Cancer Cells with Alternative Lengthening of Telomeres Do Not Display a General Hypersensitivity to ATR Inhibition

Abstract

Telomere maintenance is a hallmark of cancer as it provides cancer cells with cellular immortality. A significant fraction of tumors uses the alternative lengthening of telomeres (ALT) pathway to elongate their telomeres and to gain an unlimited proliferation potential. Since the ALT pathway is unique to cancer cells, it represents a potentially valuable, currently unexploited target for anti-cancer therapies. Recently, it was proposed that ALT renders cells hypersensitive to ataxia telangiectasia-and RAD3-related (ATR) protein inhibitors (Flynn et al., Science 347, 273). Here, we measured the response of various ALT-or telomerase-positive cell lines to the ATR inhibitor VE-821. In addition, we compared the effect of the inhibitor on cell viability in isogenic cell lines, in which ALT was active or suppressed. In these experiments, a general ATR inhibitor sensitivity of cells with ALT could not be confirmed. We rather propose that the observed variations in sensitivity reflect differences between cell lines that are unrelated to ALT.

Dissecting telomere maintenance mechanisms in pediatric glioblastoma

“…To better compare the results of the cell viability assays with FACS results, we tested the influence of cell density on VE-821 sensitivity and observed that a higher starting cell density results in a lower sensitivity (S5B Fig). This is consistent with our previous observation of a strong influence of the initial cell number in this assay [42]. In general, we did not observe a selective killing of ALT cells by ATR inhibition in these experiments.…”

“…Accordingly, we tested ATR inhibitor sensitivity for the panel of 7 pedGBM cell lines introduced here. In line with our previous study on non-glioma cell lines [42], we found no correlation of ALT status and response to the VE-821 ATR inhibitor ( Fig 5A). Instead, the sensitivity varied between cell lines irrespective of the telomere maintenance mechanism.…”

“…In order to validate this finding in an isogenic setting, we generated ATRX knockout cells of one of the pedGBM cell lines, NEM168, using CRISPR/Cas9. ATRX has been shown to repress the ALT phenotype upon re-introduction into ATRX-deficient, ALT-positive cells [42,50]. Accordingly, we detected a more pronounced ALT phenotype in ALT-positive NEM168 cells after ATRX knockout ( Fig 5C) when evaluating C-circle levels.…”

ATR inhibitors as a synthetic lethal therapy for tumours deficient in ARID1A

“…Although we cannot find evidence for ATR activation defects in ARID1A defective cells, we cannot formally exclude the possibility that these processes play a part in the synthetic lethal effect and act in parallel to the TOP2A and cell cycle defects. In addition, cells utilizing the ALT-pathway of telomere maintenance have also been shown to have increased ATRi sensitivity44, although whether this effect operates in all tumour cells with an ALT defect is not clear45. To our knowledge, none of the models used here are ALT-positive.…”

Alternative lengthening of telomeres phenotype and loss of ATRX expression in sarcomas (Review)

“…At present, there have been two highly selective and effective ATR inhibitors, AZD6738 and VX-970, which have reached phase I clinical trials. These drugs are being used either as a monotherapy or combined with a series of genotoxic chemotherapies for the treatment of ALT-positive solid tumors and refractory cancer (47). Furthermore, a series of studies have revealed the possible mechanism underlying the manner in which ATRX loss leads to sarcoma formation.…”