Developing drugs to treat NT5C2 mediated resistance in pediatric ALL
The cure rate for childhood acute lymphoblastic leukemia (ALL) has improved remarkably over the last four decades. However in spite of this improvement 10% to 15% of children will suffer a recurrence and their prognosis is dismal making ALL one of the leading causes of death due to cancer in children. We and others have shown that relapse is due to the outgrowth of a resistant subclone and we have discovered that these subclones contain mutations in genes that regulate response to the drugs used in therapy. This is true for both conventional, as well as, new immunotherapeutic agents. One of the most common mutations occurs in a gene called NT5C2 and results in resistance to 6-mercaptopurine which is a cornerstone of therapy for both childhood and adult ALL. We have already completed a large chemical screen looking for inhibitors of NT5C2 and in this application we propose to optimize their chemical structure so that such compounds can be used to eradicate NT5C2 mutant leukemia cells in patients and therefore prevent relapse. In a parallel group of studies we have developed laboratory tests to screen patients early in treatment to see if their leukemia cells contain NT5C2 mutations. Patients that test positive for the mutation would be ideal candidates for NT5C2 inhibitors.
Project Goal: Our long term goal is to develop the first precision-based clinical trial to prevent relapse rather than waiting for relapse to occur, at which time the leukemia is more difficult to treat.
Project Update 2021: In an effort to identify inhibitors specific for mutant NT5C2, we previously conducted high-throughput screening of a small-molecule library of nearly 240,000 compounds. The screen initially identified 469 compounds that appeared to inhibit NT5C2, but after running controls and confirmatory assays to remove false positives we were able to winnow it down to 51 validated hits that inhibited NT5C2 activity in a replicable manner. With the funds from Alex’s Lemonade Stand Foundation we have been able to work with medicinal chemists to see if we can develop these 51 chemical hits into more drug-like compounds. Some of the hits clustered into chemical series that had similar features to one another, while others were singletons that looked unique. A series of related compounds is promising because it indicates that there are some shared features causing inhibition of the target. We therefore sought to identify additional compounds that share some features with our hits while having other chemically distinct regions and test them for their ability to inhibit NT5C2. This trial-and-error process allows us to home in on those parts of the chemical compounds that are important for providing inhibition. Eventually the goal is to maintain the core scaffold of the compounds that is responsible for the inhibitory activity while modifying other regions to improve affinity, cell potency and drug-like properties. After analyzing our 51 hits, our medicinal chemist selected 8 series and 6 singletons to study in further detail. We have now tested over 280 compounds in the process described above. Based on this work we have now been able to home in on two chemotypes with a total of 16 compounds. Three of these have demonstrated promising results in sensitizing B ALL cell lines to thiopurines. Our studies will now focus on improving drug-like properties. The funds we have received have allowed us to work with experts in medicinal chemistry and drug design to select the best candidate compounds for confirmatory preclinical animal models with the overall goal of identifying the most promising drug lead that selectively inhibits the relapse-driving mutant forms of NT5C2.
