) inhibitor, olaparib. Colony forming assays were assessed after 4 days of treatment with either AVB-500 alone, olaparib alone or combination treatment (olaparib + AVB-500). Colonies were stained and absorbance was obtained to calculate relative cell survival using Graph Pad Prism. In vivo studies were performed using NOD-SCID mice injected with 1 × 107 ARK1 cells intraperitoneally followed by treatment q3 days for 14-day treatment period. Treatment groups were vehicle control, AVB-500 alone, olaparib alone and olaparib with AVB-500. Results: ARK1 and ARK4 cells were found to have an increase in gamma-H2AX and RAD51 foci after radiation that was consistent with HRP. In clonogenic assays, colonies were stained and absorbance was obtained for each experimental arm. Olaparib + AVB-500 had significantly less absorbance than the olaparib only group for ARK1s (0.417nm vs 0.756nm, p=0.001) as well as in ARK4s (0.186nm vs 0.641nm, p=0.003). In an intraperitoneal model with ARK1 tumors, the olaparib + AVB-500 treated group had less tumor weight than those treated with olaparib alone (0.008g vs 0.138g, p=0.002) and AVB-500 alone (0.008g vs 0.145g, p=0.0006) after a 14-day treatment period. Conclusions: AVB-500 in combination with olaparib demonstrates an improved response than olaparib alone with a greater decrease in tumor burden. This was demonstrated in two HRP cell lines. Additional therapeutic and mechanistic experiments are ongoing. Citation Format: Michael D. Toboni, Mary Mullen, Jo'an Tankou, Hollie Noia, Alyssa Oplt, Daniel Wilke, Dineo Khabele, Lindsay Kuroki, Andrea Hagemann, Carolyn McCourt, Premal Thaker, David Mutch, Matthew Powell, Katherine Fuh. AVB-500, a receptor tyrosine kinase AXL inhibitor, improves response to olaparib in uterine serous cancer [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 PO047.