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UCL Antibody targeted Cancer Therapy Kerry Chester Tuesday 25th April 2006. 4pm-5pm Chemistry Auditorium CANCER BIOLOGY MODULE Antigen Binding VH VH CH1 VL CL CL S-S S-S CH3 S-S S-S S-S S-S CH2 VL CH1 CH2 CH3 Antibodies can Native antibodies •Recruit natural effectors (e.g. ADCC, Complement mediated lysis) •Neutralize growth factors (e.g. VEGF) •Block receptors/signal transduction •Stimulate apoptotic signaling •Activate T-cells •Act as catalysts (catalytic antibodies or abzymes) Conjugated Antibodies •Deliver radioactivity •Deliver drugs or toxins •Pre-targeted therapies eg ADEPT •Target genes •Recombinant bi-specifics (eg anti tumour linked to anti T-cell) Most clinically useful antibodies……… Native antibodies •Recruit natural effectors (e.g. ADCC, Complement mediated lysis) •Neutralize growth factors (e.g. VEGF) •Block receptors/signal transduction •Stimulate apoptotic signaling Conjugated Antibodies •Deliver radioactivity •Deliver drugs or toxins •Pre-targeted therapies eg ADEPT Antibody dependant cellular cytotoxicity (ADCC) (a) MAbs bind to antigen on the tumour cell surface, providing the target for Fc receptors on the surface of natural killer (NK) cells. Cross-linking of Fc receptors triggers release of molecules that lyse tumour cells. (b) Cell debris is taken up by APC (c) APC present the tumour antigens to B cells, triggering the release of antibodies (d) APC present to cytotoxic T lymphocytes (CTLs) that can recognize and kill cells that express the target antigen Adams & Weiner (2005) Nat biotech Native Monoclonal Antibodies can •Recruit natural effectors (e.g. ADCC, Complement mediated lysis) •Neutralize growth factors •Block receptors/signal transduction •Stimulate apoptotic signaling but…….. Definitions Monoclonal antibody Antibody produced from a single B-lymphocyte Murine monoclonal antibody Monoclonal antibody derived entirely from mice Chimeric antibody Monoclonal antibody constructed from Mouse V-regions and human C-regions Humanized antibody Monoclonal antibody constructed with only antigen binding regions (CDRs) from mouse. Remainder is human Rituximab • • • The original ®ituximab (Rituxan) FDA approved 1997 Indication: Lymphoma Anti-CD 20 CD20 expressed on 95% of malignant Bcell lymphomas, but also on normal B-cells Human IgG1 C-regions mouse human Chimeric antibody Monoclonal antibody constructed from Mouse V-regions and human C-regions Therapeutic mechanism: Complement mediated cytotoxicity Antibody dependent cell-mediated cytotoxicity Induction of apoptosis Trastuzumab (Herceptin) • • • FDA approved 1998 Indication: Breast cancer Anti HER2 (human epidermal growth factor receptor 2) HER2 is a gene that helps control how cells cells grow, divide and repair themselves Human IgG1 C-regions Therapeutic mechanism: mouse human Humanized antibody Monoclonal antibody constructed with only antigen binding regions (CDRs) from mouse. Remainder is human Inhibit growth signals Antibody dependent cell-mediated cytotoxicity Other mechanisms are also possible Bevacizumab (Avastin) FDA approved 2004 Indication: Colorectal and lung cancer Avastin • • • Anti VEGF (vascular endothelial growth factor) VEGF stimulates growth of tumour blood vessels Humanized with human IgG1 C-regions Therapeutic mechanism: Tumor growth is dependent on angiogenesis. Angiogenesis is dependent on VEGF. Avastin directly binds to VEGF to directly inhibit angiogenesis (See R. B. Pedley and T. Meyer Lecture) First anti-angiogenesis therapy to increase survival in cancer patients Conjugated Antibodies •Deliver radioactivity •Deliver drugs or toxins •Pre-targeted therapies eg ADEPT Radioimmunotherapy • Radionuclide attached to antibody • Usually ß-emitters, e.g. 131I, 90Y • Cytotoxic over a distance from its source depending on path length Experimental radioimmunotherapy in IL2Rexpressing lymphomas (Phase I study) • IL2R (CD25) expressed on tumour cells • 131I anti-IL2R antibody UCL Engineered scFv antibodies and filamentous bacteriophage Genes encoding V regions can be obtained by PCR using primers in conserved (framework) regions flanking CDRs (hypervariable regions).....see diagram on next slide mRNA from mice or humans is commonly used as a source of V regions that are being expressed by plasma cells......see diagram on next slide The amplified V regions are linked by PCR into scFv format and cloned into filamentous bacteriohage phage (virus that grows in bacteria). Here genotype is linked to phenotype – each phage expresses an scFv on its surface and carries the gene for that scFv in its DNA. .....see diagram on next slide A phage antibody library contains millions of different antibody specificities in just a 1ml tube It is therefore relatively simple to get cloned scFvs to any antigen or tumour cell by selecting phage which bind to that antigen or tumour cell......see diagram on next slide •After each round of selection with antigen the selected phage are amplified in number by growing in bacteria The phage system has been used to make an MFE-23, an scFv antibody to the tumour associated antigen CEA (carcinoembryonic antigen), which is overexpressed in many GI carcinomas ......see next slide MFE-23 targets to tumours in man i.v. injection of MFE-23 Tumor UCL Engineered antibodies in ADEPT In ADEPT, an antibody directed against a tumour associated antigen is linked to an enzyme and given intravenously, resulting in selective accumulation of enzyme in the tumour. When the discrimination between tumour and normal tissue enzyme levels is sufficient a prodrug is given intravenously, which is converted to an active cytotoxic drug by enzyme within the tumour. This gives higher tumour to normal tissue ratios at the time when therapy is given than can be achieved with direct tumour targeting. ......see next slide ADEPT also has the advantage of achieving a bystander effect. ADEPT Antibody directed enzyme prodrug therapy prodrug toxic drug enzyme antibody Amplification effect: High concentration of drug within tumours Bagshawe 1987 Bystander effect: Cancer cell death cell Neighbouring tumour cells are also killed by diffusing active drug. Important as all cells may not be reached by antibody-enzyme Summary Antibodies: are complex protein based molecules produced by Blymphocytes as part of the immune response. Their normal function is to bind to and help eliminate foreign and infectious agents in the body Antibodies are increasingly used in cancer treatment Examples: •Recruit natural effectors (ADCC, Complement mediated lysis) •Neutralize growth factors (eg VEGF) •Block a receptor •Stimulate apoptotic signaling •Deliver radioactivity (RIT) •Deliver a toxin •Pre-targeted therapies eg ADEPT Definitions Monoclonal antibody Antibody produced from a single B-lymphocyte Murine monoclonal antibody Monoclonal antibody derived entirely from mice Chimeric antibody Monoclonal antibody constructed from Mouse V-regions and human C-regions Humanized antibody Monoclonal antibody constructed with only antigen binding regions (CDRs) from mouse. Remainder is human Further reading UCL Allen TM (2002) Ligand-targeted therapeutics in anticancer therapy. Nat Rev Cancer 2: 750-763 Adams GP, Weiner LM (2005) Monoclonal antibody therapy of cancer. Nat Biotechnol 23: 1147-1157 The antibody resource page: http://www.antibodyresource.com/educational.html (Contains links to many interesting antibody sites)