Transcript The Mode of Action and Possible Target of Artemisinin

The Mode of Action
and Possible Target
of Artemisinin
Mike Van Linn
Chemistry 496
23 April 2004
Outline
 Introduction


Malaria
Artemisinin
 Rationale for Research
 Modes of Action



Iron-Oxo route
Epoxidation reactions
Alkylation reactions
 The Target of Artemisinin
Introduction
 Malaria
 Four species of
Plasmodium
 Infects 200 million
people annually
 1 million lethal
 Resistance to current
drugs
Introduction
 Artemisinin
 Natural product
extracted from sweet
wormwood, Artemisia
annua
 Used by Chinese for
over 2000 years
 A. absinthium used to
make absinthe
Rationale for Research
 Anti-malarial Activity of Artemisinin
 Artemisinin Derivatives

Used currently for life threatening cases
Rationale for Research
 Anti-malarial Activity of Artemisinin
 Artemisinin Derivatives
•
Used currently for life threatening cases
 Drug Resistance of Plasmodium
•
•
Malaria spreading
Synthesis of new drugs
Possible Modes of Action
 Iron-Oxo Route
 Epoxidation Reactions
 Alkylation Reactions
Iron-Oxo Route
 Donation of Oxygen from Peroxide Bridge to
Iron

Generate Fe(IV)=O
 No Support from Raman Resonance Data


Signal/Noise < 2
Should be ~10 or 20
Epoxidation Reactions
MnIITPP
or FeCl2
+
OR
O
NO EPOXIDE FORMATION
ARTEMISININ
+
MnIITPP
or FeCl2
Na+ -OCl
EPOXIDE FORMATION
Ph
Ph
N
H
N
Fe
Cl
Cl
MnII
N
H
N
Ph
Ph
Robert, et al
Cazelles, et al
Cazelles, et al
1,5 H Shift Possible???
 Critical Distance
Calculated to be 2.1Å
 Exceeded in Stable
Conformation
 Boat-like Conformation
(High energy state)

Houk
Comparing Route 1 and 2
 Route 1 Dominant to Route 2

90/10 ratio from isolated products


Artemisinin + MnIITPP
1,5 H shift?
 Route 1 Biologically Active
 Route 2 Inactive
 Stereochemistry Effecting Alkylation
Robert, et al
Cazelles, et al
Mode of Action
 Route 1 Dominant
 Alkyl radical formation
from reduction of
peroxide bridge
 Derivatives Used
 Observe correlation of
alkylating ability to
drug activity
 Alkylate MnIITPP
Pharm. active
The Target
 Alkylation of Heme within Infected
Erythrocytes (RBC’s)



Free heme in food vacuole of erythrocyte
Cleavage of peroxide bond
Alkylation of heme or specific parasite proteins
can occur
 Too General…
The Target, More Specifically
 Sarco/Endoplasmic Reticulum Ca2+-ATPase
(SERCA) Enzyme


PfATP6 gene sequence
Testing the hypothesis
 Heme Not Required?

Free heme blocked with Ro 40-4388 protease
inhibitor
 Localized in the Food Vacuole?

Fluorescent labeled artemisinin
Conclusions
 Malaria Remains as a Problem
 Resistant strains
 Anti-malarial Activity of Artemisinin
 Mode of Action is Now Understood
 Alkylation via route 1
 A Specific Target Found
 PfATP6 gene sequence of the SERCA
enzyme
 Fe2+ is required
 Activity not localized in the food vacuole
References
1.
Robert, Anne, et al. “From Mechanistic Studies on Artemisinin Derivatives to New Modular
Antimalarial Drugs.” Accounts of Chemical Research, 2002, Vol. 35, pp. 167-174.
2.
Cazelles, Jerome, et al. “Alkylating Capacity and Reaction Products of Antimalarial
Trioxanes after Activation by a Heme Model.” The Journal of Organic Chemistry, 2002, Vol.
67, Number 3, pp. 609-619.
3.
Wu, Wen-Min, et al. “Unified Mechanistic Framework for the Fe(II)-Induced Cleavage of
Qinghaosu and Derivatives/Analogues. The First Spin-Trapping Evidence for the Previously
Postulated Secondary C-4 Radical.” J. Am. Chem. Soc., 1998, Vol. 120, pp. 3316-3325.
4.
Biot, Christophe, et al. “Synthesis and Antimalarial Activity in Vitro and in Vivo of a New
Ferrocene-Chloroquine Analogue.” J. of Medicinal Chemistry, 1997, Vol. 40, pp. 3715-3718.
5.
Yarnell, Amanda; “Rethinking How Artemisinin Kills,” Chemical and Engineering News, Aug.
25, 2003, Vol. 81 (24), pp. 6.
6.
Eckstein-Ludwig, Ursula, et al. “Artemisinins Target the SERCA of Plasmodium falciparum,”
Nature, 2003, Vol. 424, pp.957.
Questions