Abstract
Simple SummaryOvarian cancer (OC) is the most common cause of cancer-related deaths among women worldwide, and its incidence has been increasing and has continued to prove resistant to a variety of therapeutics. This observation is principally disturbing given the amount of money invested in identifying novel therapies for this disease. A comparatively rapid and economical pipeline for identification of novel drugs is drug repurposing. We reported earlier that the antimalarial drug Quinacrine (QC) also has anticancer activity and here we discovered that QC significantly upregulates cathepsin L (CTSL) and promoting autophagic flux in ovarian cancer. QC-induced CTSL activation promotes lysosomal membrane permeability resulting in active CTSL release into the cytosol, which promotes Bid cleavage, mitochondrial membrane permeability, cytochrome-c release and cell death in both in-vitro and in-vivo models. Therefore, QC is a promising candidate for OC treatment.We previously reported that the antimalarial compound quinacrine (QC) induces autophagy in ovarian cancer cells. In the current study, we uncovered that QC significantly upregulates cathepsin L (CTSL) but not cathepsin B and D levels, implicating the specific role of CTSL in promoting QC-induced autophagic flux and apoptotic cell death in OC cells. Using a Magic Red® cathepsin L activity assay and LysoTracker red, we discerned that QC-induced CTSL activation promotes lysosomal membrane permeability (LMP) resulting in the release of active CTSL into the cytosol to promote apoptotic cell death. We found that QC-induced LMP and CTSL activation promotes Bid cleavage, mitochondrial outer membrane permeabilization (MOMP), and mitochondrial cytochrome-c release. Genetic (shRNA) and pharmacological (Z-FY(tBU)-DMK) inhibition of CTSL markedly reduces QC-induced autophagy, LMP, MOMP, apoptosis, and cell death; whereas induced overexpression of CTSL in ovarian cancer cell lines has an opposite effect. Using recombinant CTSL, we identified p62/SQSTM1 as a novel substrate of CTSL, suggesting that CTSL promotes QC-induced autophagic flux. CTSL activation is specific to QC-induced autophagy since no CTSL activation is seen in ATG5 knockout cells or with the anti-malarial autophagy-inhibiting drug chloroquine. Importantly, we showed that upregulation of CTSL in QC-treated HeyA8MDR xenografts corresponds with attenuation of p62, upregulation of LC3BII, cytochrome-c, tBid, cleaved PARP, and caspase3. Taken together, the data suggest that QC-induced autophagy and CTSL upregulation promote a positive feedback loop leading to excessive autophagic flux, LMP, and MOMP to promote QC-induced cell death in ovarian cancer cells.
Highlights
Ovarian cancer (OC) is the leading cause of death in women with gynecological malignancy, resulting in an estimated 14,070 deaths in 2018 [1]
Given that QC is highly concentrated in lysosomes and lysosomal membrane permeability (LMP) plays a role in autophagic and apoptotic cell death [21,24,32], we investigated whether QC induces LMP using LysoTracker (Thermofisher, Waltham, MA, USA) red live cell stain
We found that ATG5 KD significantly attenuated QC-induced apoptosis similar to treating non-targeted control transduced (NTC) cells with caspase inhibitor, indicating that autophagy is essential for QC-induced apoptosis (Figure 3a, 33.8% of cell death in QC treated in NTC whereas no apoptotic cell death in the presence of caspase inhibitor in NTC or ATG5 KD cells)
Summary
Ovarian cancer (OC) is the leading cause of death in women with gynecological malignancy, resulting in an estimated 14,070 deaths in 2018 [1]. The success rate for de novo ovarian cancer drugs from. Phase I trial to U.S Food and Drug Administration and Likelihood of Approval was very low (4.6%) from 2003 to 2011 [6]. Drug repurposing has developed into an attractive approach for discovering new ovarian cancer therapeutics, since repurposed drugs have approved pharmaceuticals with known pharmacokinetic and safety profiles [7,8,9]. The acridine derivative quinacrine (QC) has historically been used for malaria prophylaxis and treatment but has recently been found to have new indications as an anticancer agent [10]. QC has been shown to have multiple anticancer mechanisms and improve the cytotoxicity of other therapeutic agents (reviewed in [19])
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
