Radical Dendrimers Based on Biocompatible Oligoethylene Glycol Dendrimers as Contrast Agents for MRI.

Finding alternatives to gadolinium (Gd)-based contrast agents (CA) with the same or even better paramagnetic properties is crucial to overcome their established toxicity. Herein we describe the synthesis and characterization of entirely organic metal-free paramagnetic macromolecules based on biocompatible oligoethylene glycol dendrimers fully functionalized with 5 and 20 organic radicals (OEG Gn-PROXYL (n = 0, 1) radical dendrimers) with the aim to be used as magnetic resonance imaging (MRI) contrast agents. Conferring high water solubility on such systems is often a concern, especially in large generation dendrimers. Our approach to overcome such an issue in this study is by synthesizing dendrimers with highly water-soluble branches themselves. In this work, we show that the highly water-soluble OEG Gn-PROXYL (n = 0, 1) radical dendrimers obtained showed properties that convert them in good candidates to be studied as contrast agents for MRI applications like diagnosis and follow-up of infectious diseases, among others. Importantly, with the first generation radical dendrimer, a similar r1 relaxivity value (3.4 mM-1s-1) in comparison to gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) used in clinics (3.2 mM-1s-1, r.t. 7T) has been obtained, and it has been shown to not be cytotoxic, avoiding the toxicity risks associated with the unwanted accumulation of Gd in the body.

Fully Water-Soluble Polyphosphorhydrazone-Based Radical Dendrimers Functionalized with Tyr-PROXYL Radicals as Metal-Free MRI T1 Contrast Agents.

The finding of alternative imaging probes to Gadolinium (Gd) and other metal based contrast agents (CA) is crucial to overcome their established toxicity. Herein we describe the synthesis and characterization of an entirely organic metal-free magnetic resonance imaging (MRI) contrast agent based on polyphosphorhydrazone (PPH) dendrimers, fully functionalized with up to 48 organic nitroxide radical units. We propose an innovative synthetic procedure based on the use of an amino acid linker (Tyr) coupled to each dendrimer's branch that permits the anchoring of the radicals and at the same time makes possible the control over their water solubility. We demonstrate that the negatively charged resulting PPH Gn-Tyr-PROXYL (n = 0-3) radical dendrimers are excellent candidates to be used as MRI contrast agents, suited for biomedical applications as they show high water solubility, no aggregation problems, and low cytotoxicity, as well as good stability in highly reducing environments. It is achieved a remarkable r1 relaxivity, ca. four times higher (13 mM-1 s-1) than the gold-standard Gd-DTPA used in clinics. Furthermore, the r1 and r2 relaxivity per unit of radical showed an increase with the increase in generation of dendrimers.

Tuning Spin-Spin Interactions in Radical Dendrimers.

Two generations of polyphosphorhydrazone (PPH) dendrimers were synthesized and fully functionalized with TEMPO radicals via acrylamido or imino group linkers to evaluate the impact of the linker substitution on the radical-radical interactions. A drastic change in the way that the radicals interacted among them was observed by EPR and CV studies: while radicals in Gn -imino-TEMPO dendrimers presented a strong spin-spin interaction, in the Gn -acrylamido-TEMPO ones they acted mainly as independent radicals. This shows that these interactions could be tuned by the solely substitution of the radical linker, opening the perspective of controlling and modulating the extension of these interactions depending on each application. The chemical properties of the linker strongly influence the spin-spin exchange between pendant radicals.

Dendrimers as Innovative Radiopharmaceuticals in Cancer Radionanotherapy.

Radiotherapy is one of the most commonly used cancer treatments, with an estimate of 40% success that could be improved further if more efficient targeting and retention of radiation at the tumor site were achieved. This review focuses on the use of dendrimers in radionanotherapy, an emerging technology aimed to improve the efficiency of radiotherapy by implementing nanovectorization, an already established praxis in drug delivery and diagnosis. The labeling of dendrimers with radionuclides also aims to reduce the dose of radiolabeled materials and, hence, their toxicity and tumor resistance. Examples of radiolabeled dendrimers with alpha, beta, and Auger electron emitters are commented, along with the use of dendrimers in boron neutron capture therapy (BNCT). The conjugation of radiolabeled dendrimers to monoclonal antibodies for a more efficient targeting and the application of dendrimers in gene delivery radiotherapy are also covered.

In vitro studies on 5-florouracil-loaded DTPA-PE containing nanosized pegylated liposomes for diagnosis and treatment of tumor.

Theranostic liposomes carry both the therapeutic active ingredients and the contrast agent into one delivery system. Codelivery of imaging contrast agent and chemotherapeutic drugs can provide real-time validation of the targeting strategy, resulting in an another step forward for individual-based therapy. The aim of this study was the incorporation of different drugs used in the diagnosis and treatment of tumors into one delivery system to develop nanosized, polyethylene glycol (PEG)-coated, different charged theranostic liposomes. Different charged liposomes consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or Phospholipon(®) 90G (PL 90G; Phospholipid GmbH, Cologne, Germany), cholesterol, poly(ethylene glycol)2000/phosphatidyl ethanolamine (PEG(2000)-PE), stearylamine (SA) or dicetyl phosphate (DCP), and diethylenetriamine pentaacetate/PE (DTPA-PE) as bilayer ingredients and 5-florouracil (5-FU) as active substance were prepared by the film technique. Characterization, 5-FU in vitro release, cytotoxicity, and physical stability studies were performed. Particle size of all liposomes was 100-150 nm. Difference was not noted between encapsulation efficiency (EE%) of neutral DPPC and PL 90G liposomes containing 5-FU. EE% of charged DPPC liposomes was higher than that of charged PL 90G liposomes. PL 90G containing liposomes had a higher phospholipid amount than the same formulation of DPPC liposomes. DPPC containing different charged liposomes were selected for cytotoxicity studies. Different charged DPPC liposomes had the same antitumoral activity with the free 5-FU solution on MCF-7 cell lines. Liposome dispersions were more stable from the point of particle-size change and 5-FU leakage during storage at refrigerated temperature. The results of this study are very encouraging for the development of theranostic liposome formulations as a targeted delivery system for drugs, such as 5-FU, used both in therapy and imaging.