De novo MYC addiction as an adaptive response of cancer cells to CDK4/6 inhibition

Cyclin-dependent kinases (CDK) are rational cancer therapeutic targets fraught with the development of acquired resistance by tumor cells. Through integrated fluxomics and transcriptomics approaches, we show that the inhibition of CDK4/6 causes enhanced metabolism of glucose, glutamine and amino acids, a metabolic reprogramming directed by the MYC transcription factor. Upon inhibition of CDK4/6, MYC is stabilized and its accumulation induces an upregulation of the mTOR pathway and increased glutamine metabolism and production of α-ketoglutarate, a prolyl hydroxylase substrate that triggers HIF1α hydroxylation and degradation. These MYC-driven adaptations to CDK4/6 inhibition render cells highly sensitive to inhibitors of mTOR and glutaminase and to hypoxia, revealing that drug resistance can mechanistically promote the emergence of new vulnerabilities that can be exploited therapeutically. We used microarrays to detail the global programme of gene expression underlying inhibition of CDK4 and CDK6. Cells were transfected with a mix (siRNA CDK4/6) containing siRNA against CDK4 and siRNA against CDK6 or with a mix (siRNA Control) containing Non-Targeting Control Pool siRNA and Silencer Select Negative Control siRNA.