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UCL
Antibody targeted Cancer Therapy Kerry
Chester Tuesday 25th April 2006. 4pm-5pm
Chemistry Auditorium
CANCER BIOLOGY MODULE
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Antigen Binding
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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)

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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

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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
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Native Monoclonal Antibodies can

• Recruit natural effectors (e.g. ADCC, Complement
  mediated lysis)
• Neutralize growth factors
• Block receptors/signal transduction
• Stimulate apoptotic signaling
• 
  
  but..

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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
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Rituximab
The original ituximab (Rituxan) FDA approved
1997 Indication Lymphoma

• Anti-CD 20
• CD20 expressed on 95 of malignant B-cell
  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
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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

mouse
human
Humanized antibody Monoclonal antibody
constructed with only antigen binding regions
(CDRs) from mouse. Remainder is human
Therapeutic mechanism Inhibit growth
signals Antibody dependent cell-mediated
cytotoxicityOther mechanisms are also possible
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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 increasesurvival in
cancer patients
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• Conjugated Antibodies
• Deliver radioactivity
• Deliver drugs or toxins
• Pre-targeted therapies eg ADEPT

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Radioimmunotherapy

• Radionuclide attached to antibody
• Usually ß-emitters, e.g. 131I, 90Y
• Cytotoxic over a distance from its source
  depending on path length

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Experimental radioimmunotherapy in
IL2R-expressing lymphomas (Phase I study)

• IL2R (CD25) expressed on tumour cells
• 131I anti-IL2R antibody

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Engineered scFv antibodies and filamentous
bacteriophage
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• Genes encoding V regions can be obtained by PCR
  using primers in conserved (framework) regions
  flanking CDRs (hypervariable regions).....see
  diagram on next slide

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• 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

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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
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• 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

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• 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

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MFE-23 targets to tumours in man
i.v. injection of MFE-23
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Engineered antibodies in ADEPT
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• 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.

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ADEPT Antibody directed enzyme prodrug therapy
antibody
Bystander effect Neighbouring tumour cells are
also killed by diffusing active drug. Important
as all cells may not be reached by
antibody-enzyme
Amplification effect High concentration of drug
within tumours
Bagshawe 1987
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Summary

• Antibodies are complex protein based molecules
  produced by B-lymphocytes 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

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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
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Further reading
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)