Transcript Interferons

Interferons
By: Katy Nassif
Discovery of Interferons
• 1957
• Isaacs and Lindenmann
• Did an experiment using chicken cell
cultures
• Found a substance that interfered with
viral replication and was therefore
named interferon
• Nagano and Kojima also
independently discovered this soluble
antiviral protein
What are Interferons?
• Naturally occurring proteins and glycoproteins
• Secreted by eukaryotic cells in response to viral
infections, tumors, and other biological inducers
• Produce clinical benefits for disease states such
as hepatitis, various cancers, multiple sclerosis,
and many other diseases
• Strucurally, they are part of the helical cytokine
family which are characterized by an amino acid
chain that is 145-166 amino acids long
General Action of
Interferons
• Interferons are small proteins
released by macrophages,
lymphocytes, and tissue cells
infected with a virus.
When a tissue cell is infected by a
virus, it releases interferon.
Interferon will diffuse to the
surrounding cells. When it binds to
receptors on the surface of those
adjacent cells, they begin the
production of a protein that prevents
the synthesis of viral proteins. This
prevents the spread of the virus
throughout the body.
• Three types of interferons: alpha,
beta and gamma.
Type I Interferons
• Type I: alpha and beta
• Alpha interferons are produced by leukocytes
• Beta interferons are produced by fibroblasts
• Both bind to interferon cell receptors type 1 and both
encoded on chromosome 9
•They have different binding affinities but similar
biological effects
•Viral infection is the stimulus for alpha and beta
expression
• Used to mobilize our 1st line of defense against
invading organisms
•Largest group and are secreted by almost all cell
types
The exact mechanism of type I interferons are
not fully understood, but this is an idea of
what happens:
• Alpha and beta bind to heterodimeric receptor on cell
surface.
• Alpha receptor is made up of at least 2 polypeptide chains:
IFNa-R1 and IFNa-R2
• IFNa-R1 is involved in signal transduction
• IFNa-R2 is the ligand-binding chain that also plays a role
in signal transduction
• Ligation induces oligomerisation and initiation of the
signal transduction pathway
• This results in phosphorylation of signal transductors and
activators of transcription proteins, which translocate to the
nucleous as a trimeric complex, ISGF-3.
• ISGF-3 activates transcription of interferon stimulated
genes, with many biological effects.
Type II Interferon (gamma)
• Bind to type 2 receptors and its genes are encoded on
chromosome 12
•Initially believed that T helper cell type 1 lymphocytes,
cytotoxic lymphocytes and natural killer cells only produced
IFNg, now evidence that B cells, natural killer T cells and
professional antigen-presenting
cells secrete IFNg also.
• Gamma production follows
activation with immune and
inflammatory stimuli rather
than viral infection.
• This production is controlled
by cytokines secreted by
interleukin 12 and 18.
Interferon Gamma Receptor
• Composed of two ligand binding IFNg-R1 chains
associated with two signal transducing IFNg-R2
chains
• The IFNg-R2 chain is generally the limiting factor
in IFNg responsiveness, as the IFNg-R1 chain is
usually in excess.
• The IFNg-R1 intracellular domain contains
binding spots for the Jak 1, latent cytosolic factor,
signal transducer and activator of transcription
(Stat1)
• IFNg only associates with IFNg-R2 when the
IFNg-R1 chain is present.
Interferon Gamma Receptor and Signalling Pathway
Receptors are encoded by separate genes
(IFNGR1 and IFNGR2, respectively) that
are located on different chromosomes.
As the ligand-binding (or a) chains interact
with IFN-g they dimerise and become
associated with two signal-transducing
chains.
Receptor assembly leads to activation of
the Janus kinases JAK1 and JAK2 and
phosphorylation of a tyrosine residue on the
intracellular domain of IFN-gR1.
This leads to the recruitment and
phosphorylation of STAT1, which forms
homodimers and translocates to the nucleus
to activate a range of IFN-g-responsive
genes.
After this, the ligand-binding chains are
internalised and dissociate.
The chains are then recycled to the cell
surface.
Different Interferon Drugs
• Interferons are broken down into recombinant versions of a specific interferon
subtype and purified blends of natural human interferon.
• Many of these are in clinical use and are given intramuscularly or
subcutaneously
• Recombinant forms of alpha interferon include:
•Alpha-2a drug name Roferon
•Alpha-2b drug name Intron A
•Alpha-n1 drug name Wellferon
•Alpha-n3 drug name AlferonN
•Alpha-con1 drug name Infergen
•Recombinant forms of beta interferon include:
•Beta-1a drug name Avonex
•Beta-1b drug name Betaseron
•Recombinant forms of gamma interferon include:
•Gamma-1b drug name Acimmune
Alpha Interferon-2a (Roferon A)
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Protein chain that is 165 amino acids long
Produced using recombinant DNA technology
Non-glycosylated protein
Short half life, short terminal elimination of half
life, a large volume of distribution, and a larger
reduction in renal clearance.
• These problems were resolved by pegylating
alpha-2a resulting in peginterferon alpha-2a that is
named Pegasys.
Pegylated Interferon-2a
(Pegasys)
Pegasys is recombinant interferon alpha-2a
that is covalently conjugated with bismonomethoxy polyethylene glycol (PEG)
Background:
• First developed by Davis, Abuchowski and colleagues in the
1970s
• In early 1990s PEG attached to alpha-2a, but it lacked the
required profile of improving pharmacokinetics
• Pegylation of interferon alpha-2b was achieved with the
addition of a linear PEG, designed to degrade to allow the full
potency of the interferon, while achieving a longer half-life.
Structure:
•PEG moieties are inert, longchain amphiphilic
molecules that are produced by linking repeating
units of ethylene oxide.
•Can be linear or branched in their structure
•Increasing the size with PEG, the absorption and
½ life are prolongued and the clearance of the IFN
is decreased.
•Goal of pegylation is to decrease clearence,
retention of biological activity, get a stable linkage
and enhance water solubility
• Pegylation is achieved by
the covalent attachment of
PEG derivatives that utilize
amino groups of lysines and
the N-terminus of
polypeptide molecules as the
modification site
CH3—(OCH2CH2)n--OH
mPEG—O—O2C—C—NH
mPEG—O—O2C—NH—(CH2)4
O
Interferon Beta-2a (Avonex)
• FDA approval on May 17 1996 for Relapsing
Remitting MS
• Clinical trials showed that it slowed MS
progression and had an extra benefit of slowing or
preventing the development of MS-related brain
atropy.
•The exact mechanism of IFN beta activity in
treating MS is unknown, but studies have shown that
interlukin 10 levels in the cerebrospinal fluid were
increased in patients
• Structurally IFNb-2a is a 166 amino acid
glycoprotein.
• Produced by recombinant DNA technology using
genetically engineered mammalian cells which the
human beta gene has been introduced into
• Amino acid sequence is the same as human beta
interferon. They are both glycosylated at the
asparagines residue at position 80
• Some side effects include:
•Flu-like symptoms
•Muscle aches
•Chills
Combination Therapy with
Ribavirin
• Many times interferons and peginterferons
are used in combination with Ribavirin
• It is a purine nucleoside analogue with a
modified base and a D-ribose sugar moiety
• 1st made in 1970 by Drs. Joseph
Witkowski and Roland Robins
• It inhibits the replication of a variety of
RNA and DNA viruses and is serves as an
immunomodulator to enhance type 1
cytokine production. This increases the
end of treatment response and reduces
post-treatment relapse.
• Mechanism is not well known, but there
are 4 proposed mechanisms
Conclusion
• Interferons have overlapping but different
biological activities
• Their mechanisms of action are not fully
understood, therefore there is a lot of room for
future growth within this field
• Interferon based strategies can possibly be further
tailored to each individual patient according to
early response dynamics
• Other immunomodulatiors that are being tested
include: Zadaxin and Ceplene
References
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