Targeting Super-Enhancer-Associated Oncogenes in Osteosarcoma with THZ2, a Covalent CDK7 Inhibitor.

Abstract

Malignancy of cancer cells depends on the active transcription of tumor-associated genes. Recently, unique clusters of transcriptional enhancers, termed super-enhancers, have been reported to drive the expression of genes that define cell identity. In this study, we characterized specific super-enhancer-associated genes of osteosarcoma, and explored their potential therapeutic value. Super-enhancer regions were characterized through chromatin immunoprecipitation sequencing (ChIP-seq). RT-qPCR was used to detect the mRNA level of <i>CDK7</i> in patient specimens and confirm the regulation of sensitive oncogenes by THZ2. The phosphorylation of the initiation-associated sites of RNA polymerase II (RNAPII) C-terminal repeat domain (CTD) was measured using Western blotting. Microarray expression analysis was conducted to explore transcriptional changes after THZ2 treatment. A variety of <i>in vitro</i> and <i>in vivo</i> assays were performed to assess the effects of CDK7 knockdown and THZ2 treatment in osteosarcoma. Super-enhancers were associated with oncogenic transcripts and key genes encoding cell-type-specific transcription factors in osteosarcoma. Knockdown of transcription factor CDK7 reduced phosphorylation of the RNAPII CTD, and suppressed the growth and metastasis of osteosarcoma. A new specific CDK7 inhibitor, THZ2, suppressed cancer biology by inhibition of transcriptional activity. Compared with typical enhancers, osteosarcoma super-enhancer-associated oncogenes were particular vulnerable to this transcriptional disruption. THZ2 exhibited a powerful anti-osteosarcoma effect <i>in vitro</i> and <i>in vivo</i>. Super-enhancer-associated genes contribute to the malignant potential of osteosarcoma, and selectively targeting super-enhancer-associated oncogenes with the specific CDK7 inhibitor THZ2 might be a promising therapeutic strategy for patients with osteosarcoma.