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