Medulloblastoma is the most common primary brain tumor in children. Current treatment for medulloblastoma includes surgical resection, radiation and chemotherapy with DNA alkylating agents, such as cisplatin. Although this approach to therapy has improved survival rates, high doses of cytotoxic chemotherapy are required to circumvent drug resistance mechanisms and to confer clinical efficacy, and unfortunately this often results in lasting neurocognitive defects, stunted growth, deafness, and even secondary tumors. The specificity and efficacy of chemotherapy must be improved to safely allow dose reductions and reduce drug-related adverse effects. Furthermore, while current therapy for standard-risk patients has resulted in improved survival rates, there is a subset of high-risk patients with Myc amplification who continue to have an extremely poor prognosis with a 5-year survival rate of less than 30%. Therefore, a more thorough understanding of the molecular pathways in medulloblastoma is critical for the development of more specific novel drugs to improve outcomes in high-risk patients. We identified Wee1 kinase as a potential new molecular target for medulloblastoma from an integrated genomic analysis using pathway analysis of gene expression and a kinome-wide siRNA screen of medulloblastoma cells. The Wee1 kinase participates in the G2-M checkpoint to prevent mitosis in the presence of DNA damage and therefore may play a role in drug resistance to DNA alkylating agents. Our preliminary data indicate that Wee1 prevents DNA damage-induced cell death by cisplatin and that the known Wee1 inhibitor MK1775 displays synergistic activity with cisplatin. However, the selectivity of MK1775 has not been rigorously assessed and it appears to have a high potential for binding to plasma protein and has a reduced capacity to diffuse across the blood brain barrier, restricting its usefulness in the clinic for the treatment of brain cancers. Therefore, a central aim of this research is to determine the structural requirements for small molecule binding to Wee1 to develop novel Wee1 selective inhibitors with improved drug properties and examine the potential of targeting Wee1 in medulloblastoma. We propose to screen the SelleckChem library of 194 kinase inhibitors by computational-based docking and in in vitro activity and binding assays. The data from these screens will be correlated to identify a subset of active compounds which will be used as a basis for inhibitor design. The fact that Wee1 lacks both the HRD and DFG motifs presents the opportunity for selective targeting. We will synthesize a small series of novel inhibitors and test them in parallel with MK1775 in our cell-based systems. We will evaluate the effect of these inhibitors on tumor cell growth as single agents and test if these inhibitors display synergistic activity with cisplatin. In addition, we will determine if p53 playsa role in mediating sensitivity to Wee1 inhibition in medulloblastoma and if Wee1 inhibition has therapeutic potential in tumors that have high Myc amplification which is characteristic of high risk patients. We will then extend our studies into in vivo models to determine the pharmacokinetics and tissue distribution of the Wee1 inhibitors and their effect on tumor growth in our xenograft model.
An integrated genomic analysis using pathway analysis of gene expression and a kinome-wide siRNA screen revealed Wee1 kinase as a molecular target in medulloblastoma, the most common pediatric brain tumor. The small molecule MK1775 has been described as a selective a potent Wee1 inhibitor;however, the selectivity of this compound has not rigorously assessed and it appears to have a high potential for binding to plasma protein and little ability to diffuse across the blood brain barrier, restricting its usefulness in the cliic for the treatment of brain cancers. Therefore, the main aims of this research are to determine the structural requirements for Wee1 binding to develop novel, selective small molecule inhibitors with improved drug properties and examine the potential of targeting Wee1 in medulloblastoma.