Our Science – Ho Website
Mitchell Ho, Ph.D.
Development of novel antibody-based cancer therapies
Research in the Ho lab aims to understand the molecular mechanisms underlying cancer pathogenesis and to develop novel antibody-based cancer therapies. In particular, we are interested in understanding the biology of cancer driven by cell surface proteins such as heparan sulfate proteoglycans and in generating monoclonal antibodies to treat cancers. We have used in vitro tumor spheroids in the field of antibody therapy and developed mammalian cell display for the identification of antibodies.
Project 1: Targeting Glypican-3 in hepatocelluar carcinoma
Heparan sulfate proteoglycans (HSPGs) are important modulators of signal transduction pathways during development and disease. They are cell-surface proteins that are modified by the addition of one or several glycosaminoglycan chains. HSPGs mainly consist of GPI-anchored glypicans and transmembrane sydecans. Several HSPGs have been suggested as candidate targets for cancer therapy because of their high expression in certain tumor types. Liver cancer is the fifth most common malignant cancer worldwide. Hepatocellular carcinoma (HCC) accounts for approximately 75% of liver cancer cases. There is an urgent need for new treatments. We are currently studying glypican-3 (GPC3) as a potential target for liver cancer therapy, given its high protein expression in HCC. To investigate the functional role of GPC3 in HCC cell proliferation, we produced a recombinant soluble GPC3 protein without the GPI anchor (GPC3ΔGPI) and discovered that GPC3ΔGPI, functioning as a dominant-negative form, directly inhibited the proliferation of GPC3-expressing HCC. We also knocked down GPC3 using shRNA and showed that GPC3 knockdown inhibited HCC cell growth in culture. Based on our work and that of others, we hypothesize that GPC3 is an oncogene in HCC, and that blocking GPC3 signaling may represent a new approach to treat liver cancer. To this end, our lab generated a panel of high affinity monoclonal antibodies to GPC3. We made high affinity mouse monoclonal antibodies (including YP7 and YP9.1) that recognize the C-terminal end (511-560) of GPC3. Subsequently, we generated HN3, a human single-domain (VH) antibody. The human antibody recognizes a unique conformational epitope in the core protein of GPC3 and inhibits proliferation of HCC cells. The underlying mechanism of HN3 action involves inhibition of Yes-associated protein (YAP) signaling in liver cancer cells. The anti-GPC3 antibodies exhibit significant inhibition of HCC xenograft tumor growth in mice and show potential for use as therapeutic candidates.
Project 2: Targeting mesothelin in mesothelioma, ovarian cancer and cholangiocarcinoma
Mesothelin is expressed at high levels in mesothelioma, ovarian cancer, pancreatic cancer, lung cancer, cholangiocarcinoma, breast cancer and other cancers. The molecular interaction between mesothelin and MUC16 (also known as CA125) may facilitate the implantation and spread of tumors. We experimentally established the 64-amino acid functional binding domain (IAB, 296-359) in the N-terminus of cell surface mesothelin for MUC16. HN125, an immunoadhesin based on the IAB domain, disrupts the cancer cell adhesion mediated by the MUC16-mesothelin interaction and elicits antibody-dependent cell mediated cytotoxicity (ADCC) against MUC16-positive tumor cells. Subsequently, we generated the HN1 and SD1 human monoclonal antibodies. HN1 binds the N-terminal end of cell surface mesothelin, disrupts the mesothelin-MUC16 interaction and elicits ADCC against tumor cells. SD1 is a human single-domain (VH) antibody that recognizes a unique site (539-588) of mesothelin close to the cell surface and exhibits complement-dependent cytotoxicity (CDC) as well as ADCC against tumor cells. The new human antibodies show potential for use as cancer therapeutic candidates.
Method 1: In vitro tumor spheroids
Most studies of anticancer drugs consider only genetic and/or cellular mechanisms at the level of the single cell. However, drug penetration is an additional yet important mechanism that requires a more complex cellular environment for study. In collaboration with Drs. V. Courtney Broaddus (UCSF) and Shuichi Takayama (University of Michigan), our lab has used in vitro tumor spheroids in the field of antibody therapy. We have used Affymetrix microarrays to profile gene expression in spheroids and monolayers and identified over 100 genes specific to the 3D biological structure of mesothelioma. Some of these genes may have potential as tumor markers and targets.
Method 2: Mammalian cell display
Antibody engineering is typically carried out by displaying human antibodies or antibody fragments on the surface of microorganisms (e.g. phage/virus, bacteria and yeast). We established a method known as 'mammalian cell display' that is adapted from Dr. Dane Wittrup's (MIT) yeast cell display. Using this approach, functional single-chain antibodies are expressed on human HEK-293 cells, and high affinity antigen binders are isolated from a combinatory library via flow cytometry.
BIOC301/302 - Biochemistry I/II
This page was last updated on 12/6/2013.