A robust method to identify compounds that undergo intracellular lysosomal sequestration
Lysosomes are acidic organelles (pH 4-5) that play a key role in various metabolic processes such as turnover of phospholipids, the breakdown of waste products (including bacteria and viruses) and apoptosis. Lipophilic and amphiphilic drugs (a.k.a. cationic amphiphilic amines or CADs) with ionizable amines (pKa>6) can accumulate in lysosomes (a process known as lysosomal trapping), which contributes to presystemic clearance in lysosome-rich organs (such as liver and lung) and, together with the binding of lipophilic amines to phospholipids, is associated with a large volume of distribution of numerous cardiovascular and CNS drugs (MacIntyre and Cutler, 1988; Daniel and Wojcikowski, 1999; Houston and Halifax, 2007). The prolonged accumulation of lipophilic amines in lysosomes and their binding to phospholipids, both of which disrupt lysosomal function, have been implicated as the major cause of phospholipidosis, where an excessive accumulation of phospholipids occurs in various tissues (Hanumegowda et al., 2010). Furthermore, elevated levels of CADs in lysosomes can lead to high organ to blood ratios of drugs that can be mistaken for active drug transport.