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

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

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

We need a new drug target

Enzymes make good drug targets what other enzymes does HIV use?

Let’s look here!

The Gag protein gets cleaved into pieces by an enzyme called a protease

And Gag protein cleavage is essential To make an infectious virion Matrix Capsid Gag

Das, Amit et al. (2006) Proc. Natl. Acad. Sci. USA 103, 18464-18469 You want a drug that fits into the “active site” Where the enzyme does its work Das, Amit et al. (2006) Proc. Natl. Acad. Sci. USA 103, 18464-18469 Copyright ©2006 by the National Academy of Sciences

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 shape In part of the molecule Retroviruses. CSHL Press Fig. 13-15

These can fit into the “active site” and stop up the works preventing the enzyme from doing its work www.clubbiotech.at/ blundell.htm

The “protease inhibitors” that pass further tests become drugs! December 1995 The 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? December 1995 The 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.

Combination therapy worked well The baseline median viral RNA level in this study was 41,000 copies/ml. Indinavir = protease inhibitor AZT + 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

With viral load reduced T cells and thus the immune system rebounded The median initial cell count was 142 cells/μl (compared to a normal value of 1000). Retroviruses. CSHL Press Fig. 13-18, Modified from Gulick et al. 1997

With the addition of these new drugs The fight against AIDS in the US Took a dramatic turn for the better

FDA-Approved Drugs to Treat HIV Infection

Of course we can’t halt evolution by natural selection Mutations associated with resistance to protease inhibitors http://atc.atccu.chula.ac.th/biosci_PR.htm

Combination treatment takes time to reduce viral load

Combination treatment takes time to reduce viral load And 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 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?

What does the future hold in terms of HIV drugs? Picture courtesy of Frank Church

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??

HIV entry into a CD4+ T cell CD4 interaction with gp120 induces conformational change that facilitates Membrane fusion THE BIOLOGY OF HIV, SIV, AND OTHER LENTIVIRUSES: Harrington and Swanstrom

Wow! HIV entry into a CD4+ T cell “Conformational change” means the viral gp120 protein changes shape dramatically Wow! THE BIOLOGY OF HIV, SIV, AND OTHER LENTIVIRUSES: Harrington and Swanstrom

Wow! Blocking this is a LOT harder than inhibiting an enzyme “Conformational change” means the viral gp120 protein changes shape dramatically Wow! THE BIOLOGY OF HIV, SIV, AND OTHER LENTIVIRUSES: Harrington and Swanstrom

Wow! Blocking this is a LOT harder than inhibiting an enzyme However, scientists found that A small piece of gp41 ( 36 amino acids) Can block HIV interaction with T cells! Wow! 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 HIV also has given us insights into other aspects of the disease

Our understanding of the biology of HIV also 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? Our understanding of the biology of HIV also 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: Down regulate CD4 so virus can escape Modulates expression of other immune effector molecules