Site-specific polysialylation of an antitumor single-chain Fv fragment.

Protein pharmacokinetic modulation is becoming an important tool in the development of biotherapeutics. Proteins can be chemically or recombinantly modified to alter their half-lives and bioavailability to suit particular applications as well as improve side effect profiles. The most successful and clinically used approach to date is chemical conjugation with poly(ethylene glycol) polymers (PEGylation). Here, therapeutic protein half-life can be increased significantly while retaining biological function, reducing immunogenicity and cross-reaction. Naturally occurring alternatives to such synthetic polymers could have major advantages such as lower side effects due to biodegradability and metabolism. Polysialic acid (PSA) has been investigated as a pharmacokinetic modulatory biopolymer with many successful examples in preclinical and clinical development. Single-chain Fvs (scFvs) are a choice antibody format for human therapeutic antibody discovery. Because of their small size, they are rapidly eliminated from the circulation and often are rebuilt into larger proteins for drug development and a longer half-life. Here we show that chemical polysialylation can increase the half-life of an antiplacental alkaline (PLAP) and anticarcinoembryonic antigen (CEA) scFv (F1 and MFE-23, respectively) 3.4-4.9-fold, resulting in a 10.6-15.2-fold increase in blood exposure. Amine-directed coupling of the MFE-23 scFv reduced its immunoreactivity 20-fold which was resolved by site-specific polysialylation through an engineered C-terminal thiol residue. The site-specifically polysialylated MFE-23 scFv demonstrated up to 30-fold improved tumor uptake while displaying favorable tumor:normal tissue specificity. This suggests that engineering antibody fragments for site-specific polysialylation could be a useful approach to increase the half-life for a variety of therapeutic applications.

Dextrins as potential carriers for drug targeting: tailored rates of dextrin degradation by introduction of pendant groups.

There is a recognised need to identify new biodegradable polymers suitable for development as targetable drug carriers. The aim of this study was to determine the rate of degradation of two dextrin fractions (Mw 15.5 and 51 KDa) by alpha-amylase and liver lysosomal enzymes (tritosomes). Also experiments were conducted to discover whether backbone modification by succinolyation (1-34 mol%) or pendant group incorporation (e.g. doxorubicin) could be used to tailor the rate of polymer degradation. Dextrin (alpha-1,4 polyglucose) is a natural polymer used clinically as a peritoneal dialysis solution and as a controlled drug delivery formulation. Size exclusion chromatography (SEC) showed that dextrin was degraded rapidly (within 20 min) by rat plasma and porcine pancreatic alpha-amylase. In contrast over 48 h no degradation was observed in the presence of tritosomes. The rate of alpha-amylase degradation of succinoylated dextrins (Mw approximately 51 KDa) was dependant on the degree of modification (dextrin >1>5>15>34 mol% succinoylation). Dextrin-doxorubicin conjugates were prepared from the 15 and 34 mol% succinoylated intermediates to have a doxorubicin loading of 8 and 12 wt.%, respectively. These doxorubicin conjugates were more stable than their parent intermediates, and SEC showed an apparently higher molecular weight. The drug conjugates did however degrade slowly over 7 days to release oligosaccharide-doxorubicin species. This fundamental study demonstrates the possibility of controlling the rate of dextrin enzymolysis by backbone modification and thus affords the potential to rationally design dextrin-drug conjugates for specific applications as targetable carriers.

Enzyme-linked immunosorbent assay for ondansetron captured from airborne samples.

A simple and relatively rapid enzyme-linked immunosorbant assay method for the anti-emetic drug ondansetron has been developed for its quantitation in solution. This has been optimised for use with samples that have been obtained following extraction of filters after the drug's capture from air samples in the workplace. The assay has the sample throughput (40 duplicate samples in 3 h), specificity, sensitivity (LOD of 10.5 ng drug ml-1) and precision (RSD < 11%) necessary for its use in determining airborne concentrations of ondansetron in such samples as part of an occupational health and hygiene monitoring programme.

Development of a specific fluoroimmunoassay for ovine albumin.

A fluoroimmunoassay has been developed to measure serum levels of albumin in sheep. It employs ovine albumin labelled with fluorescein as the tracer and a rabbit antiserum raised against ovine albumin. Separation of the antibody bound and free fractions is achieved using a second antiserum directed against the Fc of rabbit immunoglobulin G and, to simplify the assay, the two antisera are premixed prior to use. Assay validation parameters are satisfactory and the reagents are predicted to be stable for at least one year at 4 degrees C. In contrast to the bromocresol green method, the assay is unaffected by immunoglobulins. A reference range for serum albumin levels has been established in lambs, normal ewes and ewes undergoing immunisation. Mean serum levels were 38.8, 51.3 and 37.8 g/l respectively. The sensitivity of the assay also enabled its use to monitor albumin levels at various stages during the production of specific antibody fragments from ovine antisera for therapeutic purposes.