CTSL and rheumatoid arthritis: Several compounds showed inhibitory activity against SARS-CoV either by increasing pH of the endosome, interfering with endocytosis, or inhibiting cathepsin L. Chloroquine (Figure 2F), and particularly the less toxic derivative hydroxychloroquine have long been used to treat malaria and autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosis (SLE) [62].