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Procedures are described for linking monomethoxypoly(ethylene glycol) (mPEG) to both epsilon and alpha amino groups of lysine. The lysine carboxyl group can then be activated as a succinimidyl ester to obtain a new mPEG derivative (mPEG2-COOSu) with improved properties for biotechnical applications. This branched reagent showed in some cases a lower reactivity toward protein amino groups than the linear mPEG from which it was derived. A comparison of mPEG- and mPEG2-modified enzymes (ribonuclease, catalase, asparaginase, trypsin) was carried out for activity, pH and temperature stability, Km and Kcat values, and protection to proteolytic digestion. Most of the adducts from mPEG and mPEG2 modification presented similar activity and stability toward temperature change and pH change, although in a few cases mPEG2 modification was found to increase temperature stability and to widen the range of pH stability of the adducts. On the other hand, all of the enzymes modified with the branched polymer presented greater stability to proteolytic digestion relative to those modified with the linear mPEG. A further advantage of this branched mPEG lies in the possibility of a precise evaluation of the number of polymer molecules bound to the proteins; upon acid hydrolysis, each molecule of mPEG2 releases a molecule of lysine which can be detected by amino acid analysis. Finally, dimerization of mPEG by coupling to lysine provides a needed route to monofunctional PEGs of high molecular weight.

Over the last few decades, nanocarriers for drug delivery have emerged as powerful tools with unquestionable potential to improve the therapeutic efficacy of anticancer drugs. Many colloidal drug delivery systems are underdevelopment to ameliorate the site specificity of drug action and reduce the systemic side effects. By virtue of their small size they can be injected intravenously and disposed into the target tissues where they release the drug. Nanocarriers interact massively with the surrounding environment, namely, endothelium vessels as well as cells and blood proteins. Consequently, they are rapidly removed from the circulation mostly by the mononuclear phagocyte system. In order to endow nanosystems with long circulation properties, new technologies aimed at the surface modification of their physicochemical features have been developed. In particular, stealth nanocarriers can be obtained by polymeric coating. In this paper, the basic concept underlining the “stealth” properties of drug nanocarriers, the parameters influencing the polymer coating performance in terms of opsonins/macrophages interaction with the colloid surface, the most commonly used materials for the coating process and the outcomes of this peculiar procedure are thoroughly discussed.

In the last decades, the staggering progress in nanotechnology brought around a wide and heterogeneous range of nanoparticle-based platforms for the diagnosis and treatment of many diseases. Most of these systems are designed to be administered intravenously. This administration route allows the nanoparticles (NPs) to widely distribute in the body and reach deep organs without invasive techniques. When these nanovectors encounter the biological environment of systemic circulation, a dynamic interplay occurs between the circulating proteins and the NPs, themselves. The set of proteins that bind to the NP surface is referred to as the protein corona (PC). PC has a critical role in making the particles easily recognized by the innate immune system, causing their quick clearance by phagocytic cells located in organs such as the lungs, liver, and spleen. For the same reason, PC defines the immunogenicity of NPs by priming the immune response to them and, ultimately, their immunological toxicity. Furthermore, the protein corona can cause the physical destabilization and agglomeration of particles. These problems induced to consider the PC only as a biological barrier to overcome in order to achieve efficient NP-based targeting. This review will discuss the latest advances in the characterization of PC, development of stealthy NP formulations, as well as the manipulation and employment of PC as an alternative resource for prolonging NP half-life, as well as its use in diagnostic applications.

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Surface decoration of gold nanoparticles with thermoresponsive polymers endows a temperature tunable colloidal system switchable for enhanced intracellular up-take. Gold nanoparticles (AuNP, 18 ± 11 nm-diameter) produced by laser ablation synthesis in liquid solution were surface coated with thermoresponsive thiol terminated poly-N-isopropylacrylamide-co-acrylamide co-polymer possessing a lower critical solution temperature (LCST) at 37 °C. Under selected conditions about 3800 polymer chains were conjugated per particle. The polymer coated nanoparticles were found to display thermosensitive properties, as in solution they exhibited reversible aggregation/deaggregation above and below the LCST, respectively. Cell culture studies showed that the polymer decorated AuNP were located into human breast adenocarcinoma MCF7 cells treated at 40 °C (12000 AuNP/cell) with more than 80-fold greater up-take compared to cells treated at 34 °C with the same particles (140 AuN/cell). This difference is attributable to a ‘switching’ of the polymer coating to a globule state at 37 °C and an increased hydrophobicity of the particles with a simultaneous loss of the ‘stealth’ properties of the polymer coating. By contrast, cell up-take of uncoated AuNP (about 6000 AuNP/cell) did not depend on the incubation temperature. These data show that good control of the AuNP cell up-take can be obtained with the new polymer-gold nanoconjugates, and suggest that these systems might find use for targeting cells in vitro by a small temperature change or in vivo in body sites, such as inflamed or tumour tissues, where a temperature variation is already present

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