Abstract 4028: Surface localized nuclear envelope proteins define a therapeuticvulnerability in MYC-driven Group 3 medulloblastoma

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor and is comprised of four molecular subgroups (WNT, SHH, Group 3, and Group 4). Regardless of subgroup, MB patients are treated with the same standard of care (SoC) (surgical resection, chemotherapy, craniospinal irradiation) that can lead to lifelong neurocognitive deficits in survivors. A subset of Group 3 MBs harbors focal amplifications of the MYC oncogene (MYC-G3MB) that invariably lead to disease recurrence which currently remains incurable. Therefore, there is an urgent need for development of therapies that are safe for the vulnerable developing brain while exerting potent anti-tumor efficacy against therapy-resistant subtypes. Here, we identify nuclear envelope (NE) proteins LBR and TMPO to be highly expressed in MYC-G3MBs in contrast to normal tissue and human neural stem cells (hNSCs), and a context-specific mislocalization of NE proteins to the plasma membrane (PM), only in MYC-G3MBs. NE protein expression correlated to worse MB patient prognosis and survival and was significantly enriched in recurrent tissue compared to the patient matched primary samples. High resolution microscopy and transcriptomic analysis implicated hyperproliferative cell states and endogenous chromosomal instability to drive NE deformation and the creation of DNA double strand break-capturing nuclear envelope tubules (dsbNETs), critical recently described factors in genome stability that mediate the repair of rapidly accumulating DNA damage in cancers such as MB. CRISPR Cas9-mediated endogenous tagging of LBR and TMPO revealed exposure of N-termini to the extracellular matrix and linked ER or ER-like vesicles to be directly trafficked to the cell surface in MYC-G3MBs. We developed single domain antibodies (sdAbs) specific to the N-terminus of LBR and TMPO and engineered second generation chimeric antigen receptor (CAR) T cell mono (LBR or TMPO) and bispecific (LBR and TMPO) therapies. We demonstrate the potent anti-tumor efficacy of NE protein-targeted CAR T cell therapies in patient derived xenograft models (PDX) of MYC-G3MBs. We present nuclear envelope proteins aberrantly mislocalized to the plasma membrane exclusively in G3MB as a novel class of cancer-selective therapeutic targets, for the development of a new class of CAR T cell therapies for treatment-refractory childhood MB. Citation Format: Sheila Kumari Singh, Yujin Suk, Martin A. Rossotti, Jorge Ibañez-Vega, Muhammad Vaseem Shaikh, Yiyun Chen, Hardikkumar Patel, Laura Escudero, Alberto Delaidelli, Aapti Khanna, Sarah Slassi, Carlos Barba Bazan, Erika Apel, Stefan Custers, Shan Grewal, William Maich, Lucas Asselstine, Dillon McKenna, Yuxi Xiao, William Gwynne, Jason Moffat, Hiromichi Suzuki, Poul H. Sorensen, Ray Truant, Kevin Henry, Elena Sotillo-Piñeiro, Chitra Venugopal, Crystal L. Mackall, Giedre Krenciute. Surface localized nuclear envelope proteins define a therapeuticvulnerability in MYC-driven Group 3 medulloblastoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4028.