1. 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”

2. Reverse transcriptase inhibitors were a
Major breakthrough in treating AIDS

3. 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: , November 3, No. 18

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

5. 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?

6. We need a new drug target

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

8. Let’s look here!

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

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

11. 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,
Copyright ©2006 by the National Academy of Sciences

12. You start with its natural substrate: a polypeptide backbone and
the site of protease cleavage (arrow)
Retroviruses. CSHL Press Fig

13. You look for things with a similar shape In part of the molecule
Retroviruses. CSHL Press Fig

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

15. 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.

16. 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.

17. 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 , Modified from Gulick et al. 1997

18. In some patients it worked exceptionally well
assay's limit of detection = 50 copies/ml
Retroviruses. CSHL Press Fig , Modified from Gulick et al. 1997

19. 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 , Modified from Gulick et al. 1997

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

21. FDA-Approved Drugs to Treat HIV Infection

22. Of course we can’t halt evolution
by natural selection
Mutations associated with resistance to protease inhibitors

23. Combination treatment takes time to reduce viral load

24. 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?

25. 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?

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

27. Go back to what happens when virus enters T cells

28. What if we could block this step?

29. Could we target Viral fusion with host cells??

30. 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

31. 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

32. 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

33. 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

34. FDA-Approved Drugs to Treat HIV Infection

35. Or as the drug company sees it….

36. But guess what happens?

37. But guess what happens?

38. More inhibitors are in the pipeline

39. 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.

40. FDA-Approved Drugs to Treat HIV Infection

41. Our understanding of the biology of HIV
also has given us insights into
other aspects of the disease

42. 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

43. 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?

44. Let’s do an experiment
Isolate CD4+ T cells from these people and add HIV

45. They do not get infected!

46. They do not get infected!
WHY NOT?

47. Remember how the virus enters T cells?

48. These people are mutants!

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

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

51. 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

52. 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