PROJECT SUMMARY

TET2 is one of the most frequently mutated tumor suppressor genes in patients with myelodysplastic syndrome (MDS), with inactivating mutations found in the bone marrow cells of 20-30% of MDS patients at the time of diagnosis. Recent findings have demonstrated that mutations in TET2 can be the “first transforming event” in hematopoietic stem and progenitors cells (HSPCs) in individuals who eventually develop MDS. When HSPCs lose function of TET2, they become more competitive and expand at the expense of the normal HSPCs, and then accumulate mutations in other genes, leading to the onset of MDS. The goal of our study is to find small-molecule drugs that will kill the blood stem cells that have TET2 mutations, but not the healthy normal stem cells, thus preventing the clones that lack the TET2 protein from expanding further and acquiring additional defects in other genes. We will test drugs already approved by the FDA for use in humans, so the specific ones that we identify can then be “repurposed” right away for clinical trials to determine their activity in MDS patients, without requiring extensive studies for adverse effects, which would be required for drugs that were not yet approved for human use.

For our study, we have developed a zebrafish model by creating tet2 mutations similar to those found in human MDS. Zebrafish are used because they share many genes with humans and provide particularly faithful models for cancers of the blood system, such as MDS. Their translucent skin allows us to watch as disease forms and grows and observe whether they respond to experimental treatments. Normal and mutant blood stem cells can be directly visualized and tested in small zebrafish larvae that can be raised in large numbers and tested with small amounts of drugs. We have shown that the tet2 mutant zebrafish are viable and develop progressive myelodysplasia as they get older, culminating in full-blown MDS with anemia at 24 months of age (Gjini et al, 35:789-804, MCB, 2015).

We will use these zebrafish mutant embryos to perform a drug screen with known drugs, including those that are in Phase I/II clinical trials or FDA-approved. This strategy, called “repurposing” of existing drugs, will accelerate the entrance of such compounds into clinical trials because the toxicity, side effects and other characteristics of the drugs have already been investigated. This project is significant because it will identify drugs that eliminate the MDS stem cells and the TET2-mutant pre-MDS stem cells that could give rise to a recurrence of MDS. We will also analyze the drugs we identify in combination with each other at a range of dosages to identify drugs that are synergistic with each other in killing TET2-deficient MDS cells. We will also test each drug that shows specificity for killing tet2-deficient zebrafish MDS cells in specifically engineered TET2-deficient human cell lines in the laboratory to make sure our findings also apply to human MDS cells. Our long-range goal is to generate preclinical evidence using our zebrafish model of MDS that will define new drug combinations and verify their activity in TET2-mutant MDS cells so that they can be incorporated into clinical trials for human patients with TET2-mutant MDS.