Burke and Rienstra Collaboration Leads to New Insights

Date

04/01/14

Scientists have solved a decades-old medical mystery – and in the process have found a potentially less toxic way to fight invasive fungal infections, which kill about 1.5 million people a year. The researchers say they now understand the mechanism of action of amphotericin, an antifungal drug that has been in use for more than 50 years – even though it is nearly as toxic to human cells as it is to the microbes it attacks.

A report of the new findings appears in Nature Chemical Biology.

“Invasive fungal infections are a very important unmet medical need,” said University of Illinois and Howard Hughes Medical Institute chemistry professor Martin Burke, who led the study with chemistry professor Chad Rienstra. “There are about 3 million cases per year and what’s striking is that, even in 2014, half the patients who come into the hospital with an invasive fungal infection in their blood die.”

More people are killed by invasive fungal infections than by malaria or tuberculosis, Burke said.

Amphotericin (am-foe-TEHR-ih-sin) is the most effective broad-spectrum antifungal drug available, Burke said. But its use is limited by its toxicity to human cells.

“When I was a medical student, they used to call it ‘amphoterrible’ in the clinic because it has very powerful side effects,” he said. “And so you’re stuck between having the fungus kill the patient, versus using too much amphotericin, which kills the patient.”

Scientists have long sought to make amphotericin less toxic, but have been hindered by an obvious problem: Because it is so hard to study, no one knew exactly how it worked.

“This molecule is one of the most challenging to work with because it has a very complex structure, is poorly soluble and is sensitive to light, oxygen and acid,” Burke said.

Amphotericin also interacts with membranes, which are notoriously difficult to study. Many labs, including Burke’s, have tried to figure out the three-dimensional structure of amphotericin by crystallizing it, a standard technique. So far, all attempts have failed.

So the team turned to one of the most powerful tools for studying non-crystalline samples: solid-state nuclear magnetic resonance (NMR) spectroscopy, which measures how atomic nuclei respond to changes in a magnetic field.

“NMR is a great technique for detecting signals and interpreting the structural properties of molecules in solution,” said Rienstra, who led the NMR work with graduate students Mary Clay and Tom Anderson. But few labs use it to track interactions between small molecules in membranes, he said. “We developed several new NMR experiments to study amphotericin in the presence of membranes.”

Previous studies had found evidence that amphotericin opens up ion channels in membranes, perhaps making them more leaky to charged atoms that could disrupt a cell. Most scientists assumed that this was the drug’s main mode of action.

But the evidence also suggested that amphotericin interacted with sterols, such as cholesterol in animal cells and ergosterol in yeast. Rienstra and Burke focused on amphotericin’s influence on sterols, hypothesizing that this might be a key to its toxicity.

The initial NMR data supported this idea, indicating that very little of the drug – less than 5 percent – actually formed channels in membranes. Using NMR and other experimental tools, the Rienstra/Burke team found that most of the amphotericin aggregates on the exterior of membranes, extracting sterols out of membranes like a sponge. Cell death follows soon after.

 “For over 50 years, the mechanism by which amphotericin kills cells has remained a mystery,” Burke said. “But we are finally seeing the fog start to clear. This new understanding allows us to focus on how to make this molecule less toxic to human cells.”

In a separate study published in the Journal of the American Chemical Society, Burke and his colleagues appear to have accomplished just that. They developed a derivative of amphotericin that, at least in cell culture, binds to ergosterol in yeast but not to human cholesterol.

“We are very excited about this discovery,” Burke said. “But a great deal of work lies ahead to see if this compound has the potential to serve as a less toxic treatment for fungal infections in human patients. At this point, we just have a very promising compound. Most importantly, thanks to the collaboration between these two labs, we now know where to look for solutions to this longstanding problem.”

Preclinical trials of the new compound have begun, the researchers said.

The National Institutes of Health and the Howard Hughes Medical Institute supported portions of this work.

Originally Printed on UIUC News Bureaus Website (original link)
by: Diana Yates

Custom Tags

Related People

Directory

scheelinAlexander
Scheeline
bjmccallBenjamin
McCall
cmartn10Calgary
Martin
r-gennisRobert
Gennis
j-gerltJohn
Gerlt
sgranickSteve
Granick
mgruebelMartin
Gruebele
hergenroPaul
Hergenrother
huangRaven
Huang
mlkraftMary
Kraft
leckbandDeborah
Leckband
yi-luYi
Lu
martinisSusan
Martinis
snairSatish
Nair
eoldfielEric
Oldfield
rienstraChad
Rienstra
cmsCharles
Schroeder
zanZaida
Luthey-Schulten
sksScott
Silverman
s-sligarStephen
Sligar
zhao5Huimin
Zhao
mselfba2Michelle
Self-Ballard
pbraunPaul
Braun
mdburkeMartin
Burke
jeffchanJefferson
Chan
sdenmarkScott
Denmark
dlottDana
Dlott
foutAlison
Fout
agewirthAndrew
Gewirth
ggirolamGregory
Girolami
shs3Sharon
Hammes-Schiffer
sohirataSo
Hirata
kamihullKami
Hull
jainPrashant
Jain
jkatzeneJohn
Katzenellenbogen
nmakriNancy
Makri
douglasmDouglas
Mitchell
jsmooreJeffrey
Moore
murphycjCatherine
Murphy
r-nuzzoRalph
Nuzzo
dimerPhilip
Phillips
rauchfuzThomas
Rauchfuss
joaquinrJoaquín
Rodríguez-López
jrogersJohn
Rogers
sarlahDavid
Sarlah
kschweizKenneth
Schweizer
jsweedleJonathan
Sweedler
vddonkWilfred
van der Donk
renskeRenske
van der Veen
vuraweisJosh
Vura-Weis
mcwhite7M.
White
sczimmerSteven
Zimmerman
beakPeter
Beak
wklemperWalter
Klemperer
jdmcdonaJ.
McDonald
mvp11Michael
Pak
pogoreloTaras
Pogorelov
mshen233Mei
Shen
dewoonDavid
Woon
wboulangWilliam
Boulanger
rxbRohit
Bhargava
qchen20Qian
Chen
jianjuncJianjun
Cheng
hy66Hong
Yang
andinomaJosé
Andino Martinez
decosteDonald
DeCoste
thhuangTina
Huang
tjhummelThomas
Hummel
dkellDavid
Kell
doctorkMichael
Koerner
marvilleKelly
Marville
crrayChristian
Ray
tlbrownTheodore
Brown
rmcoatesRobert
Coates
thdjrThom
Dunning,
dykstraClifford
Dykstra
j-jonasJiri
Jonas
j-lisyJames
Lisy
shapleyJohn
Shapley
pshapleyPatricia
Shapley
awieckowAndrzej
Wieckowski
zumdahl2Steven
Zumdahl
ksuslickKenneth
Suslick
jlbearJodi
Bear
jcoxJenny
Cox
ealthausEllen
Althaus
staciryStaci
Ryan
sqdSean
Drummond
dmillsDouglas
Mills
sheeleySarah
Sheeley
jsmaddenJoseph
Madden
cknight4Connie
Knight
schulzeHeather
Schulze
slangleySamantha
Langley
ssmurrayStar
Murray
kbaumgarKeena
Finney
adkssnBeatrice
Adkisson
bmylerBeth
Myler
trabari1Katie
Trabaris
kewatsonKaren
Watson
strussTheresa
Struss
metclfKara
Metcalf
ljohnso2Lori
Johnson
jlwJamison
Lowe
jenruslJennifer
Russell
lchenoweLeslie
Chenoweth
jcfJonathan
Freiman
wdedoWolali
Dedo
ebielserElaina
Kutz
spinnerDavid
Spinner
plblumPatricia
Simpson
stevens2Chad
Stevens
lsagekarLori
Sage-Karlson
bertholdDeborah
Berthold
kecarlsoKathryn
Carlson
tlchen4Timothy
Chen
sdesmondSerenity
Desmond
angelaecAngela
Crawford
hsahmed3Hajira
Ahmed
kakinsKenye
Akins
asali3Arzeena
Ali
axelson2Jordan
Axelson
bai11Yugang
Bai
scbakerStephanie
Baker
duffin2Kevin
Duffin
duttadDebapriya
Dutta
pflotschPriscila
Falagan Lotsch
iflemingIan
Fleming
dgrayDanielle
Gray
thennes2Thomas
Hennessey
mhettingMary Jo
Hettinger
holdaNancy
Holda
holler2Jordan
Holler
aibarrAlejandro
Ibarra
kimshSung Hoon
Kim
kocherg2Nikolai
Kocherginsky
philipk2Philip
Kocheril
dlee106David
Lee
legare2Stephanie
Legare
alewandoAgnieszka
Lewandowska
qianliliQianli
Li
bdmccallBirgit
McCall
smccombiStuart
McCombie
jdm5Justin
McGlauchlen
egmooreEdwin
Moore
myerscouKathleen
Myerscough
snalla2Siva
Nalla
oraham2Aaron
Oraham
lah5LeeAnn
Pannebaker
poonawa2Maria
Poonawalla
rrollerR.
Roller
romanovaElena
Romanova
roubakhiStanislav
Rubakhin
vsfVictoria
Shepherd-Fortner
shvedalxAlexander
Shved
asoudaAlexander
Soudakov
ktsween2Kalee
Sweeney
sktarterSamantha
Tarter
aathoma2Andy
Thomas
kwilhelKaren
Wilhelmsen
wilkeyRandy
Wilkey
luxu3Lu
Xu
yuanyao4Yuan
Yao
silongSilong
Zhang
schlembaMary
Schlembach
emccarr2Elise
McCarren
cmercierChristen
Mercier
atimpermAaron
Timperman
niesShuming
Nie
hshanHee-Sun
Han
mmgMutha
Gunasekera