title: Comparative toxicity and efficacy of engineered anthrax lethal toxin variants with broad anti-tumor activities.
abstract: We have previously designed and characterized versions of anthrax lethal toxin that are selectively cytotoxic in the tumor microenvironment and which display broad and potent anti-tumor activities in vivo. Here, we have performed the first direct comparison of the safety and efficacy of three engineered anthrax lethal toxin variants requiring activation by either matrix-metalloproteinases (MMPs), urokinase plasminogen activator (uPA) or co-localized MMP/uPA activities. C57BL/6J mice were challenged with six doses of engineered toxins via intraperitoneal (I.P.) or intravenous (I.V.) dose routes to determine the maximum tolerated dose for six administrations (MTD6) and dose-limiting toxicities. Efficacy was evaluated using the B16-BL6 syngraft model of melanoma; mice bearing established tumors were treated with six I.P. doses of toxin and tumor measurements and immunohistochemistry, paired with terminal blood work, were used to elaborate upon the anti-tumor mechanism and relative efficacy of each variant. We found that MMP-, uPA- and dual MMP/uPA-activated anthrax lethal toxins exhibited the same dose-limiting toxicity; dose-dependent GI toxicity. In terms of efficacy, all three toxins significantly reduced primary B16-BL6 tumor burden, ranging from 32% to 87% reduction, and they also delayed disease progression as evidenced by dose-dependent normalization of blood work values. While target organ toxicity and effective doses were similar amongst the variants, the dual MMP/uPA-activated anthrax lethal toxin exhibited the highest I.P. MTD6 and was 1.5-3-fold better tolerated than the single MMP- and uPA-activated toxins. Overall, we demonstrate that this dual MMP/uPA-activated anthrax lethal toxin can be administered safely and is highly effective in a preclinical model of melanoma. This modified bacterial cytotoxin is thus a promising candidate for further clinical development and evaluation for use in treating human cancers.
authors: Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA; Program of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA.
authors: Diane E
authors: DE
authors: Peters
authors: Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
authors: Benjamin
authors: B
authors: Hoover
authors: Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA.
authors: Loretta Grey
authors: LG
authors: Cloud
authors: Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
authors: Shihui
authors: S
authors: Liu
authors: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA.
authors: Alfredo A
authors: AA
authors: Molinolo
authors: Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
authors: Stephen H
authors: SH
authors: Leppla
authors: Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA. Electronic address: thomas.bugge@nih.go.
authors: Thomas H
authors: TH
authors: Bugge
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D001427:Bacterial Toxins / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D014408:Biomarkers, Tumor / Q000097:blood; D004305:Dose-Response Relationship, Drug; D005260:Female; D007274:Injections, Intraperitoneal; D007275:Injections, Intravenous; D020782:Matrix Metalloproteinases / Q000378:metabolism; D020714:Maximum Tolerated Dose; D008546:Melanoma, Experimental / Q000097:blood / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D011355:Prodrugs / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D015202:Protein Engineering; D012878:Skin Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D013997:Time Factors; D047368:Tumor Burden / Q000187:drug effects; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D000970:Antineoplastic Agents; D001427:Bacterial Toxins; D014408:Biomarkers, Tumor; D011355:Prodrugs; C030325:anthrax toxin; D014568:Urokinase-Type Plasminogen Activator; D020782:Matrix Metalloproteinases
keywords: Bacterial cytotoxin; Cancer; Melanoma; Prodrug; Protease