Our Science – Ho Website
Mitchell Ho, Ph.D.
Development of novel human 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 glypican-3 (GPC3) and mesothelin and in generating new human monoclonal antibodies to treat liver cancer as well as other cancers. We have used in vitro tumor spheroids in the field of antibody therapy and developed mammalian cell display for the identification of therapeutic antibodies.
Liver cancer is the fifth most common cancer and the third leading cause of cancer mortality in the world. Hepatocelluar carcinoma (HCC) accounts for approximately 75% of liver cancer cases, while intrahepatic cholangiocarcinoma (ICC) is the second most common primary liver tumor. There is an urgent need to develop new drugs for the treatment of liver cancer.
Project 1: Targeting GPC3 in HCC and other cancers
GPC3 is highly expressed in HCC and holds potential for liver cancer therapy. The biological functions of GPC3 and its role in liver tumorigenesis remain elusive. Our work (and that of other labs) helps uncover the role of GPC3 in liver cancer cell growth. We produced and analyzed a recombinant soluble GPC3 (25-559) that inhibited the growth of HCC cells and presumed to compete with endogenous glypican-3 for binding to growth factors on the cancer cell surface. Our lab isolated a panel of mouse monoclonal antibodies including YP7 that recognize the C-terminal end (511-560) of GPC3. YP7 binds GPC3 with high affinity for HCC. It is highly sensitive in that it also detects GPC3 in low expression ovarian clear cell carcinoma and melanoma cells. Recently, we generated a human single-domain antibody, HN3, with high affinity for cell-surface-associated GPC3 molecules. The human antibody recognizes a conformational epitope that requires both the N- and C-terminal domains of GPC3. HN3 inhibits proliferation of HCC cells and exhibits significant inhibition of HCC xenograft tumor growth in mice. The underlying mechanism of HN3 action may involve cell-cycle arrest at G1 phase through Yes-associated protein (YAP) signaling, suggesting a novel mechanism for GPC3-targeted cancer therapy.
Project 2: Targeting mesothelin in ICC and other cancers
Mesothelin is expressed at high levels in ICC, mesothelioma, ovarian cancer, and other cancers. The 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 that consists of the IAB domain and the Fc portion of a human antibody, disrupts the cancer cell adhesion mediated by the MUC16-mesothelin interaction, and elicits antibody-dependent cell mediated cytotoxicity 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 antibody-dependent cell mediated cytotoxicity against tumor cells. SD1 is a human single-domain antibody that recognizes the C-terminal end (539-588) of mesothelin close to the cell surface and exhibits complement-dependent cytotoxicity 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 highly 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 group has used in vitro tumor spheroids in the field of antibody therapy. These tumor spheroids may prove invaluable for identifying potential therapeutic targets in addition to providing an innovative platform for screening and analyzing anti-tumor antibodies. 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. All the datasets are downloadable from NCBI database (GEO accession number GSE37629).
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 antibody variable fragments 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 5/21/2013.