Pegylation of 1,4,8,11-tetraazacyclotetradecane (cyclam) and its Cu(II) complexation

Dendrimers as Nd3+ ligands: effect of generation on the efficiency of the sensitized lanthanide emission

We have designed two novel dendrimers with cyclam cores with appended poly(amido amine) (PAMAM) dendrons, decorated at the periphery with four and eight dansyl chromophores, respectively. The photophysical properties of the dendrimers and their Nd(3+) complexes have been investigated. The energy-transfer efficiency to the lanthanide ions from these dendrimers has been studied as a function of the generation. It has been observed that an increase in the dendrimer generation as well as the number of amide units enhances the energy transfer to the lanthanide ion.

Nanomaterials: applications in cancer imaging and therapy

The application of nanomaterials (NMs) in biomedicine is increasing rapidly and offers excellent prospects for the development of new non-invasive strategies for the diagnosis and treatment of cancer. In this review, we provide a brief description of cancer pathology and the characteristics that are important for tumor-targeted NM design, followed by an overview of the different types of NMs explored to date, covering synthetic aspects and approaches explored for their application in unimodal and multimodal imaging, diagnosis and therapy. Significant synthetic advances now allow for the preparation of NMs with highly controlled geometry, surface charge, physicochemical properties, and the decoration of their surfaces with polymers and bioactive molecules in order to improve biocompatibility and to achieve active targeting. This is stimulating the development of a diverse range of nanometer-sized objects that can recognize cancer tissue, enabling visualization of tumors, delivery of anti-cancer drugs and/or the destruction of tumors by different therapeutic techniques.

A novel tetrabranched neurotensin(8-13) cyclam derivative: synthesis, 64Cu-labeling and biological evaluation

New macrocyclic 1,4,8,11-tetraazacyclotetradecane (cyclam) derivatives with 1, 2 and 4 neurotensin(8-13) units 4, 5 and 7 have been synthesized. Compounds 4 and 5 were prepared by the reaction of non-stabilized neurotensin(8-13) and cyclamtetrapropionic acid 2 using 1-ethyl-3-(3-dimethylaminocarbonyl)carbodiimide-hydrochloride and N-hydroxysulfosuccinimide. The tetrameric compound 7 was synthesized by Michael addition of neurotensin(8-13) acrylamide 6 and cyclam 1. The copper(II) complexation behavior of 4, 5 and 7 was investigated by UV/visible spectrophotometry and shows that the metal center resides inside the N4 chromophore with additional apical interactions established with pendant arms. The novel tetrabranched NT(8-13) cyclam 7 with nanomolar neurotensin receptor 1 binding affinity was efficiently radiolabeled with (64)Cu under mild conditions. (64)Cu⊂7 showed slow transchelation in the presence of a large amount of cyclam as competing ligand, while it completely remains intact in the presence of EDTA. The in vivo behavior of (64)Cu⊂7 was studied in rats and mice. The metabolic stability in rodent models was high with a half-life of intact (64)Cu⊂7 in plasma of 34 min in rats and 60 min in the mice, respectively. The binding affinity was high enough to demonstrate in vivo binding of (64)Cu⊂7 to NTR1 overexpressing HT-29 tumor xenotransplants in nude mice. Regarding elimination, (64)Cu⊂7 showed a substantial renal and reticuloendothelial accumulation. On the other hand, metabolization of the compound in vivo with a resulting metabolite-postulated to be the (64)Cu-cyclam-tetraarginine complex-also showed long retention in the circulating blood, preventing a better contrast of tumor imaging.

Sugar-decorated dendritic nanocarriers: encapsulation and release of the octahedral rhenium cluster complex [Re6S8(OH)6]4-

The encapsulation of a nanometer-sized octahedral anionic rhenium cluster complex with six terminal hydroxo ligands [Re(6)S(8)(OH)(6)](4-) in maltose-decorated poly(propylene amine) dendrimers (POPAM, generation 4 and 5) has been investigated. Ultrafiltration experiments showed that maximal loading capacity of the dendrimers with the cluster complex is achieved after about ten hours in aqueous solution. To study the inclusion phenomena, three different methods have been applied: UV/Vis, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and laser-induced liquid bead ion desorption mass spectrometry (LILBID-MS). From the results obtained, it could be concluded that: a) the hydrolytic stability of the rhenium cluster complex is significantly enhanced in the presence of dendritic hosts; b) the cluster anions are preferentially bound inside the dendrimers; c) the number of cluster complexes encapsulated in the dendrimers increases with rising dendrimer generation. On average, four to five cluster anions can preferentially be captured in the interior of sugar-coated dendritic carriers. An asymptotic progression of the release of cluster complexes from the loaded dendrimers was observed under physiologically relevant conditions (isotonic sodium chloride solution: approximately 93 % within 4 days for loaded POPAM-G4-maltose; approximately 86 % within 4 days for loaded POPAM-G5-maltose). These encapsulation and release properties of maltose-decorated nanocarriers imply the possibility for the development of the next generation of dendritic nanocarriers with specific targeting of destined tissue for therapeutic treatments.

Fragmentation reactions of singly and doubly protonated thiourea- and sugar-substituted cyclams and their transition-metal complexes

Cyclam macrocycles tetrasubstituted with amino-, thiourea-, and sugar-terminated side chains are ionized by electrospray ionization mass spectrometry (ESI-MS) as singly or doubly protonated species or as transition-metal complexes. Their fragmentation behavior is examined in a Fourier-transform ion-cyclotron-resonance (FT-ICR) mass spectrometer by collision-induced dissociation (CID) experiments. Typically, fragmentation occurs within the side chains through a number of different 1,2-elimination reactions irrespective of the absence or presence of a transition metal ion such as Co(2+), Ni(2+), or Zn(2+). A remarkable exception is Cu(2+), which induces ring cleavage reactions. This is traced back to an electron transfer from the cyclam nitrogen atoms to the Cu(2+) ion. The electron transfer creates a cation-radical within the macrocycle, which induces typical fragmentation reactions such as alpha-cleavages that lead to fragmentation within the macrocycle. This interpretation is in line with fragmentation experiments on unsubstituted cyclam and its complexes.

Intramolecular Charge Transfer in 1:1 Cu(II)/Pyrenylcyclam Dendrimer Complexes

Two newly synthesized pyrenylcyclam dendrons (1 and 2) exhibit a new emission band centered at 450 nm when coordinated with copper triflate. Observed fluorescence shifts induced by coordinative metalation indicate an unusual intramolecular charge transfer from a pyrenyl excited state to the coordinated metal ion that competes with pyrene excimer formation. This interaction likely proceeds by photoexcitation of pi-complex of the appended arene, followed by intramolecular charge transfer within the dendritic 1:1 cyclam/metal complex, effecting reduction of the bound Cu(II) metal ion. The appended dendritic groups not only decrease the equilibrium binding constant with Cu(II) but also participate in a new excited-state pathway as an alternative to energy-dissipative excimer formation.