ALT cells and further experiments aiming to determine whether Topo III controls recombination at telomeres in mammalian cells or results from the indirect loss of TRF2 triggered by the telomestatin treatment would be of great interest. In conclusion, our results show that the G-quadruplex ligand telomestatin induces a telomere dysfunction in ALT cells, associated with APBs disruption and Topo III/BLM/TRF2 complex depletion. This emphasizes the interest of G-quadruplex ligands as potential therapeutics in tumor cells with alternative telomere maintenance mechanism. Supporting Information Figure S1 Topo III/TRF2 complex is impaired in MRC5V1/ YFP-Topo III cells treated with 2 mM telomestatin for 48 h. In contrast, Topo III/BLM complex is not modified by telomestatin treatment. Co-Immunoprecipitation was performed with D6 rabbit polyclonal antibody directed against Topo III as described previously [1]. Briefly, 26107 cells were lysed using RIPA buffer supplemented with 330 mM NaCl. 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