DDAH1 and neoplasm: However, it is also important to emphasise that the observed intra-tumour concentrations of L-257 remained above the IC50 [32] and the Ki values for DDAH1 inhibition [18,22] for a relatively short period of time, an estimated 4 and 3.5 h after acute and chronic ZST316 treatment, respectively, when compared to the time above the IC50 and Ki values for ZST316, 15.5 and 16.5 h after acute and chronic ZST316 treatment (Figure 5 and Figure 7) [22,30].