Abstract 1617: TGFBR1 as a novel therapeutic target in adult granulosa cell tumors (2023)

Abstract Adult granulosa cell tumor (AGCT) is a subtype of sex-cord stromal tumors and accounts for ~5% of all ovarian neoplasms. Nearly 100% of AGCT cases are caused by an oncogenic point mutation in the Forkhead Box L2 (FOXL2) transcription factor. Weis-Banke et al. found this gain-of-function mutation (FOXL2C134W) allows FOXL2 to hijack the nuclear SMAD2/3/4 complex, the downstream effector of transforming growth factor- ß (TGF-ß), and redirect to novel transcription sites, inducing transcription of epithelial to mesenchymal transition (EMT) and other oncogenes. We hypothesized that FOXL2 mutant AGCT would be sensitive to TGF-ß inhibition. To test this hypothesis, we treated two GCT cell lines with TP-6379, an orally available, investigational small molecule kinase inhibitor of TGFBR1 that has been shown to block the phosphorylation and nuclear translocation of SMAD2 and SMAD3 in cells. TP-6379 was tested in the KGN cell line, derived from an AGCT patient and heterozygous for the FOXL2C134W mutation, and the COV434 cell line, derived from a juvenile GCT patient, which is FOXL2 wild type (WT). KGN cells (IC50 = 135 nM) were observed to be more than 70-fold more sensitive to TP-6379 treatment than COV434 (IC50 = &amp;gt;10,000 nM), after a 6- and 7- day treatment, respectively. KGN cells that were edited to remove the WT FOXL2 or both the WT and FOXL2C134W alleles were observed to be 1.6-fold more sensitive to TP-6379 and 22-fold less sensitive than the parental KGN cells. In vivo testing using KGN cells is ongoing. Viably cryopreserved dissociated tumor cells (DTCs) from two AGCT patients and one JGCT patient, which contain a mixture of tumor, immune, endothelial, and other stromal cells, were also tested in proliferation assays with TP-6379. All three ex vivo samples were positive for the FOXL2C134W mutation as detected by a qPCR genotyping assay and were sensitive to TP-6379 (IC50 = 555-1600 nM) after 6-day treatment. Xenograft models using these patient samples are currently under development. TGF-ß signaling is also a master regulator of the tumor microenvironment (TME) and immune evasion by modulating deposition of extracellular matrix and suppression of immune cells. We performed an immunophenotyping assay in tissue microarrays of thin-needle biopsy cores of multiple cancer types by looking at the distribution of CD8 T cells within tumor and stroma. AGCT showed the strongest excluded and desert phenotype among the tested cancer types, where CD8 T cells were confined to the stroma or absent entirely. TP-6379 treatment was observed to increase expression and reverse TGF-ß induced suppression of HLA class I in KGN cells. These data suggest that TGF-ß may play a significant role in the TME of AGCT. In conclusion, preclinical data shows inhibition of TGFß signaling with TP-6379 in FOXL2C134W mutant AGCT is active at blocking cell growth and may prove to be a potential therapy in this rare disease. Citation Format: Curtis A. Allred, Richard E. Heinz, Yuta Matsumura, Tetyana V. Forostyan, David Kircher, Salah Sommakia, Thomas Welte, Veena Vuttaradhi, Jason M. Foulks, Steven L. Warner, R Tyler Hillman. TGFBR1 as a novel therapeutic target in adult granulosa cell tumors [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 1617.