title: Chloroquine sensitizes breast cancer cells to chemotherapy independent of autophagy.
abstract: Chloroquine (CQ) is a 4-aminoquinoline drug used for the treatment of diverse diseases. It inhibits lysosomal acidification and therefore prevents autophagy by blocking autophagosome fusion and degradation. In cancer treatment, CQ is often used in combination with chemotherapeutic drugs and radiation because it has been shown to enhance the efficacy of tumor cell killing. Since CQ and its derivatives are the only inhibitors of autophagy that are available for use in the clinic, multiple ongoing clinical trials are currently using CQ or hydroxychloroquine (HCQ) for this purpose, either alone, or in combination with other anticancer drugs. Here we show that in the mouse breast cancer cell lines, 67NR and 4T1, autophagy is induced by the DNA damaging agent cisplatin or by drugs that selectively target autophagy regulation, the PtdIns3K inhibitor LY294002, and the mTOR inhibitor rapamycin. In combination with these drugs, CQ sensitized to these treatments, though this effect was more evident with LY294002 and rapamycin treatment. Surprisingly, however, in these experiments CQ sensitization occurred independent of autophagy inhibition, since sensitization was not mimicked by Atg12, Beclin 1 knockdown or bafilomycin treatment, and occurred even in the absence of Atg12. We therefore propose that although CQ might be helpful in combination with cancer therapeutic drugs, its sensitizing effects can occur independently of autophagy inhibition. Consequently, this possibility should be considered in the ongoing clinical trials where CQ or HCQ are used in the treatment of cancer, and caution is warranted when CQ treatment is used in cytotoxic assays in autophagy research.
authors.affiliation: Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, USA.
authors.forename: Paola
authors.initials: P
authors.lastname: Maycotte
authors.forename: Suraj
authors.initials: S
authors.lastname: Aryal
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Cummings
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Thorburn
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Morgan
authors.forename: Andrew
authors.initials: A
authors.lastname: Thorburn
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D001343:Autophagy / Q000187:drug effects*; D000071192:Autophagy-Related Protein 12; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002738:Chloroquine / Q000494:pharmacology* / Q000627:therapeutic use*; D002867:Chromones / Q000494:pharmacology; D002945:Cisplatin / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D018942:Macrolides / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D013217:Starvation
chemical_list: D000970:Antineoplastic Agents; C491971:Atg12 protein, mouse; D000071192:Autophagy-Related Protein 12; D002867:Chromones; D018942:Macrolides; D009025:Morpholines; D011506:Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D002738:Chloroquine; C040929:bafilomycin A1; D002945:Cisplatin; D020123:Sirolimus