WT1 as an oncogene and therapeutic target in anaplastic Wilms tumor

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PROJECT SUMMARY/ABSTRACT Wilms tumor is the most common kidney cancer in children. High-risk patient groups continue to have dismal outcomes. The greatest predictor of a poor outcome is microscopic detection of diffuse anaplasia (unfavorable histology). This finding accounts for 50% of deaths from this disease and is associated with treatment resistance. Diffuse anaplasia (unfavorable histology) is caused by mutation in the TP53 gene that occurs late in a tumor with previously favorable histology. While TP53 mutation is associated with treatment resistance and poor outcomes, it could also result in new tumor vulnerabilities. The long-term goal of our research is to identify and exploit new therapeutic vulnerabilities in anaplastic Wilms tumor using targeted approaches. Wilms tumors with WT1 mutation do not go on to develop TP53 mutation and do not develop anaplasia. Previous evidence shows that the gene WT1 serves as a tumor suppressor in Wilms tumor. However, our central hypothesis is that WT1 functions as an oncogene in anaplastic Wilms tumor. Tumors with WT1 mutation do not develop anaplasia and WT1 and TP53 mutations do not occur in the same pediatric cancer patient tumors of any histology. Therefore, we hypothesize that WT1 mutations and TP53 mutations in the same Wilms tumor cell could be lethal events to the cancer cell. Aim 1 will test the hypothesis that loss of function WT1 and TP53 mutations are synthetic lethal events in Wilms tumor cancer cells. To test this hypothesis, we will model knockout of WT1 in TP53-mutant anaplastic Wilms tumor cells in vitro. We will also introduce a TP53 mutation into a mouse Wilms tumor model that has loss of WT1 function. Our preliminary data show that WT1 is necessary for activation of the telomerase pathway in Wilms tumor. Telomerase (critical portion coded by TERT gene) adds DNA repeats to the ends of chromosomes to counteract chromosomal shortening caused by rapidly dividing cancer cells. Aim 2 will test the hypothesis that functional WT1 is necessary for increased TERT expression and telomerase activity in anaplastic Wilms tumor. By knocking out WT1 in vitro and in a mouse model system, we aim to determine if WT1 is necessary for gain of telomerase function. We also will test the telomere targeted therapy 6-Thio-dG in mouse xenograft models using human patient tumor samples. We have identified that the histone demethylase KDM6B (an enzyme that modifies how DNA is bound to histones) regulates WT1 levels in Wilms tumor cells. We have shown that inhibition of KDM6B lowers WT1 levels. Aim 3 will test the hypothesis that KDM6B upregulates WT1 in Wilms tumor and can therefore be exploited as a therapeutic target. We plan to perform in vitro experiments which impair KDM6B function on the chemical and genetic levels in order to determine its effect on WT1 and anaplastic Wilms tumor cell behavior. We also aim to test the KDM6B inhibitor GSK-J4 in mouse xenograft models using human patient tumor samples. The expected outcome of these studies will be a greatly improved understanding of how WT1 functions in anaplastic Wilms tumor and the evaluation of WT1, telomerase, and KDM6B as preclinical therapeutic targets in anaplastic Wilms tumor.