Novel Bioconjugation Strategy Using Elevated Hydrostatic Pressure: A Case Study for the Site-Specific Attachment of Polyethylene Glycol (PEGylation) of Recombinant Human Ciliary Neurotrophic Factor

Microwave-Induced Transient Heating Accelerates Protein PEGylation

PEGylation is one of the most widely employed strategies to increase the circulatory half-life of proteins and to reduce immune responses. However, conventional PEGylation protocols often require excess reagents and extended reaction times because of their inefficiency. This study demonstrates that a microwave-induced transient heating phenomenon can be exploited to significantly accelerate protein PEGylation and even increase the degree of PEGylation achievable beyond what is possible at room temperature. This can be accomplished under conditions that do not compromise protein integrity. Several PEGylation chemistries and proteins are tested, and mechanistic insight is provided. Under certain conditions, extremely high levels of PEGylation were achieved in a matter of minutes. Moreover, considering the significantly reduced reaction times, the microwave-induced transient heating concept was adapted for continuous flow manufacturing of bioconjugates.

High-resolution purification of a therapeutic PEGylated protein using a cuboid packed-bed device

PEGylated proteins which are a class of protein-synthetic polymer conjugates that have shown significant promise in the area of biotherapeutics are difficult to purify. A cuboid packed-bed device was used to purify a mono-PEGylated therapeutic protein from impurities such as high molecular weight (HMW) species (e.g., tri- and/or di-PEGylated forms), and low molecular weight (LMW) species such as unreacted protein and polyethylene glycol (or PEG). The separation efficiency of this device was compared with that of an equivalent cylindrical column. The effects of operating conditions such as flow rate, buffer composition, elution gradient, and column loading were systematically compared. An equivalent column with the same bed volume, same resin and same bed height was served as control. In mono-PEGylated protein purifications experiments, the cuboid packed-bed device exhibited sharper peaks and gave better resolution at all conditions examined in this study. The purity of mono-PEGylated protein in the samples collected from the cuboid packed-bed device and the column were comparable, i.e., 98.1% and 97.9% respectively. The recovery of mono-PEGylated protein in the pooled eluate from the cuboid packed-bed device was 31.7% greater than that recovered in the pooled eluate from the column. Therefore, significantly higher recovery of mono-PEGylated protein was obtained with the cuboid packed-bed device while maintaining the same purity specification as obtained with the column.

Amphiphilic Nanoaggregates with Bimodal MRI and Optical Properties Exhibiting Magnetic Field Dependent Switching from Positive to Negative Contrast Enhancement

Mixed micelles based on amphiphilic gadolinium(III)-DOTA and europium(III)-DTPA complexes were synthesized and evaluated for their paramagnetic and optical properties as potential bimodal contrast agents. Amphiphilic folate molecule for targeting the folate receptor protein, which is commonly expressed on the surface of many human cancer cells, was used in the self-assembly process in order to create nanoaggregates with targeting properties. Both targeted and nontargeted nanoaggregates formed monodisperse micelles having distribution maxima of 10 nm. The micelles show characteristic europium(III) emission with quantum yields of 2% and 1.1% for the nontargeted and targeted micelles, respectively. Fluorescence microscopy using excitation at 405 nm and emission at 575-675 nm was employed to visualize the nanoaggregates in cultured HeLa cells. The uptake of folate-targeted and nontargeted micelles is already visible after 5 h of incubation and was characterized with the europium(III) emission, which is clearly observable in the cytoplasm of the cells. The very fast longitudinal relaxivity r₁ of ca. 26 s^-1 mM^-1 per gadolinium(III) ion was observed for both micelles at 60 MHz and 310 K. Upon increasing the magnetic field to 300 MHz, the nanoaggregates exhibited a large switching to transversal relaxivity with r₂ value of ca. 52 s^-1 mM^-1 at 310 K. Theoretical fitting of the ¹H NMRD profiles indicate that the efficient T₁ and T₂ relaxations are sustained by the favorable magnetic and electron-configuration properties of the gadolinium(III) ion, rotational correlation time, and coordinated water molecule. These nanoaggregates could have versatile application as a positive contrast agent at the currently used magnetic imaging field strengths and a negative contrast agent in higher field applications, while at the same time offering the possibility for the loading of hydrophobic therapeutics or targeting molecules.

Continuous flow microreactor for protein PEGylation

PEGylation is increasingly being utilized to enhance the therapeutic efficacy of biopharmaceuticals. Various chemistries and reaction conditions have been established to synthesize PEGylated proteins and more are being developed. Both the extent of conversion and selectivity of protein PEGylation are highly sensitive to process variables and parameters. Therefore, microfluidic-based high-throughput screening platforms would be highly suitable for optimization of protein PEGylation. As part of this study, a poly-dimethylsiloxane-based continuous flow microreactor system was designed and its performance was compared head-to-head with a batch reactor. The reactants within the microreactor were contacted by passive micromixing based on chaotic advection generated by staggered herringbone grooves embedded in serpentine microchannels. The microreactor system was provided with means for on-chip reaction quenching. Lysozyme was used as the model protein while methoxy-polyethylene glycol-(CH2)5COO-NHS was used as the PEGylation reagent. Full mixing was achieved close to the microreactor inlet, making the device suitable for protein PEGylation. The effect of mixing type, i.e., simple stirring versus chaotic laminar mixing on PEGylation, was investigated. Higher selectivity (as high as 100% selectivity) was obtained with the microreactor while the conversion was marginally lower.

Amphiphilic complexes of Ho(iii), Dy(iii), Tb(iii) and Eu(iii) for optical and high field magnetic resonance imaging

Amphiphilic lanthanide(iii) complexes self-assemble into monodisperse micelles with favourable properties for optical and high field magnetic resonance imaging.