High-Throughput Fluorescence Polarization Method for Identification of FKBP12 Ligands

FKBP12 is best known as the target of the widely used immunosuppressive drug FK506 but may also play a role in neuronal survival. Nonimmunosuppressive ligands of FKBP12 have been shown to have neuroprotective and neuroregenerative activity both in vitro and in vivo, stimulating interest in the development of high-throughput screens to rapidly identify novel ligands. FKBP12 was expressed as a His6-fusion in bacteria and purified by metal ion affinity and gel filtration chromatography. A high-throughput fluorescence polarization assay was developed to identify novel ligands of FKBP12. Dissociation constant values of known FKBP12 ligands measured by the new method agreed closely with Kivalues obtained by assaying inhibition of the rotamase activity of the enzyme. The fluorescence polarization assay is rapid, robust, and inexpensive and does not generate radioactive waste. It is very well suited for high-throughput screening efforts.

2-Aryl-2,2-difluoroacetamide FKBP12 ligands: synthesis and X-ray structural studies

[structure: see text] 2-Aryl-2,2-difluoroacetamido-proline and pipecolate esters are high affinity FKBP12 ligands whose rotamase inhibitory activity is comparable to that seen for the corresponding ketoamides. X-ray structural studies suggest that the fluorine atoms participate in discrete interactions with the Phe36 phenyl ring and the Tyr26 hydroxyl group, with the latter resembling a moderate-to-weak hydrogen bond.

Fluoresceinated FKBP12 ligands for a high-throughput fluorescence polarization assay

Several fluoresceinated FKBP12 ligands have been prepared for a high-throughput fluorescence polarization assay. K(i)s for FKBP12 rotamase inhibition by these ligands range from 1.3 microM to 32 nM, and their design is based on X-ray crystal structures of FKBP12 complexed with known immunophilin ligands.

Induction of cell death by the lysosomotropic detergent MSDH

Controlled lysosomal rupture was initiated in lysosome-rich, macrophage-like cells by the synthetic lysosomotropic detergent, O-methyl-serine dodecylamide hydrochloride (MSDH). When MSDH was applied at low concentrations, resulting in partial lysosomal rupture, activation of pro-caspase-3-like proteases and apoptosis followed after some hours. Early during apoptosis, but clearly secondary to lysosomal destabilization, the mitochondrial transmembrane potential declined. At high concentrations, MSDH caused extensive lysosomal rupture and necrosis. It is suggested that lysosomal proteases, if released to the cytosol, may cause apoptosis directly by pro-caspase activation and/or indirectly by mitochondrial attack with ensuing discharge of pro-apoptotic factors.

Receptor-mediated and enzyme-dependent targeting of cytotoxic anticancer drugs

This review is a survey of various approaches to targeting cytotoxic anticancer drugs to tumors primarily through biomolecules expressed by cancer cells or associated vasculature and stroma. These include monoclonal antibody immunoconjugates; enzyme prodrug therapies, such as antibody-directed enzyme prodrug therapy, gene-directed enzyme prodrug therapy, and bacterial-directed enzyme prodrug therapy; and metabolism-based therapies that seek to exploit increased tumor expression of, e.g., proteases, low-density lipoprotein receptors, hormones, and adhesion molecules. Following a discussion of factors that positively and negatively affect drug delivery to solid tumors, we concentrate on a mechanistic understanding of selective drug release or generation at the tumor site.

Cathepsin B-sensitive dipeptide prodrugs. 1. A model study of structural requirements for efficient release of doxorubicin

A series of lysosomal protease-sensitive peptides attached to doxorubicin (DOX) was prepared as model substrates for internalizing anticancer immunoconjugates and potential antimetastasis prodrugs. Rates of cathepsin B-mediated release of free drug was measured for each, and human plasma stabilities for representative examples.

Cathepsin B-sensitive dipeptide prodrugs. 2. Models of anticancer drugs paclitaxel (Taxol), mitomycin C and doxorubicin

Substrates containing doxorubicin (DOX), paclitaxel (taxol), and mitomycin C (MMC) attached to the cathepsin B-sensitive dipeptide Phe-Lys via a self-immolative spacer were prepared as model compounds for internalizing anticancer immunoconjugates. Cathepsin B-mediated release rates of free drug, rat liver lysosomal susceptibility and human plasma stability were measured for each.

Improved cytotoxicity of antitumor compounds deliverable by the LDL pathway

The concept of LDL-based chemotherapy of cancer is based on the fact that many tumors have high LDL requirements. A series of compounds has been synthesized, some of which meet all criteria for such therapy, i.e., they can be reconstituted with LDL, they do not leak out of the reconstituted LDL (rLDL), and they are potent enough to kill cells exclusively via the LDL receptor pathway. Two of these compounds are significantly superior to the best one from our earlier study [Firestone et al. (1984) J. Med. Chem. 27, 1037-1043], being cytotoxic in rLDL at concentrations reasonably attainable in vivo.

Reversal of doxorubicin resistance and catalytic neutralization of lysosomes by a lipophilic imidazole

A number of lipophilic nitrogenous bases, designed to act as membrane-active, catalytic proton transfer agents, were tested for their ability to neutralize the acidity of lysosomes, a model for other acidic intracellular vesicles involved in drug sorting. The most successful of these, an imidazole 1, caused a 1.7 unit rise in lysosomal pH of RAW cells at 100 microM, compared to a 0.2 and 1.4 unit rise for ammonium chloride at 100 microM and 10 mM, respectively. Compound 1 also exhibited potent reversal of doxorubicin (DOX) resistance in the HCT116-VM46 cell line by a factor of 14 over the sensitive strain, and superior to that of widely used verapamil (VRP) by a factor of 1.75 at 20 microM. It also has antiviral properties, and potential applications in other lysosome-related areas such as immunotoxin potentiation and the control of bacterial toxins, immune response, prion replication, malaria and intralysosomal microorganisms.