Albumin-based nanoparticles as magnetic resonance contrast agents: I. Concept, first syntheses and characterisation

Abstract

To develop a platform for molecular magnetic resonance imaging, we prepared gadolinium-bearing albumin-polylactic acid nanoparticles in the size range 20-40 nm diameter. Iterative cycles of design and testing upscaled the synthesis procedures to gram amounts for physicochemical characterisation and for pharmacokinetic testing. Morphological analyses showed that the nanoparticles were spheroidal with rough surfaces. Particle sizes were measured by direct transmission electron microscopical measurements from negatively contrasted preparations, and by use of photon correlation spectroscopy; the two methods each documented nanoparticle sizes less than 100 nm and generally 10-40 nm diameter, though with significant intrabatch and interbatch variability. The particles' charge sufficed to hold them in suspension. HSA retained its tertiary structure in the particles. The nanoparticles were stable against turbulent flow conditions and against heat, though not against detergents. MRI imaging of liquid columns was possible at nanoparticle concentrations below 10 mg/ml. The particles were non-cytotoxic, non-thrombogenic and non-immunogenic in a range of assay systems developed for toxicity testing of nanoparticles. They were micellar prior to lyophilisation, but loosely structured aggregated masses after lyophilisation and subsequent resuspension. These nanoparticles provide a platform for further development, based on non-toxic materials of low immunogenicity already in clinical use, not expensive, and synthesized using methods which can be upscaled for industrial production.

Albumin-based nanoparticles as magnetic resonance contrast agents: II. Physicochemical characterisation of purified and standardised nanoparticles

“…In addition to materials listed in our previous paper (Stollenwerk et al 2010), charcoal, sodium chloride, caprylic acid, gadolinium chloride (GdCl 3 ), 2,7-bis(o-arsenophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid (arsenazo III), sodium cyano-borohydride (NaCNBH 3 ), iodine and ninhydrine were purchased from Sigma-Aldrich (Munich, Germany). Rotilabo Ò injection filter (PP-Gehä-use, sterile, PVDF 0.2 lm), Rotilabo Ò paper filter (type 600P, ø 185 mm) were purchased from Carl Roth GmbH & Co (Karlsruhe, Germany).…”

“…To purify the reaction products diafiltration was introduced, replacing simple dialysis (Stollenwerk et al 2010). Diafiltration was carried out after each derivatization step to separate the reaction product (conjugate, nanoparticles) from contaminating component molecules (HSA-DTPAGd and also small molecular weight species), by use of a Minimate TFF System, and Minimate TFF membrane cassettes with membranes of Omega Ò type (Pall Life Sciences, MI, USA), having cutoffs of 10, 100 and 500 kDa.…”

“…The major advance achieved at this stage was upscaling the synthesis to produce 3-5 g of nanoparticles as product. However, the variability of the nanoparticles was too high to allow precise interbatch comparisons, and much too high to consider use of the particles in any clinical application (Stollenwerk et al 2010). In this paper, we address the question of standardising the nanoparticles, aiming to reduce the intra-and interbatch variability and to increase the purity of the batches.…”

“…This paper is the second of a series describing our design, synthesis and optimisation of successive generations of albumin-based nanoparticles for eventual application in clinical imaging and therapy. We recently reported synthesis and characterisation of two generations of nanoparticles formed from HSA emulsified with polylactic acid, the nanoparticles of approximately 30 nm diameter, and each bearing several hundred gadolinium-DTPA-chelates (Stollenwerk et al 2010). The major advance achieved at this stage was upscaling the synthesis to produce 3-5 g of nanoparticles as product.…”

“…MRMI requires use of nanoparticles as amplifiers for specific signals (Debbage and Jaschke 2008). Since nanoparticles are novel agents with largely unknown toxicological and immunological potential (Debbage 2009;Stollenwerk et al 2010;Robbens et al 2010;Vega-Villa et al 2008;Suh et al 2009), adequate development and testing in iterative developmental cycles are necessary to develop safe and effective agents for clinical use. This paper is the second of a series describing our design, synthesis and optimisation of successive generations of albumin-based nanoparticles for eventual application in clinical imaging and therapy.…”