Pharmacological modulation of the cytosolic oscillator affects glioblastoma cell biology

The circadian system is a conserved time-keeping machinery that regulates a wide range of processes such as sleep/wake, feeding/fasting, and activity/rest cycles to coordinate behavior and physiology. Circadian disruption can be a contributing factor in the development of metabolic diseases, inflammatory disorders, and higher risk of cancer. Glioblastoma (GBM) is a highly aggressive grade 4 brain tumor that is resistant to conventional therapies and has a poor prognosis after diagnosis, with a median survival of only 12–15 months. GBM cells kept in culture were shown to contain a functional circadian oscillator. In seeking more efficient therapies with lower side effects, we evaluated the pharmacological modulation of the circadian clock by targeting the cytosolic kinases glycogen synthase kinase-3 (GSK-3) and casein kinase ε/δ (CK1ε/δ) with specific inhibitors (CHIR99022 and PF670462, respectively), the cryptochrome protein stabilizer (KL001), or circadian disruption after Per 2 knockdown expression in GBM-derived cells. CHIR99022-treated cells had a significant effect on cell viability, clock protein expression, migration, and cell cycle distribution. Moreover, cultures exhibited higher levels of reactive oxygen species and alterations in lipid droplet content after GSK-3 inhibition compared to control cells. The combined treatment of CHIR99022 with temozolomide was found to improve the effect on cell viability compared to temozolomide therapy alone. Per 2 disruption affected both GBM migration and cell cycle progression. Overall, our results suggest that pharmacological modulation or molecular clock disruption severely affects glioblastoma cell biology.