Targeting processive transcription for Myc-driven circuitry in medulloblastoma

Abstract

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSBackgroundC_ST_ABSMedulloblastoma is the most common malignant brain tumor of childhood. The highest-risk tumors are driven by recurrent Myc amplifications (Myc-MB) and experience poorer outcomes despite intensive multimodal therapy. The Myc transcription factor defines core regulatory circuitry for these tumors and acts to broadly amplify downstream pro-survival transcriptional programs. Therapeutic targeting of Myc directly has proven elusive, but inhibiting transcriptional cofactors may present an indirect means of drugging the oncogenic transcriptional circuitry sustaining Myc-MB. MethodsIndependent CRISPR-Cas9 screens were pooled to identify conserved dependencies in Myc-MB. We performed chromatin conformation capture (Hi-C) from primary patient Myc-MB samples to map enhancer-promoter interactions. We then treated in vitro and xenograft models with CDK9/7 inhibitors to evaluate effect on Myc-driven programs and tumor growth. ResultsEight CRISPR-Cas9 screens performed across three independent labs identify CDK9 as a conserved dependency in Myc-MB. Myc-MB cells are susceptible to CDK9 inhibition, which is synergistic with concurrent inhibition of CDK7. Inhibition of transcriptional CDKs disrupts enhancer-promoter activity in Myc-MB and downregulates Myc-driven transcriptional programs, exerting potent anti-tumor effect. ConclusionsOur findings identify CDK9 inhibition as a translationally promising strategy for the treatment of Myc-MB. KO_SCPLOWEYC_SCPLOW PO_SCPLOWOINTSC_SCPLOWO_LICDK9 is an intrinsic dependency in Myc-driven medulloblastoma C_LIO_LIDual CDK9/7 inhibition disrupts Myc-driven transcriptional circuitry C_LIO_LICDK9 inhibitors should be developed as pharmaceutical agents for Myc-MB C_LI IO_SCPLOWMPORTANCEC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWOFC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWTHEC_SCPLOW SO_SCPLOWTUDYC_SCPLOWMedulloblastoma is the most common malignant brain tumor of childhood, and outcomes for high-risk subgroups remain unsatisfactory despite intensive multimodal therapy. In this study, we pool multiple independent CRISPR-Cas9 screens to identify transcriptional cofactors such as CDK9 as conserved dependencies in Myc-MB. Using Hi-C from primary patient samples, we map Myc enhancer-promoter interactions and show that they can be disrupted using inhibition of transcriptional CDKs. CDK9 inhibitor treatment depletes Myc-driven transcriptional programs, leading to potent anti-tumor effect in vitro and prolongation of xenograft survival in vivo. With a large number of CDK9 inhibitory compounds now in clinical development, this study highlights the opportunity for clinical translation of these for children diagnosed with Myc-MB.