title: Cathepsin L inhibition suppresses drug resistance in vitro and in vivo: a putative mechanism.
abstract: Cathepsin L is a lysosomal enzyme thought to play a key role in malignant transformation. Recent work from our laboratory has demonstrated that this enzyme may also regulate cancer cell resistance to chemotherapy. The present study was undertaken to define the relevance of targeting cathepsin L in the suppression of drug resistance in vitro and in vivo and also to understand the mechanism(s) of its action. In vitro experiments indicated that cancer cell adaptation to increased amounts of doxorubicin over time was prevented in the presence of a cathepsin L inhibitor, suggesting that inhibition of this enzyme not only reverses but also prevents the development of drug resistance. The combination of the cathepsin L inhibitor with doxorubicin also strongly suppressed the proliferation of drug-resistant tumors in nude mice. An investigation of the underlying mechanism(s) led to the finding that the active form of this enzyme shuttles between the cytoplasm and nucleus. As a result, its inhibition stabilizes and enhances the availability of cytoplasmic and nuclear protein drug targets including estrogen receptor-alpha, Bcr-Abl, topoisomerase-IIalpha, histone deacetylase 1, and the androgen receptor. In support of this, the cellular response to doxorubicin, tamoxifen, imatinib, trichostatin A, and flutamide increased in the presence of the cathepsin L inhibitor. Together, these findings provided evidence for the potential role of cathepsin L as a target to suppress cancer resistance to chemotherapy and uncovered a novel mechanism by which protease inhibition-mediated drug target stabilization may enhance cellular visibility and, thus, susceptibility to anticancer agents.
authors.affiliation: Department of Pediatrics, Children's Memorial Research Center, Children's Memorial Hospital, Chicago, IL, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zheng
authors.forename: Fei
authors.initials: F
authors.lastname: Chu
authors.forename: Pauline M
authors.initials: PM
authors.lastname: Chou
authors.forename: Christine
authors.initials: C
authors.lastname: Gallati
authors.forename: Usawadee
authors.initials: U
authors.lastname: Dier
authors.forename: Bernard L
authors.initials: BL
authors.lastname: Mirkin
authors.forename: Shaker A
authors.initials: SA
authors.lastname: Mousa
authors.forename: Abdelhadi
authors.initials: A
authors.lastname: Rebbaa
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage; D000951:Antigens, Neoplasm / Q000378:metabolism; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000008:administration & dosage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000008:administration & dosage; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009447:Neuroblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D012516:Osteosarcoma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D055550:Protein Stability; D021381:Protein Transport; D013997:Time Factors
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D000951:Antigens, Neoplasm; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D004317:Doxorubicin; D002403:Cathepsins; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse; D004250:DNA Topoisomerases, Type II