Failed Repurposing of Lysosomotropic Drugs for COVID-19 Treatment or Prevention

The hope for the rapid discovery of an effective drug therapy for COVID-19 has led to several efforts to repurpose drugs approved for other indications. Lysosomotropic drugs, organic amines such as chloroquine, hydroxychloroquine, amiodarone and many others, were found to interfere with the viral life cycle in vitro but have failed in clinical trials. The properties of lysosomotropic drugs and the vacuolar cytopathology induced by them are briefly reviewed, including the critical role of lipophilicity, the central role of vacuolar (V)-ATPase for their concentration in acidic organelles, the altered function of these organelles including impaired endocytosis and secretion, macroautophagic accumulation and secondary phospholipidosis. The apparent preferential uptake of lysosomotropic drugs by phagocytic leukocytes (macrophages, neutrophils) and the high concentrations needed for a sustained disruption of vacuolar trafficking may have contributed to the failure of lysosomotropic drug repurposing for COVID-19.