Development of a PET Tracer for OGA with Improved Kinetics in the Living Brain.

O-GlcNAcylation is thought to play a role in the development of tau pathology in Alzheimer's disease because of its ability to modulate tau's aggregation propensity. O-GlcNAcylation is regulated by 2 enzymes: O-GlcNAc transferase and O-GlcNAcase (OGA). Development of a PET tracer would therefore be an essential tool for developing therapeutic small-molecule inhibitors of OGA, enabling clinical testing of target engagement and dose selection. Methods: A collection of small-molecule compounds was screened for inhibitory activity and high-affinity binding to OGA, as well as favorable PET tracer attributes (multidrug resistance protein 1 efflux, central nervous system PET multiparameter optimization, etc.). Two lead compounds with high affinity and selectivity for OGA were selected for further profiling, including OGA binding to tissue homogenate using a radioligand competition binding assay. In vivo pharmacokinetics were established using a microdosing approach with unlabeled compounds in rats. In vivo imaging studies were performed in rodents and nonhuman primates (NHPs) with 11C-labeled compounds. Results: Two selected candidates, BIO-735 and BIO-578, displayed promising attributes in vitro. After radiolabeling with tritium, [3H]BIO-735 and [3H]BIO-578 binding in rodent brain homogenates demonstrated dissociation constants of 0.6 and 2.3 nM, respectively. Binding was inhibited, concentration-dependently, by homologous compounds and thiamet G, a well-characterized and structurally diverse OGA inhibitor. Imaging studies in rats and NHPs showed both tracers had high uptake in the brain and inhibition of binding to OGA in the presence of a nonradioactive compound. However, only BIO-578 demonstrated reversible binding kinetics within the time frame of a PET study with a 11C-labeled molecule to enable quantification using kinetic modeling. Specificity of tracer uptake was confirmed with a 10 mg/kg blocking dose of thiamet G. Conclusion: We describe the development and testing of 2 11C PET tracers targeting the protein OGA. The lead compound BIO-578 demonstrated high affinity and selectivity for OGA in rodent and human postmortem brain tissue, leading to its further testing in NHPs. NHP PET imaging studies showed that the tracer had excellent brain kinetics, with full inhibition of specific binding by thiamet G. These results suggest that the tracer [11C]BIO-578 is well suited for further characterization in humans.

18F-Trifluoromethanesulfinate Enables Direct C-H 18F-Trifluoromethylation of Native Aromatic Residues in Peptides.

18F labeling strategies for unmodified peptides with [18F]fluoride require 18F-labeled prosthetics for bioconjugation more often with cysteine thiols or lysine amines. Here we explore selective radical chemistry to target aromatic residues applying C-H 18F-trifluoromethylation. We report a one-step route to [18F]CF3SO2NH4 from [18F]fluoride and its application to direct [18F]CF3 incorporation at tryptophan or tyrosine residues using unmodified peptides as complex as recombinant human insulin. The fully automated radiosynthesis of octreotide[Trp(2-CF218F)] enables in vivo positron emission tomography imaging.

PET Radioligands for imaging of the PDE10A in human: current status.

The development of ß+ emitter tracers labelled with carbon-11 or fluorine-18 having optimal characteristics of affinity and selectivity for the phosphodiesterase 10 A protein has received considerable attention, due to the major implication of this enzyme in neurological and psychiatric disorders, such as Hungtington's disease, Parkinson's disease and schizophrenia. The ability to quantify PDE10 A availability in the human brain in vivo will thus aid understanding its role in neurodegenerative and neuropsychiatric pathophysiology as well as providing a valuable tool for drug development. This manuscript reviews the different compound series assessed to date as PET radioligand for the PDE10 A in human and their use to support the development programmes of novel drugs or to evaluate PDE10 A alterations in pathologies as Huntington`s, Parkinson`s Diseases and Schizophrenia.

Anticancer Gold(III) Peptidomimetics: From Synthesis to in vitro and ex vivo Biological Evaluations.

Five new AuIII -peptidodithiocarbamato complexes of the type [AuIII Br2 (dtc-AA1 -AA2 -OR] (in which AA1 =N-methylglycine (Sar), l/d-Pro; AA2 =l/d-Ala, α-aminoisobutyric acid (Aib); R=OtBu, triethylene glycol methyl ether), differing with regard to the amino acid sequence and/or the chiral amino acid configuration, were designed to enhance tumor selectivity and bioavailability. The gold(III)-based moiety was functionalized to exploit the targeting properties of the peptidomimetic ligand toward two peptide transporters (namely PEPT1 and PEPT2), which are upregulated in several tumor cells. The compounds were synthesized and fully characterized, mainly by means of elemental analysis, one- and two-dimensional NMR spectroscopy, FT-IR, and UV/Vis spectrophotometry. The crystal structures of three compounds were also solved by X-ray diffraction. In vitro cytotoxicity studies using a panel of human tumor cell lines (A549 [non-small-cell lung carcinoma], MCF-7 [breast cancer], A2780 [ovarian carcinoma], H1975 [non-small-cell lung carcinoma], H460 [large-cell lung carcinoma], and A431 [human epidermoid carcinoma]) showed the dtc-Pro-Aib-OtBu derivative to be very effective, with GI50 values much lower than those of cisplatin. This complex was thus selected for evaluating stability under physiological conditions and possible interactions with serum albumin, as well in PARP-1 enzyme inhibition assays and preliminary ex vivo toxicity experiments on healthy rat tissues.

Use of carbon-11 labelled tool compounds in support of drug development.

The pharmaceutical industry is facing key challenges to improve return on R&D investment. Positron emission tomography (PET), by itself or in combination with complementary technologies such as magnetic resonance imaging (MRI), provides a unique opportunity to confirm a candidate's ability to meet the so-called 'three pillars' of drug development. Positive confirmation provides confidence for go/no-go decision making at an early stage of the development process and enables informed clinical progression. Whereas fluorine-18 has probably gained wider use in the community, there are benefits to using carbon-11 given the greater flexibility the use of this isotope permits in adaptive clinical study design. This review explores the scope of available carbon-11 chemistries and provides clinical examples to highlight its value in PET studies in support of drug development.

Beyond platinums: gold complexes as anticancer agents.

The accidental discovery of the anticancer properties of cisplatin in the mid-1960s triggered the development of alternative platinum-based drugs. However, the platinum-based treatment of tumor diseases is massively hampered by severe side-effects and development of resistance. Sulfur-containing biomolecules play a significant role in platinum anticancer chemotherapy because of their high affinity to the platinum(II) ion. Sulfur is involved in the entire metabolic processing of platinum drugs. Strong and irreversible binding of cisplatin to intracellular thiolato ligands is considered a major step of inactivation, and reactions with sulfur donors in proteins are believed to affect enzymatic processes. Consequently, the development of novel metal-based compounds with a pharmacological profile different from that of clinically-established platinum drugs is a major goal of modern medicinal chemistry and drug design. Among the non-platinum antitumor agents, gold(III) complexes have recently gained increasing attention due to their strong tumor cell growth-inhibiting effects, generally achieved by exploiting non-cisplatin-like mechanisms of action. The real breakthrough is not simply the use of gold compounds to treat cancer, but the rational design of gold-based drugs which may be very effective, non-toxic and potentially selective towards cancer cells, their potential impact relying on the possible site-specific delivery in localized cancer, thus strongly improving cellular uptake and minimizing unwanted side-effects. Cancer cells are known to overexpress specific proteins and receptors needed for tumor growth. Among them, two integral plasma membrane proteins mediate the cellular uptake of di- and tripeptides and peptide-like drugs. They are present predominantly in epithelial cells of the small intestine, bile duct, mammary glands, lung, choroid plexus, and kidney but are also localized in other tissues and are up-regulated in some types of tumors. Accordingly, we have been designing gold(III)-peptide dithiocarbamato derivatives which combine both the antitumor properties and reduced side-effects of the previously reported gold(III) analogues with enhanced bioavailability and tumor selectivity achieved by exploiting peptide transporters. Our compounds showed interesting cytotoxic properties towards a number of cancer cell lines in vitro and in vivo on xenograft models, together with negligible organ and acute toxicity. With respect to their mechanisms of action, we identified mitochondria and proteasome as major in vitro and in vivo targets. These results allowed the filing of an international patent for the use of gold(III) peptidomimetics in cancer chemotherapy, as well as providing a solid starting point for them to enter phase I clinical trials in a few months.

Insights into the reactivity of gold-dithiocarbamato anticancer agents toward model biomolecules by using multinuclear NMR spectroscopy.

Some gold(III)-dithiocarbamato derivatives of either single amino acids or oligopeptides have shown promise as potential anticancer agents, but their capability to interact with biologically relevant macromolecules is still poorly understood. We investigated the affinity of the representative complex [Au(III)Br2(dtc-Sar-OCH3)] (dtc: dithiocarbamate; Sar: sarcosine (N-methylglycine)) with selected model molecules for histidine-, methionine-, and cysteine-rich proteins (that is, 1-methylimidazole, dimethylsulfide, and N-acetyl-L-cysteine, respectively). In particular, detailed mono- and multinuclear NMR studies, in combination with multiple (13)C/(15)N enrichments, allowed interactions to be followed over time and indicated somewhat unexpected reaction pathways. Whereas dimethylsulfide proved to be unreactive, a sudden multistep redox reaction occurred in the presence of the other potential sulfur donor, N-acetyl-L-cysteine (confirmed if glutathione was used instead). On the other hand, 1-methylimidazole underwent an unprecedented acid-base reaction with the gold(III) complex, rather than the expected coordination to the metal center by replacing, for instance, a bromide. Our results are discussed herein and compared with the data available in the literature on related complexes; our findings confirm that the peculiar reactivity of gold(III)-dithiocarbamato complexes can lead to novel reaction pathways and, therefore, to new cytotoxic mechanisms in cancer cells.

Ruthenium(II/III)-based compounds with encouraging antiproliferative activity against non-small-cell lung cancer.

Hereby we present the synthesis of several ruthenium(II) and ruthenium(III) dithiocarbamato complexes. Proceeding from the Na[trans-Ru(III)(dmso)(2)Cl(4)] (2) and cis-[Ru(II)(dmso)(4)Cl(2)] (3) precursors, the diamagnetic, mixed-ligand [Ru(II)L(2)(dmso)(2)] complexes 4 and 5, the paramagnetic, neutral [Ru(III)L(3)] monomers 6 and 7, the antiferromagnetically coupled ionic α-[Ru(III)(2)L(5)]Cl complexes 8 and 9 as well as the ß-[Ru(III)(2)L(5)]Cl dinuclear species 10 and 11 (L = dimethyl- (DMDT) and pyrrolidinedithiocarbamate (PDT)) were obtained. All the compounds were fully characterised by elemental analysis as well as (1)H NMR and FTIR spectroscopy. Moreover, for the first time the crystal structures of the dinuclear ß-[Ru(III)(2)(dmdt)(5)]BF(4)⋅CHCl(3)⋅CH(3)CN and of the novel [Ru(II)L(2)(dmso)(2)] complexes were also determined and discussed. For both the mono- and dinuclear Ru(II) and Ru(III) complexes the central metal atoms assume a distorted octahedral geometry. Furthermore, in vitro cytotoxicity of the complexes has been evaluated on non-small-cell lung cancer (NSCLC) NCI-H1975 cells. All the mono- and dinuclear Ru(III) dithiocarbamato compounds (i.e., complexes 6-10) show interesting cytotoxic activity, up to one order of magnitude higher with respect to cisplatin. Otherwise, no significant antiproliferative effect for either the precursors 2 and 3 or the Ru(II) complexes 4 and 5 has been observed.

Rational design of gold(III)-dithiocarbamato peptidomimetics for the targeted anticancer chemotherapy.

As a further extension of our research work focusing on the development of gold(III)-dithiocarbamato dtc derivatives of oligopeptides as potential anticancer agents, complexes [Au(III)X(2)(dtc-Sar-L-Ser(t-Bu)-O(t-Bu))] (X=Br (1a)/Cl (1b)), [Au(III)X(2)(dtc-AA-Aib(2)-O(t-Bu))] (AA=Sar (sarcosine, N-methylglycine), X=Br (2a)/Cl (2b); AA=D,L-Pro, X=Br (3a)/Cl (3b)), [Au(III)X(2)(dtc-Sar-Aib(3)-O(t-Bu))] (X=Br (4a)/Cl (4b)), and [Au(III)X(2)(dtc-Sar-Aib(3)-Gly-OEt)] (X=Br (5a)/Cl (5b)) (Aib = "alpha"-aminoisobutyric acid, 2-methylalanine) were designed to obtain metal-based peptidomimetics that may specifically target two peptide transporters (namely, PEPT1 and PEPT2) upregulated in several human tumor cells. All the compounds were characterized by means of FT-IR and mono- and multidimensional NMR spectroscopy. According to in vitro cytotoxicity studies, complex [Au(III)Cl(2)(dtc-D,L-Pro-Aib(2)-O(t-Bu))] (3b) turned out to be the most effective toward the four human tumor cell lines evaluated (PC3, 2008, C13, and L540), for which the IC(50) values were lower than cisplatin. Remarkably, it showed no cross-resistance with cisplatin itself and was proved to inhibit tumor cell proliferation by inducing almost exclusively late apoptosis/necrosis. Biological results are here reported and discussed in terms of the structure-activity relationship.