OLIGONUCLEOTIDES and VACCINES
DEPT OF PHARMACEUTICS,
1ST M.PHARM SEM-2
DEPT OF PHARMACEUTICS
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OLIGONUCLEOTIDES
• Therapeutic oligonucleotides are short strands of
nucleotides (about 20–30 nucleotides in length)
which interfere with unwanted or pathogenic
proteins. As with other new fields of
biotechnology, there are at present only a few
oligonucleotides that have been approved as
drug products or whose approval is imminent.
• Other compounds of this type have not been able
to translate positive early results into compelling
results in large clinical trials.
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• These compounds can often be engineered in the
laboratory with some degree of facility, they can be
quickly produced and screened for activity. Then the
oligonucleotides showing activity can serve as the basis
for the production of monoclonal antibodies or other
compounds which may more easily be approved for
clinical use.
• The first of only two therapeutic oligonucleotides that
have been approved for human use as of this writing is
fomvirsen (Vitravene). It was approved by the FDA in
1998 for the local treatment of cytomegalovirus
retinitis.
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• This compound represents the original type of
therapeutic oligonucleotide, i.e., an antisense
compound. It is a single-stranded DNA nucleotide
chain, 21 nucleotides long, with the substitution of a
phosphorothioate backbone for greater stability.
• This molecule is complementary to, and therefore
interferes with, a messenger RNA (mRNA) sequence in
the human cytomegalovirus (HCMV).
• This inhibits the production of some HCMV proteins
that are essential for viral replication. The compound is
injected intravitreally on a monthly basis.
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• The second oligonucleotide to be approved is
pegaptanib (Macugen). This compound is an
antagonist to vascular endothelial growth factor
(VEGF). It was approved by the FDA in 2004 for
the treatment of neovascular (wet) age-related
macular degeneration (AMD).
• This oligonucleotide, 28 bases in length, is classed
as an aptamer, or nucleic acid ligand. Aptamers,
like their protein counterparts the monoclonal
antibodies, bind with high affinity to various
molecular targets, thereby inactivating them.
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• Pegaptanib binds with high affinity to the protein VEGF,
which inhibits the binding of VEGF to its receptor and,
thereby, inactivates it. The objective is the suppression
of the neovascularization that is characteristic of wet
AMD. Pegaptanib is pegylated to extend its elimination
half life. This product is also administered by
intravitreal injection.
• Two monoclonal antibodies are also used in this
condition: Lucentis and (off-label) Avastin.
• Other oligonucleotides are currently in clinical trials.
Genasense is an antisense oligonucleotide, comprising
a short segment of DNA, with a phosphorothioate
backbone.
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• This compound inhibits production of the Bcl-2
protein which is produced by cancer cells and
which facilitates their survival. Phase III clinical
trials for the use of Genasense in the treatment
of melanoma are currently being evaluated. In
2009 the FDA stated that this compound “needs a
confirmatory trial.”
• Resten-CP, an antisense compound that interferes
with the mRNA of a gene involved in the stenosis
of vein grafts in coronary artery bypass grafting,
is currently undergoing clinical trials.
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• OGX-011, an antisense compound that inhibits
the cancer cell survival molecule clusterin, is
beginning Phase III trials for prostate cancer and
planning Phase III trials for non-small cell lung
cancer (NSCLC).
• An emerging use of aptamers, or nucleic acid
ligands, is in the field of targeted drug delivery.
For example, progress has been made in the
study of nanoparticle–aptamer bioconjugates.
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• Nanoparticles, 50–250 nanometers in diameter, can act
to facilitate the entry of encapsulated drug across
biological membranes.
• Aptamers conjugated to these nanoparticles seek out
cancer cells and direct the nanoparticles to the cancer
cells, into which they can then enter and introduce
their anticancer drug “payload.”
• Payloads can include cytotoxic small molecules as well
as anti-cancer siRNAs. Considerations regarding the
effective production and use of oligonucleotide drugs
include stability, delivery, and pharmacokinetics.
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• Along with the usual protection from extremes of
temperature, pH, and exposure to light, oligonucleotides
need to be protected from organic and reactive molecules
as well as from nucleases in the body.
• Most oligos are stable indefinitely when stored in
lyophilized form at −20 ◦C. The drug Vitravene is stable for
some time in a buffered, preservative-free solution of fixed
osmolality if the usual precautions are observed.
• Unlike the case of proteins and peptides, oligos can be
administered by topical/local delivery. Oral delivery is even
possible. Because of nucleases in the blood, systemic
delivery by intravenous injection or infusion has been
challenging.
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• Unlike the complex pharmacokinetics of proteins and
peptides, the pharmacokinetics of oligos are usually quite
classic, i.e., distributing to one or two compartments and
undergoing linear (first-order) elimination.
• The newer classes of oligos can enter cells naturally by
receptor-mediated endocytosis.
• There is also good distribution to kidney, spleen, and bone
marrow. The challenge has been to get distribution to the
brain.
• Most oligos under development incorporate technologies
that assure reasonably long elimination half lives for these
compounds. Moreover, systemic bioavailability of most
oligos is adequate.
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Vaccines(immunotherapy)
• The use of immunotherapy to treat disorders
other than microbiological infections is
increasingly being studied. A vaccine called
NicVAX which stimulates the production of
anti-nicotine antibodies is currently in a
second Phase III test after initial negative
results in a nicotine addiction prevention
study. There is also much current interest the
use of vaccines for the treatment of various
cancers.
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• Several of these anticancer vaccines that are currently in
Phase III clinical trials or for which Phase III trials are imminent
will now be discussed:
• BiovaxID is a vaccine showing activity against follicular non-
Hodgkin lymphoma (f-NHL). This vaccine is an example of
active idiotype, or personalized, anticancer vaccines since
they are based on the genetic make-up of an individual
patient’s tumor.
• Besides a protein derived from the patient’s own tumor, this
vaccine contains an antigenic carrier protein, called
KLH(keyhole limpet hemocyanin), and an adjuvant, GM-
CSF(granular macrophage colony stimulating factor). BiovaxID
is currently in Phase III trials.
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• In contrast, a vaccine called Gvax, which has
shown promise in the treatment of prostate
cancer, is not personalized. It employs
allogeneic prostate cancer cells expressing the
GM-CSF gene. As of this writing, Gvax is
preparing for Phase III clinical trials.
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• Vaccines for ocular melanoma are undergoing Phase III
testing in both the USA and Europe. These studies are
particularly designed to see whether liver metastases
of this ocular cancer can be prevented. Both
compounds contain melanoma differentiation peptides
and adjuvants.
• Two vaccines for the treatment of multiple myeloma
developed at the University of Arkansas for Medical
Sciences are being prepared for Phase III trials. Each
vaccine contains peptide fragments from a tumor
protein found on myeloma cells.
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• Finally, mention should be made of a promising new class
of cancer immunotherapy undergoing early-stage testing.
In this therapy, called adoptive cell transfer (ACT), tumor
reactive lymphocytes are harvested from a patient with
melanoma, activated and expanded ex vivo, and then
infused back into the patient.
• The result in many patients is the production of
lymphocytes with increased tumor-fighting capacity.
Research is ongoing to optimize clinical results from this
type of treatment.
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REFERENCE
• Basic Pharmacokinetics (SECONDEDITION)
SunilS.Jambhekar and PhilipJ.Breen, PageNumber:423-424.
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THANK
YOU
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