Selective MCL-1 inhibitor ABBV-467 is efficacious in tumor models but is associated with cardiac troponin increases in patients

BACKGROUND

MCL-1 is a prosurvival B-cell lymphoma 2 family protein that plays a critical role in tumor maintenance and survival and can act as a resistance factor to multiple anticancer therapies. Herein, we describe the generation and characterization of the highly potent and selective MCL-1 inhibitor ABBV-467 and present findings from a first-in-human trial that included patients with relapsed/refractory multiple myeloma (NCT04178902).

METHODS

Binding of ABBV-467 to human MCL-1 was assessed in multiple cell lines. The ability of ABBV-467 to induce tumor growth inhibition was investigated in xenograft models of human multiple myeloma and acute myelogenous leukemia. The first-in-human study was a multicenter, open-label, dose-escalation study assessing safety, pharmacokinetics, and efficacy of ABBV-467 monotherapy.

RESULTS

Here we show that administration of ABBV-467 to MCL-1-dependent tumor cell lines triggers rapid and mechanism-based apoptosis. In vivo, intermittent dosing of ABBV-467 as monotherapy or in combination with venetoclax inhibits the growth of xenografts from human hematologic cancers. Results from a clinical trial evaluating ABBV-467 in patients with multiple myeloma based on these preclinical data indicate that treatment with ABBV-467 can result in disease control (seen in 1 patient), but may also cause increases in cardiac troponin levels in the plasma in some patients (seen in 4 of 8 patients), without other corresponding cardiac findings.

CONCLUSIONS

The selectivity of ABBV-467 suggests that treatment-induced troponin release is a consequence of MCL-1 inhibition and therefore may represent a class effect of MCL-1 inhibitors in human patients.

In-vitro modeling of intravenous drug precipitation by the optical spatial precipitation analyzer (OSPREY)

Intravenous (IV) administration of poorly water-soluble small molecule therapeutics can lead to precipitation during mixing with blood. This can limit characterization of pharmacological and safety endpoints in preclinical models. Most often, tests of kinetic and thermodynamic solubility are used to optimize the formulation for solubility prior to infusion in animals, but these do not capture the dynamic precipitation processes that take place during in-vivo administration. To better capture the fluid dynamic processes that occur during IV administration, we developed the Optical Spatial PREcipitation analYzer (OSPREY) as a method to quantify the amount and size of compound precipitates in whole blood using a flow-through system that mimics IV administration. Here, we describe the OSPREY device and its underlying imaging processing methods. We then validate the ability to accurately segment particles according to their size using monodisperse suspensions of microspheres (diameter 50 to 425 µm). Next, we use a tool compound, ABT-737, to study the effects of compound concentration, vessel flow rate, compound infusion rate and vessel diameter on precipitation. Finally, we use the physiological diameter and flow rate of rat femoral vein and dog saphenous vein to demonstrate the potential of OSPREY to model in-vivo precipitation in a controlled, dynamic in-vitro assay.

Drug-induced QT prolongation: Concordance of preclinical anesthetized canine model in relation to published clinical observations for ten CiPA drugs

INTRODUCTION

The Comprehensive In Vitro Proarrhythmia Assay (CiPA) initiative differentiates torsadogenic risk of 28 drugs affecting ventricular repolarization based on multiple in vitro human derived ionic currents. However, a standardized prospective assessment of the electrophysiologic effects of these drugs in an integrated in vivo preclinical cardiovascular model is lacking. This study questioned whether QTc interval prolongation in a preclinical in vivo model could detect clinically reported QTc prolongation and assign torsadogenic risk for ten CiPA drugs.

METHODS

An acute intravenous administered ascending dose anesthetized dog cardiovascular model was used to assess QTc prolongation along with other electrocardiographic (PR, QRS intervals) and hemodynamic (heart rate, blood pressures, left ventricular contractility) parameters at plasma concentrations spanning and exceeding clinical exposures. hERG current block potency was characterized using IC₅₀ values from automated patch clamp.

RESULTS

All eight drugs eliciting clinical QTc prolongation also delayed repolarization in anesthetized dogs at plasma concentrations within four-fold clinical exposures. In vitro QTc safety margins (defined based on clinical C_max values/plasma concentrations eliciting statistically significant QTc prolongation in dogs) were lower for high vs intermediate torsadogenic risk drugs. In comparison, hERG IC₁₀ values represented as total drug concentrations were better predictors of preclinical QTc prolongation than hERG IC₅₀ values.

CONCLUSION

There was good concordance for QTc prolongation in the anesthetized dog model and clinical torsadogenic risk assignment. QTc assessment in the anesthetized dog remains a valuable part of a more comprehensive preclinical integrated risk assessment for delayed repolarization and torsadogenic risk as part of a global cardiovascular evaluation.

Author Correction: Discovery of a selective catalytic p300/CBP inhibitor that targets lineage-specific tumours

In the originally published version of this Letter, the authors Arthur F. Kluge, Michael A. Patane and Ce Wang were inadvertently omitted from the author list. Their affiliations are: I-to-D, Inc., PO Box 6177, Lincoln, Massachusetts 01773, USA (A.F.K.); Mitobridge, Inc. 1030 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA (M.A.P.); and China Novartis Institutes for BioMedical Research, No. 4218 Jinke Road, Zhangjiang Hi-Tech Park, Pudong District, Shanghai 201203, China (C.W.). These authors contributed to the interpretation of results and design of compounds. In addition, author 'Edward A. Kesicki' was misspelled as 'Ed Kesicki'. These errors have been corrected online.

Abstract LB-A23: Discovery of a potent catalytic p300/CBP inhibitor that targets lineage-specific tumors

The dynamic and reversible acetylation of proteins catalyzed by histone acetyltransferases (HATs) and histone deacetylases (HDACs) is a major epigenetic regulatory mechanism of gene transcription associated with multiple diseases. While HDAC inhibitors are approved to treat certain cancers, progress on the development of drug-like HAT inhibitors has lagged. The HAT paralogs p300 and CBP (p300/CBP) are key transcriptional co-activators essential for a multitude of cellular processes and also implicated in human pathological conditions, including cancer. Current p300/CBP HAT domain inhibitors including natural products, bi-substrate analogs (Lys-CoA) and the widely utilized C646 lack potency or selectivity. Here, we describe A-485, a potent, selective and drug-like p300/CBP catalytic inhibitor. We show the first high resolution (1.95Å) co-crystal structure of a small molecule bound to the catalytic active site of p300 and demonstrate that A-485 is acetyl-CoA competitive. A-485 selectively inhibited proliferation across lineage-specific tumor types, including several hematological malignancies and androgen receptor-positive prostate cancer. A-485 inhibited the androgen receptor transcriptional program in both androgen sensitive and castrate resistant prostate cancer and inhibited tumor growth in a castration resistant xenograft model. These results demonstrate the feasibility of selectively targeting the catalytic activity of histone acetyltransferases.

Citation Format: Kenneth D. Bromberg, Loren M. Lasko, Clarissa G. Jakob, Wei Qiu, Debra Montgomery, Enrico L. Digiammarino, Todd M. Hansen, Roberto M. Risi, Robin R. Frey, Vlasios Manaves, Bailin Shaw, Mikkel Algire, Paul Hessler, Lloyd T. Lam, Tamar Uziel, Emily Favire, Debra Ferguson, Fritz G. Buchanan, Ruth L. Martin, Maricel Torrent, Saul H. Rosenberg, Michael R. Michaelides, Albert Lai. Discovery of a potent catalytic p300/CBP inhibitor that targets lineage-specific tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-A23.

Utility of hERG Assays as Surrogate Markers of Delayed Cardiac Repolarization and QT Safety

HERG (human-ether-a-go-go-related gene) encodes for a cardiac potassium channel that plays a critical role in defining ventricular repolarization. Noncardiovascular drugs associated with a rare but potentially lethal ventricular arrhythmia (Torsades de Pointes) have been linked to delayed cardiac repolarization and block of hERG current. This brief overview will discuss the role of hERG current in cardiac electrophysiology, its involvement in drug-induced delayed repolarization, and approaches used to define drug effects on hERG current. In addition, examples of hERG blocking drugs acting differently (i.e., overt and covert hERG blockade due to multichannel block) together with the utility and limitations of hERG assays as tools to predict the risk of delayed repolarization and proarrhythmia are discussed.

Negative inotropic effect of a CB2 agonist A-955840 in isolated rabbit ventricular myocytes is independent of CB1 and CB2 receptors

A-955840, a selective CB2 agonist, has been shown to elicit concentration-dependent decreases in cardiac contractility in the anesthetized dog (decreased maximal velocity of left ventricular pressure development [LV dP/dt max]). However, it is unknown whether this represents a direct effect or a response dependent on other factors (such as autonomic tone and neurohumoral factors) present in vivo. This study examined if A-955840 had a direct effect on contractility of isolated cardiac myocytes, and if so to determine the potential mechanisms. Contractility was assessed in vitro using percent changes in maximal shortening velocity of sarcomeres (dL/dt max) and fractional shortening of sarcomere length (FS) in rabbit left ventricular myocytes. L-type calcium current in myocytes was recorded using wholecell voltage-clamp techniques. A-955840 reduced dL/dt max and FS in a reversible and concentration-dependent manner with an IC50 of 11.4 μg/mL (based on dL/dt max) which is similar to the estimated IC50 value of 9.8 μg/mL based on the effects of A-955840 on LV dP/dt max in anesthetized dogs. A-955840 (4.1 μg/mL) reduced myocyte contractility (%FS) to a similar extent in the absence and presence of a CB2 antagonist, SR-2 (24.0 ± 3.4 vs 23.1 ± 3.0 %, n=5) or a CB1 antagonist, Rimonabant (18.8 ± 2.3 vs 19.8 ± 2.7 %, n=5). A-955840 (4.1 μg/mL) also reduced L-type calcium current of rabbit ventricular myocytes (1.05 ± 0.11 vs 0.70 ± 0.12 nA, n=5, P < 0.01). These results suggest that A-955840 exerts direct negative inotropic effects on isolated rabbit ventricular myocytes, which is mediated by neither CB2 nor CB1 receptors, and consistent with off-target negative inotropy mediated by inhibition of the cardiac L-type calcium current.

Characterization of A-935142, a hERG enhancer, in the presence and absence of standard hERG blockers

AIMS

In a previous study we found that A-935142 enhanced hERG current in a concentration-dependent manner by facilitating activation, reducing inactivation, and slowing deactivation (Su et al., 2009). A-935142 also shortened action potential duration (APD90) in canine Purkinje fibers and guinea pig atrial tissue. This study focused on the combined effects of the prototypical hERG enhancer, A-935142 and two hERG current blockers (sotalol and terfenadine).

MAIN METHODS

The whole-cell voltage clamp method with HEK 293 cells heterologously expressing the hERG channel (Kv 11.1) was used.

KEY FINDINGS

A-935142 did not compete with 3H-dofetilide binding, suggesting that A-935142 does not overlap the binding site of typical hERG blockers. In whole-cell voltage clamp studies we found: 1) 60 μM A-935142 enhanced hERG current in the presence of 150 μM sotalol (57.5±5.8%) to a similar extent as seen with A-935142 alone (55.6±5.1%); 2) 150 μM sotalol blocked hERG current in the presence of 60 μM A-935142 (43.5±1.5%) to a similar extent as that seen with sotalol alone (42.0±3.2%) and 3) during co-application, hERG current enhancement was followed by current blockade. Similar results were obtained with 60 nM terfenadine combined with A-935142.

SIGNIFICANCE

These results suggest that the hERG enhancer, A-935142 does not compete with these two known hERG blockers at their binding site within the hERG channel. This selective hERG current enhancement may be useful as a treatment for inherited or acquired LQTS (Casis et al., 2006).

Abstract C202: Discovery and initial characterization of the clinical compound ABT-348, a potent inhibitor of the VEGF, PDGF, and Aurora kinase families

The Aurora kinases are a family of serine/threonine kinases that mediate multiple events in cell division. Humans have three Aurora kinases, A, B and C, that are differentially localized and mediate distinct functions during mitosis. Because the Aurora kinases play a key role in mitosis and are overexpressed in multiple human tumor types, there has been considerable interest in developing Aurora kinase inhibitors as antitumor agents. A number of small-molecule Aurora kinase inhibitors have been reported and there are several compounds currently in Phase I/II clinical trials for cancer. ABT-348 is a novel, potent and orally bioavailable inhibitor of the Aurora kinases as well as the VEGF and PDGF families of receptor tyrosine kinases and is currently in Phase I clinical trials. Herein we describe the discovery and preparation of this molecule including the SAR work that provided improved Aurora kinase potency, aqueous solubility and oral bioavailability with reduced hERG and CYP liabilities relative to earlier analogs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C202.

A novel secretagogue increases cardiac contractility by enhancement of L-type Ca2+ current

N'1-(3,3,6,8-tetramethyl-1-oxo-1,2,3,4-tetrahydronaphthalen-2-yliden)-2-cyanoethanohydrazide (TTYC) increases secretion of glucagon-like peptide-1 and intracellular Ca(2+) concentration in GLUTag cells. The purpose of the present study was to examine if TTYC exerts positive inotropic effects on isolated rabbit ventricular myocytes and in vivo heart in anesthetized rats, and if so to further define the potential mechanism of action. Contractility was assessed in vitro using changes in fractional shortening (FS) of myocyte sarcomere length and in vivo using changes in the velocity of left ventricular pressure. Changes in L-type Ca(2+) current of ventricular myocytes were evaluated using whole-cell voltage-clamp techniques. TTYC increased FS of myocyte sarcomere length in a concentration-dependent manner. The positive inotropic effect was not abrogated by beta-adrenergic blockade (propranolol) or protein kinase A inhibition. TTYC enhanced peak L-type Ca(2+) current in a voltage-dependent manner (current amplitudes increased by 4.0-fold at -10 mV and 1.5-fold at +10 mV). Voltage-dependence of steady-state activation of L-type Ca(2+) current was shifted by 15 mV in the negative direction. Inactivation time course of the L-type Ca(2+) currents at voltages of -10 to 20 mV was significantly slowed by 0.3 microM TTYC. In vivo studies demonstrated that TTYC increased cardiac contractility in a dose-dependent manner. In conclusion, TTYC is a novel L-type Ca(2+) current activator with positive cardiac inotropic effects. Negative shifting of the voltage-dependence of L-type Ca(2+) current activation and reduced inactivation are two mechanisms responsible for the enhanced L-type Ca(2+) current that contribute to the positive inotropic effects.

Morphology effectively controls singlet-triplet exciton relaxation and charge transport in organic semiconductors

We present a comparative study of ultrafast photoconversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photoinduced absorption in Tc and Pc crystals is activated and temperature-independent, respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as C60-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.

Preclinical characterization of A-582941: a novel alpha7 neuronal nicotinic receptor agonist with broad spectrum cognition-enhancing properties

Among the diverse sets of nicotinic acetylcholine receptors (nAChRs), the alpha7 subtype is highly expressed in the hippocampus and cortex and is thought to play important roles in a variety of cognitive processes. In this review, we describe the properties of a novel biaryl diamine alpha7 nAChR agonist, A-582941. A-582941 was found to exhibit high-affinity binding and partial agonism at alpha7 nAChRs, with acceptable pharmacokinetic properties and excellent distribution to the central nervous system (CNS). In vitro and in vivo studies indicated that A-582941 activates signaling pathways known to be involved in cognitive function such as ERK1/2 and CREB phosphorylation. A-582941 enhanced cognitive performance in behavioral models that capture domains of working memory, short-term recognition memory, memory consolidation, and sensory gating deficit. A-582941 exhibited a benign secondary pharmacodynamic and tolerability profile as assessed in a battery of assays of cardiovascular, gastrointestinal, and CNS function. The studies summarized in this review collectively provide preclinical validation that alpha7 nAChR agonism offers a mechanism with potential to improve cognitive deficits associated with various neurodegenerative and psychiatric disorders.

Functional consequences of methionine oxidation of hERG potassium channels

Reactive species oxidatively modify numerous proteins including ion channels. Oxidative sensitivity of ion channels is often conferred by amino acids containing sulfur atoms, such as cysteine and methionine. Functional consequences of oxidative modification of methionine in human ether à go-go related gene 1 (hERG1), which encodes cardiac I(Kr) channels, are unknown. Here we used chloramine-T (ChT), which preferentially oxidizes methionine, to examine the functional consequences of methionine oxidation of hERG channels stably expressed in a human embryonic kidney cell line (HEK 293) and native hERG channels in a human neuroblastoma cell line (SH-SY5Y). ChT (300 microM) significantly decreased whole-cell hERG current in both HEK 293 and SH-SY5Y cells. In HEK 293 cells, the effects of ChT on hERG current were time- and concentration-dependent, and were markedly attenuated in the presence of enzyme methionine sulfoxide reductase A that specifically repairs oxidized methionine. After treatment with ChT, the channel deactivation upon repolarization to -60 or -100 mV was significantly accelerated. The effect of ChT on channel activation kinetics was voltage-dependent; activation slowed during depolarization to +30 mV but accelerated during depolarization to 0 or -10mV. In contrast, the reversal potential, inactivation kinetics, and voltage-dependence of steady-state inactivation remained unaltered. Our results demonstrate that the redox status of methionine is an important modulator of hERG channel.

Syntheses of Potent, Selective, and Orally Bioavailable Indazole-Pyridine Series of Protein Kinase B/Akt Inhibitors with Reduced Hypotension

Compound 7 was identified as a potent (IC50 = 14 nM), selective, and orally bioavailable (F = 70% in mouse) inhibitor of protein kinase B/Akt. While promising efficacy was observed in vivo, this compound showed effects on depolarization of Purkinje fibers in an in vitro assay and CV hypotension in vivo. Guided by an X-ray structure of 7 bound to protein kinase A, which has 80% homology with Akt in the kinase domain, our efforts have focused on structure-activity relationship (SAR) studies of the phenyl moiety, in an attempt to address the cardiovascular liability and further improve the Akt potency. A novel and efficient synthetic route toward diversely substituted phenyl derivatives of 7 was developed utilizing a copper-mediated aziridine ring-opening reaction as the key step. To improve the selectivity of these Akt inhibitors over other protein kinases, a nitrogen atom was incorporated into selected phenyl analogues of 7 at the C-6 position of the methyl indazole scaffold. These modifications resulted in the discovery of inhibitor 37c with greater potency (IC50 = 0.6 nM vs Akt), selectivity, and improved cardiovascular safety profile. The SARs, pharmacokinetic profile, and CV safety of selected Akt inhibitors will be discussed.

Sealing properties of two contemporary single-cone obturation systems

AIM

To compare the sealing of root canals filled with two single-cone obturation systems and a warm vertical compaction technique.

METHODOLOGY

Forty-two single-rooted teeth were decoronated to obtain 17-mm-long root segments. The root canals were cleaned and shaped to size 40, 0.06 taper and filled with: (i) warm vertical compaction with AH Plus (control); (ii) ActiV GP and (iii) GuttaFlow with single master cones. Leakage was evaluated by fluid filtration at 10 psi before root resection, and after 3, 6, 9 and 12 mm apical resections. Repeated measures anovas on ranks and Dunn's multiple comparison tests were performed to examine differences in fluid flow rates amongst different resection lengths for each filling technique. The surface and interior aspects of glass-ionomer filler-coated ActiV GP gutta-percha cones was evaluated with SEM.

RESULTS

No statistical difference amongst the filling techniques was seen at 0 and 3 mm root resections. ActiV GP and GuttaFlow exhibited more leakage than AH Plus at 6, 9 and 12 mm resections. AH Plus recorded the best overall results. A nonhomogeneous coating of glass-ionomer fillers on the surface of ActiV GP cones was detected.

CONCLUSIONS

The two single-cone techniques examined are as effective in sealing the apex as AH Plus when the latter was used with warm vertical compaction. It is further hypothesized that the inferior coronal seal of these single-cone techniques may be improved with the placement of accessory cones to reduce sealer thickness or an immediate coronal adhesive restoration.

Hydroxypropyl β-Cyclodextrins: A Misleading Vehicle for the In Vitro hERG Current Assay

Delayed cardiac repolarization and fatal proarrhythmia have been linked to block of the repolarizing current, Ikr or hERG (human ether-a-go-go related gene) current. Thus, determining the potency of hERG block is critical in evaluating cardiac safety during preclinical development. Hydroxypropyl beta-cyclodextrins (HbetaC) are cyclic oligosaccharides used to enhance drug solubility. To evaluate the utility of HbetaC to enhance drug solubility in hERG screening assays, we studied the effect of HbetaC on hERG current and the sensitivity of the hERG assay to 3 structurally different hERG blocking drugs using whole-cell voltage clamp technique and HEK-293 cells expressing the hERG channel. HbetaC inhibited hERG activation and tail current and accelerated current deactivation in a concentration-dependent manner. HbetaC (6%) reduced the apparent potency of block by terfenadine (IC50 12000 nM vs 45 nM), cisapride (IC50 281 nM vs 28 nM), and E-4031 (163 nM vs 26 nM). Reduced potency of block was consistent with loss of activity as a result of complexation with HbetaC by terfenadine and cisapride (demonstrated in solubility studies) and interactions with HbetaC by E-4031 (demonstrated in absorbance studies). These results demonstrate that HbetaC is an unsuitable agent for enhancing compound solubility in the in vitro hERG current assay and may mask drug effects, allowing potentially dangerous drugs to advance into clinical development.

1,4-Dihydroindeno[1,2-c]pyrazoles with Acetylenic Side Chains as Novel and Potent Multitargeted Receptor Tyrosine Kinase Inhibitors with Low Affinity for the hERG Ion Channel

The synthesis of a novel series of 1,4-dihydroindeno[1,2-c]pyrazoles with acetylene-type side chains is described. Optimization of those compounds as KDR kinase inhibitors identified 8, which displayed an oral activity in an estradiol-induced murine uterine edema model (ED50 = 3 mg/kg) superior to Sutent (ED50 = 9 mg/kg) and showed potent antitumor efficacy in an MX-1 human breast carcinoma xenograft tumor growth model (tumor growth inhibition = 90% at 25 mg/kg.day po). The compound was docked into a homology model of the homo-tetrameric pore domain of the hERG potassium channel to identify strategies to improve its cardiac safety profile. Systematic interruption of key binding interactions between 8 and Phe656, Tyr652, and Ser624 yielded 90, which only showed an IC50 of 11.6 microM in the hERG patch clamp assay. The selectivity profile for 8 and 90 revealed that both compounds are multitargeted receptor tyrosine kinase inhibitors with low nanomolar potencies against the members of the VEGFR and PDGFR kinase subfamilies.

Discovery of N-(4-(3-amino-1H-indazol-4-yl)phenyl)-N'-(2-fluoro-5-methylphenyl)urea (ABT-869), a 3-aminoindazole-based orally active multitargeted receptor tyrosine kinase inhibitor

In our continued efforts to search for potent and novel receptor tyrosine kinase (RTK) inhibitors as potential anticancer agents, we discovered, through a structure-based design, that 3-aminoindazole could serve as an efficient hinge-binding template for kinase inhibitors. By incorporating an N,N'-diaryl urea moiety at the C4-position of 3-aminodazole, a series of RTK inhibitors were generated, which potently inhibited the tyrosine kinase activity of the vascular endothelial growth factor receptor and the platelet-derived growth factor receptor families. A number of compounds with potent oral activity were identified by utilizing an estradiol-induced mouse uterine edema model and an HT1080 human fibrosarcoma xenograft tumor model. In particular, compound 17p (ABT-869) was found to possess favorable pharmacokinetic profiles across different species and display significant tumor growth inhibition in multiple preclinical animal models.

An evaluation of 3,4-methylenedioxy phenyl replacements in the aminopiperidine chromone class of MCHr1 antagonists

The optimization of potent MCHr1 antagonist 1 with respect to improving its in vitro profile by replacement of the 3,4-methylenedioxy phenyl (piperonyl) moiety led to the discovery of 19, a compound that showed excellent MCHr1 binding and functional potencies in addition to possessing superior hERG separation, CYP3A4 profile, and receptor cross-reactivity profiles.

ALTERING EXTRACELLULAR POTASSIUM CONCENTRATION DOES NOT MODULATE DRUG BLOCK OF HUMAN ETHER-A-GO-GO-RELATED GENE (hERG) CHANNELS

1. Drug-induced block of the rapidly activating delayed rectifier K+ current (I(Kr)), encoded by human ether-a-go-go-related gene (hERG), has been linked to acquired long QT syndrome (aLQTS). Hypokalaemia is a recognized risk factor in aLQTS. To further understand why hypokalaemia is a risk factor in aLQTS, we examined the effect of [K+]o on drug block of the hERG potassium channel stably expressed in human embryonic kidney (HEK-293) cells using whole-cell voltage-clamp techniques. 2. The effects of selected [K+]o (1-20 mmol/L) on hERG block with four structurally diverse compounds (dofetilide, mesoridazine, quinidine and terfenadine) from different therapeutic classes were evaluated. Reducing [K+]o from 20 to 1 mmol/L had little effect on IC50 values for hERG current block for all four compounds. For example, evaluating quinidine in external potassium concentrations of 20, 10, 5 and 1 mmol/L resulted in IC50 values of 1.82 +/- 0.33, 2.04 +/- 0.28, 1.57 +/- 0.52 and 1.14 +/- 0.21 mmol/L, respectively. No statistically significant difference (P > 0.35, anova) was observed between drug block of hERG in different external potassium concentrations. These data are in contrast with previously reported results examining hERG channel modulation expressed in AT-1 cells under similar experimental conditions. 3. These results demonstrate that [K+]o does not directly modulate drug block of hERG channels expressed in an HEK-293 cell line. The enhanced risk of Torsades de Pointes associated with hypokalaemia in aLQTS may be due to reduction of other (non-hERG) potassium currents, further reducing the repolarization reserve, and not due to direct modulation of hERG block by [K+]o.

In Vitro Preclinical Cardiac Assessment of Tolterodine and Terodiline: Multiple Factors Predict the Clinical Experience

Terodiline and tolterodine are drugs used to treat urinary incontinence. Terodiline was removed from the market in 1991 for proarrhythmia, whereas tolterodine has a generally benign clinical cardiac profile. To assess differences in the electrophysiologic actions of these drugs, we evaluated their effects on hERG current (HEK cells) and cardiac Purkinje fiber repolarization. The IC50 for hERG block (37 degrees C) by tolterodine was 9.6 nM and by terodiline was 375 nM, values near or below clinical concentrations. Tolterodine elicited concentration-dependent prolongation of the action potential duration (APD90). In contrast, terodiline depressed the action potential plateau and induced triangulation without affecting APD90. The triangulation ratios (normalized ratio of APD50 over APD90) for terodiline were 0.94 and 0.59 for 1.0 and 10 microM and for tolterodine, were 0.99 and 0.97 at 7 and 70 nM. In summary, tolterodine, a potent hERG blocker, has a benign clinical cardiac profile at therapeutic concentrations that may be due to its lack of triangulation, as well as extensive plasma protein binding. However, at supratherapeutic concentrations, preclinical data predict risk of QT prolongation. These data suggest that hERG block and triangulation are among multiple factors that must be considered in preclinical cardiac safety assessments.

Block of hERG channel by ziprasidone: biophysical properties and molecular determinants

Ziprasidone, an antipsychotic agent, delays cardiac repolarization and, thus, prolongs the QT interval of the cardiac ECG. In this study, we examined the biophysical properties and the molecular determinants of the ziprasidone block of wild-type hERG potassium channels stably expressed in HEK-293 cells or wild-type and mutant hERG channels expressed in Xenopus oocytes. In stably transfected HEK-293 cells, ziprasidone blocked wild-type hERG current in a voltage- and concentration-dependent manner (IC(50)=120nM, 0mV, 37 degrees C). Ziprasidone showed minimal tonic block of hERG current estimated during a depolarizing voltage (-20 or +30mV) or evaluated by the envelope of tails test (+30mV). Rate of the block onset was rapid, but not significantly affected by test potentials ranging from -20 to +30mV (time constant (tau)=114+/-14ms at +30mV). The time constant of the slow component of hERG current deactivation (at -50mV) was significantly increased by ziprasidone (tau=1776+/-90 versus 1008+/-71ms, P<0.01). Time course of channel inactivation was slowed by ziprasidone in a voltage-dependent manner. The V(1/2) values for steady-state activation and inactivation of hERG channel in HEK-293 cells were not significantly altered by ziprasidone. In Xenopus oocytes, ziprasidone exhibited less potent block of wild-type hERG current (IC(50)=2.8microM, 0mV, 23 degrees C). Mutation of the aromatic residues (Tyr-652 or Phe-656) located in the S6 domain of hERG dramatically reduced the potency of channel block by ziprasidone (IC(50)>0.4 and 1mM at 0mV for Y652A and F656A, respectively). In conclusion, ziprasidone preferentially binds to and blocks open hERG channels. Tyr-652 and Phe-656 are two critical residues in the ziprasidone-binding site.

The [3H]dofetilide binding assay is a predictive screening tool for hERG blockade and proarrhythmia: Comparison of intact cell and membrane preparations and effects of altering [K+]o

INTRODUCTION

The human ether-a-go-go-related gene (hERG) encodes a potassium channel responsible for the cardiac delayed rectifier current (IKr) involved in ventricular repolarization. Drugs that block hERG have been associated with QT interval prolongation and serious, sometimes fatal, cardiac arrhythmias (including torsade de pointes). While displacement of [3H]dofetilide, a potent methanesulfonanilide hERG blocker, from cells heterologously expressing hERG has been suggested as a screening assay, questions have been raised about its predictive value.

METHODS

To validate the utility of this assay as a screening tool, we performed a series of saturation and competition binding studies using [3H]dofetilide as ligand and either intact cells or membrane preparations from HEK 293 cells stably transfected with hERG K+ channels. The object of these experiments was to (1) compare binding Ki values for 22 hERG blockers using intact cells or membrane homogenates to determine whether maintaining cell integrity enhanced assay reliability; (2) evaluate the ability of different K+ concentrations (2, 5, 10, 20, and 60 mM) to modulate hERG binding; and (3) to establish the predictive value of the assay by comparing Ki values from binding studies at 5 and 60 mM [K+]o to functional IC50 values for hERG current block using 56 structurally diverse drugs.

RESULTS

We found (a) comparable Ki values in the intact cell and isolated membrane binding assays, although there were some differences in rank order; (b) increasing [K+]o lowered the Kd and increased the Bmax for [3H]dofetilide, particularly in the membrane assay; and (c) good correlation between binding Ki values and functional IC50 values for hERG current block.

DISCUSSION

In conclusion, increasing K+ concentrations results in an increase in both [3H]dofetilide affinity for hERG and available binding sites, particularly when using membrane homogenates. There are no meaningful differences between Ki values when comparing intact cell versus membrane assay, neither are there meaningful trends with increasing [K+]o within assays. There is good correlation between binding Ki values and functional (whole-cell patch clamp) IC50 values at both 5 and 60 mM K+ concentrations (R2 values of .824 and .863, respectively). The simplicity, predictability, and adaptability to high-throughput platforms make the [3H]dofetilide membrane binding assay a useful tool for screening and ranking compounds for their potential to block the hERG K+ channel.

ABT-089: pharmacological properties of a neuronal nicotinic acetylcholine receptor agonist for the potential treatment of cognitive disorders

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine dihydrochloride salt] is a selective neuronal nicotinic receptor (NNR) modulator with cognitive enhancing properties in animal models of cognitive functioning. Amongst NNR subtypes, ABT-089 shows selectivity for the cytisine binding site on the alpha4beta2 receptor subtype as compared to the alpha-bungarotoxin (alpha-BgT) binding sites on the alpha7 and alpha1beta1deltagamma receptor subtypes. In functional in vitro electrophysiological and cation flux assays, ABT-089 displays differential activity including agonism, partial agonism and antagonism depending upon the NNR subtype and assay. ABT-089 is as potent and efficacious as (-)-nicotine at evoking acetylcholine (ACh) release from hippocampal synaptosomes. Furthermore, ABT-089 is neuroprotective against excitotoxic glutamate insults, with even greater potency seen after chronic treatment. Similarly, ABT-089 is effective in models of cognitive functioning, including enhancement of baseline functioning as well as improvement of impaired cognitive functioning seen following septal lesioning and natural aging. In neuroprotective assays the compound is most potent by chronic administration. In stark contrast to the positive effects in the cognitive models, ABT-089 shows little propensity to induce adverse effects such as ataxia, hypothermia, seizures, cardiovascular or gastrointestinal side effects. Together these data suggest that ABT-089 is a NNR modulator with the potential for treating cognitive disorders with markedly limited adverse cardiovascular and gastrointestinal side effects.

The utility of hERG and repolarization assays in evaluating delayed cardiac repolarization: influence of multi-channel block

Drug-induced delayed cardiac repolarization is a recognized risk factor for proarrhythmia and is associated with block of IKr (the potassium current encoded by the human ether-a- go-go-related gene [hERG]). To evaluate the utility of 2 in vitro assays widely used to assess delayed repolarization, we compared the effects of haloperidol and 9 structurally diverse drugs in a hERG and repolarization (canine Purkinje fiber action potential duration [APD]) assay over wide concentrations. Despite potent hERG current block (IC50 = 0.174 microM), haloperidol elicited a bell-shaped concentration-response relationship for APD prolongation, with lesser prolongation (and reduced plateau height) observed with concentrations eliciting maximal hERG block, consistent with multi-channel block at higher concentrations. Consistent with this hypothesis, APD prolongation with the specific IKr blocker dofetilide was a) reduced by concomitant administration of nifedipine (calcium current block) and b) reversed by lidocaine (late sodium current block). Additional studies demonstrated prominent (>50%) hERG inhibition with most (9/10) drugs despite wide APD changes (158% prolongation - 16% shortening), consistent with multi-channel block. The poor correlation between hERG and repolarization assays suggests that the hERG assay oversimplifies drug effects on the complex repolarization process for drugs demonstrating multi-channel block and that neither assay alone adequately predicts proarrhythmic risk.

Novel inhibitors of procollagen C-proteinase. Part 2: glutamic acid hydroxamates

Glutamic acid derived hydroxamates were identified as potent and selective inhibitors of procollagen C-proteinase, an essential enzyme for the processing of procollagens to fibrillar collagens. Such compounds have potential therapeutic application in the treatment of fibrosis.

Novel inhibitors of procollagen C-terminal proteinase. Part 1: diamino Acid hydroxamates

The parallel synthesis of novel inhibitors of procollagen C-terminal proteinase is described. The synthetic strategy allowed for the facile synthesis of a large number of side-chain diversified diamino acid hydroxamates, of which the D-diaminopropionic acid derivatives were shown to be single digit nanomolar PCP inhibitors.

Photoexcited breathers in conjugated polyenes: an excited-state molecular dynamics study

pi-conjugated polymers have become an important class of materials for electronic devices. Design of these devices requires understanding such processes as photochemical reactions, spatial dynamics of photoexcitations, and energy and charge transport, which in turn involve complex coupled electron-vibrational dynamics. Here we study nonlinear photoexcitation dynamics in the polyene oligomers by using a quantum-chemical method suitable for the simulation of excited-state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. The method is based on the adiabatic propagation of the ground-state and transition single-electron density matrices along the trajectory. The simulations reveal formation of a self-localized vibronic excitation ("breather" or multiquanta bound state) with a typical period of 34 fs and allows us to identify specific slow and fast nuclear motions strongly coupled to the electronic degrees of freedom. The effect of chain imperfections and chemical defects on the dynamics is also investigated. A complementary two-dimensional analysis of corresponding transition density matrices provides an efficient way to monitor time-dependent real-space localization of the photoexcitation by identifying the underlying changes in charge densities and bond orders. Possible correlated electronic and vibrational spectroscopic signatures of photoexcited breathers are predicted, and generalizations to energy localization in complex macromolecules are discussed.

Photopigment gene expression and rhabdom formation in the crayfish (Procambarus clarkii)

This study examines the expression of the photopigment gene in the developing retina of the freshwater crayfish Procambarus clarkii(Crustacea, Malacostraca, Decapoda). Both sense and anti-sense RNA probes were used for in situ hybridization (ISH) of whole embryos collected at various stages during development. A characteristic of retinal development is the formation of screening pigment in the retinular cells of the retinal ommatidia. This pigmentation is seen as a band that begins at the lateral side of the retinal field and progresses medially. At hatching the retina is approximately 50% pigmented. ISH of whole embryos shows that expression of the photopigment gene by the retinular cells correlates with the extent of the screening pigment band in the retina and with the presence of rhabdoms within the ommatidia. Sections taken through embryos after being hybridized indicate that staining is localized in the cytoplasm of the retinular cells and in the axonal region below the basement membrane. No staining reaction was seen in the rhabdoms of older ommatidia. ISH staining was also seen at the anterior midline of the protocerebrum where extraretinal photoreceptors have been reported. The data presented here show a close correlation of opsin expression within the retinular cells of the ommatidia and the formation of the very early rhabdoms, similar to Drosophila. The results will be discussed in relation to recent studies in Drosophila that suggest rhodopsin plays a role in effecting the organization of the terminal web-like cytoskeleton at the base of the developing rhabdom microvilli.

RNA-mediated interference as a tool for identifying drug targets

The nematode Caenorhabditis elegans is the first multicellular organism with a fully sequenced genome. As a model organism, C. elegans is playing a special role in functional genomic analyses because it is experimentally tractable on many levels. Moreover, the lessons learned from C. elegans are often applicable across phyla because many of the key biologic processes involved in development and disease have been well conserved. Many global approaches for analysing gene activity are being pursued in C. elegans. RNA-mediated interference (RNAi) is an efficient high-throughput method to disrupt gene function. The basic technique of RNAi involves introducing sequence-specific double-stranded RNA into C. elegans in order to generate a nonheritable, epigenetic knockout of gene function that phenocopies a null mutation in the targeted gene. This technique drastically reduces the time needed to jump from the identification of an interesting gene sequence to achieving an understanding of its function. Thus, RNAi facilitates the high-throughput functional analysis of gene targets identified during drug discovery. RNAi can also help to identify the biochemical mode of action of a drug or pesticide and to identify other genes encoding products that may respond or interact with specific compounds.

Ontogeny and regulation of ovine placental prostaglandin E2 synthase

Recent evidence suggests that ovine placental output of prostaglandin (PG) E2 rises through late gestation partly because of a direct effect of cortisol on PGH2 synthase 2 (PGHS-2) expression and activity within trophoblast tissue. Synthesis of PGE2 is also dependent, however, on PGE2 synthase (PGES), which converts PGH2 to PGE2. We hypothesized that PGES is expressed in the ovine placenta, and that, similar to PGHS-2, expression increases through gestation and is regulated positively by cortisol. Placental tissues from pregnant ewes in mid and late gestation, at term, and during early and active labor were analyzed to determine the gestational profile of PGES. The regulation of PGES expression was assessed in placental tissues from pregnant ewes in which intrafetal cortisol infusion was administered in late gestation, in the presence or absence of an aromatase inhibitor, to block the cortisol-stimulated rise in estradiol. Expression of PGES was analyzed by in situ hybridization, Western blot analysis, and immunohistochemistry. In the placentome, PGES localized to fetal trophoblast cells and endothelial cells in maternal blood vessels, consistent with its contribution to the rise in placental PGE2 output toward the onset of labor and with a role of PGE2 in the local regulation of uteroplacental blood flow, respectively. Expression of PGES mRNA and protein increased with gestation. However, there was no significant further change with labor or during cortisol infusion in the presence or absence of a rise in fetal plasma estradiol, in contrast to reported changes in PGHS-2. These results suggest that PGES is not coregulated with PGHS-2 in the sheep placenta at term. The progressive increase in PGES, however, likely contributes to the rise in circulating PGE2 in the fetus in late pregnancy.

Conformational dynamics of photoexcited conjugated molecules

Time-dependent photoexcitation and optical spectroscopy of pi-conjugated molecules is described using a new method for the simulation of excited state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. Applications are made to poly(p-phenylene vinylene) oligomers. Our analysis shows self-trapping of excitations on about six repeat units in the course of photoexcitation relaxation, identifies specific slow (torsion) and fast (bond-stretch) nuclear motions strongly coupled to the electronic degrees of freedom, and predicts spectroscopic signatures of molecular conformations.

Amino acid derived sulfonamide hydroxamates as inhibitors of procollagen C-proteinase: solid-phase synthesis of ornithine analogues

A discussion of the solid-phase synthesis of ornithine derived sulfonamide hydroxamic acids is illustrated. These analogues are shown to be potent, non-peptide inhibitors of procollagen C-proteinase (PCP).

Venom from the platypus, Ornithorhynchus anatinus, induces a calcium-dependent current in cultured dorsal root ganglion cells

The platypus (Ornithorhynchus anatinus), a uniquely Australian species, is one of the few living venomous mammals. Although envenomation of humans by many vertebrate and invertebrate species results in pain, this is often not the principal symptom of envenomation. However, platypus envenomation results in an immediate excruciating pain that develops into a very long-lasting hyperalgesia. We have previously shown that the venom contains a C-type natriuretic peptide that causes mast cell degranulation, and this probably contributes to the development of the painful response. Now we demonstrate that platypus venom has a potent action on putative nociceptors. Application of the venom to small to medium diameter dorsal root ganglion cells for 10 s resulted in an inward current lasting several minutes when the venom was diluted in buffer at pH 6.1 but not at pH 7.4. The venom itself has a pH of 6.3. The venom activated a current with a linear current-voltage relationship between -100 and -25 mV and with a reversal potential of -11 mV. Ion substitution experiments indicate that the current is a nonspecific cationic current. The response to the venom was blocked by the membrane-permeant Ca(2+)-ATPase inhibitor, thapsigargin, and by the tyrosine- and serine-kinase inhibitor, k252a. Thus the response appears to be dependent on calcium release from intracellular stores. The identity of the venom component(s) that is responsible for the responses we have described is yet to be determined but is probably not the C-type natriuretic peptide or the defensin-like peptides that are present in the venom.

Myotoxicity studies of injectable biodegradable in-situ forming drug delivery systems

The objective of the study was to investigate the potential in-vitro and in-vivo myotoxicity of different in-situ forming biodegradable drug delivery systems, namely in-situ Microparticle (ISM) systems and polymer solutions (in-situ implant systems). The acute myotoxicity was evaluated in-vitro using the isolated rodent skeletal muscle model by measuring the cumulative creatine kinase (CK) efflux. For the in-vivo study, following intramuscular injection (i.m.) into male Sprague Dawley rats, the area under the plasma CK-curve was used to evaluate muscle damage. The formulations included ISM-systems [a poly (lactide)-solvent phase dispersed into an external oil phase] and poly (lactide) solutions (in-situ implant systems). Phenytoin and normal saline served as positive and negative controls, respectively. Poly (lactide) in different solvents (in-situ implant systems) resulted in 14.4-24.3 times higher CK-values compared to normal saline, indicating a high myotoxic potential. With the ISM-system, the CK-release was significantly lower, decreased with a lower polymer phase: oil phase ratio, and approached the values of normal saline at a ratio of 1:4. Bupivacaine HCl- and Buserelin acetate- containing ISM-systems resulted in significantly lower CK-levels when compared to the corresponding drug formulation in normal saline. The in-vivo studies confirmed the in-vitro data and showed good muscle compatibility of the ISM-systems.

Specificity of perceptual learning in a frequency discrimination task

On a variety of visual tasks, improvement in perceptual discrimination with practice (perceptual learning) has been found to be specific to features of the training stimulus, including retinal location. This specificity has been interpreted as evidence that the learning reflects changes in neuronal tuning at relatively early processing stages. The aim of the present study was to examine the frequency specificity of human auditory perceptual learning in a frequency discrimination task. Difference limens for frequency (DLFs) were determined at 5 and 8 kHz, using a three-alternative forced choice method, for two groups of eight subjects before and after extensive training at one or the other frequency. Both groups showed substantial improvement at the training frequency, and much of this improvement generalized to the nontrained frequency. However, a small but statistically significant component of the improvement was specific to the training frequency. Whether this specificity reflects changes in neural frequency tuning or attentional changes remains unclear.