An innovative new method to screen for potential cancer drugs has been developed by researchers from The Scripps Research Institute.
The technique makes use of tiny, three-dimensional ball-like aggregates of cells called spheroids. These structures can be used to interrogate hundreds or even thousands of compounds rapidly using a technique called high throughput screening.
By using this approach, the team has already identified one potential drug for an important cancer gene.
Blocking Tumor Growth
Cancer is a disease often driven by mutations in genes. As researchers learn more about these genes, and the proteins they code for, they are seeking smarter drugs to target them.
The ultimate goal is to find ways to stop cancer cells from multiplying out of control, thereby blocking the growth and spread of tumors.
“What’s important about this research is that we’re able to do studies using a form of cancer cells that is more physiologically relevant and better recapitulates how these cells appear in the body,”
said Timothy Spicer, director of Lead Identification Discovery Biology and High Throughput Screening on Scripps Research’s Florida campus and one of the study’s corresponding authors.
“Until now, most of the research to screen for cancer drugs has used cells that are growing flat on a plate. With these 3-D spheroids, we emulate much more closely what’s found in living tissues,”
added Louis Scampavia, director of HTS Chemistry and Technologies at Scripps Research and one of the study’s co-authors.
The spheroids are 100 to 600 microns in diameter-equivalent to the thickness of a few sheets of paper. In contrast to single layers of cells normally used to screen for drugs, which tend to all grow at the same rate because they get the same exposure to oxygen and nutrients, the spheroids mimic what might happen in a tumor: Some cells are on the outside and some are on the inside.
The researchers focused on a cancer-driving protein called KRAS. The KRAS gene and other members of the related RAS gene family are found to be mutated in nearly one-third of all cancers.
They are common in lung cancer, colorectal cancer, and especially pancreatic cancer. In fact, up to 90 percent of pancreatic cancers are driven by KRAS mutations, and the investigators used pancreatic cancer cell lines for the current study.
“In the past, KRAS has been a very tricky protein to target. People have spent several decades trying, but so far there has been little success. The KRAS protein is relatively small, and that’s made it hard to attack it directly. But the method of screening that we used in this study allowed us to come at the question in a different way,”
said Joseph Kissil, PhD, professor at Scripps Research Medicine and the other co-corresponding author.
The investigators performed what is called a phenotypic screen, which means they were looking for drugs that had an effect on cell growth, but didn’t have a preconceived idea about how they might work.
“We came at this in an unbiased way. We were not trying to design something to attack a specific part of the KRAS protein. We were just looking for something that acted on some part of the pathway that’s driving cell growth,”
Proof Of Principle
The investigators report in the new paper that they have already identified one compound that was previously not know to affect KRAS, called Proscillaridin A. The compound is similar to a class of drugs used to treat some heart conditions.
Although the team says this particular drug is unlikely to be developed as a cancer treatment, it validates the approach of conducting drug screenings using spheroids.
“It’s unlikely we would have discovered this connection using standard 2-D methods,”
“From our perspective, this is a proof-of-principle study. It shows you can look at libraries of drugs that have already been approved for other diseases, and find drugs that may also work for cancer. In theory, you could use this screening method for any line of cancer cells, and any mutation you want,”
“We would love to use this research to create a pipeline for new oncology drugs,” Spicer concluded. “Many of the most promising compounds may be overlooked with 2-D screening. This study provides direct evidence that screening for drugs using 3-D structures of cancer cells may be more appropriate.”
The work was supported in part by the National Cancer Institute of the National Institutes of Health.
Smitha Kota, Shurong Hou, William Guerrant, Franck Madoux, Scott Troutman, Virneliz Fernandez-Vega, Nina Alekseeva, Neeharika Madala, Louis Scampavia, Joseph Kissil & Timothy P. Spicer
A novel three-dimensional high-throughput screening approach identifies inducers of a mutant KRAS selective lethal phenotype
Oncogene (2018) doi:10.1038/s41388-018-0257-5
Top Image: confocal microscopy of the BxPC-3-KRASG12V cell line. Credit: Kota et. al./The Scripps Research Institute