Showing papers in "Journal of Medicinal Chemistry in 2008"

Multi-Target-Directed Ligands To Combat Neurodegenerative Diseases

Abstract: Our understanding of the pathogenesis of diseases has advanced enormously in recent decades. As a consequence, drug discovery has gradually shifted from an entirely humanphenotype-based endeavor to today’s reductionist approach centered on single molecular targets. The focus has shifted from the early animal models to isolated proteins via cellular models. This change has led to a decrease in complexity but also to a decrease in relevance to the human condition. In this context, drug research has become (and still is) aimed mainly at the discovery of small molecules able to modulate the biological function of a single protein target thought to be fully responsible for a certain disease. Much effort has been devoted to achieving selectivity for that given target, and indeed, nowadays, many ligands endowed with outstanding in vitro selectivity are available. This one-molecule, one-target paradigm has led to the discovery of many successful drugs, and it will probably remain a milestone for years to come. However, it should be noted that a highly selective ligand for a given target does not always result in a clinically efficacious drug. This may be because (a) the ligand does not recognize the target in vivo, (b) the ligand does not reach the site of action, or (c) the interaction with the respective target does not have enough impact on the diseased system to restore it effectively. Reasons for the latter might lie in both the multifactorial nature of many diseases and the fact that cells can often find ways to compensate for a protein whose activity is affected by a drug, by taking advantage of the redundancy of the system, i.e., of the existence of parallel pathways. Medicinal chemists are often faced with these frustrating aspects of drug research. Drawbacks a and b can be addressed through the well-established rational ligand modification approaches. But issue c is more problematic and needs to be carefully discussed. This is one of the aims of the present article.

Generation of a set of simple, interpretable ADMET rules of thumb.

Abstract: A set of simple, consistent structure-property guides have been determined from an analysis of a number of key ADMET assays run within GSK: solubility, permeability, bioavailability, volume of distribution, plasma protein binding, CNS penetration, brain tissue binding, P-gp efflux, hERG inhibition, and cytochrome P450 1A2/2C9/2C19/2D6/3A4 inhibition. The rules have been formulated using molecular properties that chemists intuitively know how to alter in a molecule, namely, molecular weight, logP, and ionization state. The rules supplement the more predictive black-box models available to us by clearly illustrating the key underlying trends, which are in line with reports in the literature. It is clear from the analyses reported herein that almost all ADMET parameters deteriorate with either increasing molecular weight, logP, or both, with ionization state playing either a beneficial or detrimental affect depending on the parameter in question. This study re-emphasizes the need to focus on a lower molecular weight and logP area of physicochemical property space to obtain improved ADMET parameters.

The Identification of 2-(1H-Indazol-4-yl)-6-(4-methanesulfonyl-piperazin-1-ylmethyl)-4-morpholin-4-yl-thieno[3,2-d]pyrimidine (GDC-0941) as a Potent, Selective, Orally Bioavailable Inhibitor of Class I PI3 Kinase for the Treatment of Cancer†

Abstract: Phosphatidylinositol-3-kinase (PI3K) is an important target in cancer due to the deregulation of the PI3K/Akt signaling pathway in a wide variety of tumors. A series of thieno[3,2-d]pyrimidine derivatives were prepared and evaluated as inhibitors of PI3 kinase p110α. The synthesis, biological activity, and further profiling of these compounds are described. This work resulted in the discovery of 17, GDC-0941, which is a potent, selective, orally bioavailable inhibitor of PI3K and is currently being evaluated in human clinical trials for the treatment of cancer.

Natural Products as Leads to Potential Drugs: An Old Process or the New Hope for Drug Discovery?

Abstract: From approximately the early 1980s, the “influence of natural products” upon drug discovery in all therapeutic areas apparently has been on the wane because of the advent of combinatorial chemistry technology and the “associated expectation” that these techniques would be the future source of massive numbers of novel skeletons and drug leads/new chemical entities (NCE) where the intellectual property aspects would be very simple. As a result, natural product work in the pharmaceutical industry, except for less than a handful of large pharmaceutical companies, effectively ceased from the end of the 1980s. What has now transpired (cf. evidence shown in Newman and Cragg, 2007 and Figures 1 and 2 below showing the continued influence of natural products as leads to or sources of drugs over the past 26 years (1981–2006)) is that, to date, there has only been one de novo combinatorial NCE approved anywhere in the world by the U.S. Food and Drug Administration (FDA) or its equivalent in other nations for any human disease, and that is the kinase inhibitor sorafenib (1, Chart 1), which was approved by the FDA in late 2005 for renal carcinoma. However, the techniques of combinatorial chemistry have revolutionized the deVelopment of active chemical leads where currently, instead of medicinal chemists making derivatives from scratch, a procedure is used whereby syntheses are based on combinatorial processes so that modifications can be made in an iterative fashion. An example of such a process would be the methods underlying the ultimate synthesis of the antibiotic linezolid (Zyvox, 2) by the Pharmacia (now Pfizer) chemists starting from the base molecules developed in the late 1980s by DuPont Pharmaceutical, who reported the underlying antibiotic activity and mechanism of action of this novel class of molecules, the oxazolidinones.

Discovery of Raltegravir, a Potent, Selective Orally Bioavailable HIV-Integrase Inhibitor for the Treatment of HIV-AIDS Infection

Abstract: Human immunodeficiency virus type-1 (HIV-1) integrase is one of the three virally encoded enzymes required for replication and therefore a rational target for chemotherapeutic intervention in the treatment of HIV-1 infection. We report here the discovery of Raltegravir, the first HIV-integrase inhibitor approved by FDA for the treatment of HIV infection. It derives from the evolution of 5,6-dihydroxypyrimidine-4-carboxamides and N-methyl-4-hydroxypyrimidinone-carboxamides, which exhibited potent inhibition of the HIV-integrase catalyzed strand transfer process. Structural modifications on these molecules were made in order to maximize potency as HIV-integrase inhibitors against the wild type virus, a selection of mutants, and optimize the selectivity, pharmacokinetic, and metabolic profiles in preclinical species. The good profile of Raltegravir has enabled its progression toward the end of phase III clinical trials for the treatment of HIV-1 infection and culminated with the FDA approval as the first HIV-integrase inhibitor for the treatment of HIV-1 infection.

Recent Developments in Fragment-Based Drug Discovery

Abstract: The field of fragment-based drug discovery (FBDD) has developed significantly over the past 10 years and is now recognized as a tangible alternative to more traditional methods of hit identification, such as high throughput screening (HTS). The number of commercial and academic groups actively engaged in fragment-based research has increased, and as a consequence, there has been continued development and refinement of techniques and methods. From its inception, the fragment-based approach had two central tenets that were critical to its success and that have set it apart from HTS and other hit identification techniques. The first is the concept that chemical space can be more efficiently probed by screening collections of small fragments rather than libraries of larger molecules. The number of potential fragments with up to 12 heavy atoms (not including threeand four-membered ring structures) has been estimated at 10, whereas the number of potential druglike molecules with up to 30 heavy atoms is estimated at more than 10. Therefore, a much greater proportion of “fragment-like” chemical space can feasibly be screened in FBDD compared to “druglike” chemical space covered in a HTS where molecular size is much larger. The second idea is that, because by definition fragment molecules are small in size (typically less than 250 Da), they should typically bind with lower affinity to their target protein (micromolar to millimolar range) compared with druglike molecules that can form many more interactions (nanomolar to micromolar range) but that the binding efficiency per atom is at least as high as for larger hit molecules. Implicitly, the screening techniques employed in FBDD must be correspondingly much more sensitive than a HTS bioassay. Generally, sensitive biophysical techniques are employed to detect these weak binding events and to characterize the fragment interactions with the target active site. Nuclear magnetic resonance (NMR) and protein X-ray crystallography have been used extensively in fragment-based research because these techniques are highly sensitive in detecting low affinity fragment binding and also give information about the fragmentprotein interactions being formed. There have been a number of recently published general review articles that have discussed the various aspects of the FBDD field. In addition, there are now two books on the subject. In this journal in 2004, Erlanson et al. summarized the major developments in FBDD since the original publication by Fesik and co-workers of the “SAR by NMR” approach in the late 1990s. Particular note was given to the biophysical methods employed to screen for fragment binding and the merits and drawbacks of each of these techniques, along with the approaches that can be used to optimize fragments into lead molecules. Herein, the trends and developments over the past 4 years will be outlined and some selected examples that are illustrative of the approaches being utilized by those active in the field examined. Additionally, this review will look in some detail at representative protein-ligand complexes observed between fragment-sized molecules and their protein targets from the Protein Data Bank (PDB). Finally, some conclusions will be drawn from these data and the future of FBDD discussed.

Discovery of Dapagliflozin: A Potent, Selective Renal Sodium-Dependent Glucose Cotransporter 2 (SGLT2) Inhibitor for the Treatment of Type 2 Diabetes

Abstract: The C-aryl glucoside 6 (dapagliflozin) was identified as a potent and selective hSGLT2 inhibitor which reduced blood glucose levels in a dose-dependent manner by as much as 55% in hyperglycemic streptozotocin (STZ) rats. These findings, combined with a favorable ADME profile, have prompted clinical evaluation of dapagliflozin for the treatment of type 2 diabetes.

Physicochemical properties of antibacterial compounds: implications for drug discovery.

Abstract: Antibacterial drug discovery peaked shortly after the middle of the past century with the discovery of most compound classes that are still in clinical use. After the introduction of streptogramins and quinolones in 1962, no novel class of antibiotics was identified and approved for clinical use until linezolid was launched in 2000. This fact is rather surprising because not only was research heavily supported during this time but also novel technologies such as genomics and high-throughput screening were introduced and applied to improve productivity. With antibacterial resistance on the rise, we will have to replenish the arsenal of antibacterial drugs to provide physicians with the tools to successfully treat infections in the future. Part of the difficulty associated with the discovery of novel antibacterial compound classes has been defined by stringent requirements for a safe, broad spectrum antibiotic: The target must be essential, highly conserved among various bacterial species, and absent, different, or nonessential in humans. The inhibitor must be potent and should ideally display target-related whole cell activity with a low propensity for the emergence of resistance. Furthermore, the initial “hit” scaffold should be amenable to structural changes to allow for optimization of the potency, efficacy, and safety of later-stage “lead” compounds. A number of authors have discussed not only the necessity of novel antibacterial drugs to ensure future treatment options but also difficulties previously encountered during the hit identification and lead optimization steps. While the declining pipeline of antibacterial compounds arguably reflects the technical complexities of these requirements, relatively little has been published providing detailed information about the difficulties encountered at various companies over the past years. A recent review from the group at GlaxoSmithKline added valuable information on multiple issues related to this topic and provided insight into the successes and failures of a target-based, genomic approach. Relatively little though has been published on the nature of the compounds themselves as a possible source for the paucity of new agents. The analysis of Payne and co-workers illustrates the challenge of antibacterial drug discovery and suggests that multiple parameters contribute to the high attrition rate. With the rise of multi-drug-resistant pathogens and the need for novel antibiotics, it is critical to understand as much as possible from prior efforts and to apply learned lessons to the discovery of future antibiotics. One important parameter in particular has previously been mentioned but, in our view, not sufficiently analyzed: the physicochemical property space of antibacterial drugs. Lipinski’s landmark study represented the first systematic attempt to correlate the physicochemical properties of drugs with the predicted successful matriculation of initial hits and subsequent late-stage leads. It was this work that connected for the first time physicochemical properties of drugs with both their oral bioavailability and their subsequent difficulties and attrition rates during preclinical and clinical development. Major findings from this analysis were the recognition of an ideal property space for orally available drug candidates (MW, lipophilicity, hydrogen bond donors and acceptors), as well as the fact that corporate compound archives had been slowly moving away from an optimal area of this physicochemical space, most likely driven by synthetic convenience rather than by design. This awareness had a major impact on drug discovery, and today it is common to analyze these properties (the “rule of five” or “Lipinski’s rules”) prior to synthesizing novel candidates.

4-[3-(4-cyclopropanecarbonylpiperazine-1-carbonyl)-4-fluorobenzyl]-2H-phthalazin-1-one: a novel bioavailable inhibitor of poly(ADP-ribose) polymerase-1.

Abstract: Poly(ADP-ribose) polymerase activation is an immediate cellular response to metabolic-, chemical-, or ionizing radiation-induced DNA damage and represents a new target for cancer therapy. In this article, we disclose a novel series of substituted 4-benzyl-2H-phthalazin-1-ones that possess high inhibitory enzyme and cellular potency for both PARP-1 and PARP-2. Optimized compounds from the series also demonstrate good pharmacokinetic profiles, oral bioavailability, and activity in vivo in an SW620 colorectal cancer xenograft model. 4-[3-(4-Cyclopropanecarbonylpiperazine-1-carbonyl)-4-fluorobenzyl]-2H-phthalazin-1-one (KU-0059436, AZD2281) 47 is a single digit nanomolar inhibitor of both PARP-1 and PARP-2 that shows standalone activity against BRCA1-deficient breast cancer cell lines. Compound 47 is currently undergoing clinical development for the treatment of BRCA1- and BRCA2-defective cancers.

Flavonoids for Controlling Starch Digestion: Structural Requirements for Inhibiting Human α-Amylase

Abstract: In this study we investigated the structural requirements for inhibition of human salivary alpha-amylase by flavonoids. Four flavonols and three flavones, out of the 19 flavonoids tested, exhibited IC50 values less than 100 microM against human salivary alpha-amylase activity. Structure-activity relationships of these inhibitors by computational ligand docking showed that the inhibitory activity of flavonols and flavones depends on (i) hydrogen bonds between the hydroxyl groups of the polyphenol ligands and the catalytic residues of the binding site and (ii) formation of a conjugated pi-system that stabilizes the interaction with the active site. Our findings show that certain naturally occurring flavonoids act as inhibitors of human alpha-amylase, which makes them promising candidates for controlling the digestion of starch and postprandial glycemia.

Identification of N-(4-piperidinyl)-4-(2,6-dichlorobenzoylamino)-1H-pyrazole-3-carboxamide (AT7519), a novel cyclin dependent kinase inhibitor using fragment-based X-ray crystallography and structure based drug design.

Abstract: The application of fragment-based screening techniques to cyclin dependent kinase 2 (CDK2) identified multiple (>30) efficient, synthetically tractable small molecule hits for further optimization. Structure-based design approaches led to the identification of multiple lead series, which retained the key interactions of the initial binding fragments and additionally explored other areas of the ATP binding site. The majority of this paper details the structure-guided optimization of indazole (6) using information gained from multiple ligand−CDK2 cocrystal structures. Identification of key binding features for this class of compounds resulted in a series of molecules with low nM affinity for CDK2. Optimisation of cellular activity and characterization of pharmacokinetic properties led to the identification of 33 (AT7519), which is currently being evaluated in clinical trials for the treatment of human cancers.

Discovery of an orally bioavailable small molecule inhibitor of prosurvival B-cell lymphoma 2 proteins.

Abstract: Overexpression of prosurvival proteins such as Bcl-2 and Bcl-X L has been correlated with tumorigenesis and resistance to chemotherapy, and thus, the development of antagonists of these proteins may provide a novel means for the treatment of cancer. We recently described the discovery of 1 (ABT-737), which binds Bcl-2, Bcl-X L, and Bcl-w with high affinity, shows robust antitumor activity in murine tumor xenograft models, but is not orally bioavailable. Herein, we report that targeted modifications at three key positions of 1 resulted in a 20-fold improvement in the pharmacokinetic/pharmacodynamic relationship (PK/PD) between oral exposure (AUC) and in vitro efficacy in human tumor cell lines (EC 50). The resulting compound, 2 (ABT-263), is orally efficacious in an established xenograft model of human small cell lung cancer, inducing complete tumor regressions in all animals. Compound 2 is currently in multiple phase 1 clinical trials in patients with small cell lung cancer and hematological malignancies.

Discovery of 5-[[4-[(2,3-Dimethyl-2H-indazol-6-yl)methylamino]-2-pyrimidinyl]amino]-2-methyl-benzenesulfonamide (Pazopanib), a Novel and Potent Vascular Endothelial Growth Factor Receptor Inhibitor†

Abstract: Inhibition of the vascular endothelial growth factor (VEGF) signaling pathway has emerged as one of the most promising new approaches for cancer therapy We describe herein the key steps starting from an initial screening hit leading to the discovery of pazopanib, N(4)-(2,3-dimethyl-2H-indazol-6-yl)-N(4)-methyl-N(2)-(4-methyl-3-sulfonamidophenyl)-2,4-pyrimidinediamine, a potent pan-VEGF receptor (VEGFR) inhibitor under clinical development for renal-cell cancer and other solid tumors

Synthesis and biological properties of benzothiazole, benzoxazole, and chromen-4-one analogues of the potent antitumor agent 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole (PMX 610, NSC 721648).

Abstract: New fluorinated 2-aryl-benzothiazoles, -benzoxazoles, and -chromen-4-ones have been synthesized and their activity against MCF-7 and MDA 468 breast cancer cell lines compared with the potent antitumor benzothiazole 5. Analogues such as 9a,b and 12a,d yielded submicromolar GI50 values in both cell lines; however, none of the new compounds approached 5 in terms of antitumor potency. For 5, binding to the aryl hydrocarbon receptor appeared to be necessary but not sufficient for growth inhibition.

Novel Potent and Selective Bile Acid Derivatives as TGR5 Agonists: Biological Screening, Structure−Activity Relationships, and Molecular Modeling Studies

Abstract: TGR5, a metabotropic receptor that is G-protein-coupled to the induction of adenylate cyclase, has been recognized as the molecular link connecting bile acids to the control of energy and glucose homeostasis. With the aim of disclosing novel selective modulators of this receptor and at the same time clarifying the molecular basis of TGR5 activation, we report herein the biological screening of a collection of natural occurring bile acids, bile acid derivatives, and some steroid hormones, which has resulted in the discovery of new potent and selective TGR5 ligands. Biological results of the tested collection of compounds were used to extend the structure-activity relationships of TGR5 agonists and to develop a binary classification model of TGR5 activity. This model in particular could unveil some hidden properties shared by the molecular shape of bile acids and steroid hormones that are relevant to TGR5 activation and may hence be used to address the design of novel selective and potent TGR5 agonists.

Predicting small-molecule solvation free energies: an informal blind test for computational chemistry.

Abstract: Experimental data on the transfer of small molecules between vacuum and water are relatively sparse. This makes it difficult to assess whether computational methods are truly predictive of this important quantity or merely good at explaining what has been seen. To explore this, a prospective test was performed of two different methods for estimating solvation free energies: an implicit solvent approach based on the Poisson–Boltzmann equation and an explicit solvent approach using alchemical free energy calculations. For a set of 17 small molecules, root mean square errors from experiment were between 1.3 and 2.6 kcal/mol, with the explicit solvent free energy approach yielding somewhat greater accuracy but at greater computational expense. Insights from outliers and suggestions for future prospective challenges of this kind are presented.

Target flexibility: an emerging consideration in drug discovery and design.

Abstract: Department of General and Inorganic Chemistry, UniVersity of Parma, Via G.P. Usberti 17/A 43100, Parma, Italy, National Institute for Biosystems and Biostructures, Rome, Italy, Department of Medicinal Chemistry and Institute for Structural Biology & Drug DiscoVery, Virginia Commonwealth UniVersity, Richmond, Virginia 23298-0540, Department of Pharmaceutics, UniVersity of Parma, Via GP Usberti 27/A, 43100 Parma, Italy, High Performance Systems, CINECA Supercomputing Centre, Casalecchio di Reno, Bologna, Italy, Dulbecco Telethon Institute, Department of Chemistry, UniVersity of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy, Department of Mathematics and Natural Sciences, Pharmaceutical Institute, Christian-Albrechts-UniVersity, Gutenbergstrasse 76, 24118 Kiel, Germany, Departments of Biochemistry & Molecular Biology, Computer Science & Engineering, and Physics & Astronomy, Michigan State UniVersity, East Lansing, Michigan 48824-1319, Department of Molecular Biology, MB-5, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037-1000, Molecular Modeling and Bioinformatics Unit, Institute of Biomedical Research, Scientific Park of Barcelona, Department of Biochemistry and Molecular Biology, UniVersity of Barcelona, Josep Samitier 1-5, Barcelona 08028, Spain, Department of Experimental Medicine, UniVersity of Parma, Via Volturno, 39, 43100, Parma, Italy, Department of Chemical, Food, Pharmaceutical and Pharmacological Sciences, UniVersity of Piemonte Orientale “Amedeo AVogadro”, Via BoVio 6, 28100 NoVara, Italy, Institute of Pharmacy and Food Chemistry, UniVersity of Wurzburg, Am Hubland, D-97074 Wurzburg, Germany

Crystal Structure of the Oxazolidinone Antibiotic Linezolid Bound to the 50S Ribosomal Subunit

Abstract: The oxazolidinone antibacterials target the 50S subunit of prokaryotic ribosomes. To gain insight into their mechanism of action, the crystal structure of the canonical oxazolidinone, linezolid, has been determined bound to the Haloarcula marismortui 50S subunit. Linezolid binds the 50S A-site, near the catalytic center, which suggests that inhibition involves competition with incoming A-site substrates. These results provide a structural basis for the discovery of improved oxazolidinones active against emerging drug-resistant clinical strains.

Discovery of a novel, orally active himbacine-based thrombin receptor antagonist (SCH 530348) with potent antiplatelet activity.

Abstract: The discovery of an exceptionally potent series of thrombin receptor (PAR-1) antagonists based on the natural product himbacine is described. Optimization of this series has led to the discovery of 4 (SCH 530348), a potent, oral antiplatelet agent that is currently undergoing Phase-III clinical trials for acute coronary syndrome (unstable angina/non-ST segment elevation myocardial infarction) and secondary prevention of cardiovascular events in high-risk patients.

Emerging protein targets for anticancer metallodrugs: inhibition of thioredoxin reductase and cathepsin B by antitumor ruthenium(II)-arene compounds

Abstract: A series of ruthenium(II)-arene (RAPTA) compounds were evaluated for their ability to inhibit thioredoxin reductase (either cytosolic or mitochondrial) and cathepsin B, two possible targets for anticancer metallodrugs. In general, inhibition of the thioredoxin reductases was lower than that of cathepsin B, although selected compounds were excellent inhibitors of both classes of enzymes in comparison to other metal-based drugs. Some initial structure-activity relationships could be established. On the basis of the obtained data, different mechanisms of binding/inhibition appear to be operative; remarkably the selectivity of the ruthenium compounds toward solid metastatic tumors also correlates to the observed trends. Notably, docking studies of the interactions of representative RAPTA compounds with cathepsin B were performed that provided realistic structures for the resulting protein-metallodrug adducts. Good agreement was generally found between the inhibiting potency of the RAPTA compounds and the computed stability of the corresponding cat B/RAPTA adducts.

Ligand binding efficiency: trends, physical basis, and implications.

Abstract: Ligand efficiency (i.e., potency/size) has emerged as an important metric in drug discovery. In general, smaller, more efficient ligands are believed to have improved prospects for good drug properties (e.g., bioavailability). Our analysis of thousands of ligands across a variety of targets shows that ligand efficiency is dependent on ligand size with smaller ligands having greater efficiencies, on average, than larger ligands. We propose two primary causes for this size dependence: the inevitable reduction in the quality of fit between ligand and receptor as the ligand becomes larger and more complex and the reduction in accessible ligand surface area on a per atom basis as size increases. These results have far-ranging implications for analysis of high-throughput screening hits, fragment-based approaches to drug discovery, and even computational models of potency.

Fluorescence Spectroscopic Profiling of Compound Libraries

Abstract: Chromo/fluorophoric properties often accompany the heterocyclic scaffolds and impurities that comprise libraries used for high-throughput screening (HTS). These properties affect assay outputs obtained with optical detection, thus complicating analysis and leading to false positives and negatives. Here, we report the fluorescence profile of more than 70 000 samples across spectral regions commonly utilized in HTS. The quantitative HTS paradigm was utilized to test each sample at seven or more concentrations over a 4-log range in 1536-well format. Raw fluorescence was compared with fluorophore standards to compute a normalized response as a function of concentration and spectral region. More than 5% of library members were brighter than the equivalent of 10 nM 4-methyl umbelliferone, a common UV-active probe. Red-shifting the spectral window by as little as 100 nm was accompanied by a dramatic decrease in autofluorescence. Native compound fluorescence, fluorescent impurities, novel fluorescent compounds, a...

Potent and Highly Selective Hypoxia-Activated Achiral Phosphoramidate Mustards as Anticancer Drugs

Abstract: A series of achiral hypoxia-activated prodrugs were synthesized on the basis of the DNA cross-linking toxin of the prodrug, ifosfamide. The hypoxia-selective cytotoxicity of several of the compounds was improved over previously reported racemic mixtures of chiral bioreductive phosphoramidate prodrugs. Prodrugs activated by 2-nitroimidazole reduction demonstrated up to 400-fold enhanced cytotoxicity toward H460 cells in culture under hypoxia versus their potency under aerobic conditions. Compounds were further assessed for their stability to cytochrome P450 metabolism using a liver microsome assay. The 2-nitroimidazole containing lead compound 3b (TH-302) was selectively potent under hypoxia and stable to liver microsomes. It was active in an in vivo MIA PaCa-2 pancreatic cancer orthotopic xenograft model as a monotherapy and demonstrated dramatic efficacy when used in combination with gemcitabine, extending survival with one of eight animals tumor free at day-44. Compound 3b has emerged as a promising antitumor agent that shows excellent in vivo efficacy and is currently being evaluated in the clinic.

Synthesis and Evaluation of Technetium-99m- and Rhenium-Labeled Inhibitors of the Prostate-Specific Membrane Antigen (PSMA)

Abstract: The prostate-specific membrane antigen (PSMA) is increasingly recognized as a viable target for imaging and therapy of cancer. We prepared seven 99mTc/Re-labeled compounds by attaching known Tc/Re chelating agents to an amino-functionalized PSMA inhibitor (lys-NHCONH-glu) with or without a variable length linker moiety. Ki values ranged from 0.17 to 199 nM. Ex vivo biodistribution and in vivo imaging demonstrated the degree of specific binding to engineered PSMA+ PC3 PIP tumors. PC3-PIP cells are derived from PC3 that have been transduced with the gene for PSMA. Despite demonstrating nearly the lowest PSMA inhibitory potency of this series, [99mTc(CO)3(L1)]+ (L1 = (2-pyridylmethyl)2N(CH2)4CH(CO2H)NHCO-(CH2)6CO-NH-lys-NHCONH-glu) showed the highest, most selective PIP tumor uptake, at 7.9 ± 4.0% injected dose per gram of tissue at 30 min postinjection. Radioactivity cleared from nontarget tissues to produce a PIP to flu (PSMA-PC3) ratio of 44:1 at 120 min postinjection. PSMA can accommodate the steric requ...

Ruthenium porphyrin compounds for photodynamic therapy of cancer.

Abstract: Five 5,10,15,20-tetra(4-pyridyl)porphyrin (TPP) areneruthenium(II) derivs., a p-cymeneosmium, a pentamethylcyclopentadienyliridium and a pentamethylcyclopentadienylrhodium analog were prepd. and characterized as potential photosensitizing chemotherapeutic agents. The dinuclear areneruthenium complexes [Ru(h6-arene)(m-Cl)Cl]2 (arene = C6H6, C6H5CH3, p-iPrC6H4Me, C6Me6, and 1,4-C6H4(COOEt)2) react with TPP in MeOH to give the corresponding tetranuclear complexes [Ru4(h6-arene)4(TPP)Cl8] (arene = C6H6 (1, 56% yield), C6H5CH3 (2, 70%), p-iPrC6H4Me (3, 70%), C6Me6 (4, 79%), 1,4-C6H4(COOEt)2 (5, 73%)). The dinuclear p-cymeneosmium complex [Os(h6-p-iPrC6H4Me)(m-Cl)Cl]2 reacts with TPP to form the tetranuclear areneosmium complex [Os4(h6-p-iPrC6H4Me)4(TPP)Cl8] (6) in 47% yield. The isoelectronic Rh and Ir pentamethylcyclopentadienyl derivs. [Rh4(h5-C3Me5)4(TPP)Cl8] (7, 73%) and [Ir4(h5-C3Me5)4(TPP)Cl8] (8, 83%) were obtained in MeOH from the reaction of [M(h5-C5Me5)(m-Cl)Cl]2 (M = Rh, Ir) with TPP. The mol. structures of 4 and 7 were detd. by x-ray crystallog. The biol. effects of all these derivs. were assessed on human melanoma tumor cells, and their cellular uptake and intracellular localization were detd. All mols., except the Rh complex which was not cytotoxic, demonstrated comparable cytotoxicity in the absence of laser irradn. The Ru complexes exhibited excellent phototoxicities toward melanoma cells when exposed to laser light at 652 nm. Cellular uptake and localization microscopy studies of [Ru4(h6-C6H5CH3)4(TPP)Cl8] and [Rh4(h5-C5Me5)4(TPP)Cl8] revealed that they accumulated in the melanoma cell cytoplasm in granular structures different from lysosomes. The fluorescent porphyrin moiety and the metal component were localized in similar structures within the cells. Thus, the porphyrin areneruthenium(II) derivs. represent a promising new class of organometallic photosensitizers able to combine chemotherapeutic activity with photodynamic therapeutic treatment of cancer.

Inhibitor Scaffolds for 2-Oxoglutarate-Dependent Histone Lysine Demethylases.

Abstract: The dynamic methylation of histone lysyl residues plays an important role in biology by regulating transcription, maintaining genomic integrity, and by contributing to epigenetic effects. Here we describe a variety of inhibitor scaffolds that inhibit the human 2-oxoglutarate-dependent JMJD2 subfamily of histone demethylases. Combined with structural data, these chemical starting points will be useful to generate small-molecule probes to analyze the physiological roles of these enzymes in epigenetic signaling.

Radiohalogenated Prostate-Specific Membrane Antigen (PSMA)-Based Ureas as Imaging Agents for Prostate Cancer

Abstract: To extend our development of new imaging agents targeting the prostate-specific membrane antigen (PSMA), we have used the versatile intermediate 2-[3-(5-amino-1-carboxy-pentyl)-ureido]-pentanedioic acid (Lys-C(O)-Glu), which allows ready incorporation of radiohalogens for single photon emission computed tomography (SPECT) and positron emission tomography (PET). We prepared 2-[3-[1-carboxy-5-(4-[(125)I]iodo-benzoylamino)-pentyl]-ureido]-pentanedioic acid ([(125)I]3), 2-[3-[1-carboxy-5-(4-[(18)F]fluoro-benzoylamino)-pentyl]-ureido]-pentanedioic acid ([(18)F]6), and 2-(3-[1-carboxy-5-[(5-[(125)I]iodo-pyridine-3-carbonyl)-amino]-pentyl]-ureido)-pentanedioic acid ([(125)I]8) in 65-80% (nondecay-corrected), 30-35% (decay corrected), and 59-75% (nondecay-corrected) radiochemical yields. Compound [(125)I]3 demonstrated 8.8 +/- 4.7% injected dose per gram (%ID/g) within PSMA(+) PC-3 PIP tumor at 30 min postinjection, which persisted, with clear delineation of the tumor by SPECT. Similar tumor uptake values at early time points were demonstrated for [(18)F]6 (using PET) and [(125)I]8. Because of the many radiohalogenated moieties that can be attached via the epsilon amino group, the intermediate Lys-C(O)-Glu is an attractive template upon which to develop new imaging agents for prostate cancer.