BACKGROUND Glioblastoma is treated with surgery to remove as much as the tumour as possible then radiation therapy (RT) and temozolomide (TMZ) to cause extensive DNA damage in any remaining tumour cells, triggering cell death by apoptosis. However, glioblastoma cells respond by upregulating the DNA damage response (DDR) triggering DNA repair that contributes to treatment resistance. Progression then generally occurs rapidly leaving patients with a poor prognosis and survival. We previously showed that gartisertib, an inhibitor of ATM- and Rad3-Related protein (ATR), a serine/threonine kinase that triggers DNA repair, sensitises glioblastoma cells to TMZ and RT. We extend this investigation to brain-penetrant ATR inhibitors elimusertib (BAY1895344) and ceralasertib (AZD6738).

MATERIAL AND METHODS Patient-derived glioblastoma cell lines were treated with a dose response of ATRi (elimusertib and ceralasertib) combined with a clinically relevant dose of TMZ (35uM) and/or RT (2Gy). A human astrocyte cell line was also treated with a dose response of single agent elimusertib and ceralasertib. Cells were incubated for 7 days and assessed for cell viability through an MTT assay or cell-cell Incucyte analysis.

RESULTS Both elimusertib and ceralasertib as single agents reduced glioblastoma cell growth, with elimusertib being more potent compared to ceralasertib. Elimusertib had greater potency in causing cell death of the glioblastoma cell lines than a human astrocyte cell line. However, there was less difference between glioblastoma and astrocyte cell death when treated with ceralasetib. When combined with RT and/or TMZ, elimusertib once again was more potent in reducing glioblastoma cell growth compared to ceralasertib.

CONCLUSION We have expanded our in vitro data showing that various ATR inhibitors (elimusertib, ceralasertib and previously gartisertib) are able to reduce the growth of glioblastoma cells in combination with RT and TMZ treatment. This provides further support for initiating a clinical trial of ATR inhibition in combination with standard treatment for patients with glioblastoma.