Small-molecule screen reveals synergy of cell cycle checkpoint kinase inhibitors with DNA-damaging chemotherapies in medulloblastoma.

Combined treatment for medulloblastoma: Certain subtypes of medulloblastoma (MB) have poor treatment outcome. To identify better treatments, Endersby et al. now screened more than 3000 compounds using six different human MB cell lines and showed that inhibitors of cell cycle checkpoint kinases (CHK1/2) increased the efficacy of clinical treatments. In vivo, the combined treatment increased DNA damage and apoptosis, resulting in increased survival and reduced tumor volume in multiple models. The results suggest that CHK1/2 inhibition could be used to increase the efficacy of standard chemotherapeutics for treating MB. Medulloblastoma (MB) consists of four core molecular subgroups with distinct clinical features and prognoses. Treatment consists of surgery, followed by radiotherapy and cytotoxic chemotherapy. Despite this intensive approach, outcome remains dismal for patients with certain subtypes of MB, namely, MYC-amplified Group 3 and TP53-mutated SHH. Using high-throughput assays, six human MB cell lines were screened against a library of 3208 unique compounds. We identified 45 effective compounds from the screen and found that cell cycle checkpoint kinase (CHK1/2) inhibition synergistically enhanced the cytotoxic activity of clinically used chemotherapeutics cyclophosphamide, cisplatin, and gemcitabine. To identify the best-in-class inhibitor, multiple CHK1/2 inhibitors were assessed in mice bearing intracranial MB. When combined with DNA-damaging chemotherapeutics, CHK1/2 inhibition reduced tumor burden and increased survival of animals with high-risk MB, across multiple different models. In total, we tested 14 different models, representing distinct MB subgroups, and data were validated in three independent laboratories. Pharmacodynamics studies confirmed central nervous system penetration. In mice, combination treatment significantly increased DNA damage and apoptosis compared to chemotherapy alone, and studies with cultured cells showed that CHK inhibition disrupted chemotherapy-induced cell cycle arrest. Our findings indicated CHK1/2 inhibition, specifically with LY2606368 (prexasertib), has strong chemosensitizing activity in MB that warrants further clinical investigation. Moreover, these data demonstrated that we developed a robust and collaborative preclinical assessment platform that can be used to identify potentially effective new therapies for clinical evaluation for pediatric MB. [ABSTRACT FROM AUTHOR]