Quantitation of Super Basic Peptides in Biological Matrices by a Generic Perfluoropentanoic Acid-Based Liquid Chromatography-Mass Spectrometry Method

Peptides represent a promising modality for the design of novel therapeutics that can potentially modulate traditionally non-druggable targets. Cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) are two large families that are being explored extensively as drug delivery vehicles, imaging reagents, or therapeutic treatments for various diseases. Many CPPs and AMPs are cationic among which a significant portion is extremely basic and hydrophilic (e.g., nona-arginine). Despite their attractive therapeutic potential, it remains challenging to directly analyze and quantify these super cationic peptides from biological matrices due to their poor chromatographic behavior and MS response. Herein, we describe a generic method that combines solid phase extraction and LC-MS/MS for analysis of these peptides. As demonstrated, using a dozen strongly basic peptides, low μM concentration of perfluoropentanoic acid (PFPeA) in the mobile phase enabled excellent compound chromatographic retention, thus avoiding co-elution with solvent front ion suppressants. PFPeA also had a charge reduction effect that allowed the selection of parent/ion fragment pairs in the higher m/z region to further reduce potential low molecular weight interferences. When the method was coupled to the optimized sample extraction process, we routinely achieved low digit ng/ml sensitivity for peptides in plasma/tissue. The method allowed an efficient evaluation of plasma stability of CPPs/AMPs without fluorescence derivatization or other tagging methods. Importantly, using the widely studied HIV-TAT CPP as an example, the method enabled us to directly assess its pharmacokinetics and tissue distribution in preclinical animal models.

Development of a Convenient In Vitro Gel Diffusion Model for Predicting the In Vivo Performance of Subcutaneous Parenteral Formulations of Large and Small Molecules

Parenteral delivery remains a compelling drug delivery route for both large- and small-molecule drugs and can bypass issues encountered with oral absorption. For injectable drug products, there is a strong patient preference for subcutaneous administration due to its convenience over intravenous infusion. However, in subcutaneous injection, in contrast to intravenous administration, the formulation is in contact with an extracellular matrix environment that behaves more like a gel than a fluid. This can impact the expected performance of a formulation. Since typical bulk fluid dissolution studies do not accurately simulate the subcutaneous environment, improved in vitro models to help better predict the behavior of the formulation are critical. Herein, we detail the development of a new model system consisting of a more physiologically relevant gel phase to simulate the rate of drug release and diffusion from a subcutaneous injection site using agarose hydrogels as a tissue mimic. This is coupled with continuous real-time data collection to accurately monitor drug diffusion. We show how this in vitro model can be used as an in vivo performance differentiator for different formulations of both large and small molecules. Thus, this model system can be used to improve optimization and understanding of new parenteral drug formulations in a rapid and convenient manner.

Investigation of piperazine benzamides as human β3 adrenergic receptor agonists for the treatment of overactive bladder

The synthesis of a novel class of piperazine benzamide (reverse amides) targeting the human β₃-adrenergic receptor for the treatment of overactive bladder (OAB) is described. The SAR studies directed towards maintaining well established β₃ potency and selectivities while improving the overall pharmacokinetic profile in the reverse amide class will be evaluated. The results and consequences associated with functional activity at the norepinephrine transporter (NET) will also be discussed.

Evaluation of CETP activity in vivo under non-steady-state conditions: influence of anacetrapib on HDL-TG flux

Studies in lipoprotein kinetics almost exclusively rely on steady-state approaches to modeling. Herein, we have used a non-steady-state experimental design to examine the role of cholesteryl ester transfer protein (CETP) in mediating HDL-TG flux in vivo in rhesus macaques, and therefore, we developed an alternative strategy to model the data. Two isotopomers ([(2)H11] and [(13)C18]) of oleic acid were administered (orally and intravenously, respectively) to serve as precursors for labeling TGs in apoB-containing lipoproteins. The flux of a specific TG (52:2) from these donor lipoproteins to HDL was used as the measure of CETP activity; calculations are also presented to estimate total HDL-TG flux. Based on our data, we estimate that the peak total postprandial TG flux to HDL via CETP is ∼ 13 mg · h(-1) · kg(-1) and show that this transfer was inhibited by 97% following anacetrapib treatment. Collectively, these data demonstrate that HDL TG flux can be used as a measure of CETP activity in vivo. The fact that the donor lipoproteins can be labeled in situ using well-established stable isotope tracer techniques suggests ways to measure this activity for native lipoproteins in free-living subjects under any physiological conditions.

Modulating Drug Release and Enhancing the Oral Bioavailability of Torcetrapib with Solid Lipid Dispersion Formulations

The development of drug dispersions using solid lipids is a novel formulation strategy that can help address the challenges of poor drug solubility and systemic exposure after oral administration. The highly lipophilic and poorly water-soluble drug torcetrapib could be effectively formulated into solid lipid microparticles (SLMs) using an anti-solvent precipitation strategy. Acoustic milling was subsequently used to obtain solid lipid nanoparticles (SLNs). Torcetrapib was successfully incorporated into the lipid matrix in an amorphous state. Spherical SLMs with mean particle size of approximately 15-18 μm were produced with high drug encapsulation efficiency (>96%) while SLNs were produced with a mean particle size of 155 nm and excellent colloidal stability. The in vitro drug release and the in vivo absorption of the solid lipid micro- and nanoparticles after oral dosing in rats were evaluated against conventional crystalline drug powders as well as a spray dried amorphous polymer dispersion formulation. Interestingly, the in vitro drug release rate from the lipid particles could be tuned for immediate or extended release by controlling either the particle size or the precipitation temperature used when forming the drug-lipid particles. This change in the rate of drug release was manifested in vivo with changes in Tmax as well. In addition, in vivo pharmacokinetic studies revealed a significant increase (∼6 to 11-fold) in oral bioavailability in rats dosed with the SLMs and SLNs compared to conventional drug powders. Importantly, this formulation approach can be performed rapidly on a small scale, making it ideal as a formulation technology for use early in the drug discovery timeframe.

Design of Potent and Orally Active GPR119 Agonists for the Treatment of Type II Diabetes

We report herein the design and synthesis of a series of potent and selective GPR119 agonists. Our objective was to develop a GPR119 agonist with properties that were suitable for fixed-dose combination with a DPP4 inhibitor. Starting from a phenoxy analogue (1), medicinal chemistry efforts directed toward reducing half-life and increasing solubility led to the synthesis of a series of benzyloxy analogues. Compound 28 was chosen for further profiling because of its favorable physicochemical properties and excellent GPR119 potency across species. This compound exhibited a clean off-target profile in counterscreens and good in vivo efficacy in mouse oGTT.

Novel sesquiterpenoids from the fermentation of Xylaria persicaria are selective ligands for the NPY Y5 receptor

Neuropeptide Y (NPY) is a polypeptide found in the peripheral and central nervous system and is involved in the regulation of feeding. Antagonists of NPY receptor activation could therefore have potential for development as antiobesity drugs. Fermentation of an isolate of Xylaria persicaria yielded two novel eremophilane sesquiterpenoids xylarenals A (1) and B (2). These compounds are selective for the NPY Y5 receptor but have only modest affinity. The isolation, structure elucidation, and biological activities of these compounds are described.

Small molecule insulin mimetics reduce food intake and body weight and prevent development of obesity

Obesity and insulin resistance are major risk factors for a number of metabolic disorders, such as type 2 diabetes mellitus. Insulin has been suggested to function as one of the adiposity signals to the brain for modulation of energy balance. Administration of insulin into the brain reduces food intake and body weight, and mice with a genetic deletion of neuronal insulin receptors are hyperphagic and obese. However, insulin is also an anabolic factor; when administered systemically, pharmacological levels of insulin are associated with body weight gain in patients. In this study, we investigated the efficacy and feasibility of small molecule insulin mimetic compounds to regulate key parameters of energy homeostasis. Central intracerebroventricular (i.c.v.) administration of an insulin mimetic resulted in a dose-dependent reduction of food intake and body weight in rats, and altered the expression of hypothalamic genes known to regulate food intake and body weight. Oral administration of a mimetic in a mouse model of high-fat diet-induced obesity reduced body weight gain, adiposity and insulin resistance. Thus, insulin mimetics have a unique advantage over insulin in the control of body weight and hold potential as a novel anti-obesity treatment.

The complestatins as HIV-1 integrase inhibitors. Efficient isolation, structure elucidation, and inhibitory activities of isocomplestatin, chloropeptin I, new complestatins, A and B, and acid-hydrolysis products of chloropeptin I

From the screening of a microbial extract library, isocomplestatin (1), a new axial-chiral isomer of complestatin (2) which is a known rigid bicyclic hexapeptide, was identified as a potent natural product inhibitor of HIV-1 integrase, a unique enzyme responsible for viral replication. Isocomplestatin showed inhibitory activities (IC(50)) in coupled 3'-end processing/strand transfer (200 nM), strand transfer (4 microM), and HIV-1 replication (200 nM) in virus-infected cells. Attempted large-scale isolation of 1 by the literature method, used for the isolation of complestatin, led to lower yield and limited availability. We have developed several new, two-step, high-yielding absorption/elution methods of isolation based on reverse-phase chromatography at pH 8 that are applicable to scales from one gram to potential industrial quantities. We have also discovered and determined the structure of two new congeners of 1, namely, complestatins A (4) and B (5), with almost equal HIV-1 integrase activity. They differ from 1 at C2' and C3' of the tryptophan moiety (residue F). Selective acid hydrolysis of chloropeptin I (3), itself a known acid-catalyzed rearranged isomer of 1 and 2 (8'- vs 7'-substitution in tryptophan residue F, respectively), an isomer of complestatin, and isocomplestatin resulted in a number of fragments (6-10) with retention of most of the HIV-1 integrase activity. The structure-activity relationship as revealed by these compounds could possibly lead to the design of better inhibitors or understanding of the HIV-1 integrase target.

Discovery of a small molecule insulin receptor activator

Insulin elicits diverse biological responses in many tissues and cell types by binding to its specific receptor. The insulin receptor (IR) is a tetramer consisting of two extracellular alpha subunits and two membrane-spanning beta subunits. The binding of insulin to the receptor causes conformational changes that lead to autophosphorylation and activation of the tyrosine kinase intrinsic to the beta subunits. Insulin receptor transphosphorylates several immediate substrates, resulting in modulation of a cascade of downstream signal transduction molecules. In order to discover small molecules that activate the human insulin receptor tyrosine kinase (IRTK), a cell-based assay was established and utilized to screen a collection of synthetic chemicals and natural product extracts. This effort led to the identification of a nonpeptidyl, small molecule, insulin-mimetic compound (demethylasterriquinone B-1, DMAQ-B1) that was isolated from a mixture of metabolites produced by a tropical endophytic fungus, Pseudomassaria sp. This compound induced human IRTK activation and increased tyrosine phosphorylation of IR beta subunit. It mediated insulin-like effects, including insulin receptor substrate-1 (IRS-1) phosphorylation and activation of phosphotidylinositide 3-kinase and Akt kinase. DMAQ-B1 also exhibited an insulin-like effect on glucose uptake in adipocytes and skeletal muscle tissue. Furthermore, the compound was relatively selective for IR vs. insulin-like growth factor-I (IGF-I) receptor and other homologous receptor tyrosine kinases. In addition, it activated partially purified native IR or recombinant IR kinase, demonstrating the direct interaction of the small molecule with the IR. Oral administration of DMAQ-B1 resulted in significant glucose lowering in two mouse models of diabetes. Thus, DMAQ-B1 represents the first orally active insulin-mimetic agent. Pharmaceutical intervention aimed at augmenting IR function ultimately may prove beneficial as a novel therapeutic option in patients with diabetes.

A novel insulin mimetic without a proliferative effect on vascular smooth muscle cells

BACKGROUND

Insulin induces vascular smooth muscle cell (VSMC) proliferation, which is an important step in the atherosclerotic process. Recently, a nonpeptidyl fungal metabolite originally referred to as L-783,281, but also known as demethylasterriquinone B-1 (DMAQB-1), was found to have hypoglycemic activity in diabetic mice through interaction with the intracellular beta subunit of the insulin receptor. This study was designed to determine whether DMAQB-1 has an insulin-like proliferative effect on human infragenicular VSMCs.

METHODS

Human infragenicular VSMCs were isolated from diabetic patients undergoing amputations. DMAQB-1 cell culture dose response was measured in both serum-free media and media with 1% fetal bovine serum (FBS). A working concentration of DMAQB-1 that ranged from 0.5 to 500 nmol/L was studied in the presence of varying concentrations of glucose and insulin. The ability of DMAQB-1 to stimulate glucose transport at less than or equal to 100 nmol/L was determined by [(14)C]-2-deoxyglucose uptake. DNA synthesis was used as the marker for proliferative stimulus and detected by [(3)H]-thymidine uptake measured at 24 hours. Analysis of variance was used to compare the results among the groups; a P value less than.05 was considered significant. Polynomial regression was used to calculate the median lethal dose.

RESULTS

In normal glucose media (100 mg/dL), various concentrations of DMAQB-1 demonstrated a small but statistically significant decrease in DNA synthesis at 0.5 nmol/L in serum-free media and at 5 nmol/L in media supplemented with 1% FBS. The corresponding median lethal dose was 107 nmol/L in serum-free media and 650 nmol/L in media supplemented with 1% FBS. A DMAQB-1 concentration of 5 nmol/L induced glucose transport that was equivalent to an insulin concentration of 100 microU/mL. In serum-free, high glucose media (200 mg/dL), DMAQB-1 concentrations up to 500 nmol/L did not cause a statistically significant change in DNA synthesis. When serum-free, high glucose media was combined with mild (100 microU/mL) or moderate (250 microU/mL) concentrations of insulin, DMAQB-1 caused no statistically significant increase in DNA synthesis.

CONCLUSION

Nontoxic doses of DMAQB-1 can induce glucose transport equivalent to insulin in the physiologic range. However, DMAQB-1 does not have an insulin-like proliferative effect on human VSMCs in normal-glucose, high-glucose, or high-insulin environments.

Activation of insulin signal transduction pathway and anti-diabetic activity of small molecule insulin receptor activators

We recently described the identification of a non-peptidyl fungal metabolite (l-783,281, compound 1), which induced activation of human insulin receptor (IR) tyrosine kinase and mediated insulin-like effects in cells, as well as decreased blood glucose levels in murine models of Type 2 diabetes (Zhang, B., Salituro, G., Szalkowski, D., Li, Z., Zhang, Y., Royo, I., Vilella, D., Diez, M. T. , Pelaez, F., Ruby, C., Kendall, R. L., Mao, X., Griffin, P., Calaycay, J., Zierath, J. R., Heck, J. V., Smith, R. G. & Moller, D. E. (1999) Science 284, 974-977). Here we report the characterization of an active analog (compound 2) with enhanced IR kinase activation potency and selectivity over related receptors (insulin-like growth factor I receptor, epidermal growth factor receptor, and platelet-derived growth factor receptor). The IR activators stimulated tyrosine kinase activity of partially purified native IR and recombinant IR tyrosine kinase domain. Administration of the IR activators to mice was associated with increased IR tyrosine kinase activity in liver. In vivo oral treatment with compound 2 resulted in significant glucose lowering in several rodent models of diabetes. In db/db mice, oral administration of compound 2 elicited significant correction of hyperglycemia. In a streptozotocin-induced diabetic mouse model, compound 2 potentiated the glucose-lowering effect of insulin. In normal rats, compound 2 improved oral glucose tolerance with significant reduction in insulin release following glucose challenge. A structurally related inactive analog (compound 3) was not effective on insulin receptor activation or glucose lowering in db/db mice. Thus, small molecule IR activators exert insulin mimetic and sensitizing effects in cells and in animal models of diabetes. These results have implications for the future development of new therapies for diabetes mellitus.

Quinoxapeptins: novel chromodepsipeptide inhibitors of HIV-1 and HIV-2 reverse transcriptase. I. The producing organism and biological activity

Quinoxapeptin A and B are novel chromodepsipeptides which were isolated from a nocardioform actinomycete with indeterminant morphology. Quinoxapeptins A and B are potent inhibitors of HIV-1 and HIV-2 reverse transcriptase and almost equally active against two single mutants forms as well as a double mutant form of HIV-1 reverse transcriptase. Quinoxapeptin A and B are specific inhibitors of HIV-1 and HIV-2 reverse transcriptase because they did not inhibit human DNA polymerase alpha, beta, gamma and delta. Quinoxapeptin A and B are structurally similar to luzopeptin A which was also active against HIV-1 and HIV-2 reverse transcriptase.

Identification of the major 4-methylumbelliferyl p-guanidinobenzoate-hydrolyzing plasma protein in cystic fibrosis: implication for intrauterine and heterozygote detection

Measurement of 4-methylumbelliferyl p-guanidinobenzoate (MUGB)-hydrolyzing activity in the plasma of normal controls, cystic fibrosis (CF) heterozygotes, and CF homozygotes did not support previously reported (35) differences in MUGB-hydrolyzing activity. We identified human plasma albumin as the major source of MUGB-hydrolyzing activity by comparison of our plasma results to those obtained with physiologic concentrations of commercial albumin samples. Substantiating evidence was obtained from gel filtration experiments and correlation of albumin levels in CF plasma with MUGB titers. We found essentially no proteolytic activity towards dinitrophenylprotamine sulfate associated with commercial albumin samples. It appears that the reaction between human albumin and MUGB represents a weak esterase activity, perhaps involving the acylation of a specific site(s) on the protein. Hypoalbuminemia has been documented (8) in some CF patients. Low albumin concentrations, indicated by MUGB titers less than 190 nmole methylumbelliferone/ml plasma, were found in 42% of CF homozygotes, 6% of heterozygotes, and 4% of controls. Gel filtration studies of a normal amniotic fluid supernatant indicated that albumin was the major MUGB-hydrolyzing substance in this fluid. We conclude that MUGB abnormalities are not associated with the basic gene defect in CF and cannot be used as the basis of a test for intrauterine or heterozygote detection.