P08.05 Irradiation of glioblastoma cells can promote enhanced motility and invasiveness, both in vitro and in vivo through activation of MRCK

Glioblastoma (GBM) is one of the most common and aggressive forms of brain cancer. It is typically associated with poor survival rates, in part due to the characteristically infiltrative nature of GBM tumour cells. This allows GBM cells to disseminate through the brain via existing white matter tracts and perivascular spaces making complete surgical resection unachievable and contributing to high recurrence rates. For the majority of patients treatment of GBM includes radiotherapy. However, radiation resistance results in populations of surviving tumour cells with the potential for modified behaviour through radiation-induced alterations in signalling and gene expression profiles Myotonic dystrophy kinase-related CDC42- binding kinase (MRCK) is involved in regulating actin-myosin dynamics during cell migration through phosphorylation of its targets MLC2 and MYPT. Upon radiation of GBM cell lines in vivo we observed an increase in MRCK activity which was concomitant with a significant increase in GBM cell motility and invasion in in vitro and ex vivo assays. In support of these data we have observed increased MRCK activity at the invasive edges of both clinical GBM samples and an orthotopic GBM xenograft model that recapitulates key histological features of human GBM. Furthermore, therapeutic doses of irradiation were found to promote GBM invasion in vivo in this xenograft model. These observations suggest that MRCK activity may be required to promote invasion following irradiation and therefore may present a promising novel target for GBM treatment. To explore this further we performed MRCK RNAi on GBM cells and found we were able to reverse the radiation dependent promotion of GBM cell motility. We then used a novel MRCK selective inhibitor BDP-9066 to recapitulate this effect, observing dose dependent effects on both MRCK biomarkers, PMLC2 and PMYPT, and motility in vitro and ex vivo. These data suggest that MRCK activity is indeed required for GBM invasion and can be targeted effectively in multiple GBM cell lines. These observations provide evidence that glioblastoma cell migration may be enhanced following radiation therapy. As such, this might provide a substrate for therapy resistance and early recurrence in these tumours whilst offering a potential target for novel therapies in GBM management.