Protease Inhibitors

1. Protease Inhibitors

2. 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

3. Protease Inhibitors

4. 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.

5. Known HIV Mutations

6. 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

7. New Targets

8. 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

9. 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

10. 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

11. 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

12. 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.

13. 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

14. 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

15. Vaccine Development • Three fundamental approaches: • Attenuation of the pathogen • Inactivation or “killing” of the virus • Creation of subunit vaccine

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. HIV: A Biological Weapon?

28. 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

29. 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

30. 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

31. 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

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