Research ArticleCancer

A subset of PARP inhibitors induces lethal telomere fusion in ALT-dependent tumor cells

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Science Translational Medicine  05 May 2021:
Vol. 13, Issue 592, eabc7211
DOI: 10.1126/scitranslmed.abc7211

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An ALTernative target for PARPi

The alternative lengthening of telomere (ALT) is a mechanism used by some tumors to stabilize their telomeres and survive. Now, Mukherjee et al. studied ALT-associated tumors and showed that they shared hypersensitivity to a subgroup of PARP inhibitors (PARPi). This hypersensitivity was mediated by the ability of PARPi to modulate PARP1 and inhibit its binding to MRE11 and BRCC3. As a result, this signaling lead to destabilization of telomeric TRF2, enabling telomeric fusion. The treatment with PARPi was effective in vivo in ALT-dependent PDX models, suggesting that PARPi might be effective in patients with ALT-dependent tumors.


About 10% of all tumors, including most lower-grade astrocytoma, rely on the alternative lengthening of telomere (ALT) mechanism to resolve telomeric shortening and avoid limitations on their growth. Here, we found that dependence on the ALT mechanism made cells hypersensitive to a subset of poly(ADP-ribose) polymerase inhibitors (PARPi). We found that this hypersensitivity was not associated with PARPi-created genomic DNA damage as in most PARPi-sensitive populations but rather with PARPi-induced telomere fusion. Mechanistically, we determined that PARP1 was recruited to the telomeres of ALT-dependent cells as part of a DNA damage response. By recruiting MRE11 and BRCC3 to stabilize TRF2 at the ends of telomeres, PARP1 blocked chromosomal fusion. Exposure of ALT-dependent tumor cells to a subset of PARPi induced a conformational change in PARP1 that limited binding to MRE11 and BRCC3 and delayed release of the TRF2-mediated block on lethal telomeric fusion. These results therefore provide a basis for PARPi treatment of ALT-dependent tumors, as well as establish chromosome fusion as a biomarker of their activity.

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