Therefore, in order to clarify whether telomeric G4 stabilization is able to hinder or to fuel the ALT pathway, the cardinal hallmarks of ALT were analyzed in three different osteosarcoma cell lines, two ALT-positive (U2OS and SAOS-2) and one ALT-negative (HOS) used as a control, treated with the G4 ligand RHPS4. The gene discussed is GPT; the disease is osteosarcoma.