No abstract

Even in immortalized cell lines, circadian clocks regulate physiological processes in a time-dependent manner, driving transcriptional and metabolic rhythms, the latter being able to persist without transcription. Circadian rhythm disruptions in modern life (shiftwork, jetlag, etc.) may lead to higher cancer risk. Here, we investigated whether the human glioblastoma T98G cells maintained quiescent or under proliferation keep a functional clock and whether cells display differential time responses to bortezomib chemotherapy. In arrested cultures, mRNAs for clock (Per1, Rev-erbα) and glycerophospholipid (GPL)-synthesizing enzyme genes, P-GPL labeling, and enzyme activities exhibited circadian rhythmicity; oscillations were also found in the redox state/peroxiredoxin oxidation. In proliferating cells, rhythms of gene expression were lost or their periodicity shortened whereas the redox and GPL metabolisms continued to fluctuate with a similar periodicity as under arrest. Cell viability significantly changed over time after bortezomib treatment; however, this rhythmicity and the redox cycles were altered after Bmal1 knock-down, indicating cross-talk between the transcriptional and the metabolic oscillators. An intrinsic metabolic clock continues to function in proliferating cells, controlling diverse metabolisms and highlighting differential states of tumor suitability for more efficient, time-dependent chemotherapy when the redox state is high and GPL metabolism low.

Tumors of the nervous system including glioblastoma multiforme (GBM) are the most frequent and aggressive form of brain tumors; however, little is known about the impact of the circadian timing system on the formation, growth, and treatment of these tumors. We investigated day/night differences in tumor growth after injection of A530 glioma cells isolated from malignant peripheral nerve sheath tumor (MPNSTs) of NPcis (Trp53 +/− ; Nf1 +/− ) mice. Synchronized A530 cell cultures expressing typical glial markers were injected at the beginning of the day or night into the sciatic nerve zone of C57BL/6 mice subject to a 12:12 hours light/dark (LD) cycle or after being released to constant darkness (DD). Tumors generated in animals injected early at night in the LD cycle or in DD showed higher growth rates than in animals injected diurnally. No differences were found when animals were injected at the same time with cultures synchronized 12 hours apart. Similar experiments performed with B16 melanoma cells showed higher tumor growth rates in animals injected at the beginning of the night compared to those injected in the daytime. A higher tumor growth rate than that in controls was observed when mice were injected with knocked-down clock gene Bmal1 cells. Finally, when we compared day/ night administration of different doses of the proteasome inhibitor Bortezomib (0.5-1.5 mg/kg) in tumor-bearing animals, we found that low-dose chemotherapy displayed higher efficacy when administered at night. Results suggest the existence of a precise temporal control of tumor growth and of drug efficacy in which the host state and susceptibility are critical. K E Y W O R D SBortezomib, cancer chronotherapy, circadian clock, light/dark differences, tumor growth 2 of 16 | WAGNER Et Al.