Figure 2.

CTSL mediates QC cytotoxicity and apoptosis. Colony-forming ability was assessed in HeyA8-MDR cells where the cells were pre-treated with cathepsin selective inhibitors (a,b) Pepstatin A (1 μM, CTSD inhibitor), (d,e) CA-074 Me (10 μM, CTSB inhibitor) and (g,h) Z-FY (tBU)-DMK (10 μM, CTSL inhibitor) and exposed with or without QC (5 µM) for 24 h followed by 10 days culture. The number of colonies were counted and plotted as mean ± standard deviation. (c,,f,i) Western analysis was performed for cleaved PARP under the similar treatment conditions, respectively. (j) Levels of cleaved caspase-9/3 and cleaved PARP were assessed by immunoblot analysis upon treatment with QC in presence and absence of Z-FY (tBU)-DMK. (k) Annexin V/PI staining of C13 and HeyA8MDR cells treated with QC in absence and presence of Z-FY (tBU)-DMK for 24 h and FACS analysis showed QC-exhibited CTSL-mediated cell death, and the corresponding bar graph shows the percentage of Annexin-V-positive cells. Significance was expressed as * p < 0.05, ** p < 0.01, *** p < 0.001. Abbreviations: QC: Quinacrine; CTSL: Cethepsin L; PARP: Poly (ADP-ribose) polymerase; PCNA: Proliferating cell nuclear antigen.