LAUSR

B7-H3 (CD276), an immune checkpoint member of the B7/CD28 family, plays a key role in the repression of the immune response by cancer cells. B7-H3 is overexpressed on tumor and tumor-associated cells, making it an interesting therapeutic target. B7-H3 also appears to play a role outside of immune evasion, contributing to the progression of cancer via invasion/migration, angiogenesis, and metastasis. Our previous data has confirmed the presence of B7-H3 in highly aggressive Myc+ medulloblastoma (MB) tumors. Data-mining studies revealed that B7-H3 is correlated with Myc expression in Group 3 and 4 MBs, and is associated with worse patient outcomes. miR-29, a tumor suppressor, has been shown downregulating the expression of B7-H3 in various cancers. We have shown that miR-29 can reduce the angiogenesis abilities of D283 and D425 cells by downregulating B7-H3 in vitro. Subsequent RNA-sequencing analysis of miR-29-transfected D283 cells revealed upregulation of STAT1 activity. Immunoblot analysis and real-time PCR of D283 and D425 cells demonstrated increased expression of p-STAT1, when transfected with miR-29 plasmid. Treatment with all-trans retinoic acid induced p-STAT1 expression, with a concomitant decrease in the expression of B7-H3 and MMP-9. This preliminary data revealed a novel role for STAT1 in potentially regulating B7-H3, and consequently, angiogenesis and metastasis in MB. To date, the role of STAT1 in MB progression has not been fully investigated, and so our results provide a new avenue for developing potential treatments for aggressive MB tumors. Citation Format: Ian J. Purvis, Janardhan Avilala, Maheedhara R. Guda, Sujatha Venkataraman, Rajeev Vibhakar, Andrew J. Tsung, Kiran K. Velpula, Swapna Asuthkar. STAT1 regulates B7H3 mediated angiogenesis in medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 202.