title: Application of a proapoptotic peptide to intratumorally spreading cancer therapy.
abstract: Bit1 is a proapoptotic mitochondrial protein associated with anoikis. Upon cell detachment, Bit1 is released into the cytoplasm and triggers caspase-independent cell death. Bit1 consists of 179 amino acids; for the C-terminal, two thirds of the molecule functions as a peptidyl-tRNA hydrolase, whereas the N-terminus contains a mitochondrial localization signal. Here, we localize the cell death domain (CDD) to the N-terminal 62 amino acids of Bit1 by transfecting cells with truncated Bit1 cDNA constructs. CDD was more potent in killing cells than the full-length Bit1 protein when equivalent amounts of cDNA were transfected. To develop Bit1 CDD into a cancer therapeutic, we engineered a recombinant protein consisting of the CDD fused to iRGD, which is a tumor-specific peptide with unique tumor-penetrating and cell-internalizing properties. iRGD-CDD internalized into cultured tumor cells through a neuropilin-1-activated pathway and triggered cell death. Importantly, iRGD-CDD spread extensively within the tumor when injected intratumorally into orthotopically implanted breast tumors in mice. Repeated treatment with iRGD-CDD strongly inhibited tumor growth, resulting in an average reduction of 77% in tumor volume and eradication of some tumors. The caspase independence of Bit1-induced cell death makes CDD a potentially attractive anticancer agent, because tumor resistance to the main mechanisms of apoptosis is circumvented. Using iRGD to facilitate the spreading of a therapeutic agent throughout the tumor mass may be a useful adjunct to local therapy for tumors that are surgically inoperable or difficult to treat systemically.
authors.affiliation: Center for Nanomedicine, Sanford-Burnham Medical Research Institute, University of California, Santa Barbara, CA, USA.
authors.forename: Renwei
authors.initials: R
authors.lastname: Chen
authors.forename: Gary B
authors.initials: GB
authors.lastname: Braun
authors.forename: Xiuquan
authors.initials: X
authors.lastname: Luo
authors.forename: Kazuki N
authors.initials: KN
authors.lastname: Sugahara
authors.forename: Tambet
authors.initials: T
authors.lastname: Teesalu
authors.forename: Erkki
authors.initials: E
authors.lastname: Ruoslahti
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000628:therapy*; D039942:Neuropilin-1 / Q000378:metabolism; D009842:Oligopeptides / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D014162:Transfection; D023041:Xenograft Model Antitumor Assays / Q000379:methods
chemical_list: D024101:Mitochondrial Proteins; C569656:N-end cysteine peptide tumor-homing peptide; D009842:Oligopeptides; D010455:Peptides; D011993:Recombinant Fusion Proteins; D039942:Neuropilin-1; D002265:Carboxylic Ester Hydrolases; C483418:PTH2 protein, human