LAUSR

Retinoblastoma is the most common intraocular cancer of childhood, with approximately 8,000 new cases each year worldwide. While survival rates are relatively high in developed countries, death can occur in up to half of children in some regions. In addition, blindness is common in patients who survive, and improved therapies are clearly needed. While loss of RB gene function is essential for the initiation of almost all retinoblastoma, additional molecular changes driving their growth and dissemination are poorly understood. Improved understanding of the molecular pathways driving retinoblastoma growth and dissemination may allow us to develop more effective and less toxic therapies. Alterations leading to BCL-6 corepressor (BCOR) loss of function are the second most common mutations in retinoblastoma after changes affecting the RB locus, and are found in more aggressive tumors. BCOR mutations are also associated with metastasis and poor prognosis in other types of pediatric cancer, suggesting that targeting it will represent a new therapeutic approach for aggressive retinoblastoma. Here, we found that BCOR knockdown or knockout in two retinoblastoma cell lines with high baseline levels of protein caused significantly increased invasion/migration, proliferation and clonogenicity. In contrast, overexpression of BCOR in retinoblastoma cells with low/no baseline expression showed opposite effects. In orthotopic xenograft models, BCOR knockout dramatically increased the size and spread of retinoblastoma xenografts as compared to parental controls. In order to determine the molecular pathways modulated by BCOR, we used RNA sequencing and found that loss of function induces IGF1 transcription, resulting in activation of IGF1R and the ERK signaling pathway. Pharmacological inhibition of IGF1/IGF1R signaling using Lincitinib or AEW541 inhibited proliferation and migration in BCOR knockout retinoblastoma cells in vitro, and Lincitinib dramatically slowed xenograft growth in vivo, suggesting that induction of IGF1 represents an important downstream effector following BCOR loss. Our studies support a functional role for BCOR mutations in aggressive retinoblastoma, and suggest that this is mediated at least in part by increased IGF1R signaling, which represents a new therapeutic target for these malignant childhood tumors of the eye. Citation Format: Su-Chan Lee, Lujain Alaali, Charles G. Eberhart. Targeting the IGF1R signaling pathway inhibits cell growth and dissemination in BCOR mutant retinoblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2557.