impaginato piccolo - Società Italiana di Parassitologia (SoIPa)

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approach and SAR studies. DDcl can also count on the
expertise of Dr Piero Olliaro from UNICEF-UNDP-
World Bank-WHO-TDR. Several research units within
the cluster are collaborating with pharmaceutical
industries for the completion of the preclinical work on
some of the most promising molecules. A summary of
the overall strategy and recent achievements of DDcl
are reported in the following sections, which recapitulate
the drug discovery process.
Target identification and validation; synthesis and collection
of new molecular entities.
Different approaches are followed by DDcl researchers
to discover new antimalarials: 1- a genomic-proteomic
approach to identify specific drug targets inside metabolic
pathways that are characteristic either of the parasite
or the invertebrate vector and not of the human
host; 2- isolation and identification of natural products
from marine or plant origin; 3- modification of existing
pharmacophore to increase efficacy and overcome
resistance; 4- rational design of new chemical entities
based on the characteristics of the microenvironment
of the parasites.
Genomic-proteomic approach.
The Kynurenine Pathway (KP) of Anopheles gambiae
is a promising target for novel transmission-blocking
compounds or insecticides (Han, Beerntsen et al. 2007)
The approach of the group of M. Rizzi of the University
of Piemonte Orientale is focused on the structural and
functional characterization of A. gambiae KP enzymes
controlling kynurenines synthesis and homeostasis in
the mosquito and of Pf kynases essential for parasite
gametogenesis within the arthropod host (Rossi,
Lombardo et al. 2005; Rossi, Garavaglia et al. 2006).
The selected enzymes, produced in recombinant forms,
will be subjected to biochemical characterization and
X-ray crystallography to determine their 3D structure
for the in silico identification and the structure-based
rational design of selective inhibitors.
Highly active inhibitors of the aspartic proteases, plasmepsins
II and IV, responsible of haemoglobin digestion
in the parasite food vacuole during the intraerythrocytic
stage have been synthesised as “double drugs”
by S. Romeo and tested on recombinant enzymes by E.
Bosisio, both groups at the University of Milan. The
double-drugs consist of primaquine joined with a peptidic
linker to a statine-based inhibitor. Some of them
are among the most active plasmepsins inhibitors ever
reported. They inhibited the recombinant PLM
enzymes with a Ki in the low nM and were toxic against
CQ-R, Pf parasites in vitro with IC50 of 200-500 nM
(Romeo, Dell’Agli et al. 2004). Optimisation of the
intraerythrocytic activity of these inhibitors has been
achieved by a systematic change of peptide’s
aminoacids, also with non-peptidic structures
(Dell’Agli, Parapini et al. 2006). One of the most
recent compounds also significantly inhibited para-
N. Basilico et al. - Innovative antimalarial compounds
sitaemia when given intraperitoneally in the rodent P.
berghei model.
Natural products from vegetable and marine sources.
Plants and traditional medicine in third world countries
are an important source of compounds with potential
antimalarial activity. The group of E. Bosisio in Milan
has been working on the antiplasmodial activity of
Ailathus excelsa (Dell’agli, Galli et al. 2008) and is
presently involved in the extraction, bio-guided purification
and identification of the active principle of a
vegetable remedy used in the ORISSA region, in India.
Promising results have also been obtained by the group
of A. Habluetzel in Camerino with neem (Azadirachta
indica) extracts on the murine P. berghei model. A
methanolic leaf extract reduced parasitaemia in treated
mice after oral administration, and a commercial seed
extract, NeemAzal ®, exerted a complete block in parasite
development in the vector. NeemAzal ® also, had an
impact on A. stephensi fitness, reducing blood feeding,
oviposition and survival of treated females (Lucantoni,
Giusti et al. 2006).
The researchers of the University of Naples Federico II,
directed by E. Fattorusso recently defined the absolute
configuration of plakortin, an endoperoxide extracted
from the sponge Plakortis simplex with relevant antimalarial
activity (Campagnuolo, Fattorusso et al.
2005). SAR studies have been conducted in a series of
natural products related to plakortin and its semi-synthetic
derivative to improve efficacy (Fattorusso,
Campiani et al. 2006). These results are particularly
interesting for understanding the mechanism of action
of endoperoxides, since the artemisinin derivatives,
which are the most potent antimalarial drugs presently
available, are also characterized by a trioxane pharmacophore,
crucial for activity (Haynes 2006).
Modification of existing pharmacophores to increase
efficacy and overcome resistance
Aminoquinoline type drugs (i.e. chloroquine) have
been the mainstay of antimalarial therapy until the
emergence and spread of resistance hampered their
usage. However, the 4 aminoquinolines are still interesting
compounds since their mechanism of action and
resistance seems to be unrelated (Egan and Kaschula
2007). The group of A. Sparatore at the University of
Milan recently synthesised new quinolizidine derivatives
of 4-aminoquinolines, characterised by the presence
of bulky bicyclic, highly basic and lipophilic lateral
chain, derived from lupinine (extracted from
Lupinus luteus) (Sparatore, Basilico et al. 2005). Two
of these compounds are extremely active against drug
resistant strains of P. falciparum in vitro and orally in
vivo in murine models at doses comparable and lower
than CQ. They are not toxic with good pharmacokinetic
profile and are presently under study for further preclinical
development in collaboration with NeED
Pharmaceutical and the financial support of the EU-