Daily glucocorticoids promote glioblastoma growth and circadian synchrony to the host.

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults with a poor prognosis despite aggressive therapy. Here, we hypothesized that daily host signaling regulates tumor growth and synchronizes circadian rhythms in GBM. We find daily glucocorticoids promote or suppress GBM growth through glucocorticoid receptor (GR) signaling depending on time of day and the clock genes, Bmal1 and Cry. Blocking circadian signals, like vasoactive intestinal peptide or glucocorticoids, dramatically slows GBM growth and disease progression. Analysis of human GBM samples from The Cancer Genome Atlas (TCGA) shows that high GR expression significantly increases hazard of mortality. Finally, mouse and human GBM models have intrinsic circadian rhythms in clock gene expression in vitro and in vivo that entrain to the host through glucocorticoid signaling, regardless of tumor type or host immune status. We conclude that GBM entrains to the circadian circuit of the brain, modulating its growth through clock-controlled cues, like glucocorticoids.