Bioanalytical Assay Development and Validation for the Pharmacokinetic Study of GMC1, a Novel FKBP52 Co-chaperone Inhibitor for Castration Resistant Prostate Cancer.

BACKGROUND: GMC1 (2-(1H-benzimidazol-2-ylsulfanyl)-N-[(Z)-(4-methoxyphenyl) methylideneamino] acetamide) effectively inhibits androgen receptor function by binding directly to FKBP52. This is a novel mechanism for the treatment of castration resistant prostate cancer (CRPC). METHODS: an LC-MS/MS method was developed and validated to quantify GMC1 in plasma and urine from pharmacokinetics studies in rats. An ultra-high-performance liquid chromatography (UHPLC) system equipped with a Waters XTerra MS C18 column was used for chromatographic separation by gradient elution with 0.1% (v/v) formic acid in water and methanol. A Sciex 4000 QTRAP® mass spectrometer was used for analysis by multiple reaction monitoring (MRM) in positive mode; the specific ions [M+H]+m/z 340.995 → m/z 191.000 and [M+H]+ m/z 266.013 → m/z 234.000 were monitored for GMC1 and internal standard (albendazole), respectively. RESULTS: GMC1 and albendazole had retention times of 1.68 and 1.66 min, respectively. The calibration curves for the determination of GMC1 in rat plasma and urine were linear from 1-1000 ng/mL. The LC-MS/MS method was validated with intra- and inter-day accuracy and precision within the 15% acceptance limit. The extraction recovery values of GMC1 from rat plasma and urine were greater than 95.0 ± 2.1% and 97.6 ± 4.6%, respectively, with no significant interfering matrix effect. GMC1 is stable under expected sample handling, storage, preparation and LC-MS/MS analysis conditions. CONCLUSIONS: Pharmacokinetic evaluation of GMC1 revealed that the molecule has a biexponential disposition in rats, is distributed rapidly and extensively, has a long elimination half-life, and appears to be eliminated primarily by first order kinetics.

Management of Hsp90-Dependent Protein Folding by Small Molecules Targeting the Aha1 Co-Chaperone.

Hsp90 plays an important role in health and is a therapeutic target for managing misfolding disease. Compounds that disrupt co-chaperone delivery of clients to Hsp90 target a subset of Hsp90 activities, thereby minimizing the toxicity of pan-Hsp90 inhibitors. Here, we have identified SEW04784 as a first-in-class inhibitor of the Aha1-stimulated Hsp90 ATPase activity without inhibiting basal Hsp90 ATPase. Nuclear magnetic resonance analysis reveals that SEW84 binds to the C-terminal domain of Aha1 to weaken its asymmetric binding to Hsp90. Consistent with this observation, SEW84 blocks Aha1-dependent Hsp90 chaperoning activities, including the in vitro and in vivo refolding of firefly luciferase, and the transcriptional activity of the androgen receptor in cell-based models of prostate cancer and promotes the clearance of phosphorylated tau in cellular and tissue models of neurodegenerative tauopathy. We propose that SEW84 provides a novel lead scaffold for developing therapeutic approaches to treat proteostatic disease.

Therapeutic Targeting of the FKBP52 Co-Chaperone in Steroid Hormone Receptor-Regulated Physiology and Disease.

Steroid hormone receptors are ligand-dependent transcription factors that require the dynamic, ordered assembly of multimeric chaperone complexes to reach a functional conformation. Heat shock protein (Hsp) 70 and Hsp90 serve as the central chaperones that mediate this process in conjunction with a variety of co-chaperones. Many of these cochaperones represent potential therapeutic targets for the disruption of Hsp90 client protein function. FKBP52 is an Hsp90-associated co-chaperone that has emerged as a promising therapeutic candidate due to its functional specificity for a small subset of Hsp90 client proteins including androgen (AR), glucocorticoid (GR), and progesterone (PR) receptors. Given its Hsp90-client protein specificity, the targeting of FKBP52 should be more specific and less toxic than the Hsp90- targeting drugs. Additionally, the fkbp52-deficient mice display specific phenotypes related to androgen, progesterone, and glucocorticoid insensitivity suggesting minimal off-target effects. Finally, the fact that FKBP52 is already a validated target of the clinically approved immunosuppressive drug, FK506 (Tacrolimus), indicates that FKBP52 is a "druggable" protein. Thus, the development of FKBP52-specific small molecule inhibitors is predicted to be a highly targeted strategy with potential for the treatment of any disease that is dependent on a functional AR, GR, and/or PR signaling pathway. Much progress has been made in understanding the residues and domains critical for FKBP52 function. The proline-rich loop overhanging the FKBP52 FK1 catalytic domain is functionally important and likely represents an interaction surface within the receptor-chaperone complex. Thus, the targeting of FKBP52 proline-rich loop interactions is the most attractive therapeutic approach to disrupt FKBP52 regulation of receptor activity in steroid hormone receptor-dependent physiology and disease.

Functions of the Hsp90-binding FKBP immunophilins.

Hsp90 functionally interacts with a broad array of client proteins, but in every case examined Hsp90 is accompanied by one or more co-chaperones. One class of co-chaperone contains a tetratricopeptide repeat domain that targets the co-chaperone to the C-terminal region of Hsp90. Within this class are Hsp90-binding peptidylprolyl isomerases, most of which belong to the FK506-binding protein (FKBP) family. Despite the common association of FKBP co-chaperones with Hsp90, it is now clear that the client protein influences, and is influenced by, the particular FKBP bound to Hsp90. Examples include Xap2 in aryl hydrocarbon receptor complexes and FKBP52 in steroid receptor complexes. In this chapter, we discuss the known functional roles played by FKBP co-chaperones and, where possible, relate distinctive functions to structural differences between FKBP members.

A novel dietary-related model of esophagitis and Barrett's esophagus, a premalignant lesion.

Barrett's esophagus (BE) is a premalignant lesion in which columnar epithelium (containing goblet cells) replaces esophageal squamous cells. Previous evidence suggested that hydrophobic bile acids and zinc deficiency each play a role in BE development. We fed wild-type C57BL/6 mice a zinc-deficient diet containing the hydrophobic bile acid, deoxycholic acid for various times up to 152 days. All mice fed this diet developed esophagitis by 69 days on the diet and 63% of the mice on this diet for 88 to 152 days also developed a BE-like lesion. Esophageal tissues showed thickened mucosa, increased proliferation, and increased expression of markers associated with oxidative and nitrosative stress. The newly formed BE-like lesions expressed Mucin-2, a marker of columnar differentiation. They also showed translocation of the p65 subunit of nuclear factor-kappaB and beta -catenin to the nucleus and typical histological changes associated with BE lesions. This mouse model of esophagitis and BE is expected to contribute to a deeper understanding of BE pathogenesis and to strategies for prevention of BE progression to cancer.