A novel designed fully peptide-based PROTAC, FPP29, demonstrates its potent cytotoxic effects to liver cancer HCCLM3 cells by targeting FOXM1.

FOXM1 (Forkhead box M1), a key transcription factor in the Forkhead box (FOX) family, is overexpressed across multiple cancer types and implicated in nearly all cancer hallmark pathways, making it a promising target for anticancer drug development. In this study, inspired by CP29, a peptide with high affinity to FOXM1-DBD and cytotoxicity to cancer cells, which was recently obtained in our lab by phage peptide library selection, we designed and synthesized a novel and fully peptide-based PROTAC, FPP29, and evaluated its cytotoxicity and molecular mechanisms in liver cancer HCCLM3 cells. CCK-8 assay determined that the IC50 value of FPP29 for HCCLM3 cells at 24 h was 3.65 ± 0.30 μM which was quite low among current reported FOXM1 inhibitors. Transwell invasion and migration, AO/EB staining, and clone formation experiments showed that FPP29 can promote apoptosis, and strongly inhibit the proliferation, invasion, and migration of HCCLM3 cells. Mechanistically, FPP29 can stably bind to FOXM1 and regulate the expression of FOXM1 and its related genes including cyclin B1, CDC25B, and c-Myc. In addition, FPP29 can enhance FOXM1 poly-ubiquitination and induce its degradation through the ubiquitin-proteasome system. In vivo studies in xenograft mice showed that 15 mg/kg FPP29 inhibited tumor growth by 75 % with no apparent toxicity. Collectively, FPP29 exhibits strong anti-cancer effects in vitro and in vivo, highlighting its promise as a lead compound for FOXM1-targeted therapeutic development with favorable safety profiles.