i guess you think you know this story. you don’t. the real one’s much more gory. the phoney one,...

I guess you think you know this story.You don’t. The real one’s much more gory.The phoney one, the one you knowWas cooked up years and years ago.”

Roald Dahl“Revolting Rhymes”

http://www.avert.org/his81_86.htm

Reverse transcriptase inhibitors were a Major breakthrough in treating AIDS

http://www.avert.org/his81_86.htm

Even as new uses for AZT were reported…

January 1993

A study, ACTG 076, showed that AZT reduced by two thirds the risk of HIV transmission from infected mothers to their babies.

Connor E.D. et al. (1994) 'Reduction of maternal-infant transmission of Human Immunodeficiency Virus type 1 with zidovudine treatment' ,The New England Journal of Medicine, Vol. 331:1173-1180, November 3, No. 18

http://www.avert.org/his81_86.htm

And AZT and other RT inhibitors started to level off the rise in AIDS cases

New RT inhibitors bought some time but by the mid 1990s resistance to AZT and other RT inhibitors was a serious problem

some people with AIDS already had resistance to AZT even though they themselves had never taken the drug.

We needed a new approach--what can TB treatmentteach us about how we might approach things?

We need a new drug target

Enzymes make good drug targetswhat other enzymes does HIV use?

Let’s look here!

The Gag protein gets cleaved into piecesby an enzyme called a protease

Gag Capsid

Matrix

The Gag protein gets cleaved into piecesby an enzyme called a protease

You want a drug that fits into the “active site”Where the enzyme does its work

Copyright ©2006 by the National Academy of Sciences

Das, Amit et al. (2006) Proc. Natl. Acad. Sci. USA 103, 18464-18469

Retroviruses. CSHL Press Fig. 13-15

You start with its natural substrate:a polypeptide backbone and the site of protease cleavage (arrow)

Retroviruses. CSHL Press Fig. 13-15

You look for things with a similar shapeIn part of the molecule

www.clubbiotech.at/ blundell.htm

These can fit into the “active site” and stop up the workspreventing the enzyme from doing its work

The “protease inhibitors” that pass further tests become drugs!

December 1995The FDA approved the first of a potent new family of anti-AIDS medications. The drug saquinavir belonged to a class of drugs called protease inhibitors.

December 1995The FDA approved the first of a potent new family of anti-AIDS medications. The drug saquinavir belonged to a class of drugs called protease inhibitors.

Do you want to use “protease inhibitors” alone?

Retroviruses. CSHL Press Fig. 13-18, Modified from Gulick et al. 1997

Combination therapy worked well

The baseline median viral RNA level in this study was 41,000 copies/ml.

Indinavir = protease inhibitorAZT + 3TC = RT inhibitors

Retroviruses. CSHL Press Fig. 13-18, Modified from Gulick et al. 1997

In some patients it worked exceptionally well

assay's limit of detection = 50 copies/ml

Retroviruses. CSHL Press Fig. 13-18, Modified from Gulick et al. 1997

The median initial cell count was 142 cells/μl (compared to a normal value of 1000).

With viral load reduced T cellsand thus the immune system rebounded

With the addition of these new drugsThe fight against AIDS in the USTook a dramatic turn for the better

FDA-Approved Drugs to Treat HIV Infection

Mutations associated with resistance to protease inhibitors

http://atc.atccu.chula.ac.th/biosci_PR.htm

Of course we can’t halt evolutionby natural selection

Combination treatment takes time to reduce viral load

Combination treatment takes time to reduce viral loadAnd it’s required for a lifetime

Why? What about the viral life cycle makes this virus so difficult to eradicate?

Remember that the virus integrates into our own DNA? One infected cell can re-start the infection

Which cells in your body might harbor HIV for a long time?

Picture courtesy of Frank Church

What does the future hold in terms of HIV drugs?

Go back to what happens when virus enters T cells

What if we could block this step?

Could we target Viral fusion with host cells??

A: Trimer of gp41/gp120 heterodimers

B: CD4 interaction with gp120 induces conformational change

C: Interaction with CCR5 or CXCR4 co-receptor induces gp41conformational change to insert fusion peptide into plasma membrane

D: Formation of a fusion pore through which viral core passes

HIV entry into a CD4+ T cell

THE BIOLOGY OF HIV, SIV, AND OTHER LENTIVIRUSES: Harrington and Swanstrom

A: Trimer of gp41/gp120 heterodimers

B: CD4 interaction with gp120 induces conformational change

C: Interaction with CCR5 or CXCR4 co-receptor induces gp41conformational change to insert fusion peptide into plasma membrane

D: Formation of a fusion pore through which viral core passes

A 36 amino acid “peptide” resembling gp41 blocks fusion

THE BIOLOGY OF HIV, SIV, AND OTHER LENTIVIRUSES: Harrington and Swanstrom

FDA-Approved Drugs to Treat HIV Infection

Or as the drug company sees it….

But guess what happens?

But guess what happens?

More inhibitors are in the pipeline

Drug designers are also targeting integrase

Merck's Isentress (raltegravir) was approved by the FDA in October 2007.A second integrase inhibitor, Gilead's elvitegravir (GS-9137), is in advanced clinical trials.

FDA-Approved Drugs to Treat HIV Infection

Our understanding of the biology of HIValso has given us insights into other aspects of the disease

Our understanding of the biology of HIValso has given us insights into other aspects of the disease

For example, clinicians noticed that a small fraction of people engaged in “high-risk” behaviors did not develop AIDS

Our understanding of the biology of HIValso has given us insights into other aspects of the disease

For example, clinicians noticed that a small fraction of people engaged in “high-risk” behaviors did not develop AIDS

WHY NOT?

Let’s do an experiment

Isolate CD4+ T cells from these people and add HIV

They do not get infected!

They do not get infected!

WHY NOT?

Remember how the virus enters T cells?

These people are mutants!

Both copies of the gene encoding the co-receptor CCR5 had deletion mutations and thus they did not express a functional co-receptor

Even individuals carrying one good copy of the gene and one bad copy of the gene have delayed progression from infection to AIDS

Other “long-term non-progressors” generate antibodies against conserved regions of gp120 and gp41

Or have a vigorous response of killer T cells to HIV

Finally, some Long-term non-progressors are infected with a mutant HIV virus lacking the accessory gene Nef

Nef function:1.Down regulate CD4 so virus can escape2.Modulates expression of other immune effector molecules

Potential Therapies- Life Cycle of HIV-1

Picture courtesy of Frank Church