PROJECT SUMMARY Nearly a thousand children are diagnosed each year with Neuroblastoma (NBL) in the United States, and this cancer is, by far, the most prevalent type in infants. Sadly, high-risk NBL, which comprises ~70% of all NBL cases, has a five-year survival rate of <50%. High-risk NBL is characterized by having amplification of the MYCN gene and deletion of the 1p36 (D1p36) region of chromosome one, which houses multiple tumor suppressors. But these signatures are difficult to exploit as pharmacologic inhibition of MYCN has proven elusive, and re-activating tumor suppressor gene expression after genomic loss is virtually impossible. Consistent with MYCN’s established role in increasing global transcription, high-risk NBLs with amplified MYCN expression are uniquely dependent on the cellular transcription and RNA processing apparatus. Among this machinery vital to MYCN function is the Integrator Complex, which is responsible for UsnRNA biosynthesis essential for co-transcriptional splicing and promoting RNA polymerase II (RNAPII) turnover and plasticity. Integrator is a 14-membered complex associated with RNAPII and is fundamental in regulating transcriptional output. My laboratory has been investigating the molecular mechanism of Integrator for over ten years(19-34), and we have found that Integrator subunit 11 (INTS11) is the critical enzymatic component of the complex. INTS11 utilizes its RNA endonuclease activity to cleave the 3'-end of spliceosomal UsnRNA and is thus required for pre- mRNA splicing. Moreover, we recently found that INTS11 is also necessary to cleave nascent protein- coding RNA to promote RNAPII recycling. Both functions are critical to support high transcription observed when MYCN is overproduced. Beyond being required in MYCN-amplified tumors, the most attractive feature nominating Integrator as a potential druggable target in NBL is that the INTS11 gene is located within 1p36 and is frequently deleted in NBLs. In support of this observation, data from DEPMAP reveals that NBL cell lines are highly sensitive to partial depletion of INTS11, indicating a unique and robust dependency on this gene. Altogether, these observations support a hypothesis that INTS11 represents a novel and unexplored target in NBL (Fig. 1), and our Specific Aims below are designed to test this directly. Specific Aim 1. Determine the sensitivity of MYCN-amplified and D1p36 NBL cell lines to INTS11 downregulation. Specific Aim 2. Test candidate inhibitors of INTS11 for differential toxicity in high-risk NBL cell lines.