Current Cancer Drug Targets

Ruiwen Zhang 
Texas Tech University Health Sciences Center
1300 Coulter Drive
Amarillo, TX 79106
USA

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Targeting Urokinase and the Transferrin Receptor with Novel, Anti-Mitotic N-Alkylisatin Cytotoxin Conjugates Causes Selective Cancer Cell Death and Reduces Tumor Growth

Author(s): K. L. Vine, V. Indira Chandran, J. M. Locke, L. Matesic, J. Lee, D. Skropeta, J. B. Bremner, M. Ranson.

Abstract:

Tumor-specific delivery of ligand-directed prodrugs can increase the therapeutic window of chemotherapeutics by maintaining efficacy whilst decreasing toxic side effects. We have previously described a series of synthetic Nalkylated isatin cytotoxins that destabilize microtubules and induce apoptosis with 10-fold greater potency than conventional anti-mitotics in vitro. Here, we report the characterization, in vitro cytotoxicity and in vivo efficacy of a lead compound, 5,7-dibromo-N-(p-hydroxymethylbenzyl)isatin (N-AI) conjugated via an esterase-labile linker (N-AIE) to two proven targeting ligands, transferrin (Tf) and plasminogen activator inhibitor type 2 (PAI-2/serpinB2). N-AI was released from N-AIE and the targeting ligands Tf/PAI-2 in an esterase-dependent manner at 37 °C and both Tf- and PAI-2-N-AIE conjugates were stable at physiological pH. Human cancer cell lines which vary in their expression levels of Tf receptor (TfR/CD71) and PAI-2 target, receptor bound urokinase (uPA) selectively internalized the conjugates. Tf-N-AIE was up to 24 times more active than the free drug and showed clear selectivity patterns based on TfR levels. PAI-2-N-AIE showed equivalent activity compared to the parent drug and strong selectivity patterns for uPA levels. In preliminary in vivo experiments, the PAI-2- and Tf-N-AIE conjugates were efficacious at 1/20th and 1/10th of the dose of the free N-AI, respectively, in a metastatic, orthotopic human breast tumor xenograft mouse model. Thus, this strategy specifically delivers and concentrates a novel class of isatin-based, tubulin destabilizing agents to tumors in vivo and warrants further detailed preclinical investigation.

Keywords: Anti-cancer prodrugs, N-alkylisatin, PAI-2/SerpinB2, selective delivery, transferring, bovine serum albumin, mean florescent intensity, mode of action, propidium iodide, receptor mediated endocytosis, quadrupole time of flight

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Article Details

VOLUME: 12
ISSUE: 1
Year: 2012
Page: [64 - 73]
Pages: 10
DOI: 10.2174/156800912798888983