Abstract C195: A Wee1 inhibitor analog of AZD1775 demonstrates synergy with cisplatin with reduced single-agent toxicity in medulloblastoma

Medulloblastoma is the most common primary brain tumor in children. Current treatment for medulloblastoma includes surgical resection, radiation and cytotoxic chemotherapy. Although this approach has improved survival rates, the high doses of chemotherapy required to circumvent drug resistance mechanisms and result in clinical efficacy often give rise to lasting neurocognitive defects, stunted growth, deafness, and even secondary tumors. Therefore, synergistic drug combinations that maintain clinical efficacy, but allow dose reductions of cytotoxic agents limiting their adverse effects would be an attractive approach for patients with medulloblastoma. We identified Wee1 kinase as a 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 and tissue. Wee1 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, such as cisplatin. Our data indicate that Wee1 prevents DNA damage-induced cell death by cisplatin and that the known Wee1 inhibitor AZD1775 (previously MK1775) displays synergistic activity with cisplatin. However, AZD1775 is known to have nanomolar activity with at least 8 other kinases and there is limited structure-activity relationship (SAR) data for AZD1775 as it was identified as a Wee1 inhibitor from a high-throughput screen. Therefore, we developed a small series of AZD1775 derivatives to establish a SAR and further examine the effects of Wee1 inhibition in medulloblastoma. The compounds, that inhibited Wee1 activity in a TR-FRET assay in the same nanomolar range as AZD1775, had significantly reduced single-agent cytotoxicity and displayed synergistic activity with cisplatin at lower concentrations than AZD1775 in medulloblastoma cells. Recently, it has been reported that AZD1775 has limited ability to diffuse across the blood-brain barrier (BBB) and this would limit its effectiveness in brain tumors. We have performed cell permeability and BBB permeability assays using AZD1775 and our lead Wee1 inhibitor and our studies support that AZD1775 has poor BBB penetration. Our studies have now transitioned into in vivo systems to determine the tissue distribution and pharmacokinetics of our lead Wee1 inhibitor compared with AZD1775. In addition, our studies will determine the effect of our lead Wee1 inhibitor and AZD1775 on tumor growth as single agents and in combination with cisplatin in medulloblastoma in vivo models. Citation Format: Christopher J. Matheson, Sujatha Venkataraman, Vladimir Amani, Peter Harris, Donald S. Backos, Nicholas K. Foreman, Rajeev Vibhakar, Philip Reigan. A Wee1 inhibitor analog of AZD1775 demonstrates synergy with cisplatin with reduced single-agent toxicity in medulloblastoma. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C195.