An improved imaging agent for malignant melanoma, based on [Nle4,D-Phe7]alpha-melanocyte stimulating hormone.

Two compounds have been synthesized based on [Nle4,D-Phe7]alpha-melanocyte stimulating hormone (NDP-MSH) in which either one or two peptide sequences were covalently linked through their N'-termini to a single molecule of diethylenetriamine pentaacetic acid (DTPA). These two compounds (monoNDP-MSH-DTPA and bisNDP-MSH-DTPA, respectively) bound indium-111 (111In) stably and showed hormonal activity as great or greater than alpha-melanocyte stimulating hormone (alpha-MSH). Both compounds were able to target 111In to Cloudman S91 melanomas in DBA2 mice. MonoNDP-MSH-DTPA gave the highest tumour:blood and tumour:tissue ratios and showed least unspecific radioactivity in the liver and kidney. Radioscintigraphy of mice showed good tumour localization of 111In with both compounds, clear images being obtainable within 2 h of injection. Scans with monoNDP-MSH-DTPA showed some kidney and thyroid but no liver radioactivity, whereas bisNDP-MSH-DTPA gave extensive abdominal radioactivity, most of which was associated with the liver and kidneys. MonoNDP-MSH-DTPA was cleared from the tumour much less rapidly and gave more favourable tumour:blood ratios than other alpha-MSH derivatives previously investigated. It is concluded that monoNDP-MSH-DTPA offers promise as a melanoma imaging agent in man.

The use of a chelating derivative of alpha melanocyte stimulating hormone for the clinical imaging of malignant melanoma.

A novel chelating derivative of alpha melanocyte stimulating hormone, bis MSH-DTPA, has been used for the diagnostic targeting of malignant melanoma. 15 patients were investigated of whom nine were shown by other means to have active disease at the time of the scan. Tumours were imaged in all of these nine patients. Of a total of 46 lesions over 10 mm encountered, 41 (89%) were imaged. There were no false positives and in two cases bisMSH-DTPA was instrumental in reversing diagnoses made using ultrasound. Derivatives of melanocyte stimulating hormone may be of considerable value in targeting melanomas.

A chelating derivative of alpha-melanocyte stimulating hormone as a potential imaging agent for malignant melanoma.

A chelating derivative of alpha-melanocyte stimulating hormone (MSH) has been synthesised, in which two molecules of the hormone are cross-linked by diethylenetriamine pentaacetic acid (DTPA). This compound, bisMSH-DTPA, was equipotent with MSH in an in vitro tyrosinase assay with Cloudman S91 melanoma cells. When DBA/2 mice bearing the same tumour were injected with bisMSH-DTPA labelled with the gamma-emitting isotope indium-111 (111In), the radioactivity became rapidly associated with the melanoma tissue. By 24 h post-injection, radioactivity in tumour tissue was significantly higher (P less than 0.001) than in spleen, lung, brain, eye and skin. Uptake of radioactivity by the tumours was inhibited by a 200-fold molar excess of MSH, whereas uptake by liver, kidney, spleen, lung, brain, eye and skin was unaffected. We conclude that bisMSH-DTPA may offer an alternative to antibody targeting in the imaging of malignant melanoma.

Factors influencing pertechnetate uptake by rabbit knees.

The accumulation of radioactivity over rabbit knees immediately after the injection of 99mTc-pertechnetate or one of two 99mTc-labelled particulate preparations has been measured in animals with and without experimental arthritis. The results indicate that in inflamed, but not normal joints, a peak of radioactivity is detectable within 9 seconds of injection and suggest that the rate of accumulation of radioactivity over the joint may be a more sensitive indicator of inflammatory activity than measurement at a fixed time. Clearance from the circulation and tissue distribution of the three radioactive preparations were also measured.

In vivo studies of articular tissue damage mediated by catabolin/interleukin 1.

A partially purified porcine synovial catabolin interleukin 1 (CF) preparation was injected intra-articularly into rabbit stifle (knee) joints. Radiolabelled CF was rapidly cleared from the joint (0.4 h). Repeated injections of CF caused a marked loss of articular cartilage glycosaminoglycan (GAG) and a great increase in synovial fluid GAG. 35SO4 uptake was inhibited. Time course experiments after a single injection produced similar loss of GAG from knee cartilages, which was maximal three days after injection. The above changes were significantly less with heat inactivated preparations. Loss of articular cartilage metachromasia was found histologically, and an acute synovitis occurred together with lymphocytic foci and plasma cell infiltration.

Effect of the intra-articular injection of lutetium-177 in chelator liposomes on the progress of an experimental arthritis in rabbits.

The treatment of rheumatoid arthritis by radiosynovectomy has been restricted by the difficulty of preventing leakage of the radioisotope from the joint cavity. We have previously shown that this leakage can be reduced to very low levels by delivering the radioisotope in liposomes containing the lipophilic chelator, 3-cholesteryl 6-[N'-iminobis-(ethylenenitrilo)tetraacetic acid]hexyl ether. The present study investigates the effectiveness of the beta-emitting isotope lutetium-177, delivered in chelator liposomes, in treating an experimental arthritis in rabbits. Chelator liposomes containing 0.35 mCi, 0.175 mCi Or 0.087 mCi of the isotope were injected into the synovial cavities of the knees of rabbits with an established experimental arthritis. The retention of the lutetium and the progress of the arthritis were followed for 47 days, and samples of the joint tissues were taken for histology at the end of the experiment. Results showed that losses of radioactivity averaged less than 1% per day over 47 days and that joints treated with 0.175 mCi showed significant reductions in both diameter and surface temperature compared with controls treated with a non-radioactive preparation. Post-mortem histology revealed that, whereas control joints showed a highly active synovitis, synovia of joints treated with 0.175 or 0.35 mCi lutetium-177 had very little inflammatory activity. Although some joints which had received 0.35 mCi showed signs of damage to the articular cartilage, this damage was not apparent wih either of the two lower doses. We conclude that, in this animal model, chelator liposomes complexed with a suitable radioisotope are capable of effecting an efficient synovectomy.

The retention and distribution in the rabbit knee of a radionuclide complexed with a lipophilic chelator in liposomes.

The application of radiosynovectomy to patients with rheumatoid arthritis has been severely restricted by the difficulty of preventing leakage of the radioisotope from the joint cavity. We have synthesised a lipophilic chelator, 3-cholesteryl 6-[N'-iminobis(ethylenenitrilo)-tetraacetic acid]hexyl ether (Chol-DTTA) which can complex with a variety of beta-emitting radionuclides and is incorporated into the lipid phase of liposomes. The retention in the synovial cavities of rabbit knees of liposomes containing Chol-DTTA, complexed with the gamma-emitting tracer 51Cr, has been measured over a period of 21 days and compared with colloidal and water-soluble preparations. The distribution of the radionuclide between the tissues of the joint was also examined. Results show retention of 51Cr delivered in chelator liposomes to be greater than 99% after 24 h. At this time, over 93% of the radioactivity had become associated with the synovium. We conclude that chelator liposomes offer considerable promise as vehicles for radioisotopes in radiosynovectomy.

Metabolism of testosterone by the epithelium and mesenchyme of the rat urogenital sinus.

Testosterone metabolism was measured in separated epithelium and mesenchyme from the urogenital sinuses of 17- and 19-day-old male and female rat embryos and compared with testosterone metabolism in the intact sinus. Both the epithelium and the mesenchyme converted testosterone to 5 alpha-dihydrotestosterone. The epithelium produced much more androstanedione and androsterone but less 3 alpha, 17 beta-androstanediol than did the mesenchyme. The whole sinus synthesized all four metabolites, but in different proportions, producing relatively more androsterone than either of its two component tissues. These data suggest that androsterone is formed by the joint action of epithelium and mesenchyme. Metabolism of testosterone did not differ with sex or foetal age in either of the separated tissues or in the intact sinus, implying that the failure of urogenital mesenchyme from 19-day-old female foetuses to induce prostatic morphogenesis is not due to the loss of 5 alpha-reductase. It is suggested that this lack of inductive capacity may be attributable to a decline in androgen levels with age in female mesenchyme.

The influence of oestradiol on the metabolism of androgens by human prostatic tissue.

The uptake and metabolism of testosterone, androstenedione and 5alpha-dihydrotestosterone (DHT) by human benign hyperplastic prostates and prostatic carcinomas have been measured in organ culture. DHT was a major metabolite of both testosterone and androstenedione in the benign tissue and the androstanediols were the principal metabolites of DHT. Over half the carcinomas produced less DHT from testosterone than the benign hyperplastic prostates, and carcinomas from the oldest patients showed an enhancement of 17beta-hydroxysteroid dehydrogenation. There was no relationship between these differences in metabolism and the degree of differentiation of the carcinomas. Oestradiol decreased the production of DHT from both testosterone and androstenedione and, at low androgen concentrations, increased the production of androstanediols from testosterone, androstenedione and DHT. Uptake of DHT, but not of the other two androgens, was stimulated by oestradiol.

3-Methylcholanthrene uptake and metabolism in organ culture.

The uptake of 3-methycholanthrene and its metabolism to water-soluble derivatives were both determined in organ cultures of mouse and rat tissues, including prostate, skin, lung and skeletal muscle. All the tissues concentrated the carcinogen from the medium and metabolized part of it to water-soluble compounds. The uptake of tritiated 3-methylcholanthrene was highest in the absence of serum and declined with rising serum concentration. Except for skeletal muscle, it was consistently higher in the murine tissues. The uptake of the hydrocarbon by rat and mouse prostates rose rapidly with time, reaching a maximum after 18 h incubation; the amounts of carcinogen in the tissue then declined and remained at a lower level for the rest of the observation period. The major part of the radioactivity was released within 5 h of transferring the explants to medium without the tracer; 25-40% of the peak concentration of carcinogen, however, still remained in the tissue and further medium changes could not remove any more. Addition of unlabelled 3-methylcholanthrene to the initial incubation increased the radioactivity taken up and caused substantially larger quantities of the carcinogen to be retained after the medium had been changed. The explants converted between 15% and 30% of the 3-methylcholanthrene which they had incorporated to water-soluble derivatives within 48 h but there was no obvious relationship between the amounts of hydrocarbon taken up by the different tissues and the proportions metabolized. A considerable part of the 3-methylcholanthrene in the explants remained unconverted 24 h after its removal from the medium.