Alan Smith

DEVELOPMENT OF A SIMPLE AND SELECTIVE SEPARATION OF 67CU FROM IRRADIATED ZINC FOR USE IN ANTIBODY LABELLING: A COMPARISON OF METHODS

A procedure for the production and separation of Cu isotopes from irradiated Zn was developed. Following a comparison of methods based on extraction, electrolysis and ion-exchange chromatography, a technique for the separation of Cu employing three ion-exchange matrices was developed which was simple, reproducible and hot cell-compatible. The specific activity of the final product was 37 MBq 67Cu/microgram Cu at EOB. The level of impurities was so low that no interference with antibody labelling was observed.

Experience with the iodine-123 and technetium-99m labelled anti-granulocyte antibody MAb47: a comparison of labelling methods

Four different methods of radiolabelling the anti-granulocyte monoclonal antibody MAW were compared and their influence on diagnostic value studied. The best clinical images were obtained following labelling with iodine-123 by the Iodogen method and direct labelling with technetium-99m after tris-(carboxyethyl)-phosphine treatment of MAW to achieve disulphide bridge reduction.99mTc labelling using a specific ligand (MAb47-mtp), or a second method involving direct reduction with mercaptoethanol, led to an increased background activity in clinical studies, thus impeding the diagnosis of chronic disease. Fresh infections were clearly localized by all four preparations. The elimination of the activity from the blood was slower in the case of the iodinated MAb47, while the collected urine samples showed an excrection of about 10% of the injected activity per day independent of the labelling method. The results in terms of sensitivity and specificity were rather similar for all labelling methods and ranged from 90% to 99%.

An improved method for the separation of 111Ag from irradiated natural palladium

Abstract A simple, high yield method for the separation of 111 Ag by liquid/liquid extraction from irradiated natural palladium for nuclear-medical purposes is described. In a first step 111 Ag is extracted almost quantitatively, together with a small amount of palladium, from an aqueous solution into toluene by complexation with triphenylphosphine. Using the different chemical and physical properties of the two elements 111 Ag is subsequently re-extracted selectively into a convenient buffer solution. The overall yields of 111 Ag are better than 70% and palladium is depleted by a factor of up to 27,000. The procedure takes about 2–3 h.

Differential inhibitory effect of L-lysine on renal accumulation of 67Cu-labelled F(ab′)2 fragments in mice

The basic amino acid L‐lysine was administered to mice in an attempt to circumvent unwanted renal accumulation of 67Cu‐labelled F(ab′)2 fragments derived from the anti‐NCAM IgG1, SEN7 and anti‐CEA IgG1 monoclonal antibody (MAb)35. In control experiments, significant renal uptake of both 67Cu‐labelled F(ab′)2 fragments was observed, radiolabel being primarily localised to proximal tubules in the renal cortex. Following optimised L‐lysine dosing protocols, renal uptake of 67Cu‐MAb35 F(ab′)2 was inhibited by up to 42%. Surprisingly, little inhibition (<10%) of 67Cu‐SEN7 F(ab′)2 uptake was observed. Experiments to investigate this differential inhibition indicated that inhibition of MAb35 F(ab′)2 uptake was relatively short‐lived (approx. 6 hr), whilst no apparent differences were found in blood clearance rates between either 67Cu‐F(ab′)2 fragment. L‐lysine administration caused a significant diuresis with high levels of intact 67Cu‐labelled SEN7 and MAb35 F(ab′)2 appearing in the urine, possibly due to blockade of renal uptake and lysine‐induced increases in glomerular membrane permeability. Iso‐electric focusing studies failed to identify any charge differences between the 67Cu‐labelled F(ab′)2 fragments, although a cathodal migration of all 67Cu‐labelled samples, presumably due to the net positive charge conferred by addition of 67Cu2+ ions, was observed. Our results demonstrate that in addition to net charge, other unidentified characteristics may influence renal accumulation of radiometal‐labelled F(ab′)2 fragments and their inhibition by L‐lysine. Int. J. Cancer 72:522–529, 1997.

Optimising the radioimmunotherapy of malignant disease: the broadening choice of carrier and effector moieties.

The treatment of cancer by radioimmunotherapy remains an experimental approach successful only in a limited number of selected disease conditions. One ground for optimism over the future of radioimmunotherapy lies in the fact that where cures have been obtained it has been despite the design of the immunoconjugate rather than because of it. As the choice of available functional components for conjugate construction increases, the process of evaluation and optimisation is underway. The replacement of the commonly used 131I with radionuclides possessing radiation characteristics more suited to particular disease states, and tailored to the behaviour of the carrier vehicle, should bring improved energy deposition within tumour while reducing whole body radiation burden. Similarly, the introduction of chemically or genetically engineered targeting molecules in place of conventional antibodies may bring improved pharmacokinetic characteristics and higher tumour accumulation. Optimisation of the therapeutic and carrier moieties employed in radioimmunotherapy should bring distinct improvements in clinical efficacy.

Differences in biodistribution of the anti-(carcinoembryonic antigen) murine monoclonal antibody CE-25, its F(ab′)2 fragment and its intact mainly human chimeric form CE 4-8-13

The effect of the size of the tumour and the amount of antibody injected on the biodistribution of a family of radioiodinated antibodies was studied. The intact mouse anti-(carcinoembryonic antigen) (anti-CEA) monoclonal antibody CE-25, its F(ab′)2 fragment and the intact human-mouse chimeric from CE 4-8-13 were evaluated in a model system using the human CEA-producing colon xenograft T 380 grown in nude mice. The relative retention (the percentage of the injected dose per gram of tissue), of mouse mAb and F(ab′)2 in tumour and most normal tissues 1 day after injection was independent of the antibody dose; after 4 days the mAb values increased with increasing antibody dose. The relative retention of chimeric mAb increased with increasing antibody dose 1 day after injection and also slightly after 4 days. The relative retention in tumour tissue was lower in bigger xenografts for all antibodies. The relative retention of mouse mAb in small tumours increased from day 1 to day 4; for chimeric mAb this value decreased. In normal tissues the relative retention of mouse mAb decreased from day 1 to day 4, but the relative retention of chimeric mAb in normal tissue dropped rapidly and changed little afterwards. Thus the biokinetics of antibodies is “species”-dependent: foreign, mainly human, chimeric antibody clears faster from normal mouse tissue than mouse antibody and reaches lower concentrations.