Biomedical subjects

G Vaidyanathan

Publications and source records attributed to G Vaidyanathan.

At least 19 recordsLinked to original sources

PubMed2000

Radioiodination and astatination of octreotide by conjugation labeling.

Octreotide was coupled to 3-iodobenzoyl and 3-iodonicotinoyl moieties to obtain [N-(3-iodobenzoyl)-D-Phe(1)]octreotide (IBO) and [N-(3-iodonicotinoyl)-D-Phe(1)]octreotide (INO), respectively. The IC(50) values for the binding of IBO and INO to CA20948 rat pancreatic tumor membranes were 0.90 and 0.13 nM, respectively, compared with 0.35 nM for octreotide itself. Starting from N-succinimidyl 3-[(131)I]iodobenzoate and N-succinimidyl 5-[(131)I]iodopyridine-3- carboxylate, [(131)I]IBO and [(131)I]INO were prepared in overall radiochemical yields of 35%-50%. Likewise, ¿N-(3-[(211)At]astatobenzoyl)-D-Phe(1)¿octreotide ([(211)At]ABO) was prepared in similar yield from N-succinimidyl 3-[(211)At]astatobenzoate. In vitro assays with AR42J rat pancreatic tumor cells demonstrated a higher retention of cell-internalized radioiodine activity for [(131)I]INO compared with [(125)I]IBO. Tissue distribution studies with both conjugates revealed low levels of activity in the thyroid suggesting that dehalogenation of these peptides was minimal.

Animals↗

PubMed2000

Astatine-211-labeled radiotherapeutics: an emerging approach to targeted alpha-particle radiotherapy.

Targeted radiotherapy or endoradiotherapy is an appealing approach to cancer treatment because of the potential for delivering curative doses of radiation to tumor while sparing normal tissues. Radionuclides that decay by the emission of alpha-particles such as the heavy halogen astatine-211 (211At) offer the exciting prospect of combining cell-specific molecular targets with radiation having a range in tissue of only a few cell diameters. Herein, the radiobiological advantages of alpha-particle targeted radiotherapy will be reviewed, and the rationale for using 211At for this purpose will be described. The chemistry of astatine is similar to that of iodine; however, there are important differences which make the synthesis and evaluation of 211At-labeled compounds more challenging. Perhaps the most successful approach that has been developed involves the astatodemetallation of tin, silicon or mercury precursors. Astatine-211 labeled agents that have been investigated for targeted radiotherapy include [211At]astatide, 211At- labeled particulates, 211At-labeled naphthoquinone derivatives, 211At-labeled methylene blue, 211At-labeled DNA precursors, meta-[211At]astatobenzylguanidine, 211At-labeled biotin conjugates, 211At-labeled bisphosphonates, and 211At-labeled antibodies and antibody fragments. The status of these 211At-labeled compounds will be discussed in terms of their labeling chemistry, cytotoxicity in cell culture, as well as their tissue distribution and therapeutic efficacy in animal models of human cancers. Finally, an update on the status of the first clinical trial with an 211At-labeled targeted therapeutic, 211At-labeled chimeric anti-tenascin antibody 81C6, will be provided.

Alpha Particles↗

PubMed1998

Effects of specific activity on meta-[(131)I]iodobenzylguanidine kinetics in isolated rat heart.

The effects of specific activity of meta-[(131)I]iodobenzylguanidine (MIBG) were studied in uptake-2 blocked isolated perfused rat heart. [(131)I]MIBG was administered in the perfusate as an 8-min pulse, followed by an 80-min washout period. Kinetic analysis of the externally monitored time-activity curves gave estimates of uptake rate and multiexponential clearance. Uptake rate showed an MIBG concentration dependence that is sigmoidal, yielding Michaelis-Menten constants KM = 52 nM and Vmax = 0.23 nmol/min/g. Clearance rate was also dependent on loading MIBG concentrations; the primary effect of increasing loading concentration was an increase in the rate of the slowest clearance component, possibly reflecting nonspecific turnover. No effect of specific activity was observed on tissue uptake and retention of [(131)I]MIBG for loading concentrations of MIBG in the heart tissue under 0.5 nmol/g. Extrapolation of these results to human studies indicates that isotope-exchange-labeled [123I]MIBG has a specific activity sufficiently high to avoid mass effects on its heart retention.

3-Iodobenzylguanidine↗

PubMed1998

Preparation of 5-[131I]iodo- and 5-[211At]astato-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) uracil by a halodestannylation reaction.

To circumvent the in vivo instability of 5-iodo-2'-deoxyuridine (IUdR), a 2'-fluorine-substituted analogue, 5-iodo-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (FIAU) recently has been introduced. To facilitate the preparation of radioiodinated FIAU as well as its astatinated analogue, a tin precursor, 5-trimethylstannyl-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)ura cil (FTAU) was synthesized. Both [125/131I]FIAU and 5-[211At]astato-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (FAAU) were prepared from FTAU in more than 85% radiochemical yield under mild conditions. The in vitro serum stability of both fluorine-substituted derivatives was higher than that of the corresponding unsubstituted parents. The enhanced stability of fluorinated derivatives was even more apparent in whole blood. The uptake of [125I]FIAU in D-247 MG human glioma cells in vitro was 20-fold higher than that of [125I]IUdR over an activity concentration range of 5-100 kBq/mL; the uptake of FAAU was not significantly different from that of 5-[211At]astato-2'-deoxyuridine (AUdR). Accumulation of radioiodine in mouse thyroid in vivo with [131I]FIAU was fivefold lower than [125I]IUdR, indicating that the former was less susceptible to deiodination. The tissue uptake of FAAU was similar to that reported for AUdR.

Animals↗

PubMed1998

Toxicity to neuroblastoma cells and spheroids of benzylguanidine conjugated to radionuclides with short-range emissions.

Radiolabelled meta-iodobenzylguanidine (MIBG) is selectively taken up by tumours of neuroendocrine origin, where its cellular localization is believed to be cytoplasmic. The radiopharmaceutical [131I]MIBG is now widely used in the treatment of neuroblastoma, but other radioconjugates of benzylguanidine have been little studied. We have investigated the cytotoxic efficacy of beta, alpha and Auger electron-emitting radioconjugates in treating neuroblastoma cells grown in monolayer or spheroid culture. Using a no-carrier-added synthesis route, we produced 123I-, 125I-, 131I- and 211At-labelled benzylguanidines and compared their in vitro toxicity to the neuroblastoma cell line SK-N-BE(2c) grown in monolayer and spheroid culture. The Auger electron-emitting conjugates ([123I]MIBG and [125I]MIBG) and the alpha-emitting conjugate ([211At]MABG) were highly toxic to monolayers and small spheroids, whereas the beta-emitting conjugate [131I]MIBG was relatively ineffective. The Auger emitters were more effective than expected if the cellular localization of MIBG is cytoplasmic. As dosimetrically predicted however, [211At]MABG was found to be extremely potent in terms of both concentration of radioactivity and number of atoms ml(-1) administered. In contrast, the Auger electron emitters were ineffective in the treatment of larger spheroids, while the beta emitter showed greater efficacy. These findings suggest that short-range emitters would be well suited to the treatment of circulating tumour cells or small clumps, whereas beta emitters would be superior in the treatment of subclinical metastases or macroscopic tumours. These experimental results provide support for a clinical strategy of combinations ('cocktails') of radioconjugates in targeted radiotherapy.

3-Iodobenzylguanidine↗

PubMed1998

Survival and DNA damage in Chinese hamster V79 cells exposed to alpha particles emitted by DNA-incorporated astatine-211.

Asynchronous Chinese hamster V79 lung fibroblasts were incubated at 37 degrees C for 30 min with the thymidine analog 5-[211At]astato-2'-deoxyuridine (211AtdU, exposure from DNA-incorporated activity) or with [211At]astatide (211At-, exposure from extracellular activity), and DNA-incorporated activity was determined. The 211AtdU content in cellular DNA increased as a function of extracellular concentration. Incorporation of 211At- was less than 1% of that of 211AtdU. After exposure, cells were frozen in the presence of 10% DMSO. One month later, survival was determined by the colony-forming assay, and DNA double-strand breaks (DSBs) were measured by the neutral elution method (pH 9.6). The survival curve for 211AtdU was biphasic (D37 = 2.8 decays per cell), reflecting killing of 211At-DNA-labeled cells and of unlabeled cells irradiated by 211At in neighboring labeled cells. The toxicity of 211At- decaying outside the cell (30-min exposure) was negligible. Analysis of the survival curve produced a D0 of 1.3 decays/cell for 211At-labeled cells. The yield of DSBs from the decay of DNA-incorporated 211At was compared with that from DNA-incorporated 125I. Each decay of 211At produced at least 10 times the number of DSBs as that obtained per 125I decay. The extreme radiotoxicity of DNA-incorporated 211AtdU seems to be associated with considerable damage to the mammalian cell genome.

Animals↗

PubMed1997

Fluorine-18-labeled [Nle4,D-Phe7]-alpha-MSH, an alpha-melanocyte stimulating hormone analogue.

The alpha-melanocyte stimulating hormone (alpha-MSH) analogue [Nle4,D-Phe7]-alpha-MSH was labeled with 18F using N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) in > 80% radiochemical yield. The IC50 values of [Nle4,D-Phe7]-alpha-MSH and para-fluorobenzoyl-[Nle4, D-Phe7]-alpha-MSH ([Nle4,D-Phe7, Lys 11 -(18F)PFB]-alpha-MSH) for inhibiting the binding of meta-[131I]iodobenzoyl -[Nle4,D-Phe7]-alpha-MSH ([Nle4,D-Phe7, Lys11-(131I)MIB]-alpha-MSH) to B16-F1 murine melanoma cells were 89 +/- 9 pM and 112 +/- 22 pM, respectively, suggesting that addition of 4-fluorobenzoate did not compromise alpha-MSH receptor binding affinity. Binding of [Nle4,D-Phe7,Lys11-(18F)PFB]-alpha-MSH was influenced by the specific activity of the preparation (400-1000 Ci/mmol). The normal tissue clearance of [Nle4, D-Phe7, Lys11-(18F) PFB]-alpha-MSH in mice was quite rapid, with little evidence for defluorination.

Animals↗

PubMed1997

3-[211At]astato-4-fluorobenzylguanidine: a potential therapeutic agent with prolonged retention by neuroblastoma cells.

An analogue of meta-iodobenzylguanidine (MIBG) in which an aromatic hydrogen was replaced with fluorine has been found to possess many properties similar to those of the parent compound. Moreover, 4-fluoro-3-iodobenzylguanidine (FIBG) was retained in vitro by human neuroblastoma cells to a much greater extent than MIBG itself. Since alpha-emitters such as 211At could be valuable for the treatment of micrometastatic disease, an FIBG analogue in which the iodine atom is replaced by 211At would be of interest. In this study, we have evaluated the in vitro and in vivo properties of 3-[211At]astato-4-fluorobenzylguanidine ([211At]AFBG). The specific binding of [211At]AFBG to SK-N-SH human neuroblastoma cells remained fairly constant over 2- to 3-log activity range and was similar to that of [131I]MIBG. The uptake of [211At]AFBG by this cell line was reduced by desipramine, ouabain, 4 degrees C incubation, noradrenaline, unlabelled MIBG and FIBG, suggesting that its uptake is specifically mediated through an active uptake-1 mechanism. Over the 16 h period studied, the amount of [211At]AFBG retained was similar to that of [131I]FIBG, whereas the per cent of retained meta-[211At]astatobenzylguanidine ([211At]MABG) was considerably less than that of [131I]FIBG (53% vs 75%; P < 0.05). The IC50 values for the inhibition of uptake of [131I]MIBG, [211At]MABG, [125I]FIBG and [211At]AFBG by unlabelled MIBG were 209, 300, 407 and 661 nM respectively, suggesting that the affinities of these tracers for the noradrenaline transporter in SK-N-SH cells increase in that order. Compared with [211At]MABG, higher uptake of [211At]AFBG was seen in vivo in normal mouse target tissues such as heart and, to a certain extent, in adrenals. That the uptake of [211At]AFBG in these tissues was related to the uptake-1 mechanism was demonstrated by its reduction when mice were pretreated with desipramine. However, the stability of [211At]AFBG towards in vivo dehalogenation was less than that of [211At]MABG, as evidenced by the higher uptake of 211At in thyroid, spleen, lungs and stomach.

3-Iodobenzylguanidine↗

PubMed1997

Cytotoxicity of alpha-particle-emitting 5-[211At]astato-2'-deoxyuridine in human cancer cells.

This study was performed to determine the cytotoxicity of alpha-particle-emitting 5-[211At]astato-2-deoxyuridine (i.e. [211At]AUdR) for monolayers of D-247 MG human glioma cells and SK-MEL-28 human melanoma cells. Cells in exponential growth were exposed to varying activity concentrations of [211At]AUdR and for comparison [211At]astatide and the Auger electron-emitting analogue, 5-[125I]iodo-2'-deoxyuridine (i.e. [125I]IUdR). Cell uptake, DNA binding and clonogenic survival as a function of activity concentration in the medium were determined following 2 and 20-h incubations. None of the survival curves had detectable shoulders, an observation consistent with high-LET effects. The A37 (initial activity concentration yielding 37% cell survival) were significantly lower for both cell lines following 20-h exposure of [211At]AUdR than [211At]astatide. After correcting for effects from non-cell-associated activity in the medium, the specific cytotoxicity of cell-associated and DNA-bound [211At]AUdR was estimated. In the 20-h incubation experiments, the A37 for DNA-associated [211At]AUdR corresponded to about one 211At atom bound per cell for both cell lines. Unlike [211At]AUdR, there was a biphasic survival response to [125I]IUdR, consistent with the lower fractional uptake of [125I]IUdR at higher activity concentrations. These studies suggest that [211At]AUdR warrants further evaluation as an endoradiotherapeutic agent for the treatment of rapidly proliferating cancers.

Alpha Particles↗

PubMed1997

No-carrier-added iodine-131-FIBG: evaluation of an MIBG analog.

UNLABELLED: The purpose of this study was to evaluate the properties of 4-fluoro-3-[131I]iodobenzylguanidine ([131I]FIBG), a potential neuroendocrine tumor and myocardial imaging radiopharmaceutical. METHODS: The binding of [131I]FIBG and [125I]MIBG was compared in vitro using the SK-N-SH human neuroblastoma cell line. The role of the active uptake-1 mechanism was investigated by determining the effect on cell binding of desipramine (DMI), ouabain, norepinephrine (NE), unlabeled MIBG and FIBG and by incubation at 4 degrees C. Finally, the tissue distributions of [131I]FIBG and [125I]MIBG were compared in normal mice. RESULTS: The specific binding of [131I]FIBG remained fairly constant (45%-60%) over a 2-3-log activity range and consistently was 11%-14% higher (p < 0.05) than that of [125I]MIBG. The uptake of [131I]FIBG was reduced to 13% of control values by 1.5 microM DMI, to 31% by 1 mM ouabain, to 8% by lower temperature, to 8% by 50 microM NE and to 6% and 5% by 10 microM each of unlabeled MIBG and FIBG, respectively. The amount of [131I]FIBG retained by SK-N-SH cells was significantly higher than that of [125I]MIBG with the maximum difference observed at 72 hr. In mice, the uptake of [131I]FIBG was higher than that of [125I]MIBG not only in target tissues (heart and adrenals) but also in many other normal tissues; conversely, thyroidal uptake of [131I]FIBG was 2-3-fold lower than that of [125I]MIBG. The uptake of [131I]FIBG in the heart and adrenals was reduced by DMI. CONCLUSION: Iodine-131-FIBG is an analog of MIBG with prolonged binding to neuroblastoma cells in vitro and retention in the myocardium in vivo.

3-Iodobenzylguanidine↗

PubMed1996

5-[211 At]astato-2'-deoxyuridine, an alpha particle-emitting endoradiotherapeutic agent undergoing DNA incorporation.

When labeled with the subcellular range Auger electron emitters 125I and 123I, the thymidine analogue 5-iodo-2'deoxyuridine (IUdR) is highly cytotoxic but only to cells going through S-phase during exposure to these radiopharmaceuticals. Since 211 At emits alpha-particles of high linear energy transfer, but with a range of a few cell diameters, an IUdR analogue labeled with 211At could markedly improve the homogeneity of tumor dose deposition. Herein we describe the synthesis of 5-[211 At]astato-2'-deoxyuridine ([211 At]AUdR) in 85-90% radiochemical yield via the astatodestannylation of 5-(trimethylstannyl)-2'-deoxyuridine. In vitro studies using the human glioma cell line D-247 MG demonstrated that [211 At]AUdR was virtually identical to [131I]IUdr; both exhibited a linear increase in cell uptake with activity concentration, an inhibition of uptake by 10 micrometers IUdR, and the incorporation of about 50% of cell-bound activity into DNA. In a clonogenic assay, [211 At]AUdR exhibited a high cytotoxicity for D-247 MG cells, with a D(0) equivalent to less than 3 211At atoms/cell.

Brain Neoplasms↗

PubMed1996

Evaluation of meta-[211At]astatobenzylguanidine in an athymic mouse human neuroblastoma xenograft model.

A paired-label biodistribution was performed in athymic mice bearing SK-N-SH human neuroblastoma xenografts to compare the tissue uptake of meta-[211At]astatobenzylguanidine ([211At]MABG) and [131I]MIBG. Significantly higher (p < 0.05) uptake of [211At]MABG was seen in tumor (3.8 +/- 0.8% ID/g vs. 3.1 +/- 0.7% ID/g at 8 h) compared to [131I]MIBG. Desipramine reduced tumor uptake of [211At] MABG by 43%, suggesting that its accumulation was related to the specific uptake-1 mechanism. Higher uptake of [211At]MABG was also seen in normal tissue targets such as heart (6.0 +/- 0.9% ID/g vs. 4.5 +/- 0.8% ID/g at 8 h; p < 0.05). Pretreatment of mice with unlabeled MIBG increased tumor uptake of [211At]MABG by 1.5-fold while reducing uptake in heart and several other normal tissues. The vesicular uptake inhibitor tetrabenazine reduced heart uptake by 30% without reducing the tumor uptake. These results suggest such strategies might be useful for improving [211At]MABG tumor-to-normal tissue ratios.

3-Iodobenzylguanidine↗

PubMed1996

Localisation of [131I]MIBG in nude mice bearing SK-N-SH human neuroblastoma xenografts: effect of specific activity.

The biodistribution of no-carrier-added (n.c.a.) meta-[131I]iodobenzylguanidine ([131I]MIBG) and that prepared by the standard isotopic exchange method were compared in athymic mice bearing SK-N-SH human neuroblastoma xenografts. No advantage in tumour uptake was observed for the n.c.a. preparation. BALB/c nu/nu mice exhibited lower uptake in highly innervated normal tissues (heart and adrenals) than normal BALB/c mice. In another experiment, the distribution of n.c.a. [131I]MIBG in the absence or presence (3-9 micrograms) of MIBG carrier was determined. At both 4 h and 24 h, the heart uptake was reduced by a factor of 1.5 even at a dose of 3 micrograms MIBG. Tumour uptake was not significantly altered by various amounts of unlabelled MIBG at either time point.

3-Iodobenzylguanidine↗

PubMed1996

Targeted therapy using alpha emitters.

Radionuclides such as 211At and 212Bi which decay by the emission of alpha-particles are attractive for certain applications of targeted radiotherapy. The tissue penetration of 212Bi and 211At alpha-particles is equivalent to only a few cell diameters, offering the possibility of combining cell-specific targeting with radiation of similar range. Unlike the beta-particles emitted by radionuclides such as 131I and 90Y, alpha-particles are radiation of high linear energy transfer and thus greater biological effectiveness. Several approaches have been explored for targeted radiotherapy with 212Bi- and 211At-labelled substances including colloids, monoclonal antibodies, metabolic precursors, receptor-avid ligands and other lower molecular weight molecules. An additional agent which exemplifies the promise of alpha-emitting radiopharmaceuticals is meta-[211At]astatobenzylguanidine. The toxicity of this compound under single-cell conditions, determined both by [3H]thymidine incorporation and by limiting dilution clonogenic assays, for human neuroblastoma cells is of the order of 1000 times higher than that of meta-[131I] iodobenzylguanidine. For meta-[211At] astatobenzylguanidine, the Do value was equivalent to only 6-7 211At atoms bound per cell. These results suggest that meta-[211At] astatobenzylguanidine might be valuable for the targeted radiotherapy of micrometastatic neuroblastomas.

Alpha Particles↗

PubMed1995

Tumor-specific anti-epidermal growth factor receptor variant III monoclonal antibodies: use of the tyramine-cellobiose radioiodination method enhances cellular retention and uptake in tumor xenografts.

Amplification and rearrangement of the epidermal growth factor receptor (EGFR) gene are characteristics of many types of tumors. One class of EGFR mutations, EGFRvIII, is characterized by an in-frame deletion resulting in a truncated external domain of the receptor. EGFRvIII was first identified in a subset of gliomas and has since been found in some non-small cell lung carcinomas and breast carcinomas. mAbs specific for this variant form of EGFR but unreactive with the wild-type EGFR have been reported from our laboratory. This study further characterizes three of these antibodies. We determined, via radiolabeling techniques and immunofluorescence microscopy, that, after cell binding in vitro, the anti-EGFRvIII-specific mAbs internalize at 37 degrees C. Furthermore, subsequent to internalization, the antibodies were processed intracellularly, presumably by lysosomal degradation. We also examined the use of an alternative radiolabeling procedure that uses nonmetabolizable radio-iodinated tyramine cellobiose. Our results show that the tyramine cellobiose labeling method allows for greater tumor cell retention of radiolabel in vitro (76% for tyramine cellobiose and 27% for Iodo-Gen after 24 h). Paired-label biodistribution studies in athymic mice indicate that anti-EGFRvIII mAb L8A4 localizes specifically to EGFRvIII-expressing tumor xenografts with a maximum of 34.3 +/- 7.6% injected dose/g when labeled using tyramine cellobiose compared with a maximum of 14.9 +/- 4.3% injected dose/g using Iodo-Gen; similar results were obtained with mAb H10. These results suggest that the anti-EGFRvIII mAbs may serve as potential carriers for radioconjugate- and immunotoxin-based therapies for tumors expressing EGFRvIII.

Animals↗

PubMed1995

Meta-[131I]iodobenzylguanidine uptake and meta-[211At]astatobenzylguanidine treatment in human medulloblastoma cell lines.

Uptake of radioiodinated meta-iodobenzylguanidine (MIBG) has been demonstrated in the neural crest tumors, including neuroblastoma, pheochromocytoma, and carcinoid tumors, and is presently in use diagnostically and therapeutically in these settings. Cells comprising medulloblastoma, the most common central nervous system malignancy in childhood, may be derived from a common germinal neuroepithelial cell as neural crest tissue, and as a result, also may have the capacity for accumulating MIBG. To investigate this hypothesis, we measured the in vitro binding of [131I]MIBG to 9 medulloblastoma-derived cell lines and the SK-N-SH neuroblastoma line known to accumulate MIBG. Seven of the medulloblastoma lines exhibited MIBG binding. The cell line with the greatest uptake, D384 Med, bound 11.2 +/- 0.9% of added [131I]MIBG activity compared with 47.1 +/- 2.3% for the SK-N-SH cell line. When 2 of the cell lines, D384 Med and D458 Med, were treated with the alpha-particle emitting analogue meta-[211At]astatobenzylguanidine ([211At]MABG), as much as a 3-log cell kill was observed in limiting dilution clonogenic assays. Exposure to considerably higher activity levels of [211At]astatide was required to achieve a similar degree of cell kill, suggesting that this cytotoxicity was not related to nonspecific effects of alpha-particle irradiation. We conclude that the uptake capacity of medulloblastoma cell lines for [131I]MIBG uptake in vitro, while lower than that seen in SK-N-SH neuroblastoma cells, is sufficient to permit [211At]MABG to be used with significant therapeutic effectiveness.

3-Iodobenzylguanidine↗

PubMed1995

Enhanced tumour uptake and in vitro radiotoxicity of no-carrier-added [131I]meta-iodobenzylguanidine: implications for the targeted radiotherapy of neuroblastoma.

In vitro and in vivo neuroblastoma models were used to determine whether improvements in tumour targeting in vivo and therapeutic efficacy in vitro could result from the use of no-carrier-added (n.c.a.) [131I]MIBG. Results were compared with use of the conventional therapy MIBG preparation (ex. [131I]MIBG) of lower specific activity which is produced by iodide exchange reaction. The efficacy of n.c.a. [131I]MIBG was compared with that of [131I]MIBG over a range of specific activities by the assessment of neuroblastoma spheroid growth delay. Whereas n.c.a. [131I]MIBG at a radioactivity concentration of 2 MBq/ml prevented the regrowth of 84% of spheroids, toxicity was significantly reduced by the addition of non-radiolabelled MIBG to the incubation medium. The time-dependent biodistribution of n.c.a. [131I]MIBG in nude mice bearing human neuroblastoma xenografts was compared with that of the conventional therapy radiopharmaceutical. The n.c.a. agent gave improved tumour uptake but also significantly greater accumulation in normal tissues known to accumulate MIBG such as heart, adrenal and skin. However, uptake and retention in the blood was unaltered. For all tissues examined, the 3-day calculations were undertaken to predict organ to tumour dose ratios which would result in human neuroblastoma patients with each of the [131I]MIBG preparations. These results suggest that significant therapeutic gain may be achieved by the use of n.c.a. [131I]MIBG as a treatment agent in neuroblastoma. neuroblastoma.

3-Iodobenzylguanidine↗

PubMed1995

Quantitation of 211At in small volumes for evaluation of targeted radiotherapy in animal models.

We have evaluated SPECT and two planar imaging methods, geometric mean (GM) and buildup factor (BF), for their potential to quantitate in vivo 211At distributions in rat spinal subarachnoid spaces using phantom studies. The use of medium-energy collimators and the small diameter (3 mm) of the subarachnoid space complicate quantitation. Net activities from distributions in various backgrounds were obtained using a large region of interest with background subtraction. Results showed quantitation accuracy within 10% for SPECT and BF in low backgrounds increasing to 25% at higher background levels while GM errors ranged from 20 to 45%. We have also obtained images of [211At]astatide distributions, administered intrathecally, in rats.

Animals↗