Synthesis and Evaluation of Ga-68-Labeled Rhein for Early Assessment of Treatment-Induced Tumor Necrosis.

PURPOSE: This study aimed to synthesize a necrosis-avid agent using rhein as a precursor and labeled with gallium-68 (Ga-68) for positron emission tomography/computed tomography (PET/CT) imaging, to evaluate response to anticancer treatment in a mouse model. PROCEDURES: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated rhein was radiolabeled with Ga-68 to formulate [68Ga]DOTA-rhein. The in vitro stability of [68Ga]DOTA-rhein was assessed by radio-HPLC. Necrosis avidity was evaluated in a mouse model of muscle necrosis by microPET/CT imaging, biodistribution study, histochemical staining, and autoradiography studies. Murine tumor models with the subcutaneous implantation of S180 cell lines were generated for the evaluation of therapeutic effect. Tumor necrosis was induced by the treatment of combretastatin A4 disodium phosphate (CA4P), and microPET/CT imaging was performed at 1 h post tracer injection. DNA binding studies were conducted to explore the necrosis avidity mechanism of the tracer. RESULTS: [68Ga]DOTA-rhein exhibited a satisfactory yield, a radiochemical purity over 97 %, and a good serum stability. The uptakes of [68Ga]DOTA-rhein in necrotic muscles and tumors were significantly higher than those in normal muscles and tumors (P < 0.05). The results of autoradiography and histochemical staining were consistent with the selective uptake of the radiotracer in necrotic regions. MicroPET/CT images showed a high uptake of the tracer in necrotic muscles and necrotic tumors. DNA binding studies suggested that necrosis avidity correlated with DNA binding to a certain extent. CONCLUSIONS: Our results demonstrated that [68Ga]DOTA-rhein showed a prominent necrosis avidity and could be a useful probe for early assessment of response to anticancer therapy by PET/CT imaging.

Synthesis and Bioevaluation of Novel [18F]FDG-Conjugated 2-Nitroimidazole Derivatives for Tumor Hypoxia Imaging.

Hypoxia imaging can guide tumor treatment and monitor changes in hypoxia during treatment. However, there is still no ideal hypoxia imaging agent for clinical applications. In this study, two novel 2-nitromidazole derivatives were synthesized and directly radiolabeled by [18F]FDG in high radiochemical yield and excellent radiochemical purity. Cell experiments, biodistribution, and positron emission tomography (PET) imaging studies were also conducted in mice-bearing S180 or OS732 tumors. [18F]FDG-2NNC2ON [(2 R,3 S,4 R, E)-2-18F-fluoro-3,4,5,6-tetrahydroxyhexanal O-3-(2-(2-nitro-1 H-imidazole-1-yl)ethylamino)-2-oxopropyl oxime] and [18F]FDG-2NNC5ON [(2 R,3 S,4 R, E)-2-18F-fluoro-3,4,5,6-tetrahydroxyhexanal-O-3-(5-(2-nitro-1 H-imidazole-1-yl)pentylamino)-2-oxopropyl oxime] can be cleared from the blood quickly and specifically target hypoxic tumor cells. The uptake of the probes by hypoxic cells gradually increases with time. After 4 h, the uptake value of [18F]FDG-2NNC2ON in hypoxic cells is 3.2 times higher than that in normoxia cells. In contrast, there is no difference in the uptake of [18F]FDG between hypoxic cells and normoxia cells. Biodistribution resulting from two tumor models indicate that the uptake values of the two radiotracers in the tumor are higher at 1 h than those at 2 and 4 h. At 1 and 2 h, the tumors are clearly observed on the PET images and the imaging features of [18F]FDG-2NNC5ON and [18F]FDG-2NNC2ON are distinct from those of [18F]FDG. Compared with [18F]FDG-2NNC5ON, [18F]FDG-2NNC2ON has a higher proportion of renal excretion, lower digestive tract uptake, and better imaging contrast because of its higher hydrophilicity. At 2 h, [18F]FDG-2NNC2ON shows a good tumor-to-blood (T/B) ratio, tumor-to-muscle ratio based on biodistribution (Bio-T/M ratio), and tumor-to-muscle ratio based on regions of interest on the PET images [region of interest (ROI)-T/M ratio] in the two tumor models (T/B, Bio-T/M, and ROI-T/M ratios are 3.2, 2.6, and 3.9 in the S180 tumor model and are 3.4, 4.2, and 4.6 in the OS732 tumor model, respectively). The imaging features visualized with autoradiography mostly coincided with the positive areas of HIF1α staining by immunofluorescence. Meanwhile, the biodistribution study and PET imaging revealed that the uptake of the radiotracers in the tumor cannot be competed by 5% glucose, confirming that [18F]FDG-2NNC2ON targets the hypoxic regions of the tumors instead of targeting tumors through the glucose metabolism pathway. These results suggest that the new 2-nitroimidazole derivative conjugated with [18F]FDG, [18F]FDG-2NNC2ON, has potential as an imaging agent for hypoxia.

99mTc labelled complexes with secnidazole xanthate: Synthesis and evaluation as potential radiotracers to target tumor hypoxia.

In this study, the commercially available secnidazole was successfully converted to secnidazole xanthate (SNXT), in which the xanthate group can act as a bifunctional chelator to coordinate with 99mTc. 99mTc-nitrido complex of SNXT(99mTcN-SNXT) and 99mTc-oxo complex of SNXT(99mTcO-SNXT) were prepared with high radiochemical purity. Both of the complexes were found to be stable in vitro and to exhibit similar hydrophilicity. In addition, comparative in vitro cell uptake studies under anoxic and normoxic conditions demonstrated that both agents were preferentially taken up by hypoxic cells. Biodistribution studies in mice bearing S180 tumor showed 99mTcO-SNXT exhibited a higher tumor uptake and tumor-to-muscle ratio than 99mTcN-SNXT. Furthermore, in SPECT imaging study, 99mTcO-SNXT exhibited a clear accumulation in tumor at 2 h post-injection, suggesting its potential to be a novel hypoxia imaging agent.

Learning of speckle statistics for in vivo and noninvasive characterization of cutaneous wound regions using laser speckle contrast imaging.

Laser speckle contrast imaging (LSCI) provides a noninvasive and cost effective solution for in vivo monitoring of blood flow. So far, most of the researches consider changes in speckle pattern (i.e. correlation time of speckle intensity fluctuation), account for relative change in blood flow during abnormal conditions. This paper introduces an application of LSCI for monitoring wound progression and characterization of cutaneous wound regions on mice model. Speckle images are captured on a tumor wound region at mice leg in periodic interval. Initially, raw speckle images are converted to their corresponding contrast images. Functional characterization begins with first segmenting the affected area using k-means clustering, taking wavelet energies in a local region as feature set. In the next stage, different regions in wound bed are clustered based on progressive and non-progressive nature of tissue properties. Changes in contrast due to heterogeneity in tissue structure and functionality are modeled using LSCI speckle statistics. Final characterization is achieved through supervised learning of these speckle statistics using support vector machine. On cross evaluation with mice model experiment, the proposed approach classifies the progressive and non-progressive wound regions with an average sensitivity of 96.18%, 97.62% and average specificity of 97.24%, 96.42% respectively. The clinical information yield with this approach is validated with the conventional immunohistochemistry result of wound to justify the ability of LSCI for in vivo, noninvasive and periodic assessment of wounds.

A Multi-Functional Tumor Theranostic Nanoplatform for MRI Guided Photothermal-Chemotherapy.

PURPOSE: To develop a multi-functional theranostic nanoplatform with increased tumor retention, improving antitumor efficacy and decreased side effects of chemotherapy drugs. METHODS: GO@Gd nanocomposites was synthesized via decorating gadolinium (Gd) nanoparticles (GdNP) onto graphene oxide (GO), and then functionalized by polyethylene glycol (PEG2000), folic acid (FA), a widely used tumor targeting molecule, was linked to GO@Gd-PEG, finally, doxorubicin (DOX) was loaded onto GO@Gd-PEG-FA and obtained a tumor-targeting drug delivery system (GO@Gd-PEG-FA/DOX). GO@Gd-PEG-FA/DOX was characterized and explored its theranostic applications both in a cultured MCF-7 cells and tumor-bearing mice. RESULTS: GO@Gd-PEG-FA/DOX could efficiently cross the cell membranes, lead to more apoptosis and afford higher antitumor efficacy without obvious toxic effects to normal organs owing to its prolonged blood circulation and 7.6-fold higher DOX uptake of tumor than DOX. Besides, GO@Gd-PEG-FA/DOX also served as a powerful photothermal therapy (PTT) agent for thermal ablation of tumor and a strong T1-weighted contrast agent for tumor MRI diagnosis. The multi-functional nanoplatform also could selectively kill cancer cells in highly localized regions via the excellent tumor-targeting and MRI guided PTT abilities. CONCLUSIONS: GO@Gd-PEG-FA/DOX exhibited excellent photothermal-chemotherapeutic efficacy, tumor-targeting property and tumor diagnostic ability.

18F-labeled pyrazolo[1,5-a]pyrimidine derivatives: synthesis from 2,4-dinitrobenzamide and tosylate precursors and comparative biological evaluation for tumor imaging with positron emission tomography.

We previously reported 18F-labeled pyrazolo[1,5-a]pyrimidine derivatives: 7-(2-[18F]fluoroethylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile ([18F]1) and N-(2-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)ethyl)-2-[18F]fluoro-4-nitro- benzamide ([18F]2). Preliminary biodistribution experiments of both compounds showed s slow clearance rate from excretory tissues which warranted further investigation for tumor imaging with PET. Here we modified [18F]1 and [18F]2 by introducing polar groups such as ester, hydroxyl and carboxyl and developed three additional 18F-18 labeled pyrazolo[1,5-a] pyrimidine derivatives: (3-Cyano-7-(2-[18F]fluoroethylamino)pyrazolo[1,5-a]-pyrimidin-5- yl)methyl acetate ([18F]3), 7-(2-[18F]fluoroethylamino)-5-(hydroxymethyl)pyrazolo[1,5-a]- pyrimidine-3-carbonitrile ([18F]4) and (S)-6-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)-2-(2-[18F]fluoro-4-nitrobenzamido)hexanoic acid ([18F]5). The radiolabeled probes were synthesized by nucleophilic substitution of the corresponding tosylate and nitro precursors with 18F-fluoride. In Vitro studies showed higher uptake of [18F]3 and [18F]4 than that of [18F]5 by S180 tumor cells. In Vivo biodistribution studies in mice bearing S180 tumors showed that the uptake of both [18F]3 and [18F]4 in tumors displayed an increasing trend while the uptake of [18F]5 in tumor decreased through the course of the 120 min study. This significant difference in tumor uptake was also found between [18F]1 and [18F]2. Thus, we compared the biological behavior of the five tracers and reported the tumor uptake kinetic differences between 2-[18F]fluoroethylamino- and 2-[18F]fluoro-4-nitro- benzamidopyrazolo[1,5-a] pyrimidine derivatives.

(18)F Labeled benzimidazole derivatives as potential radiotracer for positron emission tomography (PET) tumor imaging.

This article reported the synthesis and bioevaluation of two [(18)F] labeled benzimidazole derivatives, 4-(5-(2-[(18)F] fluoro-4-nitrobenzamido)-1-methyl-1H-benzimidazol-2-yl) butanoic acid ([(18)F] FNBMBBA, [(18)F]a1) and 3-(2-fluoroethyl)-7-methyl-2-propyl-3H-benzimidazole-5-carboxylic acid ([(18)F] FEMPBBA, [(18)F]b1) for PET tumor imaging. The preparation [(18)F] FEMPBBA was completed in 1h with overall radiochemical yield of 50-60% (without decay corrected). Biodistribution assay in S180 tumor bearing mice of both compounds were carried out, and the results are both meaningful. [(18)F] FEMPBBA which can be taken as a revision of [(18)F] FNBMBBA got an excellent result, and has significant advantages in some aspects compared with L-[(18)F] FET and [(18)F]-FDG in the same animal model, especially in tumor/brain uptake ratio. The tumor/brain uptake ratio of [(18)F] FEMPBBA gets to 4.81, 7.15, and 9.8 at 30min, 60min and 120min, and is much higher than that of L-[(18)F] FET (2.54, 2.92 and 2.95) and [(18)F]-FDG (0.61, 1.02, 1.33) at the same time point. The tumor/muscle and tumor/blood uptake ratio of [(18)F] FEMPBBA is also higher than that of L-[(18)F] FET at 30min and 60min. This result indicates compound [(18)F] FEMPBBA is a promising radiotracer for PET tumor imaging.

Antitumor effect of acridine orange under ultrasonic irradiation in vitro.

BACKGROUND: Sonodynamic synergistic antitumor therapy is a promising new methodology for cancer treatment. MATERIALS AND METHODS: To determine the antitumor effects of ultrasound (US) in the presence of acridine orange (AO), 1.0 microg/ml solution of AO was tested as a sonodynamic compound against sarcoma 180 cells in vitro. RESULTS: After US irradiation at 2.0 W/cm2 for 60 sec, the survival rate of tumor cells in the presence of AO was significantly lower than in its absence (p < 0.001). In the AO-treated group, the tumor cells were mostly fragmented. When D-mannitol or L-histidine was used along with the AO, the survival rate of tumor cells after irradiation was significantly higher than that when AO alone was applied. CONCLUSION: AO could exhibit useful antitumor activity under US irradiation, and the generation of singlet oxygen and hydroxyl radicals is involved in the processes of tumor cell damage.

Synergistic anti-tumor effect of ultrasound and hematoporphyrin on sarcoma180 cells with special reference to the changes of morphology and cytochrome oxidase activity of tumor cells.

This study is aimed at evaluating the inhibitory effects of the association of hematoporphyrin and ultrasound at variable intensities with a fixed frequency of 1.1MHz in tumor nodules. Specifically, the effects were studied both in solid and ascitic S180 tumors transplanted in mice by clinical, cytochemical and ultrastructural evaluation. The results indicated that the use of hematoporphyrin alone had no significant effect on destroying tumor cells. The ultrasound alone had little effect. Interestingly, the inhibition was much more effective when hematoporphyrin was combined with ultrasound. The inhibition was 3 times better than ultrasound alone and 8 times better than hematoporphyrin used alone. Our results also indicated that the changes on cell structure and cytochrome oxidation activity are important factors that could inhibit tumor cell growth and induce cell death. Apoptosis of tumor cells could be induced by hematoporphyrin. Our study investigated the killing mechanism on S180 tumor cells by using hematoporphyrin and low frequency ultrasound at cell, tissue and individual level.

Ultrastructure of sarcoma 180 cells after ultrasound irradiation in the presence of sparfloxacin.

BACKGROUND: Sonodynamic synergistic antitumor effects have been well described to date, but detailed ultrastructural studies in this field are still lacking. MATERIALS AND METHODS: A suspension of sarcoma 180 cells was exposed to ultrasound (US) in the presence of sparfloxacin (SPFX), one of the new quinolone antibiotics, at 2 W (0.64 W/cm2) for 30 seconds. The antitumor effect was evaluated by the survival rate of cells and cell morphology by scanning and transmission electron microscopy. RESULTS: After US irradiation, the survival rate of tumor cells in the SPFX-added group was 30.9%, significantly lower than 78.7% in the control group (p = 0.0002). Most cells in the control group were spherical, but in the SPFX-added group the cells were aspherical. Cell membranes were often ruptured and numerous pores of various sizes were observed. Some cells were totally disintegrated. CONCLUSION: The most characteristic changes of the synergistic antitumor activities of US and SPFX were on the cell membrane.

Synthesis and biological results of the technetium-99m-labeled 4-nitroimidazole for imaging tumor hypoxia.

1-(4-Nitroimidazole-1-yl)-propanhydroxyiminoamide (N4IPA) was synthesized. The biodistribution of 99mTc-N4IPA in mice bearing S180 tumor demonstrated that the complex showed accumulation in tumor and slow clearance from it. The tumor-to-tissue uptake ratios increase with time. These results suggest that 99mTc-N4IPA would be a marker for imaging tumor hypoxia.

[Synthesis and radiopharmacology of S-(2-18F-fluoroethyl)-L-methionine for tumor imaging].

AIM: To develop S-(2-18F-fluoroethyl)-L-methionine (18FEMET) as an amino acid positron emission tomography (PET) tracer for tumors, and to evaluate the value of 18FEMET in the differentiation of experimental tumor and experimental inflammation. METHODS: 18FEMET was prepared by nucleophilic fluorination reaction via a two-step procedure. Biodistribution of 18FEMET in normal mice, carcinoma-bearing mice and inflammatory mice, and 18FEMET PET imaging for carcinoma-bearing mice and inflammatory mice were performed compared with 2-[18F] fluoro-2-deoxy-D-glucose (FDG) and O-(2-[18F] fluoroethyl)-L-tyrosine (FET). RESULTS: The overall radiochemical yield with no decay correction was 15%-25%, the whole synthesis time was about 70 min by manual operation, and the radiochemical purity was above 95%. High uptake and long retention of 18FEMET in pancreas, kidney, colon, liver and heart were observed. But low uptakes in brain and blood were found. Furthermore, high uptake of 18FEMET, FDG and FET in tumor, high uptake of FDG in inflammatory tissue, and almost no uptake of 18FEMET and FET in inflammatory tissue were also observed. CONCLUSION: 18FEMET is easy to prepare and can be used to differentiate between tumor and inflammatory tissue. It seems to be a potential amino acid tracer for tumors with PET imaging.

[Synthesis and preliminary studies of O-(2-[18F] fluoroethyl)-L-tyrosine as a positron emission tomography imaging agent].

OBJECTIVE: To develop a 18F-labeled amino acid, O-(2-[18F]fluoroethyl) - L-tyrosine(18F-FET), as a positron emission tomography (PET) tracer for imaging cerebral tumors. METHODS: 18F-FET was synthesized. Preclinical studies including sterility, endotoxin, and toxicity tests were performed. Two brain tumor cases were studied using 18F-FET and compared with 18F-FDG. RESULTS: Radiochemical purity of 18F-FET was over 95% which remained stable for 6 hours. The 18F-FET injection was sterile and its endotoxin content accorded with the standards of Chinese Pharmacopoeia. The uptake of 18F-FET in the normal brain tissues was significantly lower than that of the tumor, and the images of the brain tumor were clearer than those of 18F-FDG. CONCLUSION: 18F-FET can accumulate in the tumor tissues to give high quality images. It suggests that 18F-FET may be a safe and effective tracer for brain tumor imaging.

The effect of tumor size on F-18-labeled fluorodeoxyglucose and fluoroerythronitroimidazole uptake in a murine sarcoma model.

The purpose of this study was to evaluate the effect of tumor size on the uptake of 18F-fluorodeoxyglucose (FDG) and fluoroerythronitroimidazole (FETNIM) in a murine sarcoma model. ICR mice were xenografted with sarcoma 180 cell line and tumors were allowed to grow to a weight of 0.26-5.82 grams. 18F-FDG and 18F-FETNIM were injected intravenously in separate groups of mice, and after 1 hr, the tumors were excised and radiotracer uptake was measured. In another group of mice tumors were autoradiographically analyzed and subjected to H & E staining. In both the FDG and FETNIM group, per-gram radiotracer uptake by a tumor was inversely proportional to tumor weight. 18F-FETNIM correlated more (r = -0.593, p < 0.05) than 18F-FDG (r = -0.447, p < 0.05). Autoradiographic studies revealed that FDG accumulated in viable tumor areas, whereas FETNIM accumulated in both viable and partially necrotic areas. In the case of 18F-FETNIM, a direct correlation between tumor weight and the no-uptake-area to total-tumor-area was demonstrated. We concluded that increased tumor size is associated with decreased uptake of 18F-FDG and FETNIM, though this depends on the type of radiotracers and distribution of necrosis.

Optimal radiolabeled liposomes for tumor imaging.

UNLABELLED: We conducted a systematic study of the effects of liposome formulation and encapsulated radionuclides on imaging ability. METHODS: Various types of liposomes were prepared and labeled with 67Ga, 111In or 99mTc. Their tumor-imaging potential was evaluated in terms of tumor accumulation and tumor-to-blood ratios of radioactivity delivered by the liposomes. Mouse sarcoma 180 and Ehrlich solid tumor were the tumor models. RESULTS: Liposomes could be labeled rapidly and with high efficiency, which was sufficient for clinical application. Tumor accumulation of liposome-encapsulated radionuclides that have intrinsic tumor affinity, such as 67Ga-NTA or 111In-NTA, was larger than that of the other nuclides. Liposomes that were fairly small, cholesterol-rich and composed of so-called rigid phospholipids, could deliver large amounts of encapsulated radionuclides to the tumor. We also found that tumor uptake of such liposomes was large and their blood retention was prolonged. Liposomal lipid dose also influenced tumor delivery and blood retention. The results suggest that these factors extended liposomal blood retention and, consequently, increased tumor uptake of the liposomes and tumor delivery of encapsulated radionuclides. Not all liposomes with long blood retention, however, are suitable for tumor imaging. Incorporation of monosialo-ganglioside in the liposomal membrane greatly extended blood retention but increased tumor uptake only slightly and, consequently, made the tumor-to-blood value worse. One of the 67Ga-labeled liposome formulations resulted in high tumor uptake and tumor-to-blood ratios in various tumor models as well as clearly visualized tumors clearly in sarcoma 180-bearing mice. CONCLUSION: For tumor imaging with radiolabeled liposomes, we should choose liposomal formulations and dose to give prolonged blood retention for large tumor delivery. We must then select liposomes that give good tumor-to-blood values. For the best results, the radionuclide should have intrinsic tumor affinity. Labeled liposomes that meet these criteria result in excellent tumor images.

Rapid tumor imaging by active background reduction using biotin-bearing liposomes and avidin.

Tumor imaging with labeled liposomes is slow; although they reach the tumor quickly, their blood clearance is slow, and the high blood background hinders early imaging. We have developed a rapid tumor imaging technique based on the active removal of liposomes from the circulation by using the avidin-biotin system. 67Ga- or 111In-labeled liposomes with biotin molecules bound on the surface were administered to mice bearing sarcoma 180, and avidin was administered 2 h later. The strong affinity between biotin and avidin initiated the aggregation of liposomes, resulting in their rapid removal from the circulation by the reticuloendothelial system, and the blood level of radioactivity was dramatically reduced without any change of the tumor level. Consequently, the tumor:blood ratio reached 14-18 only 2.5 h after liposome injection. Increased accumulation in the liver was also observed. By this method, an acceptable tumor image could be obtained no more than 2 h after administration of labeled liposomes.

Tumor imaging with technetium-99m-DTPA encapsulated in RES-avoiding liposomes.

For passive targeting of liposomes to tumor tissues, we earlier developed reticuloendothelial system (RES)-avoiding liposomes modified with a uronic acid derivative, palmityl-D-glucuronide (PGlcUA). In the present study, we encapsulated technetium-99m (99mTc)-diethylenetriaminepentaacetic acid (DTPA) in PGlcUA-liposomes (dipalmitoylphosphatidylcholine:cholesterol:PGlcUA = 40:40:20 as a molar ratio) and studied the biodistribution of the liposomes in tumor-bearing mice. 99mTc-DTPA encapsulated in liposomes effectively accumulated in tumor tissues after intravenous administration. Corresponding to these results, tumor was strongly imaged by a gamma-camera when 99mTc-DTPA-encapsulated PGlcUA-liposomes were used.

Active removal of radioactivity in the blood circulation using biotin-bearing liposomes and avidin for rapid tumour imaging.

In order to shorten the delay between the administration of tumour-imaging agents and obtainment of scintigrams, rapid delivery of radionuclide to tumours followed by rapid clearance from the blood is required. We used liposomes with biotin bound on their surface (B-liposomes) as carriers for rapid delivery. For rapid blood clearance, we employed avidin in the expectation that the strong affinity between biotin and avidin would result in the aggregation of B-liposomes in the blood circulation, and that these aggregates would be taken up rapidly by the reticuloendothelial system, resulting in the rapid elimination of liposomes and the radionuclide encapsulated in them. When B-liposomes encapsulating gallium-67 deferoxamine were intravenously administered to mice bearing sarcoma 180, large amounts of 67Ga were delivered to tumours by 4 h after injection, though the 67Ga blood level remained high. On the other hand, administration of avidin 4 h after administration of the B-liposomes dramatically reduced the blood level so that it was only 5% of that in the non-treated group 1 h later. As a result, the tumour-to-blood ratio reached nearly 14 at 5 h after radionuclide administration, suggesting that rapid tumour-imaging will be feasible by means of this method.

Rapid background reduction of circulating sodium iodide I 125-labelled Pisum sativum agglutinin used as a tumor-imaging radiopharmaceutical by the chemically galactosylated antibody.

Influence on the clearance of background radioactivity from the blood was studied by using a chemically galactosylated antibody to the radiopharmaceutical. Sodium iodide I 125-labelled Pisum sativum agglutinin (125I-PSA) was used as the model tumor-imaging radiopharmaceutical in this series of experiments. Rabbit (anti-PSA) immunoglobulin G (IgG) was chemically galactosylated with varying amounts of cyanomethylgalactose. Galactose concentration ranged from 11 to 17 mol/mol protein. Antibody activity was not affected by chemical galactosylation under the experimental conditions used. Blood clearance of the galactosylated anti-PSA (GAP) in normal mice was enhanced to varying degrees, depending on the degree of galactosylation; similarly, liver uptake was increased with the degree of galactosylation. Following injection of 125I-PSA in normal mice, the lectin was rapidly removed from the blood by subsequent injection of GAP. Increased hepatic uptake of the complex (lectin-galactosylated antibody) via protein-carbohydrate recognition caused the pronounced decrease in the 125I-PSA blood level. The effective time for 125I-PSA removal was as short as 15 min. The potency was dependent on the degree of galactosylation of the antibody. In sarcoma 180 (S-180) tumor-bearing mice, the capacity for blood clearance of 125I-PSA was also positively correlated to the degree of galactosylation. Moreover, the variation in the delivered dose ratio of antibody to lectin proved to lead to a further increase in background clearance. As a result, especially the tumor:blood ratio was significantly improved by a single administration of chemically galactosylated antibody, as compared with the value measured in the presence of unmodified antibody. These initial studies suggest that administration of GAP may improve nuclear imaging with radiopharmaceuticals.

Enhancement of clearance of plant lectins as radiopharmaceuticals by chemically glycosylated antilectin antibody.

The influence of chemical glycosylation on clearance of plant lectins, employed as radiopharmaceuticals, was assessed. Controlled chemical modification of the antibody to concanavalia ensiformis agglutinin did not affect its immunologic activity, but led to rapid clearance from circulation. In tumor-bearing mice, notable increases of selected tumor/non tumor ratios even after only 1 h of presence of the galactosylated antibody to the lectin in circulation were observed. Similarly, galactosylated antibody to pisum sativum agglutinin caused significant increases of tumor/non tumor ratios.