Abstract 3150: Utilizing the HiBiT system to identify CARM1 degraders for targeted cancer therapy

Abstract Coactivator-associated arginine methyltransferase 1 (CARM1) is a member of the protein arginine methyltransferase (PRMT) family that asymmetrically dimethylates proteins on arginine residues. Methylation of BAF155 by CARM1 in triple-negative breast cancer (TNBC) drives cancer metastasis. Amplification and overexpression of CARM1 has been observed in a variety of cancers, including breast cancer, and its overexpression correlates with poor prognosis. Potent small molecule inhibitors for CARM1 have been developed but the effects of inhibiting CARM1 differ from the effects of knocking out (KO) CARM1 in cancer cells. CARM1 KO, but not CARM1 inhibition, decreases cancer cell proliferation. This implies that CARM1 also has non-enzymatic roles in driving cancer progression which necessitates the development of small molecule degraders of CARM1 to inhibit both structural roles and enzymatic activity. We have developed CARM1-specific proteolysis targeting chimeras (PROTACs), which contain a CARM1 ligand (TP-064), a rigid chemical linker, and an E3 ligase ligand (von-Hippel Lindau) to target CARM1 for proteasomal degradation. We characterized the degradation activity of the best compound, 3b, which has a DC50 of 8.1 nM and a Dmax of 97%. While PROTAC 3b is potent and selective, many challenges remain in using PROTACs in clinical settings. There are still no PROTACs that have received FDA-approval. A possible way to overcome the potential toxicity and side effects of chemically synthesized drugs is to utilize naturally occurring products. We generated a breast cancer cell line containing HiBiT-tagged CARM1 to perform high-throughput unbiased screening of 1408 natural products. Two natural product fractions, named 5_9 and 10A, decreased luciferase signal and CARM1 protein levels by Western blot. Treatment with either natural product did not impact the protein levels of another PRMT family member, PRMT6. Ongoing studies will determine the biological consequences of 5_9 and 10A on breast cancer cell lines and organoids. CARM1 PROTACs and natural products may be developed as therapeutic agents for targeting CARM1-driven cancers more effectively than currently available inhibitors. Citation Format: Megan Bacabac, Fabao Liu, Eui-Jun Kim, Isaac Hayes, Yidan Wang, Weiping Tang, Tim S. Bugni, Wei Xu. Utilizing the HiBiT system to identify CARM1 degraders for targeted cancer therapy [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 3150.