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Mitchell Ho, Ph.D.

Portait Photo of Mitchell Ho
Laboratory of Molecular Biology
Head, Antibody Therapy Section
Investigator
Center for Cancer Research
National Cancer Institute
Building 37, Room 5002C
Bethesda, MD 20892-4264
Phone:  
301-451-8727
Fax:  
301-480-4667
E-Mail:  
homi@mail.nih.gov

Biography

Dr. Ho received his Ph.D. in Immunology from the University of Illinois at Urbana-Champaign under Mariangela Segre. He won a National Research Service Award Predoctoral Fellowship from NIDA for his Ph.D. thesis research on the discovery of monoclonal antibodies against cocaine addiction. He was a postdoctoral fellow under Ira Pastan at NCI and generated immunotoxins against cancer. He also conducted research at PDL BioPharma and DNAX (now Merck Research Labs), where he developed an interest in phage display antibody engineering and high-throughput flow cytometry technologies. Dr. Ho is a recipient of the NCI Director's Intramural Innovation Award for Principal Investigators, the Mesothelioma Applied Research Foundation Grant Award, and the Ovarian Cancer Research Fund Individual Investigator Award. He is Chair of the NIH Antibody Interest Group, and he is on the Antibody Society's Board of Distinguished Advisors. He has served on the editorial boards of peer-reviewed journals. He has also served on grant review panels for NIH, FDA and DOD as well as major cancer foundations. Dr. Ho regularly presents at international symposia and is a member of the organizing committees for several international conferences on therapeutic antibodies. He is an honorary Zijiang Lecture Professor of East China Normal University and a faculty member in the Department of Biochemistry and Biophysics in the FAES Graduate School at the NIH.

Research

Development of novel antibody-based cancer therapies

Research in the Ho lab aims to understand the biology of cancer driven by cell surface glycoproteins and to develop novel antibody-based cancer therapies. We are currently studying heparan sulfate proteoglycans and mesothelin as potential targets for cancer therapy. We have used in vitro tumor spheroids in the field of therapeutic antibody research and developed mammalian cell display for antibody discovery.

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 new monoclonal antibodies to GPC3. We made high affinity mouse monoclonal antibodies (YP7 and YP9.1) that recognize a C-terminal site (511-560) in GPC3. Subsequently, we generated two human monoclonal antibodies (HN3 and HS20). HN3 is a human single-domain (VH) antibody that 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 Yap signaling in liver cancer cells. HS20 preferentially recognizes the heparan sulfate chains of GPC3. The human antibody disrupts the interaction of Wnt3a and GPC3 and inactivates Wnt/β-catenin signaling. 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 in mesothelioma, ovarian cancer, pancreatic cancer, lung cancer, gastric cancer, colorectal cancer, breast cancer and cholangiocarcinoma. The molecular interaction between mesothelin and MUC16 (also known as CA125) may facilitate the implantation and spread of tumors. We experimentally established the functional binding domain (IAB, 296-359) in 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 specific for mesothelin. HN1 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) in 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: Use of tumor spheroids for therapeutic antibody research
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 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 genes specific to the 3D biological structure of mesothelioma. Some of these genes may have potential as tumor targets.

Method 2: Use of mammalian cell display for therapeutic antibody discovery
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 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.

Teaching Interests
BIOC301/302 - Biochemistry I/II

This page was last updated on 1/22/2014.