Transcript Malaria Drugs and Vaccine

I never found the order I searched for
But always a sinister
And well-planned disorder
That increases in the hands
Of those who hold power
While the others who clamor for
A more kindly world
A world with less hunger and more hopefulness
Die of torture in the prisons
Claribel Alegria, Nicaraguan poet
How can we defeat this disease?
Leading causes of death in Sub-Saharan Africa, South Asia, and Southeast Asia for persons age
0-44 (World Health Organization)
First, how does your body strike back?
Can you say antibodies and T cells?
Antibodies work at all stages
but T cells are only effective
when the parasite is in the liver
Why?
Red blood cells do NOT express MHC proteins
and thus infected cells cannot
generate a T cell response!
In adults the immune system does
a pretty good job,
but in kids it’s a different story
Young kids are hit much harder by malaria
Because of differences in their immune response
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
How does the malaria parasite respond to
the natural selection produced by immune attack?
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
One
comes
fromdo
theNOT
fact that
malaria makes
Redclue
blood
cells
express
MHC
Red blood cells “sticky” so they lodge in capillaries
and thus infected cells cannot
generate a T cell response
proteins
This
them
to prevent
theirexpress
host cells MHC
from
Redallows
blood
cells
do NOT
Going through the spleen where they can be killed
and thus infected cells cannot
generate a T cell response
proteins
Infected red blood cells can be recognized by a change
Red blood cells do NOT express MHC proteins
In shape--the cells get “knobs”
and thus infected cells cannot
generate a T cell response
parasite
www3.niaid.nih.gov/.../ malariaGeneticsSection/
The
“knobs”
and
the stickiness
from
Red
blood
cells
do NOTresult
express
MHC proteins
Plasmodium proteins that are put on the plasma membrane
and
thus
infected
cells
cannot
of the red blood cell including the PfEMP proteins
generate a T cell response
www3.niaid.nih.gov/.../ malariaGeneticsSection/
Red blood
cells
NOTbyexpress
MHC
proteins
PfEMP-1
proteins
aredo
encoded
the var (for
variable)
genes.
individual parasite
genomes
containcells
50-150
var genes
and thus
infected
cannot
but only one is expressed at any one time.
generate a T cell response
PfEMP-1 proteins are very antigenic and thus we mount
a strong and effective response
Parasites
fight back:
theyNOT
switchexpress
on different
var genes
Red blood
cells do
MHC
proteins
during asexual reproduction allowing them
and
thus
infected
cells
cannot
to evade the initial immune response!
generate a T cell response
Nature 415: 673 (2002)
Variation also allows the parasite
to re-infect previously exposed hosts
Nature 415: 673 (2002)
Despite this, as we have seen, most adults
fight off the infection over time
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
How can we speed up this process, protect children
and the elderly, and reduce the death rate?
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
How can we speed up this process, protect children
and the elderly, and reduce the death rate?
We need drugs
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
We’ll focus on the deadliest parasite
But there is a problem that takes us
back to the family tree
mushrooms
You and me
Plasmodium
plants
http://drnelson.utmem.edu/Woods.Hole/slide5.png
We seem like distant relatives
but this is only part of the tree of life
mushrooms
You and me
Plasmodium
plants
http://drnelson.utmem.edu/Woods.Hole/slide5.png
Here’s the bigger picture--we are actually
relatively closely related to Plasmodium
Staph. aureus
TB bug
E. coli
Plasmodium and me!
Genome Research 12, 1080-1090 (2002)
We share much more of our cellular machinery
Than we do with bacteria.
Staph. aureus
TB bug
E. coli
Plasmodium and me!
Genome Research 12, 1080-1090 (2002)
We need to find drug targets
that Plasmodium have
And people do not share
The first insight goes back >400 years
Following their arrival
in the New World,
Spanish Jesuit missionaries
in Peru learned of a medicinal bark
That the native Quechua
used to treat “fever”.
web1.caryacademy.org/.../ Quinine/history.htm
Legend suggests that
the Countess of Chinchón, wife of
the Viceroy of Peru, was cured
of her fever with the bark.
The tree was named
Cinchona after the countess.
The Quechua called it
Quinquina = “bark of barks”
In 1820 J.B. Caventou
and P.J. Pelletier
isolated the active chemical
and named it quinine
A synthesis approach was
discovered in the 1940s
But most is still purified
From Cinchona bark
Quinine remains an effective drug
and was dominant through 1950.
But chemists sought
more effective derivatives
that had less side effects
Hans Andersag at Bayer
discovered chloroquine in 1934
and by the 1950’s it
became the drug of choice
How do quinine
And its derivatives
kill Plasmodium?
Most current drugs target the red blood cell stage
Plasmodium eats blood!
(actually really hemoglobin)
Plasmodium eats blood!
When living in red blood cells
It survives by digesting
Hemoglobin in its food vacuole
(the parasite lysosome).
However, the leftover
“heme”, the metal complex
that actually carries oxygen,
Is quite toxic.
Wikipedia.com
Plasmodium eats blood!
The parasite’s
heme polymerase converts
the toxic heme into
non-toxic hemazoin
Which then crystalizes
Chloroquine accumulates in the food vacoule
Where it inhibits conversion of heme to hemazoin
Either by directly binding heme and/or
By inhibiting heme polymerase
http://www.tulane.edu/~wiser/protozoology/notes/drugs.html
Chloroquine accumulates in the food vacoule
Where it inhibits conversion of heme to hemazoin
Either by directly binding heme and/or
By inhibiting heme polymerase
No, not chloroquine!
Ahhhhhhhhh…..
http://www.tulane.edu/~wiser/protozoology/notes/drugs.html
Chloroquine allowed major progress against malaria-What do you think happened next?
No, not chloroquine!
Ahhhhhhhhh…..
http://www.tulane.edu/~wiser/protozoology/notes/drugs.html
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
What cellular changes underline resistance?
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
Chloroquine
is linked
to a mutation
in a
Red bloodresistance
cells do NOT
express
MHC proteins
membrane-located food vacuolar
drug-metabolite
transporter
protein
and thus
infected
cells cannot
T move
cell response
Mutant PfCRTgenerate
is thoughtato
Chloroquine
out of the food vacuole
www3.niaid.nih.gov/.../ malariaGeneticsSection/
Choroquine resistance set back
the fight against malaria
www.uhhg.org/mcrh/resources/video/malariappt.pdf
www.uhhg.org/mcrh/resources/video/malariappt.pdf
Option 1: make more derivatives of quinine or use quinine again
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
Option 2: new drug targets
http://www.tulane.edu/~wiser/protozoology/notes/drugs.html
Pyrimethamine (DHFR) + sulfadoxine or dapsone (DHPS)
attack enzymes involved in making nucleotides
(we can take in folate from our diet- they cannot)
www.columbia.edu/itc/hs/medical/pathophys/parasitology/2006/PAR-05Color .pdf
One of the newest medicines has one of the longest histories
Artemisia has been used by Chinese herbalists
for >1000years to treat many illnesses including malaria
Med Trop (Mars). 1998;58(3 Suppl):13-7.
Int J Parasitol. 2002 Dec 4;32(13):1655-60.
The active compound was found to be Artemisinin
Med Trop (Mars). 1998;58(3 Suppl):13-7.
Int J Parasitol. 2002 Dec 4;32(13):1655-60.
Artemisinin is not toxic until it is cleaved
inside the parasite by exposure to heme-iron
A resulting free radical intermediate may
kill the parasite by poisoning
one or more essential malarial protein(s).
Med Trop (Mars). 1998;58(3 Suppl):13-7.
Int J Parasitol. 2002 Dec 4;32(13):1655-60.
What’s another rule to prevent resistance
we learned from treating TB?
When you use new drugs, use
them in combination!
Current CDC guidelines are:
If malaria was acquired in areas without
chloroquine resistance
Then Treat with chloroquine
Current CDC guidelines are:
If from area with resistance :
1. quinine plus doxycycline or tetracycline
or
2. Atovaquone + proguanil (Malarone)
Current CDC guidelines are:
If P. vivax or P. Ovale
Chloroquine plus PRIMAQUINE to hit liver stage

Plasmodium is also evolving
resistance to other drugs
http://www.tulane.edu/~wiser/protozoology/notes/drugs.html
Research continues to identify new drugs
Nature 415: 686 (2002)
Scientists also sequenced the genome of P. falciparum
In 2002 looking for new drug targets
23 million base pairs
5,300 proteins encoded
60% are not similar
to known proteins!
Nature 415: 686 (2002)
The genome of P. vivax was completed this past month
(October 2008)
More similar to P. falciparum than expected
Only 150 unique proteins
Hey wait a minute, aren’t you
forgetting something?
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
What about a vaccine
against malaria?
pathmicro.med.sc.edu/ppt-vir/vaccine.ppt
(Program for Appropriate Technology in Health)
Genetically attenuated P. falciparum sporozoites.
Developmentally arrested at an early stage
following liver cell invasion,
or
Radiation attenuated sporozoite
Of all malaria vaccines, GlaxoSmithKline’s
RTS,S/AS02A is the furthest along
in clinical testing, "at least by four to five years,"
Zarifah Reed at the WHO Initiative for Vaccine Research
RTS,S/AS02A is generated against CSP,
the most abundant cell surface protein
during the malaria parasite's infectious sporozoite stage
The RTS,S/AS02A antigen is a fusion of CSP
with a surface protein from hepatitis B,
to stimulate a more effective immune response
CS is attached to the plasma membrane
and contains a large immunodominant domain
that consists of repeats of a short, species-specific peptide.
It is important for invasion of liver cells
Membrane anchor
Since RTS,S incorporates a hepatitis B antigen,
it "will also be a hepatitis B vaccine," she adds.
An estimated one million people die annually worldwide
from hepatitis B and ensuing liver complications.
After Phase I trials demonstrated safety,
the vaccine entered Phase II trials in children in Africa
Here’s the data--did it work?
It continues to look good after a longer follow up
The Lancet 366 10 December 2005, pp. 2012-2018
Other vaccines are following this
though trials are less far along
That’s high tech—how
about low tech
Reduce Contact Between
Humans And Mosquitoes

Personal protective measures
– DEET
– PERMETHRIN
– Bed nets
Insecticide treated bednets
can reduce infection by 63%
For example, 20 million Bednets
have been distributed in Ethiopia
Legend: PSI - Population Services International;
WB -World Bank.
GFATM 2, 5 - Global Fund for AIDS, TB and Malaria
Cum nets: Cumulative number of nets distributed.
UNICEF Ethiopia
WHO, UNICEF, the World Bank and
the UN Development Program formed a
new partnership in 1998
It’s goal: eliminate malaria as a major
disease by 2015
Accessible drugs
Nets and Insecticide
Rapid diagnostic tests
More Artemesia
A U.S. government initiative designed to
cut malaria deaths in half in sub-Saharan Africa.
Announced by President Bush on June 30, 2005.
Pledges to increase U.S. funding of malaria prevention
and treatment in sub-Saharan Africa
by > $1.2 billion over 5 years.
Before we end, let’s consider one other cool aspect of malaria
This brings us back to blood and how it carries oxygen
J. Mol. Biol., 235, 657
Hemoglobin is a finely tuned machine crafted by natural selection
to deliver oxygen and remove CO2
J. Mol. Biol., 235, 657
A single amino acid change alters hemoglobin structure
And allows the protein to form long “rods”
A single amino acid change alters hemoglobin structure
And allows the protein to form long “rods”
These protein “rods” change the shape of the Red blood cell
and this change occurs when hemoglobin is not bound to oxygen
Sickled cell block capillaries and trigger
lower oxygen and more “sickling”
The disease is treatable in the developed world
But still shortens life expectancy
Untreated, as in much of the developing world,
the disease is fatal in childhood
The mutation responsible for sickle cell anemia
is surprisingly common in parts of the world
anthro.palomar.edu/synthetic/synth_4.htm
Why hasn’t natural selection eliminated this allele?
anthro.palomar.edu/synthetic/synth_4.htm
Does this map look familiar?
anthro.palomar.edu/synthetic/synth_4.htm
Does this map look familiar?
Malaria distribution
Heterozygotes have an advantage!
While red blood cells from heterozygotes are usually normal,
they are prone to sickle and be destroyed if infected by Plasmodium,
eliminating the blood stage of the parasite before it can reproduce
And this is not the only such example!
Glucose-6-phosphate dehydrogenase plays a key role
in glucose metabolism but also generates glutathione
Protects red blood cells
Against oxidative stress
200 million people are deficient in this process
Protects red blood cells
Against oxidative stress
Complete loss of function can
lead to episodes of anemia
Protects red blood cells
Against oxidative stress
Milder reductions can provide partial resistance
to malaria as malaria-infected red cells
are susceptible to more rapid death
Protects red blood cells
Against oxidative stress
However, these individuals are also
hypersensitive to certain antimalarials
like primaquine that affect oxidative stress
Protects red blood cells
Against oxidative stress