GPT and osteosarcoma: In the present work, the effect of RHPS4, a well-known and potent telomeric G4 stabilizer, was evaluated in U2OS, SAOS-2 (ALT-positive), and HOS (telomerase positive/ALT-negative) osteosarcoma cell lines, in terms of cell growth inhibition, cell cycle progression, and modulation of the cardinal ALT hallmarks.