The fitting algorithm was the same as that used for scenario I (full brain concentration profiles available) (Figure ). Additionally, to investigate the effect of initial parameter setting in the ML model, scenario III' was designed as a negative control for scenario III, which used the same initial values as scenario I. The initial values for kin, kout, kdeep_br_in, and kdeep_br_out were 1, 1, 0.1, and 0.1, respectively. Before building predictive models for brain concentration-time profiles, we investigated the chemical space, comparing FDA-approved drugs and ChEMBL compounds using UMAP. The result of this analysis is shown in Figure , which shows that the compounds in project B and D