Figure 5.

Improved brain bioavailability of KDC203 relative to oleandrin. (A) Oleandrin enriches in kidney and liver tissue and its brain and heart levels are similar 24 h following its acute subcutaneous injection as a tritium-labeled compound into cohorts of five mice. In contrast, KDC203 reaches the highest levels in the brain and its brain levels exceeded its heart levels 3.5-fold 24 h after subcutaneous injection. ‘ns’ denotes non-significance. Asterisks indicate the level of statistical significance, i.e., one asterisk denotes p < 0.05, with each additional asterisk denoting tenfold lower p-values. (B) KDC203 is a lesser hMDR1 substrate than oleandrin. Recorded values of apparent permeability (Papp) from apical to basolateral (A–B) and vice versa (B–A). The efflux ratio is calculated as Papp_B-A/Papp_A-B. Zosuquidar was deployed as a selective inhibitor of MDR1. Measurements of the TEER on the day of experiment (day 5) resulted in a mean value of 107 ± 8 Ω·cm² (±SD, n = 22). Lucifer Yellow Permeability data (n = 22) were generated prior to the bidirectional assay with oleandrin and KDC203 (n = 3). (C) Rapid equilibrium dialyses of brain and plasma samples establish that KDC203 has a lower propensity than oleandrin to associate nonspecifically with components in the respective extracts, predictive of a higher concentration of free KDC203 that is available for specific engagement with its NKA target. (D) Pertinent pharmacological characteristics of oleandrin and KDC203 computed based on their in vivo tissue and plasma concentrations and the in vitro measurement of their unbound fractions in rapid equilibrium dialyses.