Development of new antibody-based cancer therapies

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

Heparan sulfate proteoglycans (HSPGs) regulate numerous cell surface signaling events. They are extracellular modulators of signal transduction pathways during development and diseases such as cancer. HSPGs are cell-surface proteins that mainly consist of glycosylphosphatidylinositol (GPI)-anchored glypicans and transmembrane syndecans. In the last over ten years, Dr Mitchell Ho's laboratory at the National Cancer Institute (NCI) has studied GPC3 and other glypicans as a new family of cancer targets and developed novel antibody and cell based immunotherapeutic technologies for treating solid tumors including liver cancer, pediatric cancers and other solid tumors. In FY2021, we created chimeric antigen receptors (CARs) using CT3 monoclonal antibody targeting GPC2 in neuroblastoma and showed single treatment of CT3 CAR T cells induced tumor regression in mesothelioma in multiple mouse xenograft models and published our preclinical studies in Cell Reports Medicine [Li et al. Cell Rep Med, 2021; PMID: 34195677]. Targeting solid tumors must overcome several major obstacles, in particular, the identification of elusive tumor-specific antigens. In this new study, we devised a strategy to help identify tumor-specific epitopes. Glypican 2 (GPC2) is overexpressed in neuroblastoma. Using RNA sequencing (RNA-seq) analysis, we showed that exon 3 and exons 7-10 of GPC2 were expressed in cancer but were minimally expressed in normal tissues. Accordingly, we discovered a monoclonal antibody (CT3) that binds exons 3 and 10 and visualized the complex structure of CT3 and GPC2 by electron microscopy. The potential of this approach was exemplified by designing CT3-derived chimeric antigen receptor (CAR) T cells that regressed neuroblastoma in mice. Genomic sequencing of T cells recovered from mice revealed the CAR integration sites that might contribute to CAR T cell proliferation and persistence. Our studies demonstrate how RNA-seq data can be exploited to help identify tumor-associated exons that can be targeted by CAR T cell therapies. We further summarized our work in studying GPC2 as a novel immunotherapeutic target in neuroblastoma and development of cancer therapies in a review article published in Pharmacology & Therapeutics [Li et al. Pharmacol Ther. 2021; PMID: 33992682]. We plan to conduct clinical trial development for testing CT3 CAR T cells in neuroblastoma patients with the support of the Cancer Moonshot program. In FY2020, our basic laboratory research studying glypican biology led to the discovery of atypical cadherin FAT1 as a novel GPC3 interacting protein in liver cancer cells [Meng et al., Sci Rep 2021; PMID: 33420124]. We previously showed that GPC3 interacts with several extracellular signaling molecules, including Wnt, HGF, and Hedgehog. In this new study, we reported a cell surface transmembrane protein (FAT1) as a new GPC3 interacting protein. The GPC3 binding region on FAT1 was initially mapped to the C-terminal region (Q14517, residues 3662-4181), which covered a putative receptor tyrosine phosphatase (RTP)-like domain, a Laminin G-like domain, and five EGF-like domains. Fine mapping by ELISA and flow cytometry showed that the last four EGF-like domains (residues 4013-4181) contained a specific GPC3 binding site, whereas the RTP domain (residues 3662-3788) and the downstream Laminin G-2nd EGF-like region (residues 3829-4050) had non-specific GPC3 binding. In support of their interaction, GPC3 and FAT1 behaved concomitantly or at a similar pattern, e.g. having elevated expression in HCC cells, being up-regulated under hypoxia conditions, and being able to regulate the expression of EMT-related genes Snail, Vimentin, and E-Cadherin and promoting HCC cell migration. Taken together, our study provides the initial evidence for the novel mechanism of GPC3 and FAT1 in promoting HCC cell migration. We also conducted series of collaborative studies to isolate a new human antibody for GPC3 [Liu et al. J Transl. Med. 2020], examine the expression of GPC3 in chronic lymphocytic leukemia [Cui et al. Sci Rep 2021], reveal the novel mechanism of glypicans in potentiating Wnt signaling through R-spondins [Dubey et al, Elife, 2020] and study the potential resistant mechanism of shed GPC3 in immune therapy [Sun et al., J Immunother Cancer 2021]. In addition to GPC2-targeted CT3 CAR T cells, we are developing GPC3 (hYP7) and mesothelin (hYP218) CAR T cells in collaboration with our clinical colleagues for the clinical trials at the NIH for treating liver cancer, mesothelioma and neuroblastoma as supported by the Cancer Moonshot program and the NCI CCR.