Abstract 4401: Dual regulation of frizzled receptors (FZD1/7) by IGF2BP3: A novel oncogenic event promotes stem-like properties and reduces carboplatin chemosensitivity in Triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is primarily driven by cancer stem cells (CSCs), resulting in treatment resistance after chemotherapy. Emerging evidence suggests that TNBC-CSC transformation is strongly dependent on m6A modification. We aim to characterize the specific m6A regulatory factor in TNBC-CSCs and its underlying mechanism. Methods: Transcriptome-based screening was used to determine the main m6A regulator in TNBC-CSCs. Mammosphere formation assay and flow cytometry were used to evaluate the role of insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) in regulating stemness in TNBC in vitro. Limiting dilution assay was used to assess the CSC frequency in vivo. Multi-omics data, including RNA immunoprecipitation sequencing (RIP-seq), Methylated RIP sequencing ((MeRIP-seq) and RNA sequencing data, were integrated to investigate the mRNA targets of IGF2BP3. RNA probes and IGF2BP3 truncations were generated to detect the direct binding location of IGF2BP3 and its target FZD1/7 mRNAs. Comet assay and homologous recomination (HR) assay were used to assess the effect of IGF2BP3 knockdown and FZD1/7 inhibitor, Fz7-21 in combination with carboplatin (CBP). Results: We demonstrated that IGF2BP3 was the dominant m6A regulator in TNBC-CSCs. Its knockdown increased chemosensitivity and reduced tumor recurrence rate after CBP therapy in vivo. Furthermore, IGF2BP3-m6A-FZD1/7 axis might act as a pivotal oncogenic event in TNBC. Stem-like properties, including higher homologous recombination repair (HRR) efficacy and chemoresistance to CBP driven by frizzled receptors 1/7 (FZD1/7), were pharmacologically targeted by a small-molecule inhibitor, Fz7-21. Mechanistic studies unveiled that the RNA-recognition motif (RRM) domain of IGF2BP3 was the functional site to recognize m6A modification on the 3'-terminal of FZD1/7 mRNAs, leading to increased RNA stability. Enhanced stability elevated the expression levels of these two transcripts, leading to FZD1/7 heterodimerization and the activation of β-catenin pathway. This was marked by the nuclear translocation of non-phosphorylated (Ser37 and Thr41) β-catenin. Conclusions: Our study highlights the critical oncogenic role of IGF2BP3 in promoting stem-like properties and reduces the TNBC sensitivity to CBP treatment. Targeting IGF2BP3 and FZD1/7 with inhibitors has the therapeutic potential to disrupt cancer stemness and reduce clinical drug dosage of CBP in TNBC patients. Citation Format: Mengyuan Cai, Peng Yin, Ziwen Wang, Yuzhou Huang, Yuxin Wang, Kefei Wu, Xu Zhang, Liang Shi, Jifu Wei, Qiang Ding. Dual regulation of frizzled receptors (FZD1/7) by IGF2BP3: A novel oncogenic event promotes stem-like properties and reduces carboplatin chemosensitivity in Triple-negative breast cancer [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 4401.