MYC-DEPENDENT lncRNAs AS POTENTIAL THERAPEUTIC VULNERABILITIES IN GROUP 3 MEDULLOBLASTOMA

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Current treatments still cause severe long-term sequelae, underscoring the need for tailored molecular strategies. While integrated - omics has identified four molecular subgroups with distinct genetic signatures and protein-coding driver genes, the contribution of long non- coding RNAs (lncRNAs) to subgroup-specific tumorigenesis remains largely unexplored. We focused on Group 3 (G3) MB, the subgroup with the highest metastatic rate at diagnosis and the worst prognosis, whose hallmark is MYC amplification. Building on our previous identification of MYC-dependent lncRNAs in G3 (Rea et al., 2021), we prioritized two candidates, lncMB1 and lncMB3 for functional dissections. LncMB3 acts as a potent pro-survival factor, whose depletion in G3 cells D283 Med induces robust apoptosis. Mechanistically, lncMB3 tunes TGF-β signaling pathway via RNA-RNA interactions involving the chromatin- associated factor HMGN5, reshaping a photoreceptor gene program that controls apoptosis in G3 MB cells. This mode-of-action, linking MYC activation to cancer phenotype in vitro, has been recently characterized (Grandioso et al., 2025) together with application-oriented efforts, ranging from lncRNA targeting/chemotherapy synergistic combinations to the use of nanocage-based carriers for RNA therapeutics. In this context, competitive antisense oligonucleotides are also being designed to interfere with pathological lncRNA complexes in G3 cells. LncMB1 is transcribed antisense to RHOT1, a key regulator of microtubule- dependent mitochondrial (MT) trafficking. LncMB1 depletion reduces RHOT1 mRNA and protein levels, downregulates gene sets involved in MT metabolism and causes fragmentation and redistribution of MT network. Ongoing lncMB1 RNA pulldown RNA-seq, mass spectrometry, and untargeted metabolomics aim to define the molecular mechanisms underlying lncMB1-mediated safeguard of MT homeostasis. Collectively, our findings reveal lncMB3 and lncMB1 as a MYC-dependent lncRNA hub that regulates two distinct yet complementary hallmarks of G3 MB biology, apoptotic signaling and MT dynamics. These results position MYC-driven lncRNA networks as critical modulators of G3 aggressiveness and nominate lncMB3 and lncMB1 as attractive RNA-based therapeutic vulnerabilities in the most lethal MB subgroup.