Assessing Potential COVID Drug Targets

SARS-CoV-2 (indicated by nucleocapsid, red) efficiently infects wild-type human gut organoids (left), while TMPRSS2-deficient organoids are completely virus-free (right). Nuclei are gray, phalloidin (green) visualizes actin filaments. Credit: Joep Beumer, copyright Hubrecht Institute

Researchers from the group of Hans Clevers, in collaboration with the group of Bart Haagmans (Erasmus MC), have set up an organoid biobank to search for the genes that are essential for the spread of a SARS-CoV2 infection. Their study, published in Nature Communications on September 17, 2021, highlights the usefulness of organoids for basic research on coronaviruses, as well as highlighting potential drug targets.

Organoids are small 3D structures grown from stem cells that mimic organ function. Researchers have previously succeeded in developing organoid models for various organs, including the gut, lung, uterus and even the snake venom gland. The organoids have been shown to be useful for diagnostic purposes, predicting therapy responses in patients, and unraveling mysteries about the development of tissues and rare cell types.

Host Factors

Researchers can add levels of complexity to the organoid cultures for specific purposes. For example, they can add immune cells to tumor organoids to study the efficacy of therapy, or inject pathogens into organoids to model their effect on the cells. The latter approach has recently been used to model coronavirus infections in human cells. One of the key questions about the coronavirus — and viruses in general — is what factors it uses to invade and replicate human cells. These so-called host factors may be attractive targets for drugs to influence viral replication and spread.

Biobank of gut organoids

To learn more about the host factors that are specifically important for the replication and spread of coronaviruses, the groups of Hans Clevers and Bart Haagmans developed a biobank of mutated gut organoids. This means that the organoids, which mimic the biology of the gut, contain several mutations in the host factors previously discovered to be relevant to coronaviruses. These mutations cause changes in the activity of the host factors.

TMPRSS2 as a therapeutic target

Therefore, the researchers injected the mutated organoids with SARS-CoV-2 – the virus responsible for COVID-19 – to study the effect of the mutations on the replication and spread of the virus. They identified, among other things, the gene TMPRSS2 involved in this process: organoids with non-functioning TMPRSS2 showed reduced replication and spread of the virus. This gene may therefore be an attractive therapeutic target for this coronavirus. Specific inhibitors for TMPRSS2 have recently been developed.

Relevance of human models

Previously, studies used animal cell lines (most importantly, from the African green monkey) to identify therapeutic targets for the coronavirus. These cell lines are easy to work with, but do not fully represent the biology of human cells targeted by SARS-CoV-2. This is illustrated by the antimalarial drug Chloroquine, which has been shown to be effective against SARS-CoV-2 infection in these cell lines, but has not been shown to be effective in clinical trials with patients. This indicates that the cell lines cannot adequately predict the effectiveness of therapies in humans. When repeating the Chloroquine experiments with the mutant organoids instead of previously used cell lines, the research groups saw no therapeutic effect. In other words, the results in organoids were comparable to results in clinical trials, suggesting that — compared to animal cell lines — the organoids may be better suited to predict the effectiveness of therapies in humans.

Future Viruses

With their study, published in Nature Communications, the groups of Hans Clevers and Bart Haagmans underline the relevance of organoids for research into coronaviruses. In addition, they identify TMPSS2 as a potential therapeutic target for SARS-CoV2. Their newly developed biobank could also help screen future emerging viruses to quickly identify therapeutic targets.

Reference: “A CRISPR/Cas9 genetically engineered organoid biobank reveals essential host factors for coronaviruses” by Joep Beumer, Maarten H. Geurts, Mart M. Lamers, Jens Puschhof, Jingshu Zhang, Jelte van der Vaart, Anna Z. Mykytyn, Tim I Breugem, Samra Riesebosch, Debby Schipper, Petra B. van den Doel, Wim de Lau, Cayetano Pleguezuelos-Manzano, Georg Busslinger, Bart L. Haagmans and Hans Clevers, 17 September 2021, Nature Communications (2021).

Hans Clevers is principal investigator at the Hubrecht Institute and the Princess Máxima Center for Pediatric Oncology, professor of Molecular Genetics at UMC Utrecht and Utrecht University, and Oncode Investigator.

Bart Haagmans is principal investigator at the Viroscience department of the Erasmus MC University Medical Center Rotterdam.