Abstract PR12: Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody

CD47 is an anti-phagocytic cell surface protein mediating cancer cell evasion of phagocytosis by the innate immune system. Preclinical data suggest that CD47 is appears to be an indispensable means by which many cancer cells, including cancer stem cells, overcome intrinsic expression of their pro-phagocytic “eat me” signals. Blockade of CD47 with mAbs enables phagocytosis of cancer cells in vitro and in vivo. We have developed a novel humanized mAb (huCD47-Ab) that specifically binds CD47 and blocks it from interacting with its ligand, signal regulatory protein–α; (SIRPα), on phagocytic cells, resulting in the phagocytosis and elimination of cancer cells through their “eat me” signals. Normal cells generally do not express eat me signals, and are unaffected by CD47 blocking mAb. We observed expression of CD47 on aggressive pediatric tumors, including acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), Ewing9s sarcoma, neuroblastoma, and several cancers of the central nervous system (CNS), including atypical tetroid rhabdoid tumor (ATRT), primitive neuroectodermal tumor (PNET), medulloblastoma (MB), and pediatric high-grade glioma (pHGG). In-vitro phagocytosis assays, of primary patient samples shows significant engulfment by human peripheral blood derived macrophages upon incubation with the HuCD47-Ab antibody as compared to control. Furthermore we observe potent anti-tumor efficacy and survival benefit in MB, pHGG, ATRT and PNET orthotopic xenografts models establishing the ability of the huCD47 antibody to across the blood brain barrier by the CD47 blocking antibody. Using a novel human neural stem cell/brain tumor co-engraftment orthotopic xenograft model we show specificity of the HuCD47 antibody to only tumor cells and not normal human cells. We further observe potent anti-tumor efficacy in non-CNS tumor (ALL, AML and Osteosarcoma) xenograft models as well. Furthermore we demonstrate that HuCD47-Ab can be administered safely to non-human primates at therapeutic serum levels. Pre-IND and IMPD meetings with the FDA in the US and the MHRA in the UK, have been held, and the clinical trials for adult patients with advanced stage malignancies will start in early 2014. After determining safety in these phase I trials, we initiate protocols for adult CNS tumors as part of expansion cohorts, and subsequently extend the trials to pediatric cancer patients, given manageable toxicity and signs of efficacy in the adult patients. This abstract is also presented as Poster A86. Citation Format: Siddhartha S. Mitra, Sharareh Gholamin, Jens-Peter Volkmer, Abdullah Feroze, Jie Liu, Achal Achrol, Lijuan Wang, Leanne Sayles, Michael Zhang, Kathleen Sakamoto, Michelle Monje-Deisseroth, Yoon-Jae Cho, Alejandro Sweet-Cordero, Ravi Majeti, Samuel Cheshier, Irving Weissman. Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr PR12.