Abstract 1415: FraAP, a peptide antagonist against the activator protein 1 transcription factor complex, demonstrates cancer cell cytotoxicity and reduced invasion in vitro and tumor regression in vivo in HNSCC models

Abstract The AP-1 transcription factor complex, comprised of Fra1 and Jun heterodimers, plays a pivotal role in the pathogenesis of head and neck squamous cell carcinoma (HNSCC). This complex significantly contributes to tumor progression and metastasis with its expression positively correlating with poor prognosis. As dimerization of components of the AP-1 complex is required for DNA binding and subsequent transcriptional activity, we designed a peptide (Fra1 antagonizing peptide, FraAP) targeting the basic leucine zipper motif of AP-1 to antagonize AP-1 complex formation and prevent associated activity. Bio-layer interferometry (BLI) and DNA ELISA assays demonstrate target binding and selectivity of FraAP towards AP-1 family members, co-immunoprecipitation experiments reveal that FraAP blocks protein-protein interactions between cJun and Fra1, and reporter assays confirm inhibition of AP-1 transcriptional activity in vitro. Transcriptomic analysis reveals that FraAP suppresses AP-1-driven pathways required for cell cycle progression, proliferation, and invasion and promotes apoptosis. RNAseq data was confirmed by qPCR analysis of relevant target genes. Corresponding functional in vitro assays reveal that FraAP exhibits an inhibitory effect on invasion in Boyden chamber assays and induces a phenotypic mesenchymal to epithelial transition characterized by decreased mesenchymal marker N-cadherin and increased epithelial marker E-cadherin. Annexin V characterization of FraAP treated cells by flow cytometry confirms that FraAP induces dose-dependent apoptosis. Further, in a HNSCC subcutaneous xenograft model, administration of FraAP results in significant tumor growth inhibition, demonstrating the anti-cancer potential of targeting the AP-1 complex. In summary, these data support FraAP as a potent peptide antagonist of the AP-1 transcription factor family that warrants further development as a potential therapeutic option for AP-1 driven tumors. Citation Format: Karen Mendelson, Zachary F. Mattes, Siok Leong, Ricardo Ramirez, Mark Koester, Claudio Scuoppo, Julia Diehl, Erin Gallagher, Binh Lee, Franco Abbate, Lila Ghamsari, Gene Merutka, Barry J. Kappel, Abi Vainstein-Haras, Jim A. Rotolo. FraAP, a peptide antagonist against the activator protein 1 transcription factor complex, demonstrates cancer cell cytotoxicity and reduced invasion in vitro and tumor regression in vivo in HNSCC models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1415.