Clinical Uses for Monoclonal Antibodies

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Clinical Uses for Monoclonal Antibodies

• In vitro diagnostic agents
• In vivo imaging agents
• Therapeutic agents (MAb works like a drug)
• Targeting agents (MAb linked to toxin)

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Monoclonal Antibodies as Therapeutics
First MAb on market was Orthoclone OKT3, a murine
MAb used to prevent renal transplant
rejection. Approved in 1986. Since 1986, 16
more MAbs have been registered Estimated that
25 (92) of medicines in clinical
development (372) are recombinant antibodies
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Cancer
Cardiovascular Diseases
Inflammatory Diseases
Infectious Diseases
Transplantation
2003
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Therapeutic Monoclonal Antibodies
Orthoclone OKT3(muromomab-CD3) Mylotarg
(gemtuzumab ozogamicin) ReoPro (abciximab) Bexxar
(tositumomab and 131I tositumomab) Rituxan
(rituximab) Herceptin (trastuzumab) Xolair
(omalizumab) Experimental Mab for Alzheimers
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Strategies for Monoclonal Antibodies as
Therapeutics
Antibody-Drug Conjugates Antibody Directed
Enzyme Prodrug Therapy (ADEPT) Genetically
Engineered mAbs
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Genetically Engineered mAbs
Engineered mAb that have cell-killing properties
on their own induce death or apoptosis in target
cell Some FDA approved genetically engineered
mAbs Rituxan - for non-Hodgkins
lymphoma Herceptin - for breast cancer Campath
- for B-cell chronic lymphocytic lymphoma
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Monoclonal Antibodies as Targeting Agents
Immunoconjugates Link a toxic drug, protein or
radioisotope to an MAb with a high specific
affinity for a tumor-associated antigen.
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Monoclonal Antibodies as Targeting Agents
Immunoconjugates - the antibody is the delivery
system - two basic types 1) Antibody Drug
Conjugates (ADCs) - payload is a isotope,
chemotherapy agent or toxin 2) Antibody Directed
Enzyme Prodrug Therapy (ADEPT) - payload is an
enzyme with specific activity Two
immunoconjugates currently on the market -
Zevalin - Mylotarg
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Antibody-Drug Conjugates (ADCs)
ADC are MAbs linked to cell-killing drugs High
affinity and selectivity of Ab to tumor
cells MAbs enter or are internalized within
cells Cell factors or environment cause the drug
to be released from the MAb Released drugs kills
the cell Very specific cell killing. Much
different than chemotherapy where all cells are
exposed to drug.
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Toxin
X
X
Toxin
Cancer cell expressing tumor antigen
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Intracellular breakdown of Antibody linked toxin
complex
Toxin

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Mylotarg (gemtuzumab ozogamicin) MAb
calcichemicin Antibody portion of molecule
targets CD33 (a cell surface molecule) CD33 is
abundant on the surface of acute myeloid leukemia
cells (AML) CD33 is absent from normal blood
stem cells AML cells accumulate in the bone
marrow and prevent normal bone marrow from
growing an functioning properly. High fatality
rate in patients with AML
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Mylotarg (gemtuzumab ozogamicin)
Mab calcichemicin Calcichemicin is a potent
anti-cancer drug Calcichemicin intercalates into
DNA
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Calcichemicin intercalates into DNA
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Mylotarg (gemtuzumab ozogamicin)
Calcichemicin causes dsDNA breaks DNA is not
replicated and cells undergo apoptosis Antibody
targets calcichemicin to AML cell specifically
through CD33 cell surface molecule Calcichemicin
kills AML cells Mylotarg - approved in 2000
for acute myeloid leukemia
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Antibody Directed Enzyme Prodrug Therapy
(ADEPT) or Antibody Prodrug Therapy
Monoclonal antibodies target cancer cells but
stay on the cell surface Delivers an enzyme to
target cells Enzyme activates prodrug (inactive
drug) into a toxic compound that kills tumor
cells MAb cytosine deaminase Cytosine
deaminase converts 5FC(prodrug) to 5FU 5FU is a
potent chemotherapeutic agent Limits drug
delivery to tumor site
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Top Hospital Drugs (dollar volume, 2000)

Source Roman/IMS, Hospital Pharmacy 36708 2001.
Biotechnology-derived
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Abciximab (ReoPro)

• Potent inhibitor of platelet aggregation.
• Prevents life-threatening occlusion of coronary
  arteries.
• Prevention of cardiac ischemic complications from
  
• angioplasty and stent implantations.

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Abciximab (ReoPro) Mechanism of Action
Binds to GPIIb/IIIa integrin receptor on
platelets major platelet surface receptor
involved in platelet aggregation Inhibits
platelet aggregation by preventing binding of
adhesion molecules (e.g., fibrinogen, von
Willebrand factor) Blocks access of large
adhesive molecules and thereby prevents the
ability of platelets to aggregate
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Abciximab (ReoPro)
ReoPro is a Fab fragment derived from chimeric
Mab produced by papain digestion of
purified chimeric 7E3 IgG to yield Fab and Fc
regions after purification, the Fab fragments
contains 50 murine and 50 human protein
sequences
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Abciximab (ReoPro)
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Bexxar (tositumomab and 131I tositumomab)
Non-Hodgkins B cell lymphoma (NHL) 300,000
cases of NHL in US currently Aggressive and
difficult to treat disease American Cancer
Society predicted 24,400 deaths in 2002 FDA
approval, March 2004
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Bexxar (tositumomab and 131I tositumomab)
Monoclonal antibody (mouse) that targets
CD20 Cd20 is a transmembrane protein expressed
on pre-B cells and mature B-cells but not
on undifferentiated pluripotent stem cells or
other lymphoid or blood cells CD20 antigen is
not shed nor internalized after antibody
binding 131I specifically and efficaciously
targets B cells Irradiation kills tumor
cells Pre-treatment with unlabeled tositumomab
thought to bind to non-tumor B cells in the
circulation and spleen Also mediates
immune-related cytotoxic effect on cancer cells
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Rituxan (rituximab)
Chimeric Mab for Non-Hodgkins B-cell
lymphoma Rituxan targets and destroys only B
cells binds specifically to the CD20 antigen
expressed on the surfaces of normal and
malignant pre-B and mature B lymphocytes
greater than 90 of B-cell NHLs express the
CD20 antigen
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Rituxan (rituximab)
Rituxan is currently indicated for relapsed or
refractory low-grade or follicular, CD20, B-cell
non-Hodgkin's lymphoma (NHL) FDA approval for
cancer therapy in 1997. Today, more than
100,000 patients have received Rituxan, and it is
part of more than 200 completed, ongoing, or
planned clinical trials.
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Her2 Gene in Breast Cancer

• Codes for a 185 kDa transmembrane human epidermal
  growth factor receptor 2 protein (HER2).
• Growth related receptor.
• Increased HER2 gene expression in 25-30 breast
  cancers.

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Herceptin (trastuzumab)
Humanized monoclonal antibody Produced in CHO
cells Herceptin use in breast cancer Therapeutic
Binds to extracellular domain of human EGF
receptor Her2 receptor Kd 5 nM
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Herceptin (trastuzumab)
MAb binds to Her2 receptors
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Herceptin (trastuzumab)
Proposed mechanism of action (1) -
downregulation of receptors
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Proposed mechanism of action (2) - recruitment
of NK cells
Herceptin (trastuzumab)
During the second mechanism of action, antibody
dependent cell-mediated cytotoxicity (ADCC),
patrolling natural killer (NK) cells are
attracted to the HER2 receptor complex cell.
Eventually, the cancer cell is consumed by the NK
cells.
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Xolair (omalizumab)
Humanized Mab Used to treat persistent asthma 17
million Americans have asthma of which 5
million suffer from allergic asthma Allergic
asthma attack is mediated by IgE IgE binds to its
receptor on mast cells and basophils causes
release of histamines Binds to IgE molecules to
prevent IgE from binding to FceRI This prevents
IgE from triggering inflammatory cascade FDA
approved in June, 2003
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Monoclonal Antibody for Alzheimers Disease
In development at Elan, a biopharmaceutical
company Hypotheses 1) use a Mab to prevent
formation of Ab1-42 2) use a Mab to remove
Ab1-42 before plaques form
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Monoclonal Antibody for Alzheimers Disease
Experimental Mab (AAB-001) in clinical
trials Humanized Mab to neutralize Ab1-42 that
accumulates in brain and causes
plaques Passive immunotherapy
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Monoclonal Antibody for Alzheimers Disease
Beta secretase target for Mab development Beta-se
cretase thought to initiate and be the rate
limiting step in the production of Ab1-42 Gamma
secretase target for Mab development Similar
role in the production of Ab1-42
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Alzheimer Amyloid Production
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Refolding -gt Sticky Proteins -gt Aggregates