LAUSR

Epigenetic regulators MLL1 and Menin plays important role in cancer progression, metastasis, and relapse. Apart from the oncogenic translocations in leukemias, MLL1 forms a COMPASS complex with Menin and other binding partners to act as an H3K4 methyltransferase. Inhibition of COMPASS complex by blocking the Menin-MLL1 interaction is reported to be effective in different cancers. In this study, we found that a specific Menin-MLL1 inhibitor, MI-503 inhibits neuroblastoma cancer stem cells (NB CSCs; CD114+ cells) to inhibit overall neuroblastoma (NB) growth in both in vitro and in vivo NB tumor models. NB is an extracranial solid pediatric cancer that accounts for about 15% of all pediatric cancer-related deaths, with the long-term survival of relapsed NB patients being less than 10%. We found that MI-503 significantly and in a dose-dependent manner inhibits cell proliferation in nine NB cell lines tested including MYCN amplified (NGP, LAN-5, IMR-32), MYCN non-amplified (SH-SY5Y, SK-N-AS, CHLA-255), and primary patient-derived NB cell lines (COG-N-415, COG-N-269, COG-N-357), in contrast to control fibroblasts. Additionally, MI-503 significantly inhibits NB 3D spheroidal tumor growth and live cell counts compared to control treatments. Further, flow cytometry analysis revealed that MI-503 specifically induces apoptosis and blocks cell cycle progression at the S phase in the NB CSCs (CD114+ cells) in comparison to non-CSCs (CD114- cells) that leads to significant inhibition of overall NB CSC levels in different NB cell lines. By inhibiting the COMPASS complex, MI-503 significantly inhibits H3K4me3 levels as determined by the histone immunoblot assays. This leads to the inhibition of multiple cancer stemness-related genes expression such as OCT4, Nanog, HOXA, AF9, and MEIS1. Further, we determined the efficacy of MI-503 in NB xenograft mouse models and found that MI-503 significantly inhibits overall NB tumor growth (12.3 fold; p<0.001) and tumor burden (10.2 fold; p<0.01) by directly inhibiting tumor NB CSCs (p<0.01). We have not observed any drug-treatment-related toxicities or gender bias. Overall, our study highlights a novel epigenetic-based therapeutic approach for high-risk NB and underlines the role of epigenetic regulators in maintaining the NB CSCs and NB growth. In our future efforts, we will develop concomitant therapeutic approaches by combining MI-503 with current chemotherapies to target both NB CSCs and bulk tumor cells. This will lead to the development of effective, targeted, and clinically tractable therapies for NB patients. Citation Format: Rameswari Chilamakuri, Saurabh Agarwal. Epigenetic regulator Menin-MLL1 maintains cancer stem cells and promotes neuroblastoma growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB314.