Antiviral Drugs:HIV treatment

Zach LaucisApril 17th, 2007

OutlineOutline

• Viruses• History of HIV/AIDS• Structure and life cycle of HIV• Therapy for HIV- highly active antiretroviral

therapy (HAART)– Nucleoside reverse transcriptase inhibitors– Non-nucleoside reverse transcriptase inhibitors– Protease inhibitors

• Statistics

VirusesVirusesStages of life cycle

• Adsorption– Virus binds to host cell

• Penetration and uncoating– Contents of the capsid are introduced into the host cell

• Replication and transcription• Synthesis and assembly of nucleocapsid

– Capsid proteins self assemble and essential DNA/RNA and proteins are taken up

• Virion release– Budding is when the viral proteins are introduced to the

host membrane and then pinched off.

HistoryHistory• First discovered on June 5, 1981 in 5

homosexual men in LA.

• First given the name GRID—Gay-Related Immune Deficiency. Changed to AIDS in 1982 when it was realized that over half of the people infected were not homosexual men.

• French and American scientists discovered the virus that caused AIDS within a year of each other. President Reagan and President Mitterrand met and agreed on the name of the virus – Human Immunodeficiency Virus (HIV).

HistoryHistory• HIV-1 is thought to have been first transmitted

to humans by wild chimpanzees in Cameroon.

• HIV-2 is believed to have been transmitted by the Old World monkey Sooty Mangabey.

• The three earliest known findings of the HIV are:– Plasma taken from a male in the Congo in 1959– In tissue taken from a 15 year old in St. Louis—he

died in 1969– In tissue taken from a Norwegian sailor who died in

1976

Structure and life cycle Structure and life cycle of HIVof HIV

• HIV is a retrovirus– Contains two strands

of (+)ssRNA

• Contains reverse transcriptase and integrase.– Integrase helps in the

insertion of HIV DNA into host DNA

• Infects helper T cells and macrophages—immune system cells

Structure and life cycle Structure and life cycle of HIVof HIV

• The outer membrane contains the proteins gp120 and gp41. Both are important to adsorption and penetration.

• Gp120 binds to the transmembrane protein CD4 on the host cell and then is removed by conformational changes.

• Gp41 then pulls the virus and host cell together allowing the membranes to fuse.

• The capsid breaks down and the viral RNA and enzymes are release into the cell.

• Reverse transcriptase converts the viral RNA into DNA. This DNA is known as proviral DNA

• Integrase inserts the proviral DNA into the host’s DNA. Once the proviral DNA is part of the host’s DNA, it is known as the provirus and can remain dormant in the DNA

Structure and life cycle Structure and life cycle of HIVof HIV

• When the provirus is transcribed, three main genes are transcribed: env, gag, and pol.

• Three non-functional poly-proteins are made from these genes, one from the env gene, one from the gag gene, and the last one is from a combination of the gag and pol genes.

• The first produces gp120 and gp41 which are placed onto the cell membrane. The other two poly-proteins move to the inner cell membrane and block out host membrane proteins. Budding occurs in this region of the membrane.

• The gag-pol protein releases protease by autocatalysing the gag-pol protein. Protease then cleaves reverse transcriptase, integrase, and other proteins.

• The capsid forms, with all viral RNA, essential enzymes, and proteins in it. The complete virus then leaves the host cell.

HIV TherapyHIV Therapy• HAART includes three different classes of

drugs– Nucleoside reverse transcriptase inhibitors

(NRTIs)– Non-nucleoside reverse transcriptase

inhibitors (NNRTIs)– Protease inhibitors (PIs)

• HAART delays the onset of AIDS. There is no known cure for HIV or AIDS

Nucleoside Reverse Nucleoside Reverse Transcriptase Inhibitors Transcriptase Inhibitors

NRTIsNRTIs

• Since reverse transcriptase is specific to the HIV virus, it serves as a good target.

• NRTIs are not active until the are taken into the cell. There they are phosphorylated into a triphosphate derivative.

NRTIsNRTIs

AbacavirAbacavir• Can attack infected CNS cells

well• It is phosphorylated to

carbovir triphosphate • Viruses build resistance

quickly• Can cause hypersensitivity

reaction• Trade name is Ziagen by

GlaxoSmithKline• Only NRTI that is a guanosine

analogue

Abacavir

NRTIsNRTIs

ZidovudineZidovudine• Originally developed as

an anticancer drug, but was the first approved HIV drug in 1987.

• Inhibits further replication because of the azide group at the 3’ position.

• Side effects include anemia and myelotoxicity

• Deoxythymidine analogue

Zidovudine

NRTIsNRTIs

LamivudineLamivudine

• An analogue of zidovudine called lamivudine was found to be less toxic but still effective as a NRTI.

• Inhibits replication because of sulfur.

• Lamivudine can also treat hepatitis B

• deoxycytidine analogue

Lamivudine

Non-nucleoside Reverse Non-nucleoside Reverse Transcriptase Inhibitors Transcriptase Inhibitors

NNRTIsNNRTIs

• NNRTIs are non-competitive reversible inhibitors.

• The allosteric binding site is next to the substrate binding site. By binding to the allosteric site, the shape of the substrate binding is changed and becomes inactive.

• NNRTIs show a higher affinity to reverse transcriptase than host DNA polymerases.

• Rapid resistance occurs by a mutation at Lys-103 to asparagine.

NNRTIsNNRTIs

NevirapineNevirapine

• Developed by random mass screening.

• Interacts using hydrophobic and van der Waals interactions.

• Causes mild to moderate rashes with a chance of life-threatening skin reactions.

• In inactivated by the mutation Val106Ala

Tyr-181

Tyr-188

Leu-100

Val-106

Val-179

Nevirapine

NNRTIsNNRTIs

DelavirdineDelavirdine• Picked from a

screening of 1500 compounds

• Larger than binding pocket, so it extends into solvent.

• Mutations in Pro-236 can cause resistance

Pro-236

Lys-103

Lys-103

Tyr-181

Tyr-188

Tyr -188

Trp-229

Protease inhibitors Protease inhibitors PIsPIs

• Developed in the 1990’s using X-ray crystallography.

• PIs do not need to be activated like NRTIs

• PIs were designed using prior research for a renin inhibitor. Renin is a mammalian aspartyl protease.

• They are transition-state inhibitors• Designed to mimic the tetrahedral

intermediate and be able to bind to the catalytic region—made up two aspartic acids.

Tehrahedral intermediate

N

OH OH

PIsPIs

PP

PP

PPPP

OH

OH

OH

OH

OH

OH

OH

O

N

N

N

N

N

N

N

4

3

Gly-48Gly-48

Asp-29 Asp-29

Gly-48’ Gly-48’

Gly-27 Gly-27’Asp-29’

Asp-29’

Asp-25 Asp-25’

Catalytic Region

Flap Region

Ile-50 Ile-50’

H-O-H

1

2 1’

2’

3’

4’

PIsPIs

SaquinavirSaquinavir• It was the first PI to be

approved for use in 1995.• Has to be taken with food

because of poor oral bioavailability.

• Shows 100-fold selectivity over human proteases

• Must be taken in high doses because it binds easily to plasma proteins

S3

S1

S2

S2’

S1’

PIsPIs

NelfinavirNelfinavir• Lower molecular weight

than saquinavir and increased aqueous solubility—more potent

• Made by using part of saquinavir

• Binds with protease like saquinavir

S3

S1

S2’

S1’

S2

PIsPIs

RitonavirRitonavir• First developed as a PI, but

deemed useless because of side effects.

• Discovered to inhibit the cytochrome enzyme CYP3A4.

• CYP3A4 is found in the liver and metabolizes protease inhibitors

• Given in low does, 100mg, with the PI.– Known as “boosting”

P3P2’

StatisticsStatistics• HIV infection is now considered a pandemic

• Killed more than 25 million people since its discovery

• Roughly 0.6% of the world’s population is infected

• Globally 33.4-46 million people live with HIV– 21.6-27.4 million of infected people live in sub-

Sahara Africa~64%– 15% are in south and south east Asia.

• 2/3 of these infections are in India