Properties of [99mTc] Technetium-Labelled Liposomes in Normal and Tumour-Bearing Rats

Abstract

Liposomes (phospholipid vesicles) have been proposed as carriers of materials of therapeutic interest, and work in this area has been reviewed (Tyrrell et al., 1976). The possibility of utilizing such a system in tumour therapy has received some attention, and Gregoriadis et al. (1974) injected patients with liposomes using entrapped l 3 I Ilabelled albumin as a marker. Tissue distribution was measured post mortem, several days after administration. As a more versatile alternative we have been investigating the use of the yemitter 9 9 m T~ (technetium) to study liposome distribution in experimental animals. This isotope has been found ideal for radioisotope imaging. Technetium, as the pertechnetate ion (99mT~04-), has previously been used as a vesicle marker to follow the short-term fate of liposomes in mice (McDougall et al., 1975), erythrocyte 'ghosts' in rats (Tyrrell & Ryman, 1976) and to follow liposome uptake by cells in tissue culture (Dunnick et al., 1976).We have prepared liposomes from combinations of the following purified lipids; phosphatidylcholine (egg lecithin), cholesterol, dicetyl phosphate and stearylamine.Rotary-evaporated lipid films were shaken with sterile 0.9 % NaCl to give a final suspension of 20% (w/v). These were surrounded by an ice bath and sonicated with a titanium probe( 1 .Ocm diameter)for20 bursts (6,um peak-to-peak) of ~O S , with 30 scoolingbetween. Technetium label was attached to these pre-formed liposomes by an SnCI, method. To the liposomes (600mg in 3.0ml) was added 0.5ml of a sterile neutral solution of 3m-SnClz previously prepared in 02-free water and stored under Nz at 4°C. The mixture was shaken well and not more than 2.5ml of sodium pertechnetate solution in 0.9% NaCl was added to the suspension, drop by drop, with vigorous shaking, and left at room temperature for 15-30min before injection. The presence of free pertechnetate was estimated by dialysis and found to be less than 2%.The possibility that a labelled SnCI, colloid was formed in the preparation of liposome batches was explored. A preparation with NaCI, SnCI, and pertechnetate formed a labelled colloid under the conditions of the labelling used for the liposomes, and this label could be removed by centrifugation at 4000rev./min for 5min in an MSE Super Minor bench centrifuge. Liposomes labelled under the same conditions remained in the supernatant. The contamination of technetium-labelled liposomes with free pertechnetate and colloid was therefore minimal.Liposomes (20mg of lipid) labelled with 1 mCi of 99mTc were injected into the tail vein of normal Wistar rats. Tissue distribution and clearance of the label from the blood was studied at various times by killing the animals and counting individual organs for radioactivity. Immediately before killing, a picture of the distribution of radioactivity in the whole animal was obtained by a y-camera-computer system (scintiscan). This provided a photographic image and a quantitative radioactivity distribution map for each rat.For the tumour studies, Wistar rats we...

Tissue distribution and tumour localization of 99m-technetium-labelled liposomes in cancer patients

“…The rate of metabolism of the liposomes may be different in the Walker 256 rat tumour used in the animal model described by Richardson et al (1977Richardson et al ( , 1978a and the human tumours. Lack of accumulation of liposomes in the human studies could conceivably be due to a rapid turnover of the liposome components, releasing the 99mTc label from the tumour cells.…”

“…There have been two studies, using animal tumour models, showing tumour localization of labelled liposomes (Neerunjun et al, 1977;Richardson et al, 1977) and one study in which no tumour localization was observed (Anghileri et al, 1976). Patient studies have also been reported (Gregoriadis et al, 1974;Segal et al, 1976) but in only one of these (Gregoriadis et al, 1974) has there been a significant tumour accumulation of the liposome label, in a single patient with cancer.…”

“…Such a possibility seems feasible in view of reports that some tumour cells have a high endocytic activity (Busch et al, 1961;Ghose et al, 1962;Easty et al, 1964;Mego & McQueen, 1965;Trouet et al, 1972) which may enhance uptake of liposomes. Previous studies with animal models have shown that tumour localization of liposome markers is possible by a careful selection of the size and membrane properties of the liposome (Dapergolas et al, 1976;Richardson et al, 1977Richardson et al, , 1978b. There have also been two reports on the possible tumour localization of liposomal markers in patients (Gregoriadis § Segal et al, 1976).…”

l-Cysteine conjugated polyl-lactide nanoparticles containing 5-fluorouracil: formulation, characterization, release and uptake by tissuesin vivo

“…Nanoparticles (NP & CNP) were labeled separately with 99m Tc pertechnetate by direct labeling method as reported (Richardson et al, 1977). Briefly, freshly eluted 0.1 mL of 99m Tc (185 MBq/mL) was mixed with 0.1 mL stannous chloride solution in 10% acetic acid and the pH of the solution was adjusted to 7.0 using sodium bicarbonate solution.…”

The use and importance of liposomes in Positron Emission Tomography

“…The use of radiolabeled liposomes in tumor imaging was first done in 1970s (Neerunjun et al 1977;Richardson et al 1977;Hamoudeh et al 2008). Since then with the developing technology in the engineering and computer science, lots of imaging modalities were developed in recent years.…”