Meloxicam can Potentiate the Therapeutic Effects of Synchrotron Microbeam Radiation Therapy on High-Grade Glioma Bearing Rats

The microbeam radiation therapy (MRT), a spatially micro-fractionated synchrotron radiotherapy, leads to better control of incurable high-grade glioma than that obtained upon homogeneous radiotherapy. We evaluated the effect of meloxicam, a non-steroidal anti-inflammatory drug (NSAID), to increase the MRT response. Survival of rats bearing intracranial 9L gliosarcoma treated with meloxicam and/or MRT (400 Gy, 50 μm-wide microbeams, 200 μm spacing) was monitored. Tumor growth was assessed on histological tissue sections and COX-2 transcriptomic expression was studied 1 to 25 days after radiotherapy. Meloxicam significantly extended the median survival of microbeam-irradiated rats (from +10.5 to +20 days). Dual treatment led to last survivors until D90 (D39 for the MRT group) and to tumor 9.5 times smaller than MRT alone. No significant modification of COX-2 expression was induced by MRT in normal and tumor tissues. The meloxicam reinforced the anti-tumor effect of MRT for glioma treatment. Although the mechanisms of interaction between meloxicam and MRT remain to be elucidated, the addition of this NSAID, easily implemented as a supplement to water for example, is a very favorable therapeutic regimen since it doubled the survival benefit compared to MRT alone.

Identification of AREG and PLK1 pathway modulation as a potential key of the response of intracranial 9L tumor to microbeam radiation therapy

Synchrotron microbeam radiation therapy (MRT) relies on the spatial fractionation of a synchrotron beam into parallel micron-wide beams allowing deposition of hectogray doses. MRT controls the intracranial tumor growth in rodent models while sparing normal brain tissues. Our aim was to identify the early biological processes underlying the differential effect of MRT on tumor and normal brain tissues. The expression of 28,000 transcripts was tested by microarray 6 hr after unidirectional MRT (400 Gy, 50 µm-wide microbeams, 200 µm spacing). The specific response of tumor tissues to MRT consisted in the significant transcriptomic modulation of 431 probesets (316 genes). Among them, 30 were not detected in normal brain tissues, neither before nor after MRT. Areg, Trib3 and Nppb were down-regulated, whereas all others were up-regulated. Twenty-two had similar expression profiles during the 2 weeks observed after MRT, including Ccnb1, Cdc20, Pttg1 and Plk1 related to the mitotic role of the Polo-like kinase (Plk) pathway. The up-regulation of Areg expression may indicate the emergence of survival processes in tumor cells triggered by the irradiation; while the modulation of the "mitotic role of Plk1" pathway, which relates to cytokinetic features of the tumor observed histologically after MRT, may partially explain the control of tumor growth by MRT. The identification of these tumor-specific responses permit to consider new strategies that might potentiate the antitumoral effect of MRT.