The autophagy inhibitor chloroquine targets cancer stem cells in triple negative breast cancer by inducing mitochondrial damage and impairing DNA break repair

Abstract

Triple negative breast cancer (TNBC), characterized by an abundance of treatment-resistant breast cancer stem cells (CSCs), has a poorer prognosis than other types of breast cancers. Despite its aggressiveness, no effective targeted therapy exists for TNBC. Here, we demonstrate that CQ effectively targets CSCs via autophagy inhibition, mitochondrial structural damage, and impairment of double-stranded DNA break repair. Electron microscopy demonstrates CQ-induced mitochondrial cristae damage, which leads to mitochondrial membrane depolarization with a significant reduction in the activity of cytochrome c oxidase and accumulation of superoxide and double-stranded DNA breaks. CQ effectively diminishes the TNBC cells’ ability to metastasize in vitro and in a TNBC xenograft model. When administered in combination with carboplatin, CQ effectively inhibits carboplatin-induced autophagy. This combination treatment significantly diminishes the expression of DNA repair proteins in CSC subpopulations, resulting in tumor growth reduction in carboplatin-resistant BRCA1 wild-type TNBC orthotopic xenografts. As TNBC’s high treatment failure rate has been attributed to enrichment of CSCs, CQ, an autophagy inhibitor with anti-CSC effects, may be an effective adjunct to current TNBC chemotherapy regimens with carboplatin.

Metalloprotease-dependent activation of EGFR modulates CD44+/CD24− populations in triple negative breast cancer cells through the MEK/ERK pathway

“…Instead, it has been proposed that EGFR inhibition reduces CSC population in breast cancer through inhibition of autophagy [19]. This notion is supported by the observations that chloroquine, a lysotropic agent that inhibits a late step of autophagy, or knock-down of autophagy-specific genes diminished the CSC populations in TNBC cell lines [57–59]. The universally positive role of autophagy in CSC maintenance is, however, at odds with a report demonstrating that autophagy deficiency stabilizes the transcription factor TWIST1, promotes EMT in vitro , and tumor growth and metastasis using a A431 squamous cell carcinoma xenograft mouse model [60, 61].…”

Dual Role of Mitophagy in Cancer Drug Resistance

“…Autophagy can act as a survival mechanism for cancer cells in response to various stresses (15)(16)(17), but the role of canonical autophagy in cancer remains unclear (5,18,19). Therefore, how about mitophagy in cancer?…”

DNA Damage Response and Autophagy: A Meaningful Partnership

“…Indeed, the autophagy inhibitor chloroquine has been shown to impair DNA damage repair and to increase the cytotoxic effect of the chemotherapeutic agent carboplatin in breast cancer stem cells (Liang et al, 2016). Accumulating evidence indicates that autophagy is exploited by tumor cells to resist radiation or chemotherapy-induced cell death and that genetic or pharmacological inhibition of autophagy sensitizes malignant cells to genotoxic therapy both in vitro and in experimental mouse models (Amaravadi et al, 2007; Pan et al, 2011; Chittaranjan et al, 2014; Wang and Wu, 2014; Filippi-Chiela et al, 2015; Liang et al, 2016; Piya et al, 2016). In line with this is the presence of autophagic vacuoles in Saos2 cells ( Figure 2 ), a p53 null human osteosarcoma cell line, which after prolonged expression of p21 WAF1/Cip1 exhibit enhanced aggressiveness and chemoresistance by deregulating the replication licensing machinery causing replication stress and fuelling genomic instability (Galanos et al, 2016).…”