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Transcriptional control of DNA repair networks by CDK7 regulates sensitivity to radiation in Myc-driven Medulloblastoma

Myc-driven Medulloblastoma remains a major therapeutic challenge due to frequent metastasis and a poor 5-year survival rate. Myc gene amplification results in transcriptional dysregulation, proliferation, and survival of malignant cells. To identify therapeutic targets in Myc-amplified medulloblastoma we performed a CRISPR-Cas9 essentiality screen targeting 1140 genes annotated as the druggable genome. CDK7 was identified as a mediator of medulloblastoma tumorigenesis. Using covalent inhibitors and genetic depletion of CDK7 we observe the cessation of tumor growth in xenograft mouse models and increase in apoptotic mechanisms. The results are attributed to repression of a core set of Myc-driven transcriptional programs mediating DNA repair. We further establish that blocking CDK7 activity sensitizes cells to ionizing radiation leading to accrual of DNA damage and extended survival and tumor latency in medulloblastoma xenograft mouse models. Our studies establish a mechanism for selective inhibition of Myc-driven MB by CDK7 inhibition combined with radiation as a viable therapeutic strategy for Myc-amplified medulloblastoma.