In Vitro Displacement by Rat Serum of Adsorbed Radiolabeled Poloxamer and Poloxamine Copolymers from Model and Biodegradable Nanospheres

Abstract

0 Poloxamer 407 and poloxamine 908 have been used by many research groups to modify the surface of both model latex and biodegradable nanospheres, thereby producing nanospheres that have shown reduced protein adsorption in vitro and extended circulation times in vivo. A potential limitation of such systems is the desorption of the copolymer coating layer. We describe a two-stage process to radiolabel poloxamer 407 and poloxamine 908 that has facilitated an investigation into this potential desorption, in vitro. The first stage of the labeling procedure involved the substitution of the terminal hydroxyl groups in each poly(ethylene oxide) (PEO) chain of poloxamer 407 and poloxamine 908 with an amino group. The aminated copolymers were then radiolabeled with 125 Iodine Bolton-Hunter reagent. The efficiency of labeling was calculated to be ∼20% for the tetramine poloxamine 908 and ∼33% for the diamine poloxamer 407. Remaining free amino groups were then either acetylated, using acetic anhydride, or left in the free amino form. Covalent linkage of the radiolabel to the copolymer was confirmed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The stability of the link between radiolabel and copolymer to hydrolysis was also confirmed; <4% loss of radiolabel occurred from poloxamine 908 after incubation in phosphate-buffered saline (PBS) at 37°C for 8 days. The radiolabeled copolymers (with the free amino groups acetylated) were then used in experiments that have given the first direct evidence that adsorbed copolymers can be displaced by serum proteins in significant amounts from the surface of model and biodegradable nanospheres. The displacement was highly dependent on copolymer− nanosphere compatibility, with up to 78% of 125 I tetramine poloxamine 908 being displaced from poly(lactide-co-glycolide) (PLGA) nanospheres in 24 h, compared with 20% displacement of 125 I tetramine poloxamine 908 in 24 h from polystyrene nanospheres. These results have direct implication for the future design of drug delivery systems based on coated nanospheres.

Distinct Polymer Architecture Mediates Switching of Complement Activation Pathways at the Nanosphere−Serum Interface: Implications for Stealth Nanoparticle Engineering

“…Earlier work with radio-labeled poloxamine 908-coated (at plateau region of the adsorption isotherm) polystyrene nanoparticles (250 nm) demonstrated that not more than 10% of poloxamine molecules are released after 3 h incubation in serum. 31 With nanospheres C and D, this translates to less than 25 and 40 g poloxamine/mL serum, respectively, which is far below the minimum free poloxamine concentration necessary to trigger complement via the lectin pathway (Figure 5a). Therefore, nanosphere-mediated lectin pathway activation is likely due to interaction between MBL and/or ficolin with projected PEO chains, resulting in activation of their associated serine protease zymogen MASP-2.…”

Factors that Control the Circulation Time of Nanoparticles in Blood: Challenges, Solutions and Future Prospects

“…In one study, PEGylated nanoparticles, 220 nm in diameter, were cleared faster from the body than those with 60 nm diameter [61]. In another study, three different sizes (80,170 and 240 nm) of nanoparticles were compared for serum protein adsorption and phagocytosis [62]. The results showed that particles with 80 nm exhibited only 6% opsonization whereas higher opsonization was found for lager particles (23% for 170 nm and 34% for 240 nm).…”

“…Guidelines have also been proposed to optimize the thickness of the PEG layer to achieve stealth properties [79]. Care must also be taken to ensure that PEG does not desorb from the nanoparticles surface in the presence of competing molecules [80].…”

Biodegradable nanoparticles for cytosolic delivery of therapeutics☆

“…These coatings can modify the biodistribution of NPs when injected into the systemic circulation. However, it has been argued that some of these polymers can be easily displaced by serum proteins, which can lead to aggregation of NPs [57]. Thus, alternative approaches of synthesizing co-polymers of PLA/PLGA with PEG [58,59] and co-encapsulation of PEG with plasmid DNA inside PLA NPs have been tried [60].…”