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Medicines for malaria elimination/eradication 5

Prof. Kelly Chibale

Founder and Director of the

University of Cape Town’s Drug

Discovery and Development

Centre (H3-D), South Africa.

Prof. Chibale talks about his work

to discover and optimize new

compounds to help populate

MMV’s antimalarial drug pipeline.

What has been achieved

to date?

We have screened 40,000 small

molecules from a commercial library

(BioFocus). Compounds that killed

the parasite and possessed the most

promising properties were selected.

The initial goal was to demonstrate

pharmacological proof-of-concept

by testing these select compounds

in a laboratory model of malaria. We

are now working on a series that has

shown activity in a laboratory model of

malaria. A single (low) oral dose of one

of the front-runner compounds pro-

vided a complete cure in the model

and shows potential as a clinical can-

didate. This is an outstanding result

because clinically used drugs such

as chloroquine, the artemisinins and

mefloquine require multiple doses to

achieve the same cure.

What does South Africa bring

to the table?

South Africa is arguably the most

technologically and economically ad-

vanced country on the African con-

tinent. We have a wealth of talent in

various scientific disciplines relevant

to drug discovery and a strong repu-

tation in basic science and clinical

studies for infectious diseases. The

country really has a lot to offer.

However, despite a number of drug

discovery programmes being initiated

in various institutions and organiza-

tions in South Africa in the last 5 years

or so, the serious lack of a critical mass

of individuals with pharmaceutical

industry experience in key areas such

as medicinal chemistry and drug meta-

bolism disciplines, threatens to render

current efforts unproductive. This issue

is being addressed through our centre,

H3-D, where we have embarked on

recruiting experienced personnel from

the pharmaceutical industry.

What is the advantage of wor-

king with MMV on a project of

this kind?

MMV has a huge network of partners,

which is partly what makes this project

unique. We can integrate medicinal

chemistry from UCT with preclinical

pharmacology and drug metabolism

from Monash University, Australia, and

parasitology expertise from Swiss TPH.

We can then screen a huge volume of

compounds with engineering tech-

nology from Eskitis (Griffith University,

page 33). This volume would just not

have been possible a few years ago.

Medicinal chemistry is about under-

standing what the liabilities are and

how you can use chemistry to over-

come them. This expert multicentre

team really provides all the informa-

tion that a medicinal chemist needs

to determine which molecules to take

forward and to move quickly.

The MMV project has also been critical

to building infrastructure at UCT and

we are now on our way towards being

able to conduct integrated antimalarial

drug discovery with parasitology, medi-

cinal chemistry and drug metabolism

all at UCT.

With our sights firmly set

on malaria elimination/

eradication, MMV’s

strategy has evolved. Our discovery

work is focused on the need for

novel medicines able to treat re-

lapsing (Plasmodium vivax) malaria

and block transmission. Yet at

the same time we must stay a

step ahead of the parasite; history

tells us it is incredibly adaptable,

having become resistant to each

medicine sent to assail it.

With these goals in mind MMV has

worked with six pharma companies

(GSK, Sanofi, Novartis, Pfizer, Gen-

zyme and AstraZeneca) and nume-

rous academic institutions (e.g. Uni-

versity of Cape Town (UCT), Dundee

University and St Jude Children’s

Research Hospital) to screen more

than six million compounds. This has

resulted in over 25,000 promising

molecules to populate the pipeline.

Furthermore, in a bid to catalyse

malaria and neglected disease drug

discovery, MMV has launched a

Malaria Box with 400 structurally di-

verse available compounds from this

screening campaign. The MMV Ma-

laria Box is being made to available

researchers at no cost (page 35).

Populating the pipeline

( )

MMVreport_ 20120503_PROD3b.indd 28 04.05.12 09:51

29

Variation in parasite density throughout the lifecycle

Transmission to man

Transmission to man

Transmission to mosquito

Asexual stage(human liver cell)

Sexual stage(mosquito gut)

Asexual stage(human blood cell)

The malaria parasite is trans-

mitted to man ( ) by a female

anopheles mosquito when

she takes a blood meal to feed her

young. The parasites are rapidly taken

up into the cells of the liver where they

become schizonts (A), multiply and

go on to invade blood cells. Current

medicines mostly kill malaria parasites

at this blood-stage, as this is when the

parasite is at its most abundant (up

to 1012 parasites in one person; B)

and the stage that leads to clinical

symptoms of malaria.

Some of the blood-stage parasites

develop into male and female game-

tocytes (see dotted line and C)

which are taken up into the mos-

quito gut during her blood meal. In

the gut these gametocytes become

gametes and fuse. This is the sexual

stage of the lifecycle. To eradicate

malaria we also need medicines that

can stop the parasite at this stage

(C to F) thereby stopping transmission.

This stage is also the most efficient to

target as this is where the parasite

density is as low as 10.

To support the elimination and era-

dication strategy, MMV and partners

(Imperial College London, Genomics

Institute of the Novartis Research

Foundation, Swiss Tropical and Public

Health Institute, University of Basel

and Scripps Research Institute) have

completed the first comparative

analysis of all currently available and

in-development antimalarials assess-

ing which stages they target in the

parasite’s lifecycle.1

This research was not only able to

tell us which in-development mole-

cules have activity where, but by

screening antimalarials that are

currently in use, it was also able to

validate screening platforms for the

future. This information will be criti-

cal in deciding which molecules

could become next-generation anti-

malarials and it provides us with the

tools to discover further promising

molecules.

Delves M et al.

“The activities of current

antimalarial drugs on

the life cycle stages of

Plasmodium:

a comparative study

with human and rodent

parasites.”

PLoS Med.

(2):e1001169 (2012).

1

A Liver-stage schizonts

B Blood-stage schizonts

C Gametocytes

D Micro- and macro-gametocytes

E Ookinetes

F Oocysts

G Sporozoites

Where do antimalarials act in the lifecycle?

MMVreport_ 20120503_PROD3b.indd 29 04.05.12 09:51

3030

Dr Alejandro Llanos

Universidad Peruana Cayetano

Heredia, Lima, Principal Inves-

tigator at the Peruvian trial site

to determine the safety and

efficacy of tafenoquine.

Dr Llanos talks about the trial

and why there is a need for new

medicines to treat relapsing

malaria in Peru.

What is the prevalence

of P. vivax in Peru?

In Peru 90% of malaria is caused by

P. vivax, with approximately 22,000

cases occurring each year. Clinically

speaking, we are only just beginning

to understand the differences between

P. falciparum and P. vivax and to make

the distinction. Previously, we assu-

med that patients with severe symp-

toms were suffering from P. falciparum,

but in my clinic at least eight of the last

10 patients with symptoms of severe

malaria were found to have P. vivax.

In fact, more than half the malaria

patients we see actually have both.

How is P. vivax malaria

managed in Peru in terms of

diagnosis and treatment?

Malaria diagnosis both for P. vivax and

P. falciparum is made based on clinical

symptoms; in facilities with a laboratory

a smear examination is conducted to

identify the parasite. When a patient is

diagnosed with P. vivax malaria, chloro-

quine plus primaquine is administered.

For P. falciparum the treatment is

artesunate plus mefloquine for 3 days.

How can the management

of P. vivax malaria be improved

in Peru?

With the current primaquine plus

chloroquine regimen we eliminate

relapse in approximately 80% of

cases. In my view that is not adequate.

Moreover, this varies with geography

as drug resistance appears to be

emerging in some areas. This could

be a big problem for us in Peru if

changes in climate lead to an increase

in mosquitoes and therefore in malaria

transmission. Additionally, the current

regimen in Peru is long, which makes

it difficult to ensure adherence. What

we need are new medicines that are

easier to take and more efficacious at

eliminating the P. vivax parasite from

the liver for all patients.

How is the trial progressing?

The trial is going well. We have already

enrolled the majority of patients requi-

red by the study, but will continue to

recruit for the next few months. We

are aiming to determine the correct

dose of tafenoquine to move to Phase

III. It stands a good chance of being

a great alternative to primaquine, but

of course we need to wait to see the

results.

TafenoquineGlaxoSmithKline, UK

Phase IIb/III

Project Leader: Dr JP Kleim, GlaxoSmithKline

MMV Project Director: Dr Jörg Möhrle

The long-held belief that

Plasmodium vivax is benign

in comparison to Plasmodium

falciparum is starting to change.

In addition, the dormant liver-

stage form (hypnozoite) of P. vivax,

which can reactivate without

warning leading to the feverish

symptoms of malaria, remains a

challenge to treat.

The only approved medicine able

to eliminate hypnozoites and thus

provide a radical cure for relapsing

P. vivax malaria is primaquine. In

practice primaquine is not always

efficacious. The reasons for this

are not entirely clear, however, the

treatment course is 14 days and

so compliance is often difficult to

achieve. Additionally, it is associ-

ated with potentially fatal side

effects in patients who are deficient

in the enzyme glucose 6-phosphate

dehydrogenase (G6PD).

Tafenoquine, the lead contender

to replace primaquine, is currently

in clinical development with MMV

and GlaxoSmithKline (GSK). Stu-

dies show tafenoquine could be

taken as a 1-day treatment course

for liver-stage malaria – a signifi-

cant improvement on primaquine’s

14-day course. However, the safety

of tafenoquine in G6PD-deficient

patients is being assessed because

it comes from the same chemical

family as primaquine. Trials are also

underway to determine the safety

and efficacy of tafenoquine for the

treatment of P. vivax malaria in non-

G6PD-deficient patients. This study

commenced in 2011 in Peru and

Thailand.

... We need ... new medicines that are easier to take and more efficacious at eliminating the P. vivax parasite from the liver for all patients.

Stopping the relapse

“

”

MMVreport_ 20120503_PROD3b.indd 30 04.05.12 09:51

31

Even with further data on pri-

maquine and the develop-

ment of tafenoquine there

will remain a need for new anti-

relapse medicines. Research to

discover new medicines has been

hampered by the lack of a suitable

model of the hypnozoite to test

new compounds. In collaboration

with scientists at the Biomedical

Primate Research Centre in the

Netherlands, we have identified

liver forms of the monkey para-

site P. cynomolgi, believed to be

hypnozoites. This breakthrough

enables us to identify a new che-

mical series with activity against

the hypnozoite, bringing us a step

closer to the next cure for relapsing

malaria.

Colonel Bagus Tjahjono

Indonesian Army Health

Command, Jakarta, is

Co-Investigator of the trials.

He explains the need for

further research on relapsing

P. vivax malaria and its treatment.

Can P. vivax cause severe

malaria and be fatal?

Recent work certainly suggests that it

can be fatal. More evidence is need-

ed, but certainly I believe the long-

held consensus of the disease being

benign is incorrect and probably quite

dangerous to patients.

How is P. vivax malaria

managed in Indonesia in terms

of diagnosis and treatment?

Is there a difference compared

to P. falciparum malaria?

Most malaria in Indonesia is diagnosed

based on symptoms initially and then

confirmed with microscopy diagnosis.

No distinction is usually made between

P. falciparum and P. vivax. The treat-

ment is DHA-PQP – the government

recommended first-line treatment for

uncomplicated malaria. In the cases

where P. vivax malaria can be confirm-

ed, the recommendation is to also treat

with 14 days of primaquine.

What are the flaws in the way

P. vivax malaria is currently

managed in Indonesia?

One of the main issues is the lack of

access to laboratory diagnosis and the

lack of a rapid test to diagnose both

P. vivax and P. falciparum malaria and

G6PD deficiency. With improved dia-

gnosis of G6PD deficiency we would

be able to use primaquine safely and

avoid using it in patients with this

enzyme deficiency. The other problem

is that primaquine is our only tool

against relapse and we don’t fully

understand it. We think the efficacy

of primaquine very much depends on

the partner drug used with it and this

is why we are running the current trial.

How can you be sure that part-

icipants in the trial are suffering

from a malaria relapse and not

just a new malaria infection?

The participants in the trial are all sol-

diers who have returned with malaria

from their duties in Papua Province and

are treated back at the base in Luma-

jang, East Java. As there is very little

malaria transmission in this region we

can be sure that any further malarial

episode is a relapse and not a comple-

tely new infection.

How is the trial progressing

and what have you learnt about

primaquine?

The trial is almost complete. Our results

offer compelling evidence affirming the

safety and efficacy of primaquine when

used with DHA-PQP for radical cure of

P. vivax malaria in eastern Indonesia.

I am very pleased with these results and

proud of my soldiers and commanders

for their enthusiastic support.

Although primaquine is the

only approved medicine

for radical cure of relapsing

malaria, very little is known about

how well it works in combination

with other medicines that treat the

blood-stage infection. In order

to maximize its effective use

until a suitable alternative can

be developed, Oxford University,

Eijkman Institute and MMV have

joined forces to run a series of trials.

The first trial compared primaquine

+ dihydroartemisinin-piperaquine

(Eurartesim®) with primaquine +

quinine and with artesunate. The

next trial will look at the efficacy

of primaquine + pyronaridine-

artesunate (Pyramax®) compared

to primaquine + Eurartesim and

to artesunate alone. The efficacy

of OZ439 against the relapse will

likely also be investigated.

The trial is almost complete. Our results offer compelling evidence affirming the safety and efficacy of primaquine when used with DHA-PQP for radical cure.

“

”

Fluorescent-stained P. cynomolgi liver forms

MMVreport_ 20120503_PROD3b.indd 31 04.05.12 09:51

Fluorescent-stained late-stage

gametocytes

Green/blue: gametocyte

Red: mitochondria

3232

MMVreport_ 20120503_PROD3b.indd 32 04.05.12 09:51

33

Blocking transmission

In an infected patient a small pro-

portion of parasites form game-

tocytes, the sexual form of the

parasite. It is these gametocytes,

taken up by the mosquito when

she feeds, that ultimately allow the

parasite to infect the next person.

In collaboration with partners

(Imperial College London, GSK,

Radboud University, the Nether-

lands and Griffith University, Aus-

tralia) MMV has developed a range

of tools to screen and identify com-

pounds with activity against game-

tocytes. These tools have enabled

us to identify a number of interes-

ting molecules that not only target

the blood stage of the lifecycle but

the sexual stages as well. To ensure

the pipeline remains populated

the hunt is on to discover further

compounds with such dual activity.

Prof. Vicky Avery

Chief Investigator & Head of

Discovery Biology, Griffith Univer-

sity, Australia. Prof. Avery talks

about her work to develop a new

late-stage gametocyte assay to

identify compounds that could

block the transmission of malaria.

How does the assay work?

The assay is based on imaging tech-

nology. We use 384-well microtiter

plates; each well contains cultured

gametocytes which express fluo-

rescent proteins. A green protein

identifies the parasite, while red tells

us whether it’s alive. We can deter-

mine that the parasite is a late-stage

gametocyte by its shape. We then add

compounds to the wells and assess

their effect on the cells by studying

changes in the parasite florescence.

What is different about your

approach?

The screening technology we use is

based on state-of-the-art imaging

technology and so is incredibly inform-

ation-rich. We are looking at the whole

parasite in one go rather than a simple

target, as with other screening tech-

nology. It’s the difference between

having a tractor and a Ferrari!

What has been achieved

so far?

We have a late-stage gametocyte as-

say up and running. Using the assay

we have started to screen the 25,000

compounds known to be active

against blood-stage malaria. The pre-

liminary data generated is very exciting

and there are already plans to screen

many more compounds. We aim to

screen 250,000 compounds this year.

What value has MMV added

to your work?

Working with MMV has provided me

with the opportunity to focus on an

area of drug discovery I otherwise

wouldn’t be able to. It means I can

bring the skills I have developed in

pharma and academia to an issue that

needs to be addressed. I enjoy co-

ming to meetings at MMV as I interact

with and learn from people who work

across the whole pipeline.

Working with MMV has also opened

doors to people doing research that is

similar or complementary to mine.

The screening technology we use is ... incredibly information rich ... It’s the difference between having a tractor and a Ferrari !

Pr

“

”

Prof. Avery operating the Opera™ High Content Screening System

MMVreport_ 20120503_PROD3b.indd 33 04.05.12 09:51

3434

Top 10 MMV publications of 2011

Nambozi M et al. “Safety and efficacy of dihydroartemisinin-piperaquine versus artemether-lumefantrine in the treatment of uncomplicated Plasmodium falciparum malaria in Zambian children.” Malar J. 10:50 (2011).

Coteron JM et al. “Structure-Guided Lead Optimization of Triazolo- pyrimidine-Ring Substituents Identifies Potent Plasmodium falciparum Dihydroorotate Dehydrogenase Inhibitors with Clinical Candidate Potential.” J Med Chem. 54(15):5540-61 (2011).

McCarthy JS et al. “A pilot randomized trial of induced blood-stage Plasmodium falciparum infections in healthy volunteers for testing efficacy of new antimalarial drugs.” PLoS One. 6(8) (2011).

Kremsner PG et al. “A simplified intravenous artesunate regimen for severe

malaria.” J Infect Dis. 15;205(2):312-9 (2012). Epub 2011 Dec 15.

Kern SE et al. “Community screening and treatment of asymptomatic carriers of Plasmodium

falciparum with artemether-lumefantrine to reduce malaria disease burden: a modelling and

simulation analysis.” Malar J. 10:210 (2011).

Poravuth Y et al. “Pyronaridine-artesunate versus chloroquine in patients with acute Plasmodium vivax malaria: a randomized, double-blind, non-inferiority trial.” PLoS One. 6(1) (2011).

Kalilani-Phiri LV, Lungu D, Coghlan R. “Knowledge and malaria treatment practices using artemisinin combination therapy (ACT) in Malawi: survey of health professionals.” Malar J. 10:279 (2011).

Meister S et al. “Imaging of Plasmodium Liver Stages to Drive Next-Generation Antimalarial Drug Discovery.” Science 334(6061) 1372-1377 (2011).

Burrows JN et al. “Challenges in antimalarial drug discovery.”

Future Med Chem. 3(11):1401-12 (2011).

Wells TN. “Natural products as starting points for future anti-malarial therapies: going back to our roots?” Malar J. 10 Suppl 1:S3 (2011).

Demonstrates the post-

treatment prophylactic

potential of dihydro-

artemisinin-piperaquine

in Zambian children.

Shows that the treatment of

asymptomatic carriers with

artemether-lumefantrine

may reduce malaria

transmission significantly.

Highlights the need for

further training of health-

care professionals to ensure

correct and optimum use of

ACT in Malawi.

Demonstrates a safe

alternative to testing the

efficacy of new antimalarials

in humans, without expos-

ing symptomatic patients

to potentially ineffective

treatment.

Details MMV’s perspective

on the challenges the malaria

eradication agenda poses for

drug discovery.

Pivotal Phase III study demonstrating

the efficacy of pyronaridine-artesunate

in treating blood-stage P. vivax malaria.

Describes the identification of

a potent and selective inhibitor

(DSM265) of the malaria parasite’s

dihydroorotate dehydrogenase

enzyme – essential for its survival.

An opinion piece extolling the need

for a patient-data led approach to

drug discovery drawing on natural

products.

Details the identification

of the imidazolopiperazine

compound series active against

the liver and blood stage

of malaria.

Shows that 3 doses of

artesunate are not inferior

to 5 doses for the treatment

of severe malaria in children.

MMVreport_ 20120503_PROD3b.indd 34 04.05.12 09:51

35

In June 2011, MMV lost a dear friend

and colleague.

Born and raised in Christchurch, New

Zealand, Dr Ian Bathurst completed

his studies in the UK, obtaining a PhD

in Biochemistry from the University of

London. He then pursued a success-

ful career in academia at the University

of Otago, New Zealand.

In 1986 Ian changed tack and moved

to San Francisco to work at Chiron

Corporation on the expression of

yeast recombinant proteins, HIV

genes and potential vaccine candi-

dates. Always a pioneer, he continued

this work through start-up companies

LXR Biotechnology Inc. and Arriva

Pharmaceuticals Inc.

Ian brought this wealth of academic

and industry experience to the MMV

team when he joined as Director of

Drug Discovery in 2004. As one of the

first members of the discovery team,

he was instrumental in helping to

establish MMV’s networks and early-

stage projects. He ensured projects

ran smoothly, with good humour and

openness to new ideas and inspiration.

For example, he was constantly

seeking novel ways to facilitate the

production of antimalarials and was

an active member of the Artemisinin

Enterprise that sought to optimize

the production and extraction of

artemisinin.

Ian was an invaluable member of the

MMV team and a much respected

mentor to the discovery team. He

was planning an active retirement in

2011, when he passed away. He is

sorely missed, but will be remembe-

red for his passion and commitment

to MMV’s work.

In his memory, MMV and the Bathurst

family have collected donations and

set up a sponsorship programme

to support 10 to 12 scientists from

malaria-endemic countries to attend

Keystone Symposia’s Malaria

Meeting in January 2013 in New

Orleans. Ian would have been de-

lighted that young researchers in

malaria and neglected diseases

were receiving support to attend the

meeting in his name.

Dr Ian Bathurst, MPhil, PhD (1949–2011)

a

r

MMVreport_ 20120503_PROD3b.indd 35 04.05.12 09:51