Desirable Pharmacokinetic Properties Research Articles

Positive allosteric modulators to peptide GPCRs: a promising class of drugs

The task of finding selective and stable peptide receptor agonists with low molecular weight, desirable pharmacokinetic properties and penetrable to the blood-brain barrier has proven too difficult for many highly coveted drug targets, including receptors for endothelin, vasoactive intestinal peptide and galanin. These receptors and ligand-gated ion channels activated by structurally simple agonists such as glutamate, glycine and GABA present such a narrow chemical space that the design of subtype-selective molecules capable of distinguishing a dozen of glutamate and GABA receptor subtypes and possessing desirable pharmacokinetic properties has also been problematic. In contrast, the pharmaceutical industry demonstrates a remarkable success in developing 1,4-benzodiazepines, positive allosteric modulators (PMAs) of the GABAA receptor. They were synthesized over 50 years ago and discovered to have anxiolytic potential through an in vivo assay. As exemplified by Librium, Valium and Dormicum, these allosteric ligands of the receptor became the world's first blockbuster drugs. Through molecular manipulation over the past 2 decades, including mutations and knockouts of the endogenous ligands or their receptors, and by in-depth physiological and pharmacological studies, more peptide and glutamate receptors have become well-validated drug targets for which an agonist is sought. In such cases, the pursuit for PAMs has also intensified, and a working paradigm to identify drug candidates that are designed as PAMs has emerged. This review, which focuses on the general principles of finding PAMs of peptide receptors in the 21st century, describes the workflow and some of its resulting compounds such as PAMs of galanin receptor 2 that act as potent anticonvulsant agents.

Reversed-phase ion-pair ultra-high-performance-liquid chromatography–mass spectrometry for fingerprinting low-molecular-weight heparins

Heparin is a complex mixture of sulfated linear carbohydrate polymers. It is widely used as an antithrombotic drug, though it has been shown to have a myriad of additional biological activities. Heparin is often partially depolymerized in order to decrease the average molecular weight, as it has been shown that low molecular weight heparins (LMWH) possess more desirable pharmacokinetic and pharmacodynamic properties than unfractionated heparin (UFH). Due to the prevalence of LMWHs in the market and the emerging availability of generic LMWH products, it is important that analytical methods be developed to ensure the drug quality. This work explores the use of tributylamine (TrBA), dibutylamine (DBA), and pentylamine (PTA) as ion-pairing reagents in conjunction with acetonitrile and methanol modified mobile phases for reversed-phase ion-pairing ultraperformance liquid chromatography coupled to mass spectrometry (RPIP-UPLC–MS) for fingerprint analysis of LMWH preparations. RPIP-UPLC–MS fingerprints are presented and compared for tinzaparinand enoxaparin.

N,N-Dimethyl-[9-(arylsulfonyl)-2,3,4,9-tetrahydro-1H-carbazol-3-yl]amines as novel, potent and selective 5-HT6 receptor antagonists

The design, synthesis and SAR of novel tetrahydrocarbazole derivatives having 5-HT6 receptor antagonist activity is presented. The racemic compound 15e was found to possess desirable pharmacokinetic properties, adequate brain penetration and activity in animal models of cognition.

Synthesis and evaluation of pyridylbenzofuran, pyridylbenzothiazole and pyridylbenzoxazole derivatives as 18F-PET imaging agents for β-amyloid plaques

The synthesis and SAR of new β-amyloid binding agents are reported. Evaluation of important properties for achieving good signal-to-background ratio is described. Compounds 27, 33, and 36 displayed desirable lipophilic and pharmacokinetic properties. Compound 27 was further evaluated with autoradiographic studies in vitro on human brain tissue and in vivo in Tg2576 mice. Compound 27 showed an increased signal-to-background ratio compared to flutemetamol 4, indicating its suitability as PET ligand for β-amyloid deposits in AD patients. The preparation of the corresponding 18F-labeled PET radioligand of compound 27 is presented.

Synthesis and antidepressant activity of arylalkanol-piperidine derivatives as triple reuptake inhibitors

A series of arylalkanol-piperidine derivatives was synthesized, and their triple reuptake inhibition and in vivo activities have been evaluated. Among them, compounds 2a, 2j, 2k, 2m and 2n exhibited high potency for 5-HT, NA and DA transporters. Optimized compounds 2j and 2m showed significant reduction of immobility time compared to that of vehicle in the mouse tail suspension test (TST) test at doses ranging from 10 to 50 mg/kg po, and were not generally motor stimulants at 50 mg/kg dose. In addition, compounds 2j and 2m displayed desirable pharmacokinetic properties in SD rats.

Discovery of Novel 1,2,4-Thiadiazole Derivatives as Potent, Orally Active Agonists of Sphingosine 1-Phosphate Receptor Subtype 1 (S1P1)

A novel series of 1,2,4-thiadiazole compounds was discovered as selective S1P(1) agonists. The extensive structure-activity relationship studies for these analogues were reported. Among them, 17g was identified to show high in vitro potency with reasonable free unbound fraction in plasma (F(u) > 0.5%), good brain penetration (BBR > 0.5), and desirable pharmacokinetic properties in mouse and rat. Oral administration of 1 mg/kg 17g resulted in significant peripheral lymphocytes reduction at 4 h after dose and rapid lymphocytes recovery at 24 h. 17g showed a transient lymphopenia profile in the repeated dose study in mouse. In addition, 17g also demonstrated efficacy comparable to that of FTY720 (1) in the mouse EAE model of MS.

Abstract 2913: Identification of GSK2636771, a potent and selective, orally bioavailable inhibitor of phosphatidylinositol 3-kinase-beta (PI3Kα) for the treatment of PTEN deficient tumors

Abstract Dysregulation of the PI3K pathway is one of the most common causes of tumorigenesis. Aberrant pathway activation occurs frequently through loss of the tumor suppressor protein, PTEN. Loss of PTEN protein has been observed in approximately 40% of glioblastoma, 50% of prostate, 57% of endometrial cancers, as well as in a number of other tumor types, including melanoma and breast cancers. Preclinical studies have shown that selective depletion of the PI3Kα isoform inhibits tumorigenesis and reduces downstream PI3K signaling in PTEN deficient tumors. This data presents an opportunity for a clear patient selection strategy based on the presence or absence of PTEN. During an extensive knowledge-based lead identification and optimization effort starting from the reported PI3K beta-selective compound TGX-221, we identified several unique series of potent and selective inhibitors with less than desirable pharmacokinetic properties. Through a combination of structure-based and knowledge-based design, we ultimately identified substituted benzimidazole GSK2636771 as a potent, orally bioavailable, PI3K beta-selective inhibitor. The evolution of our selective inhibitors, leading to the discovery, design, and optimization of GSK2636771 and related analogs, will be described. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2913. doi:1538-7445.AM2012-2913

Prodrug design, synthesis and pharmacokinetic evaluation of (3′R, 4′R)-3-hydroxymethyl-4-methyl-3′, 4′-di-O-(S)-camphanoyl-(+)-cis-khellactone

3-Hydroxymethyl-4-methyl-DCK (3, HMDCK) was discovered previously as a potent HIV non-nucleoside reverse transcriptase inhibitor (NNRTIs) (EC50: 0.004μM, TI: 6225) with a novel mechanism of action. It exerts anti-HIV activity by inhibiting the production of HIV-1 double-stranded viral DNA from a single-stranded DNA intermediate, rather than blocking the generation of single-stranded DNA from a RNA template, which is the mechanism of action of current HIV-1 RT inhibitors. However, the insufficient metabolic stability of 3 limits its further clinical development. In the current study, a series of ester prodrugs of 3 was designed and synthesized to explore the new drug candidates as NNRTIs. The l-alanine ester prodrug 10 exhibited desirable pharmacokinetic properties in vitro and in vivo and showed improved oral bioavailability of 26% in rat, and would be a potential clinical candidate as a new anti-AIDS drug.

Clinical Pharmacokinetics and Pharmacodynamics of Vildagliptin

Clinical Pharmacokinetics and Pharmacodynamics of Vildagliptin

A phase I study of MEK inhibitor MEK162 (ARRY-438162) in patients with biliary tract cancer.

220 Background: The RAS/RAF/MEK/ERK pathway plays a major role in cell growth and survival and is aberrantly activated in many cancers. MEK162 (ARRY-438162) is a potent, selective, ATP-uncompetitive inhibitor of MEK1/2. The objectives of this Phase 1 expansion study were to characterize the safety, pharmacokinetics (PK), pharmacodynamics (PD) and preliminary efficacy of MEK162 in patients (pts) with biliary tract cancer (BTC). Methods: Pts with unresectable, locally advanced or metastatic BTC who had received ≤ 1 prior systemic therapy received oral MEK162 at 60 mg twice daily (BID). Mutation status of RAS, BRAF and other relevant genes were assessed from tumor samples. Tumor response was assessed every 6 weeks. Results: Twenty-eight pts, median age 64 years (range 30-86) with gallbladder (7), intrahepatic (14) or extrahepatic (7) cholangiocarcinoma (CC) were enrolled. All pts were ECOG 0-1 and 43% received previous first-line therapy (primarily gemcitabine combinations). Of the 23 tumors assessed, 17 were wild type (WT) on all loci tested and 6 had mutations (1 MET, 1 PIK3CA, 2 KRAS, 2 PTEN null). The most common treatment-related AEs were rash, nausea, vomiting, diarrhea, peripheral edema, fatigue and central serous-like retinopathy, and most were Grade (G) 1 or 2. G3/4 treatment-related AEs were anasarca, hypokalemia, hyponatremia, upper/lower gastrointestinal hemorrhage and mucositis (1 each). Thirteen pts were dose reduced for AEs, of which, G1/2 central serous-like retinopathy was the most frequently reported event (6). Three pts were discontinued for treatment-related AEs (G2 central serous-like retinopathy, G1 nausea, G4 anasarca). Of the 26 pts evaluable for response, 1 CR, 1 PR and 11 SD (≥ 6 weeks) were observed. Of note, both responders were WT on all loci tested and had extrahepatic CC. The PK in this population was equivalent to that observed in prior studies. A consistent mean reduction (40-60%) of circulating TNFα was observed. Conclusions: MEK162 has an acceptable safety profile and desirable PK properties at 60 mg BID and RECIST responses were observed in pts with BTC. Additional expansion cohorts are ongoing in pts with KRAS- or BRAF-mutant metastatic colorectal cancer.

Abstract B243: A phase I dose-escalation study of MEK inhibitor MEK162 (ARRY-438162) in patients with advanced solid tumors.

Abstract Background: The RAS/RAF/MEK/ERK pathway plays a major role in cell growth and survival, and is often aberrantly activated in many cancers. MEK162 (ARRY-438162) is a potent, selective, ATP-uncompetitive inhibitor of MEK1/2. The objectives of this completed Phase 1 dose-escalation study were to determine the maximum tolerated dose (MTD) and characterize the safety profile, pharmacokinetics (PK), pharmacodynamics (PD) and preliminary efficacy of MEK162 in patients (pts) with advanced solid tumors. An expansion phase of the study is ongoing in order to further explore toxicity and PK in pts with biliary cancer and in pts with KRAS- or BRAF-mutant metastatic colorectal cancer. Methods: Pts were enrolled in successive cohorts using a 3 + 3 design and received MEK162 as a single oral dose on Day (D) 1 followed by twice daily (BID) dosing starting on D2. Safety was assessed by adverse events (AEs), clinical laboratory tests, physical exams, ECGs, ECHO/MUGA scans and ophthalmic exams. Plasma samples were used to assess PK. Levels of circulating cytokines and growth factors in serum and expression and/or phosphorylation status changes in relevant growth factor pathway proteins in skin were evaluated to assess PD. Mutation status of RAS, RAF and other relevant genes and expression and/or phosphorylation status of MEK pathway protein were assessed from archival tumor samples. Tumor response was assessed every 6 weeks. Results: Nineteen pts of median age 57 years (range 33–79) were enrolled in 4 dose cohorts (30 [4], 45 [4], 60 [7] and 80 [4] mg BID). All pts had prior chemotherapy and were ECOG 0–1. Tumor types included colorectal (7), pancreatic (3), cholangiocarcinoma (2) and other (7). The most common treatment-related AEs were rash, diarrhea, nausea, vomiting and peripheral edema, and most were Grade (G) 1/2. G3/4 treatment-related AEs included G3 rash (2), G3 palmar-planter syndrome (1), G3 central serous-like retinopathy (1) and G3/4 creatine kinase elevation (1 each). Seventeen pts were evaluable for MTD determination (30 [4], 45 [3], 60 [7] and 80 [3] mg BID). All DLTs occurred at 80 mg BID (G3 rash and central serous-like retinopathy, 1 pt each); thus, the MTD was 60 mg BID. Of the 17 pts evaluable for response, 1 pt with NRAS-mutant cholangiocarcinoma achieved a PR, and SD was achieved in 9 pts. Of the 11 other evaluable pts with known mutational status, 2 were wild type on all loci tested, plus 5 KRAS, 1 NRAS, 1 BRAF, 1 PIK3Ca and 1 dual KRAS/PIK3Ca mutants. Exposure increased in a dose-proportional manner with good inter-pt variability (∼30% CV). Exposure by D15 averaged 36% > corresponding D1 values indicating modest accumulation. The median t1/2 was ∼5 hr. Mean steady-state plasma concentrations were continuously maintained above the in vitro IC50 value for cell proliferation at all dose levels. In 7 paired skin biopsies from the 60 mg cohort, decreases in pERK and Ki67 were observed post-dose by immunohistochemistry. In serum, a decrease in TNFα was also observed across all dose cohorts. Conclusions: MEK162 had an acceptable safety profile at doses up to the MTD of 60 mg BID and showed preliminary signs of clinical activity. MEK162 displayed desirable PK properties with dose-dependent exposures. MEK162-induced changes in PD markers of MEK activity suggest that MEK162 has target-related PD activity at multiple-dose levels at and below the MTD. 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 B243.

Pharmacokinetics, tissue distribution, excretion, and antiviral activity of pegylated recombinant human consensus interferon-α variant in monkeys, rats and guinea pigs

The study aims to characterize the pharmacokinetic, tissue distribution, excretion, and antiviral activity properties of a novel pegylated recombinant human consensus interferon-α variant (PEG-IFN-SA) following a single subcutaneous administration to monkeys, rats and guinea pigs. Studies included: (1) pharmacokinetic properties of PEG-IFN-SA and comparison with those of non-pegylated IFN-SA in rhesus monkeys and rats; (2) tissue distribution and urinary, fecal, and biliary excretion patterns of 125I-PEG-IFN-SA in guinea pigs; and (3) antiviral activity assessment of PEG-IFN-SA in cynomolgus monkeys. The pegylated protein exhibited improved pharmacokinetic properties compared to IFN-SA in both monkeys and rats, with a 12-fold and 15-fold increase in elimination half-life, and a 100-fold and 10-fold decrease in serum clearance, as well as a 2.5-fold and 10-fold increase in the time to reach peak serum concentration, respectively. 125I-PEG-IFN-SA was found to be distributed to most of the tissues examined and has character of targeting special distribution, and urinary appeared to be a major route for the excretion of PEG-IFN-SA in guinea pigs. Serum sample analysis from PEG-IFN-SA-treated monkeys showed dose-dependent antiviral activity for one week. These findings demonstrate that pegylation of IFN-SA results in more desirable pharmacokinetic properties, enhanced drug exposure and sustained-efficacy of in vivo antiviral action.

Pilot Pharmacokinetic and Dosimetric Studies of18F-FPPRGD2: A PET Radiopharmaceutical Agent for Imaging αvβ3Integrin Levels

To assess the safety, biodistribution, and dosimetric properties of the positron emission tomography (PET) radiopharmaceutical agent fluorine 18 ((18)F) FPPRGD2 (2-fluoropropionyl labeled PEGylated dimeric RGD peptide [PEG3-E{c(RGDyk)}2]), which is based on the dimeric arginine-glycine-aspartic acid (RGD) peptide sequence and targets α(v)β(3) integrin, in the first volunteers imaged with this tracer. The protocol was approved by the institutional review board, and written informed consent was obtained from all participants. Five healthy volunteers underwent whole-body combined PET-computed tomography 0.5, 1.0, 2.0, and 3.0 hours after tracer injection (mean dose, 9.5 mCi ± 3.4 [standard deviation] [351.5 MBq ± 125.8]; mean specific radioactivity, 1200 mCi/mmol ± 714 [44.4 GBq/mmol ± 26.4]). During this time, standard vital signs, electrocardiographic (ECG) readings, and blood sample values (for chemistry, hematologic, and liver function tests) were checked at regular intervals and 1 and 7 days after the injection. These data were used to evaluate tracer biodistribution and dosimetric properties, time-activity curves, and the stability of laboratory values. Significant changes in vital signs and laboratory values were evaluated by using a combination of population-averaged generalized estimating equation regression and exact paired Wilcoxon tests. The administration of (18)F-FPPRGD2 was well tolerated, with no marked effects on vital signs, ECG readings, or laboratory values. The tracer showed the same pattern of biodistribution in all volunteers: primary clearance through the kidneys (0.360 rem/mCi ± 0.185 [0.098 mSv/MBq ± 0.050]) and bladder (0.862 rem/mCi ± 0.436 [0.233 mSv/MBq ± 0.118], voiding model) and uptake in the spleen (0.250 rem/mCi ± 0.168 [0.068 mSv/MBq ± 0.046]) and large intestine (0.529 rem/mCi ± 0.236 [0.143 mSv/MBq ± 0.064]). The mean effective dose of (18)F-FPPRGD2 was 0.1462 rem/mCi ± 0.0669 (0.0396 mSv/MBq ± 0.0181). With an injected dose of 10 mCi (370 MBq) and a 1-hour voiding interval, a patient would be exposed to an effective radiation dose of 1.5 rem (15 mSv). Above the diaphragm, there was minimal uptake in the brain ventricles, salivary glands, and thyroid gland. Time-activity curves showed rapid clearance from the vasculature, with a mean 26% ± 17 of the tracer remaining in the circulation at 30 minutes and most of the activity occurring in the plasma relative to cells (mean whole blood-plasma ratio, 0.799 ± 0.096). (18)F-FPPRGD2 has desirable pharmacokinetic and biodistribution properties. The primary application is likely to be PET evaluation of oncologic patients-especially those with brain, breast, or lung cancer. Specific indications may include tumor staging, identifying patients who would benefit from antiangiogenesis therapy, and separating treatment responders from nonresponders early.

Diverse approaches for the enhancement of oral drug bioavailability

In conscious and co-operating patients, oral drug delivery remains the preferable route of drug administration. However, not all drugs possess the desirable physicochemical and pharmacokinetic properties which favor oral administration mainly due to poor bioavailability. This has in some cases led to the choice of other routes of administration, which may compromise the convenience and increase the risk of non-compliance. Poor bioavailability has necessitated the administration of higher than normally required oral doses which often leads to economic wastages, risk of toxicity, erratic and unpredictable responses. The challenge over the years has been to design techniques that will allow oral administration of most drugs, irrespective of their properties, to achieve a therapeutic systemic availability. This will be a worthy achievement since over 90% of therapeutic compounds are known to possess oral bioavailability limitations. In this review, an attempt has been made to explore various approaches that have been used in recent years to improve oral drug bioavailability, including physical and chemical means. This review strives to provide a comprehensive overview of advances made over the past 10 years (2000-2010) in the improvement of the oral bioavailability of drugs. Briefly, the design of prodrugs to bypass metabolism or to enhance solubility as well as modification of formulation techniques such as the use of additives, permeation enhancers, solubilizers, emulsifiers and non-aqueous vehicles have been discussed. Arising approaches, such as formulation modification techniques; novel drug delivery systems, which exploit the gastrointestinal regionality of drugs, and include the pharmaceutical application of nanotechnology as an emerging area in drug delivery; inhibition of efflux pumps; and inhibition of presystemic metabolism have been more extensively addressed. This critical review sought to assess each method aimed at enhancing the oral bioavailability of drugs in terms of the purpose, scientific basis, limitations, commercial application, as well as the areas in which current research efforts are being focused and should be focused in the future.

First experience with clinical-grade ([18F]FPP(RGD₂): an automated multi-step radiosynthesis for clinical PET studies.

A reliable and routine process to introduce a new ¹⁸F-labeled dimeric RGD-peptide tracer ([¹⁸F]FPP(RGD₂) for noninvasive imaging of α(v)β₃ expression in tumors needed to be developed so the tracer could be evaluated for the first time in man. Clinical-grade [¹⁸F]FPP(RGD)₂ was screened in mouse prior to our first pilot study in human. [¹⁸F]FPP(RGD)₂ was synthesized by coupling 4-nitrophenyl-2-[¹⁸F]fluoropropionate ([¹⁸F]NPE) with the dimeric RGD-peptide (PEG₃-c(RGDyK)₂). Imaging studies with [¹⁸F]FPP(RGD)₂ in normal mice and a healthy human volunteer were carried out using small animal and clinical PET scanners, respectively. Through optimization of each radiosynthetic step, [¹⁸F]FPP(RGD)₂ was obtained with RCYs of 16.9 ± 2.7% (n = 8, EOB) and specific radioactivity of 114 ± 72 GBq/μmol (3.08 ± 1.95 Ci/μmol; n = 8, EOB) after 170 min of radiosynthesis. In our mouse studies, high radioactivity uptake was only observed in the kidneys and bladder with the clinical-grade tracer. Favorable [¹⁸F]FPP(RGD)₂ biodistribution in human studies, with low background signal in the head, neck, and thorax, showed the potential applications of this RGD-peptide tracer for detecting and monitoring tumor growth and metastasis. A reliable, routine, and automated radiosynthesis of clinical-grade [¹⁸F]FPP(RGD)₂ was established. PET imaging in a healthy human volunteer illustrates that [¹⁸F]FPP(RGD)₂ possesses desirable pharmacokinetic properties for clinical noninvasive imaging of α(v)β₃ expression. Further imaging studies using [¹⁸F]FPP(RGD)₂ in patient volunteers are now under active investigation.

Inhalation by design: Dual pharmacology β-2 agonists/M3 antagonists for the treatment of COPD

This paper describes the successful design and development of dual pharmacology β-2 agonists-M3 antagonists, for the treatment of chronic obstructive pulmonary disorder using the principles of 'inhalation by design'. A key feature of this work is the combination of balanced potency and pharmacodynamic duration with desirable pharmacokinetic and material properties, whilst keeping synthetic complexity to a minimum.

Bioactivation of Isothiazoles: Minimizing the Risk of Potential Toxicity in Drug Discovery

Compound 1, (7-methoxy-N-((6-(3-methylisothiazol-5-yl)-[1,2,4]triazolo[4,3-b]pyridazin-3-yl)methyl)-1,5-naphthyridin-4-amine) is a potent, selective inhibitor of c-Met (mesenchymal-epithelial transition factor), a receptor tyrosine kinase that is often deregulated in cancer. Compound 1 displayed desirable pharmacokinetic properties in multiple preclinical species. Glutathione trapping studies in liver microsomes resulted in the NADPH-dependent formation of a glutathione conjugate. Compound 1 also exhibited very high in vitro NADPH-dependent covalent binding to microsomal proteins. Species differences in covalent binding were observed, with the highest binding in rats, mice, and monkeys (1100-1300 pmol/mg/h), followed by dogs (400 pmol/mg/h) and humans (144 pmol/mg/h). This covalent binding to protein was abolished by coincubation with glutathione. Together, these in vitro data suggest that covalent binding and glutathione conjugation proceed via bioactivation to a chemically reactive intermediate. The cytochrome (CYP) P450 enzymes responsible for this bioactivation were identified as cytochrome P450 3A4, 1A2, and 2D6 in human and cytochrome P450 2A2, 3A1, and 3A2 in rats. The glutathione metabolite was detected in the bile of rats and mice, thus demonstrating bioactivation occurring in vivo. Efforts to elucidate the structure of the glutathione adduct led to the isolation and characterization of the metabolite by NMR and mass spectrometry. The analytical data confirmed conclusively that the glutathione conjugation was on the 4-C position of the isothiazole ring. Such P450-mediated bioactivation of an isothiazole or thiazole group has not been previously reported. We propose a mechanism of bioactivation via sulfur oxidation followed by glutathione attack at the 4-position with subsequent loss of water resulting in the formation of the glutathione conjugate. Efforts to reduce bioactivation without compromising potency and pharmacokinetics were undertaken in order to minimize the potential risk of toxicity. Because of the exemplary pharmacokinetic/pharmacodynamic (PK/PD) properties of the isothiazole group, initial attempts were focused on introducing alternative metabolic soft spots into the molecule. These efforts resulted in the discovery of 7-(2-methoxyethoxy)-N-((6-(3-methyl-5-isothiazolyl)[1,2,4]triazolo[4,3-b]pyridazin-3-yl)methyl)-1,5-naphthyridin-4-amine (compound 2), with the major metabolic transformation occurring on the naphthyridine ring alkoxy substituent. However, a glutathione conjugate of compound 2 was produced in vitro and in vivo in a manner similar to that observed for compound 1. Furthermore, the covalent binding was high across species (360, 300, 529, 208, and 98 pmol/mg/h in rats, mice, dogs, monkeys, and humans, respectively), but coincubation with glutathione reduced the extent of covalent binding. The second viable alternative in reducing bioactivation involved replacing the isothiazole ring with bioisosteric heterocycles. Replacement of the isothiazole ring with an isoxazole or a pyrazole reduced the bioactivation while retaining the desirable PK/PD characteristics of compounds 1 and 2.

A chemical genetic screen in Mycobacterium tuberculosis identifies carbon-source-dependent growth inhibitors devoid of in vivo efficacy

Candidate antibacterials are usually identified on the basis of their in vitro activity. However, the apparent inhibitory activity of new leads can be misleading because most culture media do not reproduce an environment relevant to infection in vivo. In this study, while screening for novel anti-tuberculars, we uncovered how carbon metabolism can affect antimicrobial activity. Novel pyrimidine–imidazoles (PIs) were identified in a whole-cell screen against Mycobacterium tuberculosis. Lead optimization generated in vitro potent derivatives with desirable pharmacokinetic properties, yet without in vivo efficacy. Mechanism of action studies linked the PI activity to glycerol metabolism, which is not relevant for M. tuberculosis during infection. PIs induced self-poisoning of M. tuberculosis by promoting the accumulation of glycerol phosphate and rapid ATP depletion. This study underlines the importance of understanding central bacterial metabolism in vivo and of developing predictive in vitro culture conditions as a prerequisite for the rational discovery of new antibiotics.

Synthesis and evaluation of 2-pyridylbenzothiazole, 2-pyridylbenzoxazole and 2-pyridylbenzofuran derivatives as 11C-PET imaging agents for β-amyloid plaques

The syntheses and SAR of new series of β-amyloid binding agents are reported. The effort to optimize signal-to-background ratios for these ligands are described. Compounds 8, 21 and 30 displayed desirable lipophilicity and pharmacokinetic properties. Compounds 8 and 21 were evaluated with in vitro autoradiographic studies and in vivo in APP/PS1 transgenic mice . It is shown that it was possible to increase the signal-to-background ratios compared to PIB 1, as demonstrated by compounds 8 and 21.

Fluorinated Molecules in the Diagnosis and Treatment of Neurodegenerative Diseases

The use of fluorinated molecules as drugs and imaging agents for CNS disorders has been studied extensively over the years. Incorporating a fluorine atom into the structure of a drug changes its physiochemical properties and can thereby lead to much more desirable pharmacokinetic and pharmacodynamic properties. This change can help to facilitate blood-brain barrier permeability, which is a critical matter for drugs intended for CNS activities. Fluorine incorporation into structures of drugs for the treatment of neurodegenerative diseases has been an attractive field for drug discovery. Such incorporation can greatly influence the physicochemical properties, metabolic stability and receptor binding affinity of the resulting molecule. Some studies have shown that when a proton was substituted with fluorine, the binding or inhibitory potency was greatly increased. The fluorine-18 isotope, (18)F, is utilized in detection and diagnosis of neurodegenerative diseases, whereas (19)F compounds are used in the treatment of these diseases and in MRI. (18)F is widely used in PET imaging because it offers the advantage of a longer half-life compared with other radionuclides. It is used for imaging various receptors and transporters that have been linked to neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and multiple system atrophy. Fluorine plays an important role in the diagnosis and treatment of many CNS diseases, including neurodegenerative disorders. The use of fluorine in the diagnosis and treatment of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, will be discussed in this review.