Chloroquine synergizes doxorubicin efficacy in cervical cancer cells through flux impairment and down regulation of proteins involved in the fusion of autophagosomes to lysosomes.

Drug repurposing holds abundant opportunity in the development of novel anticancer drugs. Chloroquine (CQ), a FDA approved anti-malarial drug, is demonstrated to enhance anticancer efficacy of standard anticancer drugs including doxorubicin (DOX) in several types of cancer cells. Here, we aimed to exploit the chemosensitizing effects of CQ against DOX in human cervical cancer (HeLa) cells that remains to be investigated yet. We show that a combination of DOX (40 nM) and CQ (40 μM) resulted in a synergistic cytotoxicity (combination index; CI < 1) in HeLa cells compared to the DOX or CQ alone. Synergistic effect of the combination (DOX + CQ) was associated with the impaired autophagic flux and enhanced apoptosis. Following treatment with the combination (DOX + CQ), the level of p62/SQSTM and LC-3II proteins was increased, while a decrease was noted in the expression of LAMP-2, Syntaxin17, Rab 5, and Rab 7 proteins that play critical roles in the fusion of autophagosomes to lysosomes. Autophagy inhibition by combination (DOX + CQ) enhanced the apoptotic cell death synergistically by increasing the cleavage of procaspase-3 and PARP1. Further, a prior incubation of HeLa cells with Z-VAD-FMK (a pan-caspase inhibitor) for 4 h, suppressed the combination (DOX + CQ)-induced cell death. Our data suggest that a combination of DOX + CQ had a better anti-cancer efficacy in HeLa cells than either of the drugs alone. Thus, CQ, as a repurposed drug, may hold the potential to synergize anticancer effects of DOX in cervical cancer cells.