DDIT3 and neoplasm: Moreover, immunohistochemical analysis of tumor tissue performed at the end of the experiment further substantiated D2O-induced anti-proliferative (Ki67, p21), pro-apoptogenic (cleaved caspase 3), and stress response (HO-1, DDIT3, p-eIF2α) modulatory activity detectable in A375 melanoma tumor-bearing SCID mice (Figure 5G and Figure S5).