Humanized Yeast for Discovery of New Splicing Modulators for Treatment of MDS
EvansMDS Discovery Research Grant 2019
Myelodysplastic syndromes (MDSs) are caused by changes in how the body produces blood cells. In patients with MDS this can cause anemia or even lead to blood cancers like acute myeloid leukemia. Unfortunately, there are very few treatment options for MDS, and new drugs for curing MDS are needed. In many cases, MDS is associated with genetic mutations in the DNA of the stem cells responsible for producing blood. Around 60-70% of MDS patients have mutations in the genes responsible for RNA splicing.
In human cells, DNA genes are transcribed into RNAs that contain the genetic information needed to make proteins used by the cell. Most RNAs are not direct copies of a DNA gene. Instead, they are built from DNA gene pieces. Just like a film editor removes some scenes and joins (splices) together other sequences to make a finished movie, the RNA splicing machinery removes unneeded sequences from genes and splices together others to make the correct RNA needed by the cell. In many MDS patients, there are mutations in this machinery, and their cells cannot make the necessary RNAs for producing healthy blood. Since these cells are unable to splice RNA correctly, they are also called “splicing sick”. Recently a new therapy for MDS has been proposed in which drugs are used to inhibit splicing in cells. The same mutations which cause cells to be splicing sick and lead to MDS also trigger sensitivity to these drugs. As a result, these drugs can kill the cells that cause MDS while leaving healthy cells unharmed.
While this represents an important advance towards curing MDS, very few drugs are available for this type of treatment. In fact, all of the most potent compounds used to inhibit splicing target the same location on the same splicing protein. Discovering new drugs that bind other locations or on other splicing proteins is challenging since testing hundreds of thousands of drug candidates for splicing inhibition is expensive, time-consuming, and can result in data that is difficult to interpret.
My laboratory has overcome these challenges by developing a fast, straightforward, and economical method for discovery of new human RNA splicing inhibitors. We do this by making use of a yeast called Saccharomyces cerevisiae—the same yeast that is used to make bread or brew beer. Like humans, yeast also perform RNA splicing. In fact, the core machinery that carries out this process is nearly identical in yeast and humans. We have genetically engineered yeast to use human splicing proteins in place of their own. Some of these are the same proteins that are mutated in MDS and cause splicing sickness. We propose to use “humanized” yeast to identify new inhibitors of human RNA splicing by growing them in the presence of more than 100,000 different drug candidates and identifying molecules which prevent growth of the humanized yeast but not the yeast lacking the human protein. Since yeast is easy, cheap, and fast to grow, we will be able to look for completely new inhibitors of different human RNA splicing proteins just by incubating different yeast strains overnight with drug candidates on a lab bench. We can even use yeast which express MDS mutant human proteins and look for drugs that prevent growth of only the cells containing MDS mutations. These molecules could lead to new, targeted therapies in which treatments are based on a patient’s own genome and the chemotherapeutics only kill the cells which cause MDS.