Circadian regulation of expression and promoter methylation underlies daily rhythms in TMZ sensitivity in glioblastoma.

BACKGROUND

Glioblastoma (GBM) is the most common primary brain tumor in adults. Despite extensive research and clinical trials, median survival post-treatment remains at 15 months. Thus, all opportunities to optimize current treatments and improve patient outcomes should be considered. A recent retrospective clinical study found that taking TMZ in the morning compared to the evening was associated with a 6-month increase in median survival in patients with -methylated GBM. Here, we hypothesized that TMZ efficacy depends on time-of-day and O-Methylguanine-DNA Methyltransferase () activity in murine and human models of GBM.

METHODS AND RESULTS

recordings using real-time bioluminescence reporters revealed that GBM cells have intrinsic circadian rhythms in the expression of the core circadian clock genes and , as well as in the DNA repair enzyme, . Independent measures of transcript levels and promoter methylation also showed daily rhythms intrinsic to GBM cells. These cells were more susceptible to TMZ when delivered at the daily peak of transcription. We found that morning administration of TMZ also decreased tumor size and increased body weight compared to evening drug delivery in mice bearing GBM xenografts. Finally, inhibition of MGMT activity with O-Benzylguanine abrogated the daily rhythm in sensitivity to TMZ by increasing sensitivity at both the peak and trough of expression.

CONCLUSION

We conclude that chemotherapy with TMZ can be dramatically enhanced by delivering at the daily maximum of tumor expression and minimum of activity.