Towards Clinical Development of Scandium Radioisotope Complexes for Use in Nuclear Medicine: Encouraging Prospects with the Chelator 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic Acid (DOTA) and Its Analogues.

Scandium (Sc) isotopes have recently attracted significant attention in the search for new radionuclides with potential uses in personalized medicine, especially in the treatment of specific cancer patient categories. In particular, Sc-43 and Sc-44, as positron emitters with a satisfactory half-life (3.9 and 4.0 h, respectively), are ideal for cancer diagnosis via Positron Emission Tomography (PET). On the other hand, Sc-47, as an emitter of beta particles and low gamma radiation, may be used as a therapeutic radionuclide, which also allows Single-Photon Emission Computed Tomography (SPECT) imaging. As these scandium isotopes follow the same biological pathway and chemical reactivity, they appear to fit perfectly into the "theranostic pair" concept. A step-by-step description, initiating from the moment of scandium isotope production and leading up to their preclinical and clinical trial applications, is presented. Recent developments related to the nuclear reactions selected and employed to produce the radionuclides Sc-43, Sc-44, and Sc-47, the chemical processing of these isotopes and the main target recovery methods are also included. Furthermore, the radiolabeling of the leading chelator, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), and its structural analogues with scandium is also discussed and the advantages and disadvantages of scandium complexation are evaluated. Finally, a review of the preclinical studies and clinical trials involving scandium, as well as future challenges for its clinical uses and applications, are presented.

Gaining Insights on the Interactions of a Class of Decorated (2-([2,2'-Bipyridin]-6-yl)phenyl)platinum Compounds with c-Myc Oncogene Promoter G-Quadruplex and Other DNA Structures.

Organometallic molecules offer some of the most promising scaffolds for interaction with G-quadruplex nucleic acids. We report the efficient synthesis of a family of organoplatinum(II) complexes, featuring a 2-([2,2'-bipyridin]-6-yl)phenyl tridentate (N∧ N∧ C) ligand, that incorporates peripheral side-chains aiming at enhancing and diversifying its interaction capabilities. These include a di-isopropyl carbamoyl amide, a morpholine ethylenamide, two enantiomeric proline imides and an oxazole. The binding affinities of the Pt-complexes were evaluated via UV-vis and fluorescence titrations, against 5 topologically-distinct DNA structures, including c-myc G-quadruplex, two telomeric (22AG) G-quadruplexes, a duplex (ds26) and a single-stranded (polyT) DNA. All compounds exhibited binding selectivity in favour of c-myc, with association constants (Ka ) in the range of 2-5×105  M-1 , lower affinity for both folds of 22AG and for ds26 and negligible affinity for polyT. Remarkable emission enhancements (up to 200-fold) upon addition of excess DNA were demonstrated by a subset of the compounds with c-myc, providing a basis for optical selectivity, since optical response to all other tested DNAs was low. A c-myc DNA-melting experiment showed significant stabilizing abilities for all compounds, with the most potent binder, the morpholine-Pt-complex, exhibiting a ΔTm >30 °C, at 1 : 5 DNA-to-ligand molar ratio. The same study implied contributions of the diverse side-chains to helix stabilization. To gain direct evidence of the nature of the interactions, mixtures of c-myc with the four most promising compounds were studied via UV Resonance Raman (UVRR) spectroscopy, which revealed end-stacking binding mode, combined with interactions of side-chains with loop nucleobase residues. Docking simulations were conducted to provide insights into the binding modes for the same four Pt-compounds, suggesting that the binding preference for two alternative orientations of the c-myc G-quadruplex thymine 'cap' ('open' vs. 'closed'), as well as the relative contributions to affinity from end-stacking and H-bonding, are highly dependent on the nature of the interacting Pt-complex side-chain.

Recent Developments in Small-Molecule Ligands of Medicinal Relevance for Harnessing the Anticancer Potential of G-Quadruplexes.

G-quadruplexes, a family of tetraplex helical nucleic acid topologies, have emerged in recent years as novel targets, with untapped potential for anticancer research. Their potential stems from the fact that G-quadruplexes occur in functionally-important regions of the human genome, such as the telomere tandem sequences, several proto-oncogene promoters, other regulatory regions and sequences of DNA (e.g. rDNA), as well as in mRNAs encoding for proteins with roles in tumorigenesis. Modulation of G-quadruplexes, via interaction with high-affinity ligands, leads to their stabilization, with numerous observed anticancer effects. Despite the fact that only a few lead compounds for G-quadruplex modulation have progressed to clinical trials so far, recent advancements in the field now create conditions that foster further development of drug candidates. This review highlights biological processes through which G-quadruplexes can exert their anticancer effects and describes, via selected case studies, progress of the last few years on the development of efficient and drug-like G-quadruplex-targeted ligands, intended to harness the anticancer potential offered by G-quadruplexes. The review finally provides a critical discussion of perceived challenges and limitations that have previously hampered the progression of G-quadruplex-targeted lead compounds to clinical trials, concluding with an optimistic future outlook.

A Novel Conjugate of Bis[((4-bromophenyl)amino)quinazoline], a EGFR-TK Ligand, with a Fluorescent Ru(II)-Bipyridine Complex Exhibits Specific Subcellular Localization in Mitochondria.

The epidermal growth factor receptor (EGFR) is a key target in anticancer research, whose aberrant function in malignancies has been linked to severe irregularities in critical cellular processes, including cell cycle progression, proliferation, differentiation, and survival. EGFR mutant variants, either transmembrane or translocated to the mitochondria and/or the nucleus, often exhibit resistance to EGFR inhibitors. The ability to noninvasively image and quantify EGFR provides novel approaches in the detection, monitoring, and treatment of EGFR-related malignancies. The current study aimed to deliver a new theranostic agent that combines fluorescence imaging properties with EGFR inhibition. This was achieved via conjugation of an in-house-developed ((4-bromophenyl)amino)quinazoline inhibitor of mutant EGFR-TK, selected from a focused aminoquinazoline library, with a [Ru(bipyridine)3]2+ fluorophore. A triethyleneglycol-derived diamino linker featuring (+)-ionizable sites was employed to link the two functional moieties, affording two unprecedented Ru conjugates with 1:1 and 2:1 stoichiometry of aminoquinazoline to the Ru complex (mono-quinazoline-Ru-conjugate and bis-quinazoline-Ru-conjugate, respectively). The bis-quinazoline-Ru-conjugate, which retains an essential inhibitory activity, was found by fluorescence imaging to be effectively uptaken by Uppsala 87 malignant glioma (grade IV malignant glioma) cells. The fluorescence imaging study and a time-resolved fluorescence resonance energy transfer study indicated a specific subcellular distribution of the conjugate that coincides with that of a mitochondria-targeted dye, suggesting mitochondrial localization of the conjugate and potential association with mitochondria-translocated forms of EGFR. Mitochondrial localization was further documented by the specific concentration of the bis-quinazoline-Ru-conjugate in a mitochondrial isolation assay.

Investigation of 'Head-to-Tail'-Connected Oligoaryl N,O-Ligands as Recognition Motifs for Cancer-Relevant G-Quadruplexes.

Oligomeric compounds, constituted of consecutive N,O-heteroaromatic rings, introduce useful and tunable properties as alternative ligands for biomolecular recognition. In this study, we have explored a synthetic scheme relying on Van Leusen oxazole formation, in conjunction with C-H activation of the formed oxazoles and their subsequent C-C cross-coupling to 2-bromopyridines in order to assemble a library of variable-length, 'head-to-tail'-connected, pyridyl-oxazole ligands. Through investigation of the interaction of the three longer ligands (5-mer, 6-mer, 7-mer) with cancer-relevant G-quadruplex structures (human telomeric/22AG and c-Myc oncogene promoter/Myc2345-Pu22), the asymmetric pyridyl-oxazole motif has been demonstrated to be a prominent recognition element for G-quadruplexes. Fluorescence titrations reveal excellent binding affinities of the 7-mer and 6-mer for a Na⁺-induced antiparallel 22AG G-quadruplex (KD = 0.6 × 10-7 M-1 and 0.8 × 10-7 M-1, respectively), and satisfactory (albeit lower) affinities for the 22AG/K⁺ and Myc2345-Pu22/K⁺ G-quadruplexes. All ligands tested exhibit substantial selectivity for G-quadruplex versus duplex (ds26) DNA, as evidenced by competitive Förster resonance energy transfer (FRET) melting assays. Additionally, the 7-mer and 6-mer are capable of promoting a sharp morphology transition of 22AG/K⁺ G-quadruplex.

LED-induced Ru-photoredox Pd-catalyzed C-H arylation of (6-phenylpyridin-2-yl)pyrimidines and heteroaryl counterparts.

N-heterocycles are essential building blocks and scaffolds in medicinal chemistry. A Pd-catalyzed, Ru-photoredox-mediated C-H arylation is applied herein, for converting a series of functionality-inclusive (6-phenylpyridin-2-yl)pyrimidines to single arylated derivatives, using phenyldiazonium tetrafluoroborate as aryl source. This green chemistry-compliant transformation is induced by LED light. The drug-like modular substrates are constructed via combination of Biginelli multi-component condensation and Suzuki C-C cross-coupling, in order to strategically install, adjacent to the Ph-ring intended to undergo C-H arylation, a (6-pyridin-2-yl)pyrimidine that plays the role of a chelating directing moiety for the C-H arylation catalyst. The scope has been demonstrated on a series of 26 substrates, comprising diverse Ph-ring substituents and substitution patterns, as well as with 13 different aryl donors. Substrates in which the Ph-ring (arylation acceptor) was replaced by an electron-rich heteroaryl counterpart (2-/3-thiophene or -benzofuran) have also been examined and found to undergo arylation regioselectively. End-product conformations afford interesting motifs for occupying 3D chemical space, as implied by single-crystal X-ray diffraction, which has allowed the elucidation of six structures of aryl derivatives and one of an unprecedented pyrimidine-pyridine-benzofuran carbopalladated complex, believed to be a C-H activation derivative.

Catalysis of a Diels-Alder Reaction between Azachalcones and Cyclopentadiene by a Recyclable Copper(II)-PEIP Metal-Organic Framework.

Metal-organic frameworks (MOFs) have attracted considerable interest as emerging heterogeneous catalysts for organic transformations of synthetic utility. Herein, a Lewis-acidic MOF, {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞, denoted as Cu(ΙΙ)-PEIP, has been synthesized via a one-pot process and deployed as an efficient heterogeneous catalyst for a Diels-Alder cycloaddition. Specifically, the [4 + 2] cycloaddition of 13 substituted azachalcone dienophiles with cyclopentadiene has been investigated. MOF-catalyzed reaction conditions were optimized, leading to the selection of water as the solvent, in the presence of 10% mol sodium dodecyl sulfate (SDS) to address substrate solubility. The Cu(II)-PEIP catalyst showed excellent activity under these green and mild conditions, exhibiting comparable or, in some cases, superior efficiency to a homogeneous catalyst often employed in Diels-Alder reactions, namely, Cu(OTf)2. The nature of the azachalcone substituent played a significant role in the reactivity of the dienophiles, with electron-withdrawing (EW) substituents enhancing conversion and electron-donating (ED) ones exhibiting the opposite effect. Coordinating substituents appeared to enhance the endo selectivity. Importantly, the Cu(II)-PEIP catalyst can be readily isolated from the reaction mixture and recycled up to four times without any significant reduction in conversion or selectivity.

Identification of a potent activator of Akt phosphorylation from a novel series of phenolic, picolinic, pyridino, and hydroxamic zinc(II) complexes.

The discovery of small-molecule modulators of signaling pathways is currently a particularly active area of research. We aimed at developing unprecedented metal-based activators of Akt signaling which can potentially find applications as tools for regulating glucose metabolism downstream of Akt or serve as lead structures for developing antidiabetic drugs. In this context, a highly diverse library of 11 new zinc(II) complexes with phenolic, picolinic, pyridino, and hydroxamic ligands, all containing features beneficial for medicinal purposes, was prepared and screened in an assay that detected levels of phospho-Akt in lysates from NIH3T3 cells after treatment with the compounds. The complexes featuring hydroxamic ligands were found to be the most prominent activators of Akt among the molecules prepared, with the most efficient compound acting at submicromolar concentrations. Further characterization revealed that this compound induces phosphorylation of the Akt downstream effector glycogen synthase kinase 3ß, but does not act as an inhibitor of tyrosine phosphatases or PTEN.

FOXO3a is broadly neuroprotective in vitro and in vivo against insults implicated in motor neuron diseases.

Aging is a risk factor for the development of adult-onset neurodegenerative diseases. Although some of the molecular pathways regulating longevity and stress resistance in lower organisms are defined (i.e., those activating the transcriptional regulators DAF-16 and HSF-1 in Caenorhabditis elegans), their relevance to mammals and disease susceptibility are unknown. We studied the signaling controlled by the mammalian homolog of DAF-16, FOXO3a, in model systems of motor neuron disease. Neuron death elicited in vitro by excitotoxic insult or the expression of mutant SOD1, mutant p150(glued), or polyQ-expanded androgen receptor was abrogated by expression of nuclear-targeted FOXO3a. We identify a compound [Psammaplysene A (PA)] that increases nuclear localization of FOXO3a in vitro and in vivo and show that PA also protects against these insults in vitro. Administration of PA to invertebrate model systems of neurodegeneration similarly blocked neuron death in a DAF-16/FOXO3a-dependent manner. These results indicate that activation of the DAF-16/FOXO3a pathway, genetically or pharmacologically, confers protection against the known causes of motor neuron diseases.

Interaction of metal complexes with G-quadruplex DNA.

Guanine-rich sequences of DNA can assemble into tetrastranded structures known as G-quadruplexes. It has been suggested that these secondary DNA structures could be involved in the regulation of several key biological processes. In the human genome, guanine-rich sequences with the potential to form G-quadruplexes exist in the telomere as well as in promoter regions of certain oncogenes. The identification of these sequences as novel targets for the development of anticancer drugs has sparked great interest in the design of molecules that can interact with quadruplex DNA. While most reported quadruplex DNA binders are based on purely organic templates, numerous metal complexes have more recently been shown to interact effectively with this DNA secondary structure. This Review provides an overview of the important roles that metal complexes can play as quadruplex DNA binding molecules, highlighting the unique properties metals can confer to these molecules.

Synthetic libraries of tyrosine-derived bacterial metabolites.

The preparation of a collection of 131 small molecules, reminiscent of families of long chain N-acyl tyrosines, enamides and enol esters that have been isolated from heterologous expression of environmental DNA (eDNA) in Escherichia coli, is reported. The synthetic libraries of N-acyl tyrosines and their 3-keto counterparts were prepared via solid-phase routes, whereas the enamides and enol esters were synthesized in solution-phase.

Preparation of a psammaplysene-based library.

A 28-member focused library, based on the pseudosymmetric template of the marine alkaloids psammaplysenes, was prepared from combinations of components that were, in turn, derived from 4-iodophenol.

Total synthesis of psammaplysenes A and B, naturally occurring inhibitors of FOXO1a nuclear export.

[reaction: see text] Two inhibitors of FOXO1a-mediated nuclear export, psammaplysenes A and B, have been synthesized by a flexible and efficient route. A common starting material, 4-iodophenol, was used to prepare both halves of these pseudosymmetric dibromotyrosine-derived metabolites.

A small molecule mimicking a phosphatidylinositol (4,5)-bisphosphate binding pleckstrin homology domain.

Inositol phospholipids have emerged as important key players in a wide variety of cellular functions. Among the seven existing inositol phospholipids, phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P(2)) has attracted much attention in recent years due to its important role in numerous cellular signaling events and regulations, which in turn impact several human diseases. This particular lipid is recognized in the cell by specific lipid binding domains, such as the Pleckstrin-homology (PH) domain, which is also employed as a tool to monitor this important lipid. Here, we describe the synthesis and biological characterization of a small molecule that mimics the PH domain as judged by its ability to bind specifically to only PI(4,5)P(2) and effectively compete with the PH domain in vitro and in a cellular environment. The binding constant of this small molecule PH domain mimetic (PHDM) was determined to be 17.6 ± 10.1 µM, similar in potency to the PH domain. Using NIH 3T3 mouse fibroblast cells we demonstrated that this compound is cell-permeable and able to modulate PI(4,5)P(2)-dependent effects in a cellular environment such as the endocytosis of the transferrin receptor, loss of mitochondria, as well as stress fiber formation. This highly PI(4,5)P(2)-specific chemical mimetic of a PH domain not only is a powerful research tool but might also be a lead compound in future drug developments targeting PI(4,5)P(2)-dependent diseases such as Lowe syndrome.

Inhibition of mitogen-activated protein kinase (MAPK) and cyclin-dependent kinase 2 (Cdk2) by platinum(II) phenanthroline complexes.

UNLABELLED: Inhibition of protein kinases in the fight against disease remains a constant challenge for medicinal chemists, who have screened multitudes of predominantly planar organic scaffolds, natural and synthetic, to identify potent-albeit not always selective-kinase inhibitors. Herein, in an effort to investigate the potential biological utility of metal-based compounds as inhibitors against the cancer-relevant targets mitogen-activated protein kinase and cyclin-dependent kinase 2, we explore various parameters in planar platinum(II) complexes with substituted phenanthroline ligands and aliphatic diamine chelate co-ligands, to identify combinations that yield promising inhibitory activity. The individual ligands' steric requirements as well as their pattern of hydrogen bond donors/acceptors appear to alter inhibitory potency when modulated. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12154-011-0059-5) contains supplementary material, which is available to authorized users.