Abstract 153: Noncoding elements of MYCN mRNA are powerful drivers on oncogenicity in neuroblastoma

Abstract Precision in genetic modeling of oncogene-driven cancer is crucial for comprehending disease pathology. Traditionally, models focused on protein expression through open-reading-frame (ORF) transgenes. This approach overlooks post-transcriptional regulation in endogenous mRNAs, which include noncoding elements like 5’ and 3’ UTRs and introns. All patient oncogene mRNAs encompass these elements, and grasping the collective impact of noncoding and protein coding components may revolutionize our comprehension of cancer origins. Neuroblastoma (NB) is the most common extracranial solid tumor in children. Genetic amplification of MYCN (MA) in NB results in very high mRNA levels and drives poor prognosis. MYCN mRNA is targeted by multiple microRNAs, including let-7. We previously demonstrated that in MA disease the 3’ UTR of MYCN can sequester let-7, inhibiting its function. MYCN mRNA thus also influences genetic patterning in NB by relieving the selective pressure to lose chromosome arms harboring let-7 loci, an event frequent in MYCN non-amplified NB but exceedingly rare in MA disease. This work established for the first time that noncoding mRNA elements within an oncogenic mRNA can itself contribute to disease pathology. To further understand the roles of noncoding elements within MYCN mRNA, we generated BALB/c 3T3 fibroblasts and murine Neuro-2a cells that express the following transgenes: 1. MYCN-ORF: expresses only MYCN open reading frame sequence. 2. MYCN-GL: intact genetic locus of MYCN, expresses full length MYCN mRNA. 3. M/GFP-GL: variant of #2 where MYCN protein coding sequences are replaced by EGFP. All three constructs demonstrated significantly enhanced in vitro proliferation compared to GFP control cells. Notably, cells expressing MYCN-GL exhibited best growth in both cell types, despite possessing an intact 3’UTR. Unexpectedly, M/GFP-GL cells demonstrated comparable growth to MYCN-ORF in 3T3s and significantly outperformed MYCN-ORF in Neuro-2a cells. This observation not only validates our prior research on the oncogenic role of the MYCN 3’ UTR but also extends it by revealing direct contributions to growth advantages, occasionally surpassing even MYCN protein. Syngeneic animal studies mirrored these trends, with MYCN-GL and M/GFP-GL inducing nearly 100% tumor incidence, surpassing the 57% incidence associated with MYCN-ORF. Tumors induced by MYCN-GL and M/GFP-GL were more than twice the size of those induced by MYCN-ORF. These observations underscore that full-length MYCN mRNA, encompassing all noncoding elements, serves as a more potent driver of cellular growth and oncogenicity than only MYCN protein expression. These findings have exciting implications for understating neuroblastoma pathology and genetic patterns, with broader implications for other oncogene-driven cancers. We are currently generating transgenic mouse models based on the above three constructs. Citation Format: Vishwa Patel, Lorraine Rana Benhamou, Dr. John T. Powers. Noncoding elements of MYCN mRNA are powerful drivers on oncogenicity in neuroblastoma 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 (6Suppl): Abstract nr 153.