Drug-induced phospholipidosis (PLD) is a lysosomal storage disorder characterized by the accumulation of phospholipids within the lysosome. This adverse drug effect can occur in various tissues and is suspected to impact cellular viability. Therefore, it is important to test chemical compounds for their potential to induce PLD during the drug design process. PLD has been reported to be a side effect of many commonly used drugs, especially those with cationic amphiphilic properties. To predict drug-induced PLD in silico, we established a high-throughput cell-culture-based method to quantitatively determine the induction of PLD by chemical compounds. Using this assay, we tested 297 drug-like compounds at two different concentrations (2.5 μm and 5.0 μm). We were able to identify 28 previously unknown PLD-inducing agents. Furthermore, our experimental results enabled the development of a binary classification model to predict PLD-inducing agents based on their molecular properties. This random forest prediction system yields a bootstrapped validated accuracy of 86 %. PLD-inducing agents overlap with those that target similar biological processes; a high degree of concordance with PLD-inducing agents was identified for cationic amphiphilic compounds, small molecules that inhibit acid sphingomyelinase, compounds that cross the blood–brain barrier, and compounds that violate Lipinski’s rule of five. Furthermore, we were able to show that PLD-inducing compounds applied in combination additively induce PLD.

Drug-induced phospholipidosis may be associated with undesirable clinical side effects, and its relationship with drug toxicity remains unclear. A means to predict the phenomenon would have significant clinical utility. The front cover picture shows that drugs such as amitripyline (left panel) elevate cellular phospholipid levels significantly, even when applied in moderate concentrations. The effect on the cells can be visualized by fluorescence microscopy (right panel). In vitro experiments identified several wellknown and widely used drugs that induce phospholipidosis. Based on these results, an in silico model was built in an attempt to predict whether a novel therapeutic agent might induce phospholipidosis in cells. For more details, see the Full Paper by Johannes Kornhuber et al. on p. 1925 ff.