title: In vitro cytotoxicity of bismuth-213 (213Bi)-labeled-plasminogen activator inhibitor type 2 (alpha-PAI-2) on human breast cancer cells.
abstract: Metastasis is the principal cause of death in breast cancer patients. New and improved treatments for eradicating micrometastases are needed. To this end, a novel alpha-emitting protein construct, 213Bi-labelled plasminogen activator inhibitor type-2 (PAI-2) (alpha-PAI-2), was evaluated in vitro. This construct exploits: (a) the overexpression of the cell-surface receptor bound urokinase plasminogen activator (uPA) in the metastatic spread of breast cancer cells; (b) the binding and inhibition of receptor-bound uPA by PAI-2; and (c) the high cytotoxicity of alpha radiation. High labeling efficiencies and stability of 213Bi bound to human recombinant PAI-2 conjugated with cyclic diethylenetriaminepentaacetic acid anhydride were achieved (greater than 90%). The uPA inhibitory activity of the chelated PAI-2 was maintained as determined by complex formation with uPA and by inhibition of uPA activity. Furthermore, the reactivity of alpha-PAI-2 was confirmed in a cell assay as this construct was highly cytotoxic to breast cancer cell lines that express active, receptor bound uPA. The specificity of alpha-PAI-2 targeting was shown using several controls. Firstly, an active uPA blocking agent that limits PAI-2 binding significantly improved cell survival by a factor greater than three. Secondly, a non-specific alpha-BSA construct had minimal cytotoxic effect. Moreover, alpha-PAI-2 was not cytotoxic to freshly isolated normal human leukocytes, confirming that cells which do not contain active, receptor bound uPA cannot be targeted by alpha-PAI-2. In conclusion, we have validated, in vitro, the potential of alpha-PAI-2 as a novel therapeutic agent for breast cancer.
authors.affiliation: Department of Biological Science, University of Wollongong, Kogarah, NSW, Australia. marieranson@uow.edu.au
authors.forename: M
authors.initials: M
authors.lastname: Ranson
authors.forename: Z
authors.initials: Z
authors.lastname: Tian
authors.forename: N M
authors.initials: NM
authors.lastname: Andronicos
authors.forename: S
authors.initials: S
authors.lastname: Rizvi
authors.forename: B J
authors.initials: BJ
authors.lastname: Allen
mesh_terms: D001729:Bismuth / Q000633:toxicity*; D001943:Breast Neoplasms; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects*; D005260:Female; D006801:Humans; D007700:Kinetics; D009362:Neoplasm Metastasis; D004369:Pentetic Acid / Q000633:toxicity; D017396:Plasminogen Activator Inhibitor 2 / Q000633:toxicity*; D011868:Radioisotopes; D011994:Recombinant Proteins / Q000633:toxicity; D014407:Tumor Cells, Cultured
chemical_list: D017396:Plasminogen Activator Inhibitor 2; D011868:Radioisotopes; D011994:Recombinant Proteins; D004369:Pentetic Acid; D001729:Bismuth