Carbonic anhydrase inhibitors: Inhibition of Plasmodium falciparum
carbonic anhydrase with aromatic/heterocyclic sulfonamides—in vitro
and in vivo studies
, Sudaratana R. Krungkrai
, Claudiu T. Supuran
Department of Biochemistry, Faculty of Medicine, Chulalongkorn University, 1873 Rama 4 Road, Pathumwan, Bangkok 10330, Thailand
Unit of Biochemistry, Department of Medical Science, Faculty of Science, Rangsit University, Paholyothin Road, Patumthani 12000, Thailand
Università degli Studi di Firenze, Polo Scientiﬁco, Laboratorio di Chimica Bioinorganica, Room 188, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy
Received 10 July 2008
Revised 5 September 2008
Accepted 6 September 2008
Available online 11 September 2008
In vivo study
A library of aromatic/heterocyclic sulfonamides possessing a large diversity of scaffolds has been assayed
for inhibition of the carbonic anhydrase (CA, EC 18.104.22.168) from the malaria parasite Plasmodium falciparum
(pfCA). Low micromolar and submicromolar in vitro inhibitors were detected, whereas several com-
pounds showed ex vivo anti-P. falciparum activity, in cell cultures. One derivative, that is, 4-(3,4-dichlor-
ophenylureido)thioureido-benzenesulfonamide was an effective in vitro pfCA inhibitor (K
inhibited the ex vivo growth of P. falciparum with an IC
M, and was also effective as an antima-
larial agent in mice infected with P. berghei, an animal model of human malaria infection, with an ID
10 mg/kg (chloroquine as standard showed an ID
of 5 mg/kg). By inhibiting the ﬁrst step of pyrimidine
nucleotide biosyntheses, that is, the CA-mediated carbamoylphosphate biosynthesis, sulfonamide inhib-
itors of the protozoan CAs may have potential for the development of novel therapies of human malaria.
Ó 2008 Elsevier Ltd. All rights reserved.
Malaria, a major parasitic disease of humans, is caused by pro-
tozoa of the genus Plasmodium, classiﬁed in the phylum Apicom-
The disease afﬂicts 515 million and kills 1.5–2.7 million
people each year, most of whom children in sub-Saharan Afri-
P. falciparum is responsible for most of these deaths.
addition to the lack of effective vector control and vaccines, the
limitations and toxicity of antimalarial drugs in current use, and
the spread of drug-resistant malaria accompanied by a worldwide
resurgence of the disease, highlights the need to develop quickly
more effective and less toxic novel antimalarial drugs, possessing
a different mechanism of action.
Drug screening procedures
have rarely been applied to identify lead molecules for this disease,
and there is a paucity of information on a number of metabolic
pathways that can be exploited for malaria chemotherapy.
better understanding of biochemical differences between the par-
asite and human metabolic processes may provide new targets
for intervention in the ﬁght against this disease.
In 1998, Sein and Aikawa
proved the in situ carbonic anhy-
drase (CA, EC 22.214.171.124) activity in P. falciparum-infected red blood
cells by using electron microscopy and CA-speciﬁc Hanssen’s stain.
Recently, we have demonstrated the existence of CA enzymatic
activities in P. falciparum and in the related mouse parasite
P. berghei, and the fact that this enzyme activity may be inhibited
by sulfonamide CA inhibitors (CAIs).
Indeed, the metalloen-
zyme CA catalyzes the interconversion between carbon dioxide
and bicarbonate, being essential in many physiologic processes
both in eukaryotes and prokaryotes, with ﬁve distinct genetically
unrelated gene families (
-, d-, and f-CA) encoding such
enzymes all over the phylogenetic tree.
Malaria CAs belong
similarly to the human enzymes, of
which 15 isoforms are presently known.
The P. falciparum CA
has been designated as pfCA.
The parasite is a purine auxotroph, that is, it is incapable of de
novo purine biosynthesis owing to the missing enzymes in the
biosynthetic pathway. It salvages the preformed purine bases/
nucleosides (e.g., hypoxanthine, adenosine) from the human host
and converts them to their mono-, di-, and triphosphates. The
parasite can on the other hand synthesize pyrimidines de novo
, adenosine 5
-triphosphate (ATP), glutamine (Gln),
aspartate (Asp), and 5-phosphoribosyl-1-pyrophosphate (PRPP),
as shown in Figure 1.
These unique properties on both pur-
ine and pyrimidine requirement of the parasite are key differ-
ences from the human host, in which both functional de novo
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
* Corresponding authors. Tel.: +66 22564482; fax: +66 22524963 (J.K.); tel.: +39
055 4573005; fax: +39 055 4573385 (C.T.S.).
E-mail addresses: email@example.com (J. Krungkrai), claudiu.supuran@
uniﬁ.it (C.T. Supuran).
Bioorganic & Medicinal Chemistry Letters 18 (2008) 5466–5471
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