Elisa Palma

Bisphosphonates as radionuclide carriers for imaging or systemic therapy

Bisphosphonates (BPs), biologically stable analogs of naturally occurring pyrophosphates, became the treatment of choice for pathologic conditions characterized by increased osteoclast-mediated bone resorption, namely Pagets disease, osteoporosis and tumor bone disease. Moreover, the clinical success of BPs is also associated with their use in (99m)Tc-based radiopharmaceuticals for bone imaging. In addition to the successful delivery of (99m)Tc (γ-emitter) to bone, BPs have also been used to deliver β(-)-particle emitting radiometals (e.g.(153)Sm, (186/188)Re) for bone-pain palliation. The main goal of this Review is to update the most recent research efforts toward the synthesis, characterization and biological evaluation of novel BP-containing radiometal complexes and radiohalogenated compounds for diagnostic or therapeutic purposes. The structure and in vivo properties of those compounds will be discussed and compared to the clinically available ones, namely in terms of image quality and therapeutic effect. We will also mention briefly the use of BPs as carriers of multimodal nuclear and optical imaging probes.

New ternary bipyridine–terpyridine copper(II) complexes as self-activating chemical nucleases

Seeking self-activating chemical nucleases with potential applications as therapeutic agents, new ternary terpyridine–bipyridine–Cu(II) complexes carrying pendant cyclic amines were developed. After detailed characterization, the nuclease activity of the synthesized compounds was evaluated by using circular plasmid DNA as substrate and analyzing the products by agarose-gel electrophoresis. The new complexes present an impressive plasmid DNA cleaving ability, which triggers double-strand DNA breaks in the absence of any exogenous agents, via an oxidative mechanism. The binding affinity towards duplex DNA was determined using UV-Vis and fluorescence spectroscopic titrations. These studies showed that the tested complexes bind moderately (in the order of 104 M−1) to duplex DNA. The copper complexes displayed high cytotoxicity against ovarian carcinoma A2780 cells (4-fold cisplatin activity), surpassing the resistance on the cisplatin-resistant cell line (A2780cisR) with lower resistance factors. Cellular uptake studies showed that the ternary complexes were able to enter the cell with a significant localization in the cytoskeleton.

New Mixed-Ligand ReV Complexes with Bis(2-mercaptoethyl) Sulfide and Functionalized Thioimidazolyl Ligands

The preparation of the mixed-ligand ReV complexes [Re(O)(κ3-SSS)(κ1-Simz)] (1), [Re(O)(κ3-SSS)(κ1-Simz)]·HCl (2) and [Re(O)(κ3-SSS)(κ1-SimzCOGlyGly)] (3) are described. These [3+1] type compounds are stabilized by tridentate bis(2-mercaptoethyl) sulfide (HSSSH) and by monodentate functionalized thioimidazolyl ligands. Complexes 1, 2 and 3 were fully characterized by IR and 1H NMR spectroscopy, and by X-ray diffraction analysis in the case of 1 and 2. In complexes 1 and 2 the Re atom is five-coordinate, presenting a distorted square pyramidal coordination geometry. Based on the angular structural parameter, τ, this distortion lies towards a trigonal bipyramidal geometry (τ = 0.40, 1; τ = 0.46, 2). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Evaluation of Acridine Orange Derivatives as DNA-Targeted Radiopharmaceuticals for Auger Therapy: Influence of the Radionuclide and Distance to DNA

A new family of 99mTc(I)- tricarbonyl complexes and 125I-heteroaromatic compounds bearing an acridine orange (AO) DNA targeting unit was evaluated for Auger therapy. Characterization of the DNA interaction, performed with the non-radioactive Re and 127I congeners, confirmed that all compounds act as DNA intercalators. Both classes of compounds induce double strand breaks (DSB) in plasmid DNA but the extent of DNA damage is strongly dependent on the linker between the Auger emitter (99mTc or 125I) and the AO moiety. The in vitro evaluation was complemented with molecular docking studies and Monte Carlo simulations of the energy deposited at the nanometric scale, which corroborated the experimental data. Two of the tested compounds, 125I-C5 and 99mTc-C3, place the corresponding radionuclide at similar distances to DNA and produce comparable DSB yields in plasmid and cellular DNA. These results provide the first evidence that 99mTc can induce DNA damage with similar efficiency to that of 125I, when both are positioned at comparable distances to the double helix. Furthermore, the high nuclear retention of 99mTc-C3 in tumoral cells suggests that 99mTc-labelled AO derivatives are more promising for the design of Auger-emitting radiopharmaceuticals than the 125I-labelled congeners.

Biophysical characterization and antineoplastic activity of new bis(thiosemicarbazonato) Cu(II) complexes

Aiming to explore alternative mechanisms of cellular uptake and cytotoxicity, we have studied a new family of copper(II) complexes (CuL1-CuL4) with bis(thiosemicarbazone) (BTSC) ligands containing pendant protonable cyclic amines (morpholine and piperidine). Herein, we report on the synthesis and characterization of these new complexes, as well as on their biological performance (cytotoxic activity, cellular uptake, protein and DNA binding), in comparison with the parental CuIIATSM (ATSM=diacetyl-bis(N4-methylthiosemicarbazonate) complex without pendant cyclic amines. The new compounds have been characterized by a range of analytical techniques including ESI-MS, IR spectroscopy, cyclic voltammetry, reverse-phase HPLC and X-ray spectroscopy. In vitro cytotoxicity studies revealed that the copper complexes are cytotoxic, unlike the corresponding ligands, with a similar potency to that of CuATSM. Unlike CuATSM, the new complexes were able to circumvent cisplatin cross-resistance. The presence of the protonable cyclic amines did not lead to an enhancement of the interaction of the complexes with human serum albumin or calf thymus DNA. However, CuL1-CuL4 showed a remarkably augmented cellular uptake compared with CuATSM, as proved by uptake, internalization and externalization studies that were performed using the radioactive congeners 64CuL1-64CuL4. The enhanced cellular uptake of CuL1-CuL4 indicates that this new family of CuIIBTSC complexes deserves to be further evaluated in the design of metallodrugs for cancer theranostics.