Download Protease Inhibitors

Protease Inhibitors
Protease Inhibitors
• Amprenavir (APV) – GlaxoSmithKline, 1999
• 1,200mg 1x/day, rare side effects: Stevens-Johnsons Synd
• More rare side effects: diabetes, increased cholesterol
levels
• Side effects: vomiting, perioral parethesias, diarrhea
• Indinavir (IDV) – Merck, 1996
• 800mg 3x/day, rare side effects: nephrolithiasis,
ketoacidosis
• More rare side effects: hyperglycemia, hemolytic anemia
• Side effects: hyperbilirubinemia, dizziness, abdominal pain
• Decreases drug metabolism, increases drug toxicity
• Ritonavir (RTV) – Abbott Labs, 1996
• 600mg 2x/day, rare side effects: circumoral paresthesias
• Side effects: anorexia, diabetes, hepatitis, pancreatitis
• Not recommended with antihistamines and cardiac drugs
Protease Inhibitors
HIV Mutations
• Approximately 10 billion HIV virions are
produced daily in an infected person.
• The mutation rate is about 10-5 nucleotides
per replication cycle; 1 mutation is
generated for each new genome.
• Taken together, novel mutated genomes
occur daily and HIV strains that are drug
resistant are becoming more common.
• Novel treatments are needed.
Known HIV Mutations
Future Treatments
• Novel treatments with new targets and
mechanisms will help reduce viral load.
• New targets
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Zinc-finger motif inhibitors
Intergrase inhibitors
HIV glycoprotein membrane domain inhibitors
Host cell chemokine receptor inhibitors
RNA interference
New Targets
Zinc-Finger Inhibitors
• The HIV gag gene codes
for the core protein
consisting of a zinc-finger
motif.
• Zinc-finger motifs have
conserved structures, but
are considerably diverse
in specificity.
• B-LFd4C – Achillion
Pharmaceuticals, 2003
• Phase II clinical trials
• Used in combination with
3TC
Intergrase Inhibitors
• The HIV pol gene codes
for intergrase that
incorporates HIV DNA
into the host genome.
• Intergrase is specific only
to cells infected by HIV.
• S-1360 –
GlaxoSmithKline, 2003
• Phase II clinical trials
HIV Glycoprotein Membrane
Domain Inhibitors
• The extracellular domain
gp41 of the HIV
glycoprotein membrane
attaches to host cells.
• Inhibitors of gp41 prevent
HIV from fusing to host
cells for infection.
• T-20 - Trimeris
Pharmaceuticals, 2003
• Phase III clinical trials
• Subcutaneous injection,
90mg 2x/day
• Side effects: rash, cysts,
swollen skin
Chemokine Receptor Inhibitors
• HIV targets CCR5 for fusion-mediated entry into the host cell for
infection.
• Six known SNPs exist within CCR5 and people who lack a
functional CCR5 receptor are largely resistant to HIV infection
(CCR5Δ32).
• Homozygous people with CCR5Δ32 gene confer high degree of
resistance to sexual and mother-to-child transmission of HIV-1 and
heterozygotes tend to display slow progression.
• CCR5Δ32 mutation frequency is 0.08 in whites and .01 in
nonwhites, 0 in Africans and Asians.
• SCH-C - Schering-Plough, 2003
• Phase I clinical trials
RNA Interference
• RNAi is the process by which dsRNA directs sequencespecific degradation of mRNA.
• 21-25 nucleotide duplexes of siRNA bind to various
regions of HIV-1 genomic RNA with silencing protein
complexes for destruction.
• Two problems associated with RNAi are accessibility to
HIV-1 genomic RNA and the mutation rate of HIV.
The basics on immune response
• Activated B cells release antibodies specific for
the viral antigen into the general circulation and
constitute humoral response
• They block or neutralize the ability of the virus to
successfully infect target cells.
• B cells prevent the infection but do not cure it
once the virus has infected host cells
• Therefore, production of Abs specific for HIV is a
desirable and necessary property of a vaccine
The basics on T cells
• T cells recognize virally infected cells and
constitute cell-mediated immunity (CMI)
• CD4+ or T-helper cells are regulators of
immune function as they recruit immune cells,
stimulate antiviral Ab production by B cells and
augment the response of CD8+ cells
• CD8+ or cytotoxic T cells act by lysing virusinfected cells or by releasing antiviral cytokines
• CD4+ subset of lymphocytes is the ultimate
target of the virus although glial cells and
macrophages are also infected
Vaccine Development
 Three fundamental
approaches:
 Attenuation of the
pathogen
 Inactivation or
“killing” of the virus
 Creation of
subunit vaccine
Attenuated Vaccine
• Achieved by repeated passage to the wildtype, disease-causing strain through
different hosts or cell lines
• To reduce virulence and pathogenicity; the
virus retains its ability to infect and
stimulate Ab formation but its ability to
cause clinical disease is impaired or
eliminated
• Provides long lasting and safe immunity
• Most human vaccines are attenuated
preparations
Risks associated with attenuated
vaccines
• The virus can spontaneously revert to the
disease-causing form
• HIV has been shown to be intrinsically highly
mutable making it difficult to ensure that no
spontaneous reversion to the pathogenic strain
would occur
• Public fear making it unattractive prospect
• To date no live attenuated HIV vaccines have
been used in human trials
Inactivated Vaccine
• Generated chemically using formaldehyde
or formalin
• Safer and with greater heat stability than
attenuated counterparts
• Basis for contemporary vaccines against
polio, influenza, rabies, encephalitis
• Numerous administrations required for
long lasting immunity
However…
• High cost as compared to attenuated vaccines
• Requirement for more administrations or
“booster” shots for long lasting immunity
• 100% inactivation of the virus cannot be
demonstrated without large-scale inoculation of
healthy volunteers
• The concept of vaccination with inactivated HIV
is not more appealing to the public than
receiving live attenuated vaccine
Subunit Vaccine
• Prepared by isolating the proteins expressed on
the virion surface which can be used as a target
for Ab formation in vivo
• Less reactive and causing fewer adverse events
than the other vaccine types
• Yeast strains express key surface antigens
stimulating effective immunity without the risk of
transmitting a virus
• Basis for Hepatitis B (HBV) and influenza virus
Problems with subunit vaccines
• Poor inducers of cell-mediated immunity
(CMI) which is important in managing HIV
thus unlikely that they will find use in the
prevention of HIV transmission
Obstacles to development of an
HIV vaccine
• Extreme mutability and hence variability of HIV
infection
• Lack of truly representative animal model as
only gibbons and chimpanzees, (rare, protected
and expensive) are susceptible
• Rapid antigenic variation permitting evasion of
the immune response and allowing for multiple
variant strains within a single host
• HIV is transmitted sexually through the mucosal
surfaces (genital or rectal) which calls for IgA
HIV Vaccine Research I
• gp120-derived vaccines - induced little CMI
despite the strong antibody response in T-cell
lines, failed to neutralize virus derived from
peripheral blood mononuclear cells
• Recombinant attenuated vaccinia virus to
express key viral envelope protein followed by a
booster of soluble envelope protein derived from
HIV produced a good humoral and CMI
response and IgA antibodies in animal models.
However, further testing was stopped.
• Vaccine containing deletions in the Nef and Vpu
genes tested in macaques
Vaccine Research II
• Vaccine derived from SIV with nef deletions
conferred protective immunity on challenge with
SIV but failed in infant macaques due to
hemolytic anemia, thrombocytopenia, and CD4+
cell suppression and then death. Important
because showed differences between adults and
infants
• Gringeri et al tried anti-Tat antibody which was
successful in inducing both humoral and CMI
responses. No protection against initial infection
but more research needed
Recent Vaccine Failure
• AIDSVAX from VaxGen Inc. is a preventive vaccine
made up of synthetic gp120
• Two Phase III clinical trials were initiated: one in North
America and Europe, the other in Thailand to determine
the safety and efficacy against strains B, and B/E
respectively
• The 5400 volunteers in North America and Europe were
all HIV-negative men (MSM), and women with HIVinfected sexual partners at high risk for infection
• The volunteers in Thailand- 2500 HIV-negative IV drug
users.
• Successful in recruiting so many volunteers who
remained on the study (95%)
• Failed due to lack of adequate protection
But there is hope…

New vaccine trial initiated
in January 2003 at 3
locations in the US
expected to last one year
 Phase I including 30 HIVnegative people
randomized into 3 groups
 2 inoculations of a DNA
vaccine priming the immune
system, followed by a
booster shot based on a
recombinant poxvirus
HIV: A Biological Weapon?
Lack of Concern
• The CDC does not classify HIV as a
biological threat
– Virus does not survive long in environment
– “Intimate” contact needed for transmission
– Long latency
Cause For Concern!
• There is no cure for HIV infection
• Nearly 100% fatal
– Every person infected with HIV will eventually
develop AIDS if an opportunistic infection
doesn’t kill them first
• Astronomical mutation rate
– Potential to mutate into airborne strain
Weaponization
• Aerosolization
– Greatly increase dissemination of virus
• HIV can access the blood stream through
contact with mucus membranes - inhalation
• Genetic Recombination
– HIV/smallpox or HIV/influenza
• greatly increase communicability
– Alterations to decrease latency of HIV
• faster killer
Challenges
• Aerosolization
– CDC laboratory studies have shown that
drying HIV reduces the viral amounts by 90
to 99 percent within several hours.
• Genetic Recombination
– Requires sophisticated molecular biology
knowledge, techniques and equipment
Defense
• Prevention
– no cure or highly
effective treatment
– lack of an effective
vaccine