Solid-phase immunoassays in mechanism-based drug discovery: their application in the development of inhibitors of the molecular chaperone heat-shock protein 90

Discovery of a Chemical Probe Bisamide (CCT251236): An Orally Bioavailable Efficacious Pirin Ligand from a Heat Shock Transcription Factor 1 (HSF1) Phenotypic Screen

Phenotypic screens, which focus on measuring and quantifying discrete cellular changes rather than affinity for individual recombinant proteins, have recently attracted renewed interest as an efficient strategy for drug discovery. In this article, we describe the discovery of a new chemical probe, bisamide (CCT251236), identified using an unbiased phenotypic screen to detect inhibitors of the HSF1 stress pathway. The chemical probe is orally bioavailable and displays efficacy in a human ovarian carcinoma xenograft model. By developing cell-based SAR and using chemical proteomics, we identified pirin as a high affinity molecular target, which was confirmed by SPR and crystallography.

Use of pharmacokinetic/pharmacodynamic biomarkers to support rational cancer drug development

The process of drug development in oncology has struggled to alter at a pace in keeping with the rapid discovery and testing of agents that act on a wide variety of molecular targets. The rational development of such agents requires an understanding of drug effect(s) on their purported target. It is likely that testing these drugs in a framework designed to examine cytotoxic agents will fail to establish their full potential. We discuss how data gained from biomarker investigation might impact on drug development and provide examples that highlight the development, validation and use of pharmacokinetic, and especially pharmacodynamic biomarkers as drug development moves from the laboratory into clinical testing. The challenges of performing assays to satisfy regulatory requirements have been the subject of much debate. We recommend the implementation of appropriate, fit-for-purpose biomarkers in clinical trials of all new cancer drugs.

A phase I study of the heat shock protein 90 inhibitor alvespimycin (17-DMAG) given intravenously to patients with advanced solid tumors

PURPOSE

A phase I study to define toxicity and recommend a phase II dose of the HSP90 inhibitor alvespimycin (17-DMAG; 17-dimethylaminoethylamino-17-demethoxygeldanamycin). Secondary endpoints included evaluation of pharmacokinetic profile, tumor response, and definition of a biologically effective dose (BED).

PATIENTS AND METHODS

Patients with advanced solid cancers were treated with weekly, intravenous (i.v.) 17-DMAG. An accelerated titration dose escalation design was used. The maximum tolerated dose (MTD) was the highest dose at which ≤ 1/6 patients experienced dose limiting toxicity (DLT). Dose de-escalation from the MTD was planned with mandatory, sequential tumor biopsies to determine a BED. Pharmacokinetic and pharmacodynamic assays were validated prior to patient accrual.

RESULTS

Twenty-five patients received 17-DMAG (range 2.5-106 mg/m(2)). At 106 mg/m(2) of 17-DMAG 2/4 patients experienced DLT, including one treatment-related death. No DLT occurred at 80 mg/m(2). Common adverse events were gastrointestinal, liver function changes, and ocular. Area under the curve and mean peak concentration increased proportionally with 17-DMAG doses 80 mg/m(2) or less. In peripheral blood mononuclear cells significant (P < 0.05) HSP72 induction was detected (≥ 20 mg/m(2)) and sustained for 96 hours (≥ 40 mg/m(2)). Plasma HSP72 levels were greatest in the two patients who experienced DLT. At 80 mg/m(2) client protein (CDK4, LCK) depletion was detected and tumor samples from 3 of 5 patients confirmed HSP90 inhibition. Clinical activity included complete response (castration refractory prostate cancer, CRPC 124 weeks), partial response (melanoma, 159 weeks), and stable disease (chondrosarcoma, CRPC, and renal cancer for 28, 59, and 76 weeks, respectively).

CONCLUSIONS

The recommended phase II dose of 17-DMAG is 80 mg/m(2) weekly i.v.

Application of meso scale technology for the measurement of phosphoproteins in human tumor xenografts

In this age of molecularly targeted drug discovery, robust techniques are required to measure pharmacodynamic (PD) responses in tumors so that drug exposures can be associated with their effects on molecular biomarkers and efficacy. Our aim was to develop a rapid screen to monitor PD responses within xenografted human tumors as an important step towards a clinically applicable technology. Currently there are various methods available to measure PD end points, including immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction, gene expression profiling, and western blotting. These may require relatively large samples of tumor, surrogate tissue, or peripheral blood lymphocytes with subsequent analyses taking several days. The phosphoinositide 3-kinase (PI3-kinase) pathway is frequently deregulated in cancer and is also important in diabetes and autoimmune conditions. In this paper, optimization of the Meso Scale Discovery (MSD) (Gaithersburg, MD) platform to quantify changes in phospho-AKT and phospho-glycogen synthase kinase-3beta in response to a PI3-kinase inhibitor, LY294002, is described, initially in vitro and then within xenografted solid tumors. This method is highly practical with high throughput since large number of samples can be run simultaneously in 96-well format. The assays are robust (coefficient of variation for phospho-AKT 13.4%) and offer significant advantages (in terms of speed and quantitation) over western blots. This optimized procedure can be used for both in vitro and in vivo analysis, unlike an established fixed-cell ELISA with a time-resolved fluorescent end point.

The heat shock proteins in cellular aging: is zinc the missing link?

T-cell functions are critical for the efficiency of the adaptive immune response. It is now clear that aging is associated with changes in the T-cell response to antigenic stimulation, one of the many changes collectively resulting in immune senescence. Several hypotheses have been proposed to explain such changes. We believe that chronic stimulation of T-cells enhances the appearance of apoptosis-resistant anergic dysfunctional cells; in humans in vivo these are predominantly specific for antigens of persistent viruses, especially CMV. Concomitantly, age-associated zinc deficiency is common and one hypothesis is that lack of zinc bioavailability contributes to impaired T-cell function. This could further compromise the integrity of T-cells under chronic antigenic stress, which can be modelled in long-term clonal cultures in vitro. Newly synthesized heat-shock proteins (HSPs) protect the cellular proteins from degradation under such conditions. In this short review we will briefly outline the role of heat-shock proteins and zinc deficiency in aging in order to finally discuss our own results in the context of a link between HSPs, aging and zinc.

Inhibition of the heat shock protein 90 molecular chaperone in vitro and in vivo by novel, synthetic, potent resorcinylic pyrazole/isoxazole amide analogues

Although the heat shock protein 90 (HSP90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) shows clinical promise, potential limitations encourage development of alternative chemotypes. We discovered the 3,4-diarylpyrazole resorcinol CCT018159 by high-throughput screening and used structure-based design to generate more potent pyrazole amide analogues, exemplified by VER-49009. Here, we describe the detailed biological properties of VER-49009 and the corresponding isoxazole VER-50589. X-ray crystallography showed a virtually identical HSP90 binding mode. However, the dissociation constant (K(d)) of VER-50589 was 4.5 +/- 2.2 nmol/L compared with 78.0 +/- 10.4 nmol/L for VER-49009, attributable to higher enthalpy for VER-50589 binding. A competitive binding assay gave a lower IC(50) of 21 +/- 4 nmol/L for VER-50589 compared with 47 +/- 9 nmol/L for VER-49009. Cellular uptake of VER-50589 was 4-fold greater than for VER-49009. Mean cellular antiproliferative GI(50) values for VER-50589 and VER-49009 for a human cancer cell line panel were 78 +/- 15 and 685 +/- 119 nmol/L, respectively, showing a 9-fold potency gain for the isoxazole. Unlike 17-AAG, but as with CCT018159, cellular potency of these analogues was independent of NAD(P)H:quinone oxidoreductase 1/DT-diaphorase and P-glycoprotein expression. Consistent with HSP90 inhibition, VER-50589 and VER-49009 caused induction of HSP72 and HSP27 alongside depletion of client proteins, including C-RAF, B-RAF, and survivin, and the protein arginine methyltransferase PRMT5. Both caused cell cycle arrest and apoptosis. Extent and duration of pharmacodynamic changes in an orthotopic human ovarian carcinoma model confirmed the superiority of VER-50589 over VER-49009. VER-50589 accumulated in HCT116 human colon cancer xenografts at levels above the cellular GI(50) for 24 h, resulting in 30% growth inhibition. The results indicate the therapeutic potential of the resorcinylic pyrazole/isoxazole amide analogues as HSP90 inhibitors.

A duplexed phenotypic screen for the simultaneous detection of inhibitors of the molecular chaperone heat shock protein 90 and modulators of cellular acetylation

Histone deacetylases (HDACs), histone acetyltransferases (HATs), and the molecular chaperone heat shock protein 90 (HSP90) are attractive anticancer drug targets. High-throughput screening plays a pivotal role in modern molecular mechanism-based drug discovery. Cell-based screens are particularly useful in that they identify compounds that are permeable and active against the selected target or pathway in a cellular context. We have previously developed time-resolved fluorescence cell immunosorbent assays (TRF-Cellisas) for compound screening and pharmacodynamic studies. These assays use a primary antibody to the single protein of interest and a matched secondary immunoglobulin labeled with an europium chelate (Eu). The availability of species-specific secondary antibodies labeled with different lanthanide chelates provides the potential for multiplexing this type of assay. The approach has been applied to the development of a 384-well duplexed cell-based screen to simultaneously detect compounds that induce the co-chaperone HSP70 as a molecular marker of potential inhibitors of HSP90 together with those that modulate cellular acetylation (i.e., potential inhibitors of histone deacetylase or histone acetyltransferase activity). The duplexed assay proved reliable in high-throughput format and approximately 64,000 compounds were screened. Following evaluation in secondary assays, 3 of 13 hits from the HSP70 arm were confirmed. Two of these directly inhibited the intrinsic ATPase activity of HSP90 whereas the third seems to have a different mechanism of action. In the acetylation arm, two compounds increased cellular acetylation, one of which inhibited histone deacetylase activity. A third compound decreased cellular histone acetylation, potentially through a novel mechanism of action.

In vitro Biological Characterization of a Novel, Synthetic Diaryl Pyrazole Resorcinol Class of Heat Shock Protein 90 Inhibitors

The molecular chaperone heat shock protein 90 (HSP90) has emerged as an exciting molecular target. Derivatives of the natural product geldanamycin, such as 17-allylamino-17-demethoxy-geldanamycin (17-AAG), were the first HSP90 ATPase inhibitors to enter clinical trial. Synthetic small-molecule HSP90 inhibitors have potential advantages. Here, we describe the biological properties of the lead compound of a new class of 3,4-diaryl pyrazole resorcinol HSP90 inhibitor (CCT018159), which we identified by high-throughput screening. CCT018159 inhibited human HSP90beta with comparable potency to 17-AAG and with similar ATP-competitive kinetics. X-ray crystallographic structures of the NH(2)-terminal domain of yeast Hsp90 complexed with CCT018159 or its analogues showed binding properties similar to radicicol. The mean cellular GI(50) value of CCT018159 across a panel of human cancer cell lines, including melanoma, was 5.3 mumol/L. Unlike 17-AAG, the in vitro antitumor activity of the pyrazole resorcinol analogues is independent of NQO1/DT-diaphorase and P-glycoprotein expression. The molecular signature of HSP90 inhibition, comprising increased expression of HSP72 protein and depletion of ERBB2, CDK4, C-RAF, and mutant B-RAF, was shown by Western blotting and quantified by time-resolved fluorescent-Cellisa in human cancer cell lines treated with CCT018159. CCT018159 caused cell cytostasis associated with a G(1) arrest and induced apoptosis. CCT018159 also inhibited key endothelial and tumor cell functions implicated in invasion and angiogenesis. Overall, we have shown that diaryl pyrazole resorcinols exhibited similar cellular properties to 17-AAG with potential advantages (e.g., aqueous solubility, independence from NQO1 and P-glycoprotein). These compounds form the basis for further structure-based optimization to identify more potent inhibitors suitable for clinical development.

A Luminescent Oxygen Channeling Immunoassay for the Determination of Insulin in Human Plasma

The authors describe a homogeneous, sensitive, and rapid bead-based sandwich immunoassay with a broad analytical range for quantifying insulin in human plasma. The assay was performed as a 2-step reaction by incubating the sample with a mixture of biotinylated anti-insulin antibody and beads covalently coated with anti-insulin antibody for 1 h. This was followed by incubation with beads covalently coated with streptavidin for 30 min. After the incubation steps, light generated from a chemiluminescent reaction within the beads was quantitated. The assay was run in 384-well plates with a sample volume of 5 μ]L. The analytical range extended from 1 to 10,000 pM. Intra-assay precision (% coefficient of variation) ranged from 1.9% to 3.8% for various insulin concentrations. Interassay precision ranged from 4.6% to 7.3%. Assay detection limit was 0.3 pM. There was no interference from moderate hemolysis (with hemoglobin up to 375 mg/dL), bilirubin (up to at least 50 mg/dL), triglyceride (up to at least 1000 mg/dL), biotin (up to at least 7.7 ng/mL), or ascorbic acid (up to 100 mg/dL). However, gross hemolysis did affect the assay. Comparable results were obtained for plasma (ethylenediamine tetra-acetic acid, citrate, and heparin treated) and serum. The correlation with enzyme-linked immunosorbent assay (ELISA) was good (y = 1.25x + 1.19, R2 = 0.98). This method is convenient and represents an alternative to ELISA.

Drugging the cancer kinome: progress and challenges in developing personalized molecular cancer therapeutics

A major goal of cancer research is to translate our understanding of the causation of malignancy at the level of the genome and biochemical pathways into the development of drugs with improved activity and cancer selectivity. This paper provides a personal perspective of the current status of efforts to achieve this goal, with a particular focus on drugging the cancer kinome. Remarkable progress has been made in this area, but many challenges remain. The value of cancer kinome sequencing is emphasized. Three projects in which the author's laboratory is involved are reviewed in detail. These involve the discovery and development of inhibitors of cyclin-dependent kinases, phosphoinositide 3-kinases, and the Hsp90 molecular chaperone.