A new study shows that mini-organs (organoids) grown from human intestines and stem cells can be used to rapidly mimic MPXV infection in the human tissues the virus attacks. The study identified several promising drug candidates, including the anticancer drug clofarabine, which inhibited all three strains of MPXV currently circulating worldwide.
An international team of researchers has used organoids derived from human intestines and stem cells to investigate whether existing drugs can slow MPXV .
Several compounds stood out, and one in particular: clofarabine, which is already approved for treating children and young people for acute lymphoblastic leukaemia.
In the study, the drug inhibited all three MPXV strains currently circulating globally at concentrations corresponding to levels that can already be achieved when the drug is used to treat leukaemia.
The finding therefore suggests that a possible new treatment for mpox may be hiding among drugs already used for other diseases.
“To identify new antiviral treatments quickly, we need models that resemble human tissue as closely as possible. With organoids that mimic the gut and skin, we can see whether the virus can actually enter the tissue, replicate and damage the cells, while also testing whether different drugs can knock down the infection. This is a step beyond the two-dimensional cell models that have previously been the standard, and it makes it easier to identify the most promising candidates for clinical trials,” explains a researcher behind the study, Karine Raymond, stem cell researcher from Leiden University Medical Center, Netherlands and the Novo Nordisk Foundation Center for Stem Cell Medicine, reNEW.
The research has been published in Science Advances.
Mpox virus does not only attack the skin
Mpox is best known for causing characteristic skin lesions, but it can also cause severe symptoms in the gastrointestinal tract.
During the global mpox outbreak in 2022 and 2023, many patients reported proctitis, in which the mucous membrane around the rectum becomes inflamed, as well as diarrhoea and severe rectal pain.
Before the study, the researchers had access to tissue samples from a deceased person with mpox. The virus had infected the lining of the colon and left open sores in the tissue that normally acts as the intestine’s protective barrier.
On that basis, the researchers cultured organoids from the human small intestine and rectum and investigated whether they could be infected by different mpox variants.
Unlike a flat layer of cells in a petri dish, organoids grow in three dimensions. They contain many of the cell types and structures found in real tissue and can therefore provide a more realistic picture of how an infection develops in the body.
The organoids could be infected by all three MPXV strains currently in circulation: IIb, which caused the global outbreak in 2022 and 2023, and Ia and Ib, which are driving the ongoing outbreak in the Democratic Republic of the Congo and several other African countries.
The researchers were also able to show that MPXV not only entered the organoids but replicated vigorously and caused cell damage resembling that seen in people’s intestines.
Twelve compounds stood out in a broad drug screen
The next step was to use the organoids to search for drugs that could slow mpox.
The researchers tested a library of broad-spectrum antiviral compounds that had already been tested on humans.
In total, the researchers identified 12 candidates that inhibited the virus as effectively as, or more effectively than, cidofovir. This drug is often used as a reference treatment for mpox, but its use is limited by factors such as toxicity and the need for intravenous administration.
Among the 12, clofarabine was the strongest candidate. Because the drug is already used to treat children and young people for acute lymphoblastic leukaemia, there is existing knowledge about its safety profile.
Clofarabine halved the viral load in the intestinal organoids at around 0.1 micromolar. What matters is not the number itself but that this level is already reached in the blood of patients receiving the drug as leukaemia treatment.
At a concentration of one micromolar, the viral load fell below the level the researchers could measure in the organoids.
The series of experiments also offered a possible explanation for why an existing mpox drug, tecovirimat, has disappointed in clinical trials.
In the organoid model, tecovirimat only reduced the viral load moderately, whereas brincidofovir, which is also approved for smallpox, almost knocked the infection out completely. In doing so, the organoids also showed their strength: they could sort through the drugs and identify those that actually slowed MPXV in human-like tissue.
The cancer drug also slowed MPXV in laboratory-grown skin
The researchers did not stop at the intestine. They also tested clofarabine in skin organoids developed from stem cells.
This enabled them to mimic the tissue damage that appeared primarily as sores on the skin during the mpox outbreak in 2022.
In the skin organoids, clofarabine also reduced the viral load, confirming that the effect was not limited to intestinal tissue. However, the effect was slightly less pronounced in the skin than in the intestine, presumably because the drug is absorbed and distributed differently in the two tissue types.
“The major advantage of being able to test in skin and intestinal organoids in parallel is that we target the tissues the virus actually infects in patients. The skin organoids mimic the architecture and cell composition of real skin far better than traditional cell models and can be kept alive much longer. This makes it possible to follow a longer course of treatment and see whether a substance can actually knock down the virus over time,” says Karine Raymond.
Organoids could offer a shortcut to new antiviral treatments
The study is not just about the current mpox outbreak.
The researchers point out that the same approach could be used to find treatments for related viruses if new outbreaks occur.
Further testing and clinical trials are still needed before clofarabine can potentially be brought into clinical use against mpox.
As a leukaemia treatment, clofarabine can affect the liver, kidneys and bone marrow. The drug therefore cannot simply be moved directly from cancer treatment to mpox treatment; the dose, form of treatment and safety must first be investigated in this new context.
Among other things, the researchers suggest that clofarabine could be developed as a cream applied directly to skin lesions. In this way, clofarabine might target MPXV locally without affecting the whole body, as happens with intravenous treatment.
“The next step is to find out which treatments are actually most effective against mpox in patients. There are several different candidates, and the field is still under discussion. The organoids give us a good starting-point because they allow us to sort through candidates much more quickly and identify the drugs that are most promising to test in patients,” concludes Karine Raymond.
