H2AX and osteosarcoma: On the other hand, TXT2 and TXT4 failed to induce DNA damage in the ALT-positive osteosarcoma U2OS cells, which in turn were characterized by a remarkable accumulation of γ-H2AX upon exposure to MTX (Fig. 3a, b), whereas equitoxic amounts of all compounds failed to elicit DNA damage in TERT-negative NHBE cells (Fig. 3a, b).