Abstract 4599: A novel small molecule inhibitor targeting MYC oncogenic signaling as an enhancer of HDAC inhibitors for the treatment of high-risk medulloblastoma

Abstract Background: Medulloblastoma (MB) is the most prevalent malignant childhood brain tumour. Although prognosis has improved over time, 95% of children with high-risk or relapsed MB eventually succumb to the disease. A key driver gene in high-risk MB is the c-MYC oncogene, for which there are currently no approved inhibitors. Histone deacetylases (HDACs) are transcriptional repressors that are dysregulated in many cancers, making them an attractive therapeutic target. Although several HDAC inhibitors have been FDA-approved for cancer treatment, they have been associated with high toxicity and limited efficacy as single agents. Therefore, simultaneously targeting c-MYC and HDACs may result in synergistic effects that could overcome drug resistance in high-risk MB. Methods and Results: We previously reported a novel pyrido-benzimidazole analogue, SE486-11, which enhanced the therapeutic effect of HDAC inhibitors in MYCN-driven cancers. We recently developed analogues (UNSW-SC compounds) with more potent activity (IC50: 0.017 to 3.70 µM). Here, we showed that these compounds significantly reduced cell viability and induced apoptosis in MB cells. MYC status was a key determinant of sensitivity of UNSW-SC compounds, with more than 3-fold higher cytotoxicity in high MYC compared to low MYC MB cells. The lead compound, UNSW-SC-22, was shown to reduce MYC protein expression and was found to be highly synergistic in enhancing the efficacy of HDAC inhibitors in MB cells. Most importantly, we demonstrated that UNSW-SC-22 was able to freely cross the blood brain barrier, reaching a concentration of 10.8 μM, with a half-life of 1.22 hours. UNSW-SC-22 directly bound to c-MYC and MYCN proteins at low micromolar equilibrium dissociation constant (KD) values which was demonstrated by surface plasmon resonance assay. In a MYCN-driven MB mouse model, we found that UNSW-SC-22 as a single agent at 90 mg/kg decreased tumor growth and prolonged survival. Through RNA-sequencing, we identified 512 differentially expressed genes after in vitro treatment with UNSW-SC-22. Importantly, GSEA analysis revealed MYC targets and cell cycle pathways as highly downregulated pathways, and upregulation in the p53 pathway. Several genes, such as MELK and USP1 were validated as down-stream targets of UNSW-SC-22. As UNSW-SC-22 is a first-in-class anticancer drug, which we are currently testing extensively in other MYC-driven MB mice models. Conclusion: Collectively, our data strongly suggest that c-Myc and MYCN are the molecular targets of UNSW-SC compounds, and these compounds have strong potential to serve as specific targeted therapy to treat subgroup 3 and 4 of MB patients with c-Myc and MYCN overexpression and amplification. Citation Format: Sin Wi Ng, Satyanarayana Gadde, Qian Wang, Belamy B. Cheung, Glenn M. Marshall. A novel small molecule inhibitor targeting MYC oncogenic signaling as an enhancer of HDAC inhibitors for the treatment of high-risk medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4599.