As PLY is associated with fatal cellular and organ damage, particularly in pneumococcal pneumonia, inhibitors PB-1, PB-2 and PB-3 were verified by preventing the PLY-induced cellular damage in human alveolar epithelial cells (A549 cells). Confluent cells were incubated with PLY alone, with PLY and multiple concentrations of inhibitors, and with inhibitor alone. After 4 h and 24 h, respectively, supernatant of each experiment was aspirated for analysis. Cellular lysis induced by PLY was quantified by determining the activity of lactate dehydrogenase (LDH) in each sample. PB-1, PB-2 (Supplementary Figure ) and PB-3 (Figure and) exhibited significant concentration-dependent inhibition of PLY and prevented more than 95% of cellular damage at their respective highest concentrations.