RESUMEN
PURPOSE: The aim of this study was to evaluate [(99m)Tc]Demotate 2 ([(99m)Tc-N(4) (0-1),Asp(0),Tyr(3)]octreotate) as a candidate for in vivo imaging of sst(2)-positive tumours and to compare it with [(111)In]DOTA-tate ([(111)In-DOTA(0),Tyr(3)]octreotate). METHODS: Labelling of Demotate 2 with (99m)Tc was performed at room temperature using SnCl(2) as reductant in the presence of citrate at alkaline pH. Radiochemical analysis involved ITLC and HPLC methods. Peptide conjugate affinities for sst(2) were determined by receptor autoradiography on rat brain cortex sections using [DOTA(0),(125)I-Tyr(3)]octreotate as the radioligand. The affinity profile of Demotate 2 for human sst(1)-sst(5) was studied by receptor autoradiography in cell preparations using the universal somatostatin radioligand [(125)I][Leu(8),(D: )Trp(22),Tyr(25)]somatostatin-28. The internalisation rates of [(99m)Tc]Demotate 2 and [(111)In]DOTA-tate were compared in sst(2)-positive and -negative control cell lines. Biodistribution of radiopeptides was studied in male Lewis rats bearing CA20948 tumours. RESULTS: Peptide conjugates showed selectivity and a high affinity binding for sst(2) (Demotate 2 IC(50)=3.2 nM and DOTA-tate IC(50)=5.4 nM). [(99m)Tc]Demotate 2, like [(111)In]DOTA-tate, internalised rapidly in all sst(2)-positive cells tested, but not in sst(2)-negative control cells. After injection in CA20948 tumour-bearing rats both radiopeptides showed high and specific uptake in the sst(2)-positive organs and in the implanted tumour and rapid excretion from non-target tissues via the kidneys. CONCLUSION: [(99m)Tc]Demotate 2, similarly to the known sst(2)-targeting agent [(111)In]DOTA-tate, showed promising biological qualities for application in the scintigraphy of sst(2)-positive tumours.
Asunto(s)
Biomarcadores de Tumor/metabolismo , Proteínas de Neoplasias/metabolismo , Octreótido/análogos & derivados , Compuestos Organometálicos/farmacocinética , Compuestos de Organotecnecio/farmacocinética , Neoplasias Pancreáticas/metabolismo , Péptidos Cíclicos/farmacocinética , Receptores de Somatostatina/metabolismo , Animales , Línea Celular Tumoral , Evaluación Preclínica de Medicamentos , Masculino , Tasa de Depuración Metabólica , Octreótido/farmacocinética , Especificidad de Órganos , Neoplasias Pancreáticas/diagnóstico por imagen , Cintigrafía , Radiofármacos/farmacocinética , Ratas , Ratas Endogámicas Lew , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Distribución TisularRESUMEN
UNLABELLED: In peptide receptor radionuclide therapy (PRRT) using somatostatin analogs labeled with beta-emitters, the radiosensitive kidney is the dose-limiting organ, because of high uptake and retention of the radionuclides after glomerular filtration. Dosimetry calculations are mostly based on the MIRD scheme, assuming homogeneous renal radioactivity distribution. The aim of this study was to reveal the radioactivity distribution in the normal human kidney after intravenous injection of [(111)In-diethylenetriaminepentaacetic acid (DTPA)]octreotide. METHODS: Three patients received intravenous injection of [(111)In-DTPA]octreotide before nephrectomy because of renal cancer. Distribution of radioactivity in the human kidney was investigated using SPECT scanning before and ex vivo autoradiography of the kidney after surgery. RESULTS: Radioactivity was localized predominantly in the cortex of the kidney. In the cortex, radioactivity was not distributed homogeneously but formed a striped pattern, with most of the radioactivity centered in the inner cortical zone. CONCLUSION: These findings show that average dose calculations using the MIRD scheme, assuming homogeneous renal radioactivity distribution, are inadequate to estimate the radiation dose to various parts of the kidney after PRRT. Different effects due to inhomogeneity can be expected from PRRT using radionuclides emitting particles with short particle ranges, for example, Auger electron emitters, alpha-emitters, and low-energy beta-emitters.
Asunto(s)
Autorradiografía/métodos , Riñón/diagnóstico por imagen , Riñón/metabolismo , Octreótido/análogos & derivados , Octreótido/farmacocinética , Ácido Pentético/análogos & derivados , Ácido Pentético/farmacocinética , Radiometría/métodos , Anciano , Carga Corporal (Radioterapia) , Humanos , Inyecciones Intravenosas , Masculino , Persona de Mediana Edad , Octreótido/administración & dosificación , Octreótido/análisis , Especificidad de Órganos , Ácido Pentético/administración & dosificación , Ácido Pentético/análisis , Dosis de Radiación , Radiofármacos/administración & dosificación , Radiofármacos/análisis , Radiofármacos/farmacocinética , Distribución Tisular , Tomografía Computarizada de Emisión de Fotón ÚnicoRESUMEN
The aim of this study was to develop and investigate a radiopeptide for the treatment of cancers which overexpress cell surface somatostatin receptors. The new radiopharmaceutical is composed of a somatostatin receptor-targeting peptide, a chelator (DTPA) to enable radiolabeling, and an apoptosis-inducing RGD (arginine-glycine-aspartate) peptide moiety. The receptor-targeting peptide portion of the molecule, Tyr3-octreotate, is specific for the somatostatin subtype-2 cell surface receptor (sst2), which is overexpressed on many tumor cells. Because of the rapid endocytosis of the somatostatin receptor, the entire molecule can thus be internalized, allowing the RGD portion to activate intracellular caspases, which in turn promotes apoptosis. In this paper, we present the synthesis and the in vitro and in vivo tumor binding and internalization characteristics of this hybrid peptide. In vitro internalization into sst2-positive tumor cells of the radiolabeled hybrid peptide appeared to be a rapid process and could be blocked by an excess of unlabeled octreotide, indicating an sst2-specific process. Tumor uptake in vivo in rats of radiolabeled RGD-DTPA-Tyr3-octreotate was in agreein vitro data and similar to that of radiolabeled DOTA-Tyr3-octreotate. The combined molecule is expected to significantly enhance the therapeutic efficacy of the somatostatin-based agent.
Asunto(s)
Radioisótopos de Indio/uso terapéutico , Neoplasias/radioterapia , Oligopéptidos/uso terapéutico , Ácido Pentético/química , Péptidos Cíclicos/metabolismo , Receptores de Somatostatina/metabolismo , Animales , Línea Celular Tumoral , Radioisótopos de Indio/metabolismo , Radioisótopos de Indio/farmacocinética , Oligopéptidos/química , Oligopéptidos/metabolismo , Oligopéptidos/farmacocinética , Ácido Pentético/farmacocinética , Péptidos Cíclicos/química , Péptidos Cíclicos/farmacocinética , Ratas , Sensibilidad y Especificidad , Distribución TisularRESUMEN
UNLABELLED: The high renal uptake of radiolabeled somatostatin analogs is dose limiting. Lowering this uptake permits higher radioactivity doses and, thus, tumor doses to be administered. We tested the effects of the microtubule drug colchicine on renal uptake of [(111)In-DTPA(0)]octreotide. Also, the effects of fructose were tested. METHODS: Organ radioactivity 24 h after injection of [(111)In-DTPA(0)]octreotide was determined in rats. RESULTS: Coinjection of 1 mg of colchicine per kilogram did not influence renal uptake of [(111)In-DTPA(0)]octreotide, whereas this dose administered 5 h before [(111)In-DTPA(0)]octreotide resulted in significant renal uptake reduction (63%). D-Lysine plus colchicine reduced the uptake by 76% (P < 0.01 vs. D-lysine alone). Liver and blood radioactivity levels were significantly elevated by colchicine. Fructose did not affect the biodistribution of [(111)In-DTPA(0)]octreotide. CONCLUSION: Renal uptake of [(111)In-DTPA(0)]octreotide is dependent on microtubule function in rats. The addition of colchicine to amino acid protocols may permit administration of higher doses, improving the therapeutic window of peptide receptor radionuclide therapy.
Asunto(s)
Adenosina Trifosfato/metabolismo , Colchicina/farmacología , Fructosa/farmacología , Riñón/diagnóstico por imagen , Riñón/metabolismo , Octreótido/análogos & derivados , Octreótido/farmacocinética , Ácido Pentético/análogos & derivados , Ácido Pentético/farmacocinética , Animales , Relación Dosis-Respuesta a Droga , Riñón/efectos de los fármacos , Masculino , Tasa de Depuración Metabólica , Octreótido/sangre , Especificidad de Órganos , Ácido Pentético/sangre , Renografía por Radioisótopo , Radiofármacos/sangre , Radiofármacos/farmacocinética , Ratas , Ratas Wistar , Distribución TisularRESUMEN
Peptide receptor-targeted radionuclide therapy is nowadays also being performed with DOTA-conjugated peptides, such as [DOTA(0),Tyr(3)]octreotate, labelled with radionuclides like (177)Lu. The incorporation of (177)Lu is typically >/=99.5%; however, since a total patient dose can be as high as 800 mCi, the amount of free (177)Lu(3+) (= non-DOTA-incorporated) can be substantial. Free (177)Lu(3+) accumulates in bone with unwanted irradiation of bone marrow as a consequence. (177)Lu-DTPA is reported to be stable in serum in vitro, and in vivo it has rapid renal excretion. Transforming free Lu(3+) to Lu-DTPA might reroute this fraction from accumulation in bone to renal clearance. We therefore investigated: (a) the biodistribution in rats of (177)LuCl(3), [(177)Lu-DOTA(0),Tyr(3)]octreotate and (177)Lu-DTPA; (b) the possibilities of complexing the free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate to (177)Lu-DTPA prior to intravenous injection; and (c) the effects of free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate, in the presence and absence of DTPA, on the biodistribution in rats. (177)LuCl(3) had high skeletal uptake (i.e. 5% ID per gram femur, with localization mainly in the epiphyseal plates) and a 24-h total body retention of 80% injected dose (ID). [(177)Lu-DOTA(0),Tyr(3)]octreotate had high and specific uptake in somatostatin receptor-positive tissues, and 24-h total body retention of 19% ID. (177)Lu-DTPA had rapid renal clearance, and 24-h total body retention of 4% ID. Free (177)Lu(3+) in [(177)Lu-DOTA(0),Tyr(3)]octreotate could be complexed to (177)Lu-DTPA. Accumulation of (177)Lu in femur, blood, liver and spleen showed a dose relation to the amount of free (177)Lu(3+), while these accumulations could be normalized by the addition of DTPA. After labelling [DOTA(0),Tyr(3)]octreotate with (177)Lu the addition of DTPA prior to intravenous administration of [(177)Lu-DOTA(0),Tyr(3)]octreotate is strongly recommended.