Selective Elimination of Osteosarcoma Cell Lines with Short Telomeres by ATR Inhibitors

To avoid replicative senescence or telomere-induced apoptosis, cancers employ telomere maintenance mechanisms (TMMs) involving either the upregulation of telomerase or the acquisition of recombination-based alternative telomere lengthening (ALT). The choice of TMM may differentially influence cancer evolution and be exploitable in targeted therapies. Here, we examine TMMs in a panel of seventeen osteosarcoma-derived cell lines defining three separate groups according to TMM. Eight were ALT-positive, including the previously uncharacterised lines, KPD and LM7. ALT-negative cell lines were further classified into two groups according to their telomere length. HOS-MNNG, OHSN, SJSA-1, HAL, 143b and HOS displayed sub-normally short telomere length, while MG-63, MHM and HuO-3N1 displayed long telomeres. Importantly, sub-normally short telomeres were significantly associated with hypersensitivity to three different therapeutics targeting the ataxia telangiectasia and Rad3-related (ATR) kinase - AZD-6738/Ceralasertib, VE-822/Berzoserib and BAY-1895344 - compared to long telomeres, maintained via ALT or telomerase. Within 24 hours of ATR inhibition, cells with short but not long telomeres displayed chromosome bridges and underwent cell death, indicating a selective dependency on ATR for chromosome stability. Collectively, our work provides a resource to identify links between TMMs and drug sensitivity in osteosarcoma and indicates that telomere length predicts ATR-inhibitor sensitivity in cancer.