MTR-03ATRX REDUCTION PROMOTES ALKYLATING AGENT RESISTANCE AND XENOGRAFT GROWTH IN A SUBSET OF GLIOMAS

BACKGROUND: Loss of ATRX function has been implicated in alternative lengthening of telomeres (ALT) and is common in IDH mutant astrocytoma of varying grades. However, the functional effects of ATRX loss on glioma growth are not clear, although it has been suggested that it can modulate response to ATR inhibitors such as VE-821. METHODS: We evaluated the ALT-positive GBM neurosphere line JHH-GBM14, which retains ATRX expression in a subset of cells, the ALT-negative neurosphere line 040821 and LN229 cells. Two distinct shRNA were used to suppress ATRX protein expression. RESULTS: ATRX knockdown had no effect on the overall in vitro growth of the three lines, but GBM14 cells became resistant to temozolamide and hydroxyurea after ATRX knockdown, while the two ALT-negative lines did not. A modest, non-significant increase in radiation resistance was also noted. Sensitivity to the ATR inhibitor VE-821 was not affected by decreased ATRX levels in any of the three lines. Interestingly, clonogenic growth of GBM14, the expression of several stem cell markers, as well as its ability to generate large flank and intracranial xenografts was increased by ATRX knockdown, while these effects were not seen in 040821 GBM neurospheres. CONCLUSIONS: While ATRX knockdown had little effect on in vitro tumor growth, it dramatically affected the treatment response, clonogenicity and in vivo growth of ALT-positive GBM14 cells, but not two GBM models lacking ALT. These data suggest that in some GBM, ATRX can modulate growth and treatment sensitivity as well as affecting telomere biology.