Low density lipoprotein as a carrier of cytostatics in cancer chemotherapy: study of stability of drug-carrier complexes in blood.

Several solid tumour and leukemia cell types have a higher low density lipoprotein (LDL) uptake than the corresponding normal cells. We are investigating the possibilities to use LDL as a drug carrier to increase the selectivity of antineoplastic drugs in cancer chemotherapy. We have developed a method to incorporate lipophilic cytotoxic agents without interfering with the in vitro and in vivo properties of LDL. In this study, we examined the stability of some drug-LDL complexes in blood and plasma as this is an important prerequisite to achieve a selective therapy. The in vitro dialysis of N-trifluoroacetyl-adriamycin-14-valerat-LDL (AD-32-LDL) against plasma revealed a slow dissociation of the complex. The same method showed a fast and total leakage of paclitaxel from paclitaxel-LDL into the plasma chamber. The dissociation of paclitaxel was confirmed by an autoradiographic study of the distribution of paclitaxel-LDL in tumour-bearing mice. In patients with leukemia the rapid plasma dissociation of AD-32 from LDL illustrated a much higher in vivo instability of this complex. With this method, cholesteryl-linoleate only could be incorporated into LDL in a stable manner as shown by dialysis and autoradiography results. The incorporation of cytotoxic drug derivatives, containing lipophilic anchors, is now under study in order to obtain LDL complexes with better plasma stability.

Increased pigmentation of iridial melanocytes in primates induced by a prostaglandin analogue.

The melanocytes in the mammalian eye have been thought to produce melanin only during fetal development and in the very young individual. The recent discovery that latanoprost, a prostaglandin analogue used in the treatment of glaucoma, causes increased pigmentation of the iris in monkeys and in humans indicates that the iridial melanocytes can produce melanin in adult individuals. Using microautoradiography of HG-(3)H-methimazole, a false melanin precursor, we observed in an earlier study that there seems to be an ongoing melanogenesis in adult mice in the iridial melanocytes and in the iridial pigment epithelium. In the present study latanoprost (13,14-dihydro-17-phenyl-18,19,20-trinor-PGF(2alpha)-isoprop yl ester) was applied once daily to the right eye of seven cynomolgus monkeys; the left eye served as an untreated control. Two animals developed clear-cut increased pigmentation of the iris in the treated eye during the first three months of treatment. These animals were injected intravenously with G-(3)H-methimazole and were killed 24 hr after the injection. The eyes were removed, fixed in 4% formalin supplemented with 10% acetic acid and embedded in paraffin or Polybed 812. Sections from the eyes were used for microautoradiography and light microscopic examination. A high uptake of radioactivity was observed in a few melanocytes in the iris of the untreated eye. There were also a low uptake in the melanocytes in the stroma of the ciliary body and the choroid. No accumulation was observed in the iridial or retinal pigment epithelium. In the iris of the treated eye the only observed difference from the untreated eye was an increased amount of melanin in the iridial melanocytes and an increased uptake of radioactivity in a great number of these cells. Thus it seems likely that treatment with latanoprost in some individuals causes an increase of the low normal melanin synthesis in iridal melanocytes.

Pheomelanin as a binding site for drugs and chemicals.

Certain drugs and chemicals, such as chloroquine, chlorpromazine, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), are bound to melanin and retained in pigment cells for long periods. This specific retention in pigmented tissues can cause adverse effects in the skin, eye, inner ear, and pigmented nerve cells of the substantia nigra of the brain. To date, all studies have been focused on eu- and neuromelanin. In the present study, we show that chloroquine, chlorpromazine, chlomipramine, paraquat, acridine orange, and nickel, which are bound to eumelanin, also bind to synthetic pheomelanin, but the binding to pheomelanin is lower. The binding varied with the cysteine content and pH, and the results indicate that the binding is complex and includes ionic interactions. In addition, we have shown that these substances also bind to synthetic thiourea-containing melanin, but to quite a low extent. We also present a microautoradiographic study on the binding of 14C-chloroquine to natural pheomelanin in vivo in yellow mice C57BL (Ay/a). Black (C57/BL) and albino (NMRI) mice were used as controls. The autoradiography demonstrated a pronounced uptake of chloroquine in the hair follicles and the dermal melanocytes in the ear of yellow mice, which was comparable to the corresponding accumulation of label in black mice. In the albino mouse, the uptake was lower and more homogeneously distributed in the skin. These results suggest that the toxicological risks of melanin-related adverse effects are applicable to persons with a high content of pheomelanin in the skin and hair.

Distribution of 2-chloro-2'-deoxyadenosine, 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine, fludarabine and cytarabine in mice: a whole-body autoradiography study.

The distribution characteristics of tritiated nucleoside analogs, 2-chloro-2'-deoxyadeonosine (CdA), 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine (CAFdA), 2-fluoroarabinosyladenine (F-ara-A) and cytosine arabinoside (ara-C) were compared in mice using whole-body autoradiography. CdA, CAFdA and F-ara-A have quite similar molecular structures, but they differ substantially in clinical activity as well as the side effects. Eight mice were injected intravenously in couples. One mouse from each pair was killed 20 min postinjection and the other mouse from each pair 4 h after the injection. The distribution of the label was then analyzed by whole-body autoradiography. The distribution of the nucleoside analogs was rapid and uniform. High concentrations were found in highly perfused organs. After 4 h the overall concentration had decreased but relatively high activities were found in the skin for CdA and CAFdA, in the thymus for ara-C and the bone marrow for CdA. Both CdA and CAFdA were found in the brain, but the concentration was surprisingly lower after 4 h for CAFdA, a lipophilic and more stable analog as compared to CdA. There was an uptake of CdA, F-ara-A and CAFdA in the skin. There were signs of retention of ara-C in parts of the thymus. The present investigations indicate that the nucleoside analog transport to the brain in mice is not primarily dependent upon passive diffusion over a lipophilic barrier, but suggestive of a specific transport mechanism.

Age-related melanogenesis in the eye of mice, studied by microautoradiography of 3H-methimazole, a specific marker of melanin synthesis.

Whether melanogenesis occurs in adult eyes is still a matter of controversy. It has been widely held that the pigment epithelial cells are fully melanized at birth, and that the uveal melanocytes cease their melanin production in the very young individual. Therefore there should be no turnover of melanin in the adult eye. A number of studies have, however, demonstrated that the enzyme involved in melanin synthesis, tyrosinase, seems to be active also in the adult eye. The recent observation that a prostaglandin analogue, used in glaucoma therapy, caused increased iridal pigmentation in the treated eye, but not in the untreated eye, of adult monkeys and in humans, indicate that the adult eye at least has the capacity to produce melanin. In the present study 3H-methimazole, a false melanin precursor, was administered to a series of DBA-mice, 3 weeks to one year of age. The eyes were removed 24 hr after a single i.p. injection of 3H-methimazole. Using microautoradiography the incorporation of radioactivity was studied in X-ray film covered sections comprising the entire eye. A very selective accumulation of radioactivity was seen in uveal melanocytes and in the pigment epithelial cells in the iris and the ciliary body. The level in the retinal pigment epithelium was low in the eyes of all ages. No uptake was seen in any non-pigmented ocular tissue. The most pronounced accumulation was seen in the pigment epithelium and melanocytes in the iris of the young mice, but some activity was seen in these cells also in the older mice. The presence of immature melanosomes seen in electron micrographs from iridal pigment cells and melanocytes of one year old mice indicate that new melanosomes are formed in these cells also in adult animals. The results of this study thus strongly indicate that there seems to be an active melanin synthesis in the adult eye of the mouse, most pronounced in iridal melanocytes and in the iridal pigment epithelium.

5-FU uptake in liver metastases after intravenous and intraperitoneal administration: an autoradiographic study in the rat.

AIM: To analyse 5-fluorouracil (5-FU) uptake in hepatic metastases and normal tissues after intravenous (i.v.), intraperitoneal (i.p.e.) and intraportal (IPO) administration. METHODS AND RESULTS: A total of 18 inbred rats with hepatic metastases were injected with 14C-labelled 5-FU either through the i.v. (n = 7), i.p.e (n = 7) or IPO (n = 4) route. Radioactivity was visualised autoradiographically and quantified by computer-based image analysis. After 20 minutes, 10 i.v. injected tumours showed a higher amount of radioactivity (mean +/- SD) 23.8 +/- 7.8 than 6 i.p.e. injected (16.5 +/- 5.1, P = 0.06). At 2 hours, 9 i.v. injected metastases contained more radioactivity (49.6 +/- 9.2) than 19 i.p.e. injected tumours (28.2 + 11.3, P = 0.00003). After 24 hours, 2 i.p.e. injected tumours had higher radioactivity (mean 25.2) compared with 7 i.v. injected (7.6 +/- 4.1). IPO administration did not confer higher radioactivity at any time point. When the calculations were based on average metastatic radioactivity of individual rats, the difference between i.v. and i.p.e. injected rats was still present at 2 hours. CONCLUSION: These results indicate that early tumour 5-FU uptake after intraperitoneal and intraportal administration may be inferior to that after intravenous injection. Deposition of the drug in the peritoneal cavity may, however, act as a slow release preparation giving continuous drug exposure for prolonged periods of time. These results suggest a role for combined intravenous and intraperitoneal adjuvant therapy.

Uptake of hyaluronan in hepatic metastases after blocking of liver endothelial cell receptors.

To follow the biodistribution of exogenous hyaluronan in tumor-bearing animals, a total of seventeen inbred rats with hepatic metastases from a colonic adenocarcinoma received 125I-labelled hyaluronan by intravenous injections. Group I received only labeled hyaluronan (25 microg), whereas group II received 2.5 mg chondroitin sulphate prior to labeled hyaluronan, to block receptor uptake in normal liver endothelial cells. Animals in group III received intravenous, as well as intraperitoneal chondroitin sulphate (2.5 mg), to see if a better and prolonged blocking could be achieved. Radioactivity was visualized by whole body autoradiography, using phosphorimaging and the average radioactivity determined as phosphoimaging density units of the total area of hepatic metastases, normal liver, and skeletal muscle by computer-based image analysis. At 5 h, tumors in groups II and III showed higher uptake (4.8+/-1.8, P = .01 and 3.6+/-1.1, P = .01, respectively), in comparison to group I (1.8+/-0.6), and the mean normal liver/tumor concentration ratio was reduced from 21.4+/-10.1 in group I to 5.7+/-2.7 in group II and 3.5+/-1.1 in group III (P = .008 and P = .01, respectively). Our study shows that hyaluronan targets liver metastases of a colon adenocarcinoma. Furthermore, chondroitin sulphate pretreatment increases tumor uptake, while uptake at normal receptor sites is significantly reduced. The results also suggest that after blocking of normal hyaluronan/chondroitin sulphate receptors in healthy tissue, hyaluronan may be used to deliver drugs to specific hyaluronan receptor-positive sites of pathology.

Lack of distant migration after injection of a 125iodine labeled dextranomer based implant into the rabbit bladder.

PURPOSE: In recent years endoscopic treatment of stress incontinence and vesicoureteral reflux has been introduced. Reports of possible particle migration of the injected material to distant organs in humans and experimental animals have led to a search for biological nonmigration products. An implant found to have a good clinical effect in these conditions is dextranomer in hyaluronan. We performed this study in rabbits to investigate the possible migration of dextranomer particles. MATERIALS AND METHODS: 125Iodine labeled dextranomer particles were injected into the submucosal space of rabbit bladders, and samples of blood and various tissues were examined for radioactivity at scheduled intervals during a 28-day period. Furthermore, whole body autoradiography was performed 1 day, and 1 and 4 weeks after injection. RESULTS: Radioactivity was found in blood samples and in all tissues but it remained at the background activity level except in the thyroid, where uptake representing free 125iodine was detected. In the bladder 41 and 45% of the injected dose remained within the bladder wall 1 day and 4 weeks, respectively, after injection. The remainder of the dose probably disappeared from the bladder wall by leakage into the urine shortly after deposition, as indicated by the finding of 10-fold higher urine radioactivity levels at day 1 than at day 28 after injection. CONCLUSIONS: No distant migration of dextranomer particles occurs after submucosal injection of such an implant in the rabbit bladder wall.

Selective incorporation of the prototype melanoma seeker thiourea into nascent melanin: a chemical insight.

The mechanism of selective incorporation of thiourea into melanotic melanoma was investigated by model experiments in which the effect of the compound was examined at various stages of melanogenesis in vitro. Up to 50% inhibition of dopachrome formation was observed in the tyrosinase-dopa reaction in the presence of thiourea at a 2:1 molar ratio with respect to the substrate. Under these conditions, a major product was formed which was isolated and identified as a 1:1 dopa-thiourea adduct (adduct I). Subsequent stages of the oxidation were characterized by the development of a yellow chromophore (lambdamax 440-460nm), virtually identical to that obtained by separate oxidation of the adduct I. A less remarkable effect of thiourea was observed on the oxidative polymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) which was apparent on spectrophotometric and high pressure liquid chromatography (HPLC) analysis. Radiolabelling experiments with 14C-thiourea showed that the label was initially incorporated into the adduct I, while in the subsequent stages of the oxidation it was associated with pigmented materials which escaped direct analysis. Incorporation of labelled thiourea into dopa-melanins was found to be significantly higher than incorporation into synthetic pigments from indole precursors. These results provide a chemical basis for the interpretation of the selective accumulation of thiourea in those melanoma areas with high rates of melanin synthesis seen in autoradiographic experiments.

Uptake of manganese and cadmium from the nasal mucosa into the central nervous system via olfactory pathways in rats.

In the olfactory epithelium the primary olfactory neurones are in contact with the environment and via the axonal projections they are also connected to the olfactory bulbs of the brain. Therefore, the primary olfactory neurones provide a pathway by which foreign materials may gain access to the brain. In the present study we used autoradiography and gamma spectrometry to show that intranasal instillation of manganese (54Mn2+) in rats results in initial uptake of the metal in the olfactory bulbs. The metal was then seen to migrate via secondary and tertiary olfactory pathways and via further connections into most parts of the brain and also to the spinal cord. Intranasal instillation of cadmium (109Cd2+) resulted in uptake of the metal in the anterior parts of the olfactory bulbs but not in other areas of the brain. This indicates that this metal is unable to pass the synapses between the primary and secondary olfactory neurones in the bulbs. Intraperitoneal administration of 54Mn2+ or 109Cd2+ showed low uptake of the metals in the olfactory bulbs, an uptake not different from the rest of the brain. Manganese is a neurotoxic metal which in man can induce an extrapyramidal motor system dysfunction associated with occupational inhalation of manganese-containing dusts or fumes. We propose that the neurotoxicity of inhaled manganese is related to an uptake of the metal into the brain via the olfactory pathways. In this way manganese can circumvent the blood-brain barrier and gain direct access to the central nervous system.

Uptake of 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene in melanin-containing tissues.

It is widely accepted that UV exposure is the main etiological factor for malignant melanoma. Epidemiologic studies, however, have indicated that also chemical carcinogens may be a risk factor for the disease. Polycyclic aromatic hydrocarbons such as 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene represent an important class of carcinogenic chemicals. It is known that 7,12-dimethylbenz(a)anthracene can induce melanotic tumours in various animal species, and human melanocytes in culture have been found to be capable of metabolizing benzo(a)pyrene to its proximate carcinogen benzo(a)pyrene-7,8-diol. In the present study the disposition of 14C- and 3H-7,12-dimethylbenz(a)anthracene and 14C-benzo(a)pyrene was studied in pigmented and albino mice and Syrian golden hamsters by whole-body autoradiography. The results showed pronounced retention of label in the melanin-containing structures of the eyes and the hair follicles in the pigmented animals. The labelling of the corresponding structures in the albino animals was low. Additional experiments showed that 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene as well as some of their metabolites are bound to melanin in vitro. The specific localization of the polycyclic aromatic hydrocarbons in pigmented tissues due to melanin affinity, combined with bioactivating capacity of melanocytes, suggest that these substances may play a role in the induction of malignant melanoma.

Thiourea as a melanoma targeting agent.

It has previously been shown that various thiourea derivatives are incorporated into nascent melanin, and a few of these substances, e.g. 2-thiouracil and its radioiodinated analogue, have been used for selective targeting of melanotic melanoma. Possible localization of thiourea itself in melanoma, however, has not been investigated so far. We have therefore performed the present autoradiographic and impulse counting study on the disposition of 14C-thiourea in mice transplanted with B16 melanoma. The results demonstrated a pronounced, but partly heterogeneous, uptake of radioactivity in the melanoma tissue, with the highest concentration 4 h after the injection. Four days after the administration of a single dose, the retention of label was still high in certain tumoral areas. The lung was the only normal tissue with a similarly high uptake of radioactivity. Additional experiments in vitro showed that the incorporation of thiourea into melanin was dose-dependent. The binding to performed melanin was found to be low, which strongly indicates that the incorporation of thiourea into melanin mainly is due to interaction with intermediates of the melanin synthetic pathway.

New thioureas and related substances intended for melanoma targeting.

Thiouracil and a few related drugs are known to be melanoma-seeking agents owing to specific incorporation into nascent melanin. The melanin-affinic properties are apparently due to binding to intermediates, preferably dopaquinone, produced in the melanin synthetic pathway by tyrosinase-catalysed oxidation of tyrosine. In the present paper, in vitro screening methods have been used for the identification of possible melanoma seekers according to the above principle. The binding of test substance to dopaquinone suppressed dopachrome formation by the withdrawal of dopaquinone from the reaction of the mixture, and the decrease in dopachrome concentration was monitored spectrophotometrically at 475 nm. In order to eliminate false results caused by tyrosinase inhibition, which also will decrease the dopachrome concentration, the oxygen consumption was followed potentiometrically. To avoid the effect of tyrosinase inhibition on dopachrome formation, additional experiments with autoxidation of L-dopa in the presence of test substance were performed. Of the 22 substances (mainly thioureylenes and thioamides) studied, 4,5,6-triamino-2(H)- pyrimidinehtionsulfate, trithiocyanuric acid, 2-thiouracil, 6-methyl-2-thiouracil, and 4- amino-2-mercaptopyrimidine most effectively decreased the dopachrome formation with no or little inhibition of tyrosinase activity. They should therefore be regarded as potential melanoma seekers. In a complementary autoradiographic study on the uptake of the potent tyrosinase inhibitor mercaptobenzothiazole (MBT) in B 16 melanoma transplanted to mice, it was found that strong tyrosinase inhibition seems to decrease incorporation into melanin in vitro. MBT was partially accumulated in restricted areas of the tumor which may be explained by the molar dose injected.

Targeting of teniposide to the mononuclear phagocytic system (MPS) by incorporation in liposomes and submicron lipid particles; an autoradiographic study in mice.

Liposomes are concentrated in the mononuclear phagocytic system in vivo and may therefore be of value as carriers of drugs when treating diseases involving phagocytic cells. Teniposide (VM-26) is a potent and lipophilic cytotoxic drug. Teniposide was incorporated in large unilamellar liposomes (LUVs) consisting of egg phosphatidylcholine and dioleoyl phosphatidic acid and into the novel submicron lipid particles containing cholesteryl oleate, cholesteryl palmitate and soybean lecithin, in order to evaluate the drug targeting effect. Radiolabelled teniposide and lipids were used and the organ distribution in mice was studied with whole-body autoradiography 20 and 90 min post i.v. injection. When the commercial formulation of teniposide (Vumon) was administered, teniposide accumulated in the liver where the drug is metabolized. Biliary excretion was rapid and considerable already after 20 min. The liposomal formulation enhanced liver uptake of teniposide slightly. The distribution of radiolabelled phosphatidyl choline differed from that of teniposide indicating instability of the liposomes in circulation. Despite this, the splenic uptake of the drug was significantly enhanced by administration in liposomes. In the red pulp of the spleen the teniposide level was 23 times higher 90 min post injection, using the liposomal formulation as compared to free drug. The submicron lipid particles were mainly accumulated in the liver and to a lesser extent in the spleen. The study shows that liposomes and lipid particles enhance splenic and liver uptake and can be used to target teniposide to the MPS.

Plasma clearance of rat bikunin: evidence for receptor-mediated uptake.

Bikunin is a chondroitin sulphate-containing protease inhibitor with a molecular mass of 25 kDa. It is secreted into the blood by hepatocytes, and recent observations indicate that it may have an extravascular function. Here we have studied the plasma clearance of bikunin in rats and mice. On intravenous injection, radiolabelled bikunin was found to have a half-life of 10 min; in rats with ligated renal arteries, the clearance time was twice as long, implying that the kidneys account for half the uptake. As judged by gel filtration, the size of bikunin is similar to that of albumin. Autoradiographic analysis of kidneys removed 2 min after the injection of radiolabelled bikunin indicated that, despite its size, bikunin is cleared by glomerular filtration. On ligation of the renal arteries, the plasma concentration of bikunin increased linearly to at least four times normal. This finding shows that the non-renal uptake system is saturated and therefore presumably receptor-mediated. Most of the non-renal uptake of injected bikunin was found to occur in non-visceral tissues such as the skin. Analysis of skin samples by autoradiography after injection of radiolabelled bikunin suggested that bikunin had been transferred from the plasma to the interstitial space.

Cellular binding of carboranylalanine and some effects of boron neutron capture. Analysis of cultured melanoma B16 cells.

The boron containing substances L- and D-carboranylalanine might be of interest for boron neutron capture therapy, BNCT. Cultured mouse melanoma B16 cells were analyzed regarding binding of these substances and some introductory studies on effects of thermal neutron irradiation were also carried out. Comparisons were made with two boron containing compounds, p-boronophenylalanine (BPA) and boronated thiouracil (BTU-1), previously proposed for BNCT of melanomas. The results showed that both L- and D-carboranylalanine bound well in the B16 cells whereas BTU-1 gave no, and BPA only a low, binding. Thus, both forms of carboranes bound better than the two previously proposed substances. The carboranes also bound rather well in two tested human melanoma cell lines, IGR1 and RPMI-7951. Both L- and D-carboranylalanine showed a certain binding to isolated melanin but were not incorporated during melanin synthesis. Cultured glioma cells, used for comparison, bound BPA and to some extent the carboranes. This indicates that the substances are not melanoma specific. The carboranes caused some acute detachment of monolayer growing cells but were not strongly toxic since they did not reduce the growth rate. The cells treated with L-carboranylalanine or BPA showed, after neutron irradiation, a clear decrease in survival compared to the controls whereas no or only small effects were seen for cells treated with D-carboranylalanine or BTU-1. These results were conflicting since BPA gave therapeutical effects although only small amounts were bound while D-carboranylalanine gave no significant therapeutical effect in spite of better binding. One explanation might be different intracellular localizations. This has to be studied in more detail.

Interaction between chemicals and melanin.

Various drugs and other chemicals, such as organic amines, metals, polycyclic aromatic hydrocarbons, etc., are bound to melanin and retained in pigmented tissues for long periods. The physiological significance of the binding is not evident, but it has been suggested that the melanin protects the pigmented cells and adjacent tissues by adsorbing potentially harmful substances, which then are slowly released in nontoxic concentrations. Long-term exposure, on the other hand, may build up high levels of noxious chemicals, stored on the melanin, which ultimately may cause degeneration in the melanin-containing cells, and secondary lesions in surrounding tissues. In the eye, e.g., and in the inner ear, the pigmented cells are located close to the receptor cells, and melanin binding may be an important factor in the development of some ocular and inner ear lesions. In the brain, neuromelanin is present in nerve cells in the extrapyramidal system, and the melanin affinity of certain neurotoxic agents may be involved in the development of parkinsonism, and possibly tardive dyskinesia. In recent years, various carcinogenic compounds have been found to accumulate selectively in the pigment cells of experimental animals, and there are many indications of a connection between the melanin affinity of these agents and the induction of malignant melanoma.

A quantitative autoradiographic study of the heterogeneous activity distribution of different indium-111-labeled radiopharmaceuticals in rat tissues.

In light of the increased interest in small scale dosimetry, this paper presents a quantitative autoradiographic method for evaluation of heterogeneous activity distribution in tissues. This was studied in rat tissues after administration of 111In-chloride, -oxine, -tropolone, 111In-labeled homologous blood cells and 111In-anti-CEA-F(ab')2, using quantitative whole-body autoradiography. Quantification was performed utilizing an image analyzing system designed for whole-body autoradiographs. Very heterogeneous activity distribution was found in several tissues including the liver, spleen, kidneys, bone marrow, lymph nodes and testes. Notable was the high 111In uptake in organs characterized as rapidly proliferating, and known to have numerous transferrin receptors. In the gastrointestinal tract, all activity was associated with the intestinal walls. The heterogeneous tissue distribution shown in this investigation accentuates the necessity for performing detailed studies of the tissue distribution of radiopharmaceuticals. This is especially important for the radiation dosimetry of radionuclides emitting beta-particles or low energy electrons. We suggest whole-body autoradiography as an excellent implement to determine local activity concentrations in organs and tissues necessary for accurate absorbed dose calculations.

Concomitant changes in MR image and morphology induced by glucose and fructose in B16 mouse melanomas.

The short proton relaxation times in the MR images of malignant melanomas make them different from most other tumors. We have previously shown that the T1 and T2 signals may be significantly influenced when the water distribution of the tumor is changed in vivo and in vitro. In the present work T1 and T2 were estimated and compared with the electron microscopy picture in subcutaneously implanted B16 melanomas in mice. Two hours after the mice were given an i.p. injection of 0.9% NaCl containing 10% glucose and 10% fructose (9 mice) both the T2 components were markedly and the T1 slightly prolonged. At the same time the electron microscopy picture displayed swelling of the melanocytes together with a marked decrease in number and size of their mitochondriae. There were no changes in the MR image or the melanocyte structure in control mice injected with 0.9% NaCl (9 mice) or 0.9% NaCl containing 10% fructose. It is concluded that the changed MR image may be coupled to the metabolism in melanoma.