Protease Inhibitors

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Protease Inhibitors
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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

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Protease Inhibitors
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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.

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Known HIV Mutations
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Future Treatments

• Novel treatments with new targets and mechanisms
  will help reduce viral load.
• New targets
• Zinc-finger motif inhibitors
• Intergrase inhibitors
• HIV glycoprotein membrane domain inhibitors
• Host cell chemokine receptor inhibitors
• RNA interference

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New Targets
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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

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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

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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

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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 (CCR5?32).
• Homozygous people with CCR5?32 gene confer high
  degree of resistance to sexual and
  mother-to-child transmission of HIV-1 and
  heterozygotes tend to display slow progression.
• CCR5?32 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

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RNA Interference

• RNAi is the process by which dsRNA directs
  sequence-specific 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.

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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

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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
  virus-infected 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

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Vaccine Development

• Three fundamental approaches
• Attenuation of the pathogen
• Inactivation or killing of the virus
• Creation of subunit vaccine

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Attenuated Vaccine

• Achieved by repeated passage to the wild-type,
  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

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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

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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

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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

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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

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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

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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

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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

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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

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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
  HIV-infected 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

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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 HIV-negative 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

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HIV A Biological Weapon?
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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

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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
  doesnt kill them first
• Astronomical mutation rate
• Potential to mutate into airborne strain

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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

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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

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Defense

• Prevention
• no cure or highly effective treatment
• lack of an effective vaccine