Spectrophotometric method for the quantitative assay of N-hydroxysulfosuccinimide esters including extinction coefficients and reaction kinetics

Determination of degradation for sulfo-SIAB, SM(PEG)2, and sulfo-GMBS by RPLC-UV analysis

Bi-functional N-Hydroxysuccinimide (NHS) linkers are widely used in the conjugation processes linking an immunogen with a carrier protein capable of boosting immunity. A potential vaccine candidate against HIV-1, called fusion peptide (FP), is covalently linked to the recombinant tetanus toxoid heavy-chain fragment C (rTTHC) via this type of linker. A reversed-phase liquid chromatography (RPLC-UV) method was used to monitor the linker's degradation kinetics in various buffers, mimicking the steps in the conjugation process. The kinetics of the reactivities of the linkers are revealed in this study and can provide a good guidance to help effective conjugation process before these linkers are completely hydrolyze to the inactive degradants. Three cross-linkers degradation pathways were evaluated: Sulfosuccinimidyl (4-iodoacetyl) aminobenzoate (Sulfo-SIAB), PEGylated SMCC (SM(PEG)2), and N-γ-maleimidobutyryl-oxysulfosuccinimide ester (Sulfo-GMBS). We have reported kinetics for Sulfo-SIAB.

Crossing the Solubility Rubicon: 15-Crown-5 Facilitates the Preparation of Water-Soluble Sulfo-NHS Esters in Organic Solvents

The Sulfo-NHS ester is a mainstay reagent for facilitating amide bond formation between carboxylic acids and amine functionalities in water. However, the preparation of Sulfo-NHS esters currently requires hydrophobic carboxylic acids, which are poorly water-soluble, to first be reacted with the N-hydroxysulfosuccinimide sodium salt, which is insoluble in organic solvents. The mutually incompatible solvation requirements thus complicate the synthesis of Sulfo-NHS esters. As a simple, rapid, and cost-effective solution to this problem, we report that the use of 15-crown-5 to complex the sodium cation of N-hydroxysulfosuccinimide sodium salt circumnavigates these solvation incompatibility issues by rendering the N-hydroxysulfosuccinimide salt soluble in organic solvents, resulting in a cleaner esterification reaction and thus improved yields of activated ester product. We also demonstrate that the resultant "crowned" Sulfo-NHS-ester remains water-soluble and is no less reactive than its classic "uncrowned" Sulfo-NHS counterpart when used in bioconjugation reactions between protein amine-functionalities and hydrophobic carboxylic acids.

Formulation and characterization of insulin nanoclusters for a controlled release

The growing interest in biopharmaceuticals combined with the challenges regarding formulation and delivery continues to encourage the development of new and improved formulations of this class of therapeutics. Nanoclusters (NCs) represent a type of formulation strategy where the biopharmaceutical is clustered in a reversible manner to function as both the therapeutic and the vehicle. In this study, insulin NCs (INCs) were formulated by a new methodology of first crosslinking proteins followed by desolvation. Crosslinking of the protein with the reducible DTSSP crosslinker improved control of the INC synthesis process to give INCs with a mean size of 198 ± 7 nm and a mean zeta potential of -39 ± 1 mV. Crosslinking and clustering of insulin did not induce cytotoxicity or major differences in the biological activity compared to the free unmodified protein. The potency of the crosslinked insulin and the INCs appeared slightly lower than that of the unmodified protein, and significantly higher doses of the INCs compared to the free protein were applied to achieve similar blood sugar lowering effects in vivo. Interestingly, the INCs allowed for high doses to be subcutaneously delivered with prolonged efficacy without being lethal in rats.