The stars aligned for David Virshup when he attended a research-in-progress meeting at the University of Utah some 26 years ago. What he learnt that day would set him on a quest that would 20 years later and halfway around the world lead to the birth of a novel cancer drug.
“Wouldn’t have happened if I had skipped out on the talks,” said Virshup, now the Director of the Programme in Cancer and Stem Cell Biology at Duke-NUS, as he reflected on how his work on Wnts began.
“It’s about going to meetings, listening to people present their data, looking at their work, watching their slides and all of a sudden, having an aha! moment,” added the professor.
He describes his encounter with Wnts—messenger proteins that are essential in the development of multicellular organisms—as serendipity. At that time, Virshup, then an assistant professor, was studying the protein phosphatase 2A (PP2A) enzyme and its binding partners to understand the enzyme’s role in cells. Unbeknownst to him, he was focusing on a small part of a much bigger protein complex that regulates the Wnt signalling pathway.
During that research-in-progress meeting, another laboratory reported that they’d observed the adenomatous polyposis coli (APC) protein interacting with another protein, which Virshup found to be all too familiar.
Putting two and two together, Virshup quickly realised that this other protein was PP2A—the enzyme that he had been working on. The two proteins, along with a few others, make up a large protein complex that regulates cell growth by keeping Wnt signalling in check.
And the plot thickens—as the very same proteins can also cause Wnt signalling in cells to spiral out of control.
“APC mutations activate a specific arm of the Wnt pathway,” explained Virshup, noting how APC is commonly mutated in colon and other cancers, in which Wnt signalling is much higher.
This “aha” moment kick-started Virshup’s foray into Wnts and their role in cancer.
A two-faced protein
Wnts, which instruct cells on what they should become, are only found in multicellular animals, but not in single cell organisms such as yeast or amoebas, which don’t have as much need for proteins that communicate with neighbouring cells.
“Wnts have been evolving for 500 million years,” said Virshup.
“So, they came about really early in development to probably signal between one cell and the next to tell them, ‘I’m left and you’re right; I’m up and you’re down’, ‘I’m going to turn into a kidney cell, so you should turn into a nerve cell’,” added Virshup to illustrate how Wnts mediate cell-to-cell communication.
In humans, cellular communication becomes much more complex, requiring 19 different Wnt genes to run smoothly, with some of the Wnts even implicated in other important cellular processes such as inflammation and immunity.
But Wnts also have an altogether more sinister side because when they go rogue and are overexpressed, they can drive the formation of cancerous growths.
“Then, it turns out that there are other ways to activate the Wnt pathway in cancer, not just overexpressing the Wnt, but for instance, mutation to parts of it,” said Virshup.
“One of the things they do in certain tissues is they tell cells whether to remain stem cells or stop being stem cells,” he added.
In cancers that are addicted to Wnt signalling, the Wnt pathway remains highly activated, allowing cancerous cells to proliferate like stem cells, thereby feeding the cancer.
Going against the flow
The next logical step, then, was to determine if Wnt signalling could be inhibited to stop the growth of these Wnt-addicted cancers.
“When I first had this idea back in Utah, there was a fair amount of skepticism that this was a good idea,” said Virshup. “Because the general idea was that Wnt signalling was so important, if you inhibit it with a broad-spectrum inhibitor, you’ll just kill people.”
But Virshup persisted and got his student at the time, Zahra Kabiri, to study how knocking out Wnt signalling would affect adult mice.
They expected the worst, but somehow, the mice survived—living proof that it was indeed possible to inhibit Wnt signalling in adults.
“Since I’m a physician, it’s always in the back of my mind—what’s druggable and where could we make a difference in understanding that might lead to drugs,” said Virshup.
Embarking on the ETC-159 journey
This vision became a reality after he arrived in Singapore in 2007 to set up his current laboratory.
Virshup reached out to Dr Alex Matter, who was then heading the Experimental Therapeutic Centre (ETC) at the Agency for Science, Technology and Research (A*STAR). At that time, Matter was in the process of scouting for new drug targets that could be validated.
“David came with a validated target,” he said, “and it’s very difficult to find drug targets that are validated, with the biology and clinical sides really matching and the target causally related to the disease.”
“With David, I knew I was dealing with a very serious, very experienced scientist whom I could trust,” added Matter.
Even with a validated target in hand, chemists and biologists at ETC had to test some 200,000 compounds in order to find some useful lead structures.
“Once we had some lead structures, we had to optimise each lead until they were fit to progress ultimately into preclinical development,” said Matter.
In 2013, ETC handed over a fully optimised lead, ETC-159, as a development candidate to D3 (Drug Discovery & Development), which later merged with ETC and the Experimental Biotherapeutics Centre to form the Experimental Drug Development Centre (EDDC).
“After that, there were extensive preclinical studies to make sure that we understood its potential toxicity before moving on to humans,” said Virshup.
“We would not have been able to make a molecule on our own. Their help was invaluable. The partnership was invaluable,” he added.
The road ahead
As ETC-159 progresses through clinical trials managed by EDDC, Dr Veronica Diermayr continues the scientific collaboration with Virshup’s laboratory.
“It’s a stimulating symbiosis,” said Diermayr, the asset development leader for this project, describing the process of collaborating with Virshup, before adding, “They (Virshup’s team) stimulate you with new ideas; they bring up targets that we wouldn't have taken on without his strong support at that time.”
Diermayr’s team led the drug into Phase 1 clinical trials, with the first patient dosed in January 2015. As the clinical trial progressed, additional test sites in the United States were added, bringing the total number of patients treated by the end of Phase 1A to 32.
For the drug to progress through clinical trials, the team decided to select a patient population in whom ETC-159 would be an effective cancer treatment by using suitable biomarkers. So, Diermayr and her team worked to establish the most robust biomarker for clinical use from a list of potential biomarkers provided by Virshup.
“When you want to see efficacy, you can do this best if you have the right kind of patients for whom this drug has a high likelihood to work,” she explained.
That data also gave the team a deeper understanding of how the drug works, leading to further studies on the effect of ETC-159 in different patient populations as the clinical trial progressed to Phase 1B, which kickstarted in July 2020.
In the Phase 1B trial, the team is studying whether ETC-159 is effective as a single agent in genetically defined subgroups of colorectal, endometrial or ovarian cancer patients with limited treatment options. The study will also determine the effectiveness of combining ETC-159 with immune checkpoint inhibitors in subsets of the same cancers that are currently unresponsive to checkpoint inhibitors.
“It would be ground-breaking if the team was able to achieve clinical proof-of-concept, demonstrating that tumours known to be unresponsive to checkpoint inhibitors could become responsive with the addition of ETC-159,” said EDDC’s Chief Executive Officer, Professor Damian O’Connell.
Unlocking endless possibilities with ETC-159
Despite having a drug in clinical trials, Virshup’s work on ETC-159 is far from finished.
He continues to lead his team in unravelling the intricacies of the Wnt signalling pathway by using ETC-159 as an experimental tool.
In fact, ETC-159 has enabled Dr Babita Madan from Virshup’s laboratory to collaborate with Assistant Professor Nathan Harmston from Yale-NUS College, who was a senior research fellow at the time, and Associate Professor Enrico Petretto from the Cardiovascular and Metabolic Disorders Programme at Duke-NUS to obtain a detailed profile of the genes that are controlled by Wnt signalling. Using ETC-159, they tracked changes in genes that are present when Wnt is active, compared with when Wnt is repressed by ETC-159.
This finding was just the tip of the iceberg. They also showed that Wnt signalling controls the expression of about 5,000 out of approximately 15,000 to 20,000 genes in the body, determining how cells grow, proliferate and differentiate.
“We’re still in the process of analysing that data. It’s been a really fantastic resource,” said Virshup, who also acknowledges the challenges faced by his team in deciding which genes to focus on.
Despite the challenges, the initial findings from the screening have been promising.
“One of the things we discovered was that Wnt signalling activates a whole series of DNA repair genes, specifically genes involved in DNA double strand breaks,” he said.
To Virshup, that made sense from a therapeutic point of view because the finding established a potential link between Wnt signalling and drug resistance in cancers, which is commonly associated with the ability of cancer cells to repair DNA double strand breaks. More importantly, it strengthens his group’s approach of blocking Wnt signalling as a therapeutic strategy in cancer therapy.
With close to four decades of research experience under his belt, Virshup is unfazed by what lies ahead.
“The thing about science is you do the experiment and you think you know what’s going to happen and, sometimes, that is what happens and, sometimes, Mother Nature has other plans for you,” he said, “and then, the fun part is when you get the results you don’t expect, you get to figure it out.”