Malaria remains a major health and social challenge. It is a life-threatening illness caused by Plasmodium parasites, which are spread to people through the bites of infected mosquitoes. The first symptoms of the disease – which include fever, headache, chills, and tiredness – usually appear around 7 to 10 days after infection. If left untreated, the illness can rapidly become severe and can lead to death.

In 2020, there were 241 million cases of malaria worldwide – and 627,000 deaths. [1] Countries in the sub-Saharan region of Africa carry a disproportionately high share of the global malaria burden, accounting for 95% of all malaria cases and 96% of deaths. [1] Sadly, around 80% of these deaths occur in children under five years of age. [1]

Defeating malaria requires a multi-pronged approach to improving the prevention, diagnosis, and treatment of the disease. Since 2015, our Global Health Institute has engaged in fighting malaria – to help with developing and providing access to innovative drugs and technologies aimed at its prevention, diagnosis, control, and elimination.

The Covid-19 pandemic demonstrated the importance of stopping the spread of infectious diseases through preventative measures. We believe the same is true for malaria – there is a need for a more holistic approach towards eliminating the disease, centered around prevention.

Malaria prevention has to be tackled through two different strategic approaches.  The first one consists of boosting immune response via vaccination and/or prophylactic medications, to reduce the likelihood/probability of getting infected. The second is by using bed nets, insect repellents, and insecticides to prevent bites.

Chemoprevention - the use of drugs to protect people living in an endemic region from contracting the disease - has recently shown real promise: significantly reducing the number of clinical malaria cases when this approach is properly applied. [2] But it relies on the standard-of-care combination treatment (Sulfadoxine-pyrimethamine plus amodiaquine), which has not been specifically developed for prevention. There is also the problem of resistance to these medications emerging in the malaria parasite.
We have recently developed a novel 3D cell-based technology to help identify safe and effective potential new drugs that may prevent the parasite from taking hold in the body; this could serve as a way to accelerate the eradication of the disease once and for all.

There are four main species of malaria parasite: Plasmodium falciparum is the deadliest type and is very common in sub–Saharan Africa. These highly specialized parasites have several stages in their life cycle that enable them to infect and move between their mosquito and human hosts.

People get malaria after being bitten by a female Anopheles mosquito infected after taking a blood meal from an infected person. After entering the body, the microscopic parasites – called sporozoites – quickly travel to the liver where they rapidly multiply to produce thousands of so-called merozoites. These are then released into the bloodstream to invade red blood cells. Once inside these cells, the parasite multiplies until the cells burst, releasing yet more merozoites into the bloodstream to invade uninfected red blood cells. The liver stage is asymptomatic while the blood-cell stage of infection is responsible for the symptoms of malaria, like high fever and chills. This is also when a person can transmit the infection to a mosquito during a blood meal, enabling it to spread to other people. Early diagnosis and prompt treatment of malaria are therefore of utmost importance before the illness becomes serious and life-threatening.

Many people are completely unaware of the fact that they are infected with the malaria parasite. In high-transmission areas of sub-Saharan Africa, it is estimated that 24% of people harbor an asymptomatic infection that can remain clinically undetectable for a long time – thus, increasing the chance of transmission to mosquitos. [3] Finding safe and effective long-lasting drugs which, either alone or in combination with existing antimalarials, can eliminate parasites in these individuals will be necessary for the complete eradication of the disease.

“People with asymptomatic infection are a reservoir for malaria,” says Thomas Spangenberg, our Head of Global Health Open Innovation & Drug Discovery. “Complete elimination of the disease will require treating the entire population, from the youngest to the oldest, to eradicate parasites that are hiding from sight.”

The next generation of chemoprevention combination medications need to integrate antimalarial activities against all stages of the parasite life cycle. While most current antimalarial drugs target the blood-cell stage of the parasite’s life cycle that causes the disease symptoms, very few target the early asymptomatic liver stage. Drugs that target this stage of the infection would not only hinder the parasite from entering the bloodstream but would also block its transmission to mosquitoes and therefore interrupt the cycle.

In the early stages of drug discovery, researchers need to carry out experiments on cells grown in laboratory dishes before moving into animal models. But until recently, there were few cell-based models for identifying and studying potential new drugs targeting the liver stage of malaria infection.

“P. falciparum sporozoites take about seven days to mature in liver cells and it has proved challenging to recapitulate this stage of the infection in laboratory dishes,” explains Spangenberg.

Traditionally, scientists have largely relied on 2D in vitro cultures of liver cells grown in a single layer in a plastic dish to model the liver stage of infection. But these 2D cell cultures don’t represent the 3D environment in which cells normally live and function in the body. Now, researchers are turning towards advanced 3D cell models that better mimic the real-life context.

Working in partnership with academic researchers at Instituto de Biologia Experimental e Technológica (iBET) and the Institute of Molecular Medicine (IMM) in Lisbon, Portugal, we have developed a novel 3D cell-based platform for the discovery and profiling of new antimalarials targeting liver-stage of the malaria parasite’s life cycle. [4]

“Growing human liver cell lines in a stirred tank encourages them to aggregate into little 3D balls of cells, called spheroids. These live for at least one month in culture and recapitulate features of liver structure and function,” describes Spangenberg. “We demonstrated that infecting these ‘mini-livers’ with Plasmodium parasites generated merozoites that could infect red blood cells.”
This advanced cell culture system provides a more accurate model of the liver stage of malaria infection for identifying and studying new compounds that could help prevent the disease. This new technology also provides a viable animal-free alternative, which supports our long-term ambition to phase out animal use in all our research.

In order to confirm the usefulness of the novel technology, we performed experiments using a potential antimalarial compound under clinical development owned by our company. [5] The investigational drug targets P. falciparum translation eukaryotic elongation factor 2 (eEF2), an enzyme that plays an essential role in protein synthesis. [5] It could potentially offer a promising treatment and preventive option against malaria due to its activity against several stages of the parasite’s life cycle. [5]

We tested it on our new 3D cell platform, showing that the concentrations needed to clear the infection in liver cells in vitro were similar to the dose required in mice [6] and that these were predictive of the prophylactic dose observed in a Phase I clinical study. [7] Indeed, in this Phase I trial where healthy volunteers were infected by malaria sporozoites, the dose predicted by the 3D model provided full protection. [8]

These data demonstrated that the results observed in the 3D culture model could be directly translated into an effective dose in humans. It also confirmed the platform as a new tool to:

1. accelerate drug discovery for a clear unmet medical need.
2. shorten the research and development time for such compounds.
3. reduce the number of laboratory animals needed for this type of research.

“It enabled us to accelerate the clinical development of our potential antimalarial candidate – currently preparing to enter a Phase II study as a combination therapy – as we could quickly define the active dose in humans and reduce the number of healthy volunteers needed in Phase I,” says Claude Oeuvray, our Head of Global Health Drug Development at the Global Health Institute. “Importantly, it also decreased the number of animals needed during the preclinical phase of research.”

Offering a bridge between traditional 2D techniques and animal models, the development of a new advanced 3D cell platform is a huge step forward in the fight against malaria.

The novel technology is already helping to accelerate the search for drug compounds with activity against the liver stage of the parasite life cycle – opening the tantalizing possibility of preventing the disease.

“We’ve created an effective new tool for testing the effects of compounds on the parasites while they are growing in the liver,” says Spangenberg. “The beauty is that it enables the faster evaluation of potential chemoprotective drugs – and importantly, it also reduces the use of animals in research.”

_{[1] https://www.who.int/news-room/fact-sheets/detail/malaria
[2] https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32227-3/fulltext
[3] https://researchblog.duke.edu/2019/11/11/malaria-hides-in-people-without-symptoms/
[4] https://pubs.acs.org/doi/10.1021/acsinfecdis.9b00144
[5] https://pubmed.ncbi.nlm.nih.gov/26085270/
[6] https://pubs.acs.org/doi/full/10.1021/acsinfecdis.1c00640
[7] https://malariajournal.biomedcentral.com/articles/10.1186/s12936-022-04171-0
[8] https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(21)00252-8/fulltext
[9] https://www.nc3rs.org.uk/the-3rs}