Synergistic Anti-Tumor Effect of Combining Selective CDK7 and BRD4 Inhibition in Neuroblastoma.

Yang Gao,Nicole Nasholm,Tinghu Zhang,Malgorzata Krajewska,Nicholas Kwiatkowski,Marina Volegova,Sanjukta Das,Rani E George,Clay Gustafson,Nathanael S Gray,Brian J Abraham

doi:10.3389/fonc.2021.773186

Abstract

PurposeCyclin-dependent kinases (CDKs) that have critical roles in RNA polymerase II (Pol II)-mediated gene transcription are emerging as therapeutic targets in cancer. We have previously shown that THZ1, a covalent inhibitor of CDKs 7/12/13, leads to cytotoxicity in MYCN-amplified neuroblastoma through the downregulation of super-enhancer-associated transcriptional upregulation. Here we determined the effects of YKL-5-124, a novel covalent inhibitor with greater selectivity for CDK7 in neuroblastoma cells.Experimental DesignWe tested YKL-5-124 in MYCN-amplified and nonamplified neuroblastoma cells individually and in combination with other inhibitors in cell line and animal models. Cell viability, target validation, effects on cell cycle and transcription were analyzed.ResultsCDK7 inhibition with YKL-5-124 did not lead to significant cell death, but resulted in aberrant cell cycle progression especially in MYCN-amplified cells. Unlike THZ1, YKL-5-124 had minimal effects on Pol II C-terminal domain phosphorylation, but significantly inhibited that of the CDK1 and CDK2 cell cycle kinases. Combining YKL-5-124 with the BRD4 inhibitor JQ1 resulted in synergistic cytotoxicity. A distinct MYCN-gene expression signature associated with resistance to BRD4 inhibition was suppressed with the combination. The synergy between YKL-5-124 and JQ1 translated into significant tumor regression in cell line and patient-derived xenograft mouse models of neuroblastoma.ConclusionsThe combination of CDK7 and BRD4 inhibition provides a therapeutic option for neuroblastoma and suggests that the addition of YKL-5-124 could improve the therapeutic efficacy of JQ1 and delay resistance to BRD4 inhibition.

Highlights

Neuroblastoma (NB) is an embryonal tumor of the sympathetic nervous system accounting for 15% of all pediatric cancer deaths [1]
To compare the on-target activity of the more selective CDK7 inhibitor, YKL-5-124 [18] with THZ1 in MYCN-amplified NB cells, we first evaluated the extent of target engagement using a biotinylated derivative of THZ1 (Figure 1A)
In contrast to THZ1, YKL-5-124 treatment strongly inhibited the pulldown of CDK7 with bio-THZ1 while completely sparing CDK12 even at relatively high doses (400 nM) and confirming its on-target selectivity for CDK7 over CDK12

Summary

Introduction

Neuroblastoma (NB) is an embryonal tumor of the sympathetic nervous system accounting for 15% of all pediatric cancer deaths [1]. This cancer of early childhood has a markedly varying clinical course, ranging from spontaneous regression to progression and poor survival of high-risk patients despite aggressive multimodal therapy. Inhibition of the bromodomain-containing protein BRD4, which selectively binds to acetylated lysine residues and facilitates the transcriptional activation of target genes, has shown potential in preclinical studies [8, 9] and is currently being tested in clinical trials. In the remaining 50% of high-risk neuroblastoma patients without tumor MYCN amplification, the lack of a unified oncogenic driver makes the design of novel therapies a challenge

Methods

Results

Conclusion