Abstract PO2-18-06: Targeting fibroblast growth factor receptor (FGFR1) expression through G-quadruplex stabilization inhibits metastatic breast cancer

Abstract Metastatic breast cancer (MBC) is the most advanced stage of breast cancer. Our understanding of the molecular mechanisms which drive MBC remain incomplete. Epithelial to mesenchymal transition (EMT) and mesenchymal to epithelial transition (MET) promote drug resistance and metastasis. It has been reported that fibroblast growth factor receptor 1 (FGFR1) plays a key role during the EMT:MET cycle. Furthermore, FGFR1 is amplified in 13% of primary and 20% of metastatic breast cancer patients. Therefore, optimizing inhibition of FGFR1 is crucial for the therapeutic targeting of the late stage breast cancer. First, we examined the efficacies of FGFR kinase inhibitors in the murine based dormant 4T07 tumor model. Inhibition of FGFR kinase activity leads to tumor growth inhibition but fail to eradicate dormant breast cancer cells. Therefore, we explored broader approaches to inhibit FGFR1 expression in addition to blockade of its kinase activity. G-quadruplex (G4) structures are secondary DNA structures commonly found upstream of transcriptional start sites (TSS) of oncogenes restricting their expression. Consequently, pharmacological stabilization of G4 structures within the promoters of cancer-related genes via use of small molecules has emerged as a promising therapeutic approach in cancer. Results herein demonstrate that the proximal promoter of FGFR1 contains sequences that form G4. Circular dichroism was used to verify formation of G4 in the FGFR1 proximal promoter. Importantly, use of the G4-binding compound CX-5461 stabilized the FGFR1 G4 structure, blocked the transcriptional activity of the FGFR1 proximal promoter and decreased FGFR1 expression. Therefore, we implemented the G4 stabilizers in FGFR1 expressing and metastatic drug-resistant BC cell lines. This approach results in dramatic downregulation of FGFR1 at the protein level after treatment with the G4 stabilizer. G4 stabilizing agents also interfere with ectopic FGFR1 expression and EMT-driven FGFR1 expression. Importantly, use of the G4-targeting compound CX5461 effectively blocked FGFR1 expression and inhibited FGFR1 downstream signaling, resulting in eradication of dormant breast cancer cells. Finally, in vivo application of CX5461 reduced FGFR1 expression, blocked pulmonary tumor formation and prolonged animal survival. In conclusion, consistent with the clinical observations our evaluation of FGFR kinase inhibitors validates the resistance to FGFR kinase inhibitors in MBC. Our findings indicate that targeting FGFR1 expression through G4 stabilization may be a potential strategy for MBC. Citation Format: Muhammad Safdar, Hang Lin, Sarah Dagher, Jonathan Dickerhoff, Mitchell Ayers, Luis Solorio, Danzhou Yang, Michael Wendt, Saeed Akhand. Targeting fibroblast growth factor receptor (FGFR1) expression through G-quadruplex stabilization inhibits metastatic breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-18-06.