Angiogenesis inhibitors (learn more in section titled Angiogenesis Inhibitors)
Tumor cells, just like normal cells, need an adequate blood supply in order to perform
vital cellular functions. Actively dividing tumors secrete special proteins that signal the
surrounding area to sprout new blood vessels.
This new blood vessel formation is called angiogenesis. The main proangiogenic factor
is called VEGF, which stands for vascular endothelial growth factor. VEGF is a ligand that binds to a VEGF receptor on the surface blood vessels, stimulating the growth and formation of new blood vessels. Secretion of VEGF by tumors, stimulates new blood vessel growth and allows them (tumors) to feed and sustain their own growth.
The concept behind angiogenesis inhibition, then, is to stop this process and thereby
fight tumor progression. An example is Avastin.
The proteasome is a structure inside the cell that breaks down proteins that have been
labeled to undergo degradation and recycling. This process is important because it
removes possibly damaged or defective proteins. But even more important, it is a
required process for normal regulation of cellular growth, division, angiogenesis, and
death.
By binding part of the proteasome, a drug can inhibit the breakdown of some of these
proteins that have been marked for destruction. This "wreaks havoc" in the cell, and can
result in growth arrest or death of the cell. An example of a protease inhibitor is
Velcade.
- Velcade (Small Molecule) - generic name Bortezomib
Immunotherapy (learn more in section titled Immunotherapy)
The classes of targeted therapies described above all bind to and block specific targets,
disrupting the chain of events needed for tumor cell proliferation. In contrast, targeted
immunotherapy agents bind to their targets, not to interfere with growth signals, but
rather to trigger immune signals.
By binding to specific protein particles (antigens) that are found on the surface of
certain types of cancer cells, targeted immunotherapy agents can lead to a series of
anti-tumor immune reactions in the body, ultimately causing the tumor cell to die.
Targeted immunotherapy drugs are essentially a collection of monoclonal antibodies,
each with different targets. Antibodies are proteins that seek out and bind to specific
antigens; every antibody has a particular antigen with which it "fits".
Antibodies are named for the antigen to which they bind, e.g. the anti-CD20 antibody
binds to the antigen CD20. An example of an immunotherapy drug is Rituxan.
- Rituxan (a monoclonal antibody) - generic name Rituximab
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- Rituxan is an antibody developed to bind to
the CD20 protein.
- CD20 is present on all B cells, including
chronic lymphocytic leukemia cells. The drug
coats the cancer cells with antibody. This
attracts natural-killer cells.
- Natural-killer cells normally destroy
antibody-coated cells. The drug may also
trigger changes inside cancer cells that lead to
programmed cell death (apoptosis) and make
the cells more sensitive to chemotherapy.
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| Image courtesy of Ohio State University |
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