Low molecular weight, high affinity ligand based drug delivery and diagnostic systems
Abstract
Although widely accepted in both the chemotherapeutic and diagnostic fields, antibody based ligands suffer from several major drawbacks including: high cost, poor tumor penetration, immunogenicity, and loss in specificity due to constantly evolving highly mutable, cell surface characteristics. To circumvent these challenges, numerous high affinity, low molecular weight ligands have been identified for both eukaryotic (e.g. mammalian cancer cells) and prokaryotic cells (e.g. bacterial cells). Although promising, there still remains a paucity of clinically approved drugs and diagnostic systems that have incorporated these ligands. In this work, we describe the use of several high affinity, low molecular ligands for the development of 1) targeted cancer chemotherapeutics 2) cancer marker detection platforms and 3) bacterial detection systems. First, a folate receptor targeted camptothecin prodrug was synthesized using a hydrophilic peptide spacer linked to folate via a releasable disulfide carbonate linker. The conjugate was found to possess high affinity for folate receptor-expressing cancer cells and inhibited cell proliferation in human KB caner cells with an IC50 of 10 nM. Activity of the prodrug was completely blocked by excess folic acid, demonstrating receptor-mediated uptake. Second, using the same general folate ligand strategy, we developed a quartz crystal microbalance (QCM) biosensor for detection of folate binding protein (a potential cancer marker) at clinically relevant concentrations. Third, we have incorporated these basic principles learned from eukaryotic systems for the detection of pathogenic organisms. A label free, direct capture based method for the detection of whole Bacillus spores (the causative agent of anthrax) using peptide functionalized microcantilever arrays was demonstrated. This is the first reported detection of a whole organism with a cantilever based system via low molecular weight, high affinity ligands. Additionally, we report the development of a pyoverdine siderophore (high affinity iron acquisition molecule secreted by bacteria) based reporter conjugate for the detection of pathogenic Pseudomonas using a commercially available flow cytometer. Given the current paradigm of "smart" or targeted drugs and their accompanying diagnostic systems, the incorporation of high affinity, low molecular weight ligands that can improve upon or augment current antibody based systems will undoubtedly be of importance.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Microbiology|Analytical chemistry
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