Advances in radiopharmaceuticals for brain imaging with single-photon emission computed tomography.
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Brain↗
Biomedical subjects
T J Hoffman
Publications and source records attributed to T J Hoffman.
Retention of [99mTc]-d,l-HM-PAO in rat brain: an autoradiographic study.
The regional cerebral distribution pattern of [99mTc]-d,l-HM-PAO in rat brain was studied by autoradiography. The regional cerebral uptake of this tracer is related to regional cerebral blood flow (rCBF); however, the ratio of retained radioactivity (determined by digital imaging techniques) in gray matter compared to white matter is lower than that reported for the blood flow ratio. Considerable inhomogeneity is observed in cortical gray matter for at least 60 min postinjection, demonstrating that minimal, if any, cerebral redistribution of this agent occurs.
Animals↗
Microcomputer-based digital image analysis system for quantitative autoradiography.
A computerized image processing system utilizing an IBM-XT personal microcomputer with the capability of performing quantitative cerebral autoradiography is described. All of the system components are standard computer and optical hardware that can be easily assembled. The system has 512 horizontal by 512 vertical axis resolution with 8 bits per pixel (256 gray levels). Unlike other dedicated image processing systems, the IBM-XT permits the assembly of an efficient, low-cost image analysis system without sacrificing other capabilities of the IBM personal computer. The application of this system in both qualitative and quantitative autoradiography has been the principal factor in developing a new radiopharmaceutical to measure regional cerebral blood flow.
Animals↗
Two populations of tyrosine hydroxylase-positive cells occur in the spinal cord of the chick embryo and hatchling.
The existence of tyrosine hydroxylase (TH)-containing neurons in the spinal cord of the chick embryo was investigated by anti-TH immunocytochemistry. Two populations of intensely immunostained cells were observed along the entire extent of the cord, beginning late in chick embryogenesis. One group of TH-positive cells was particularly numerous and found ventral to the central canal. The other group, which was smaller in number, was located along the superficial and lateral border of the dorsal horn of the spinal cord. When examined by the glyoxylic acid histofluorescence technique, cells could be visualized only very infrequently ventral to the central canal, and not at all within the dorsal horn. However, after pretreatment of hatchlings with the catecholamine synthesis precursor L-DOPA, cells ventral to the canal were readily observed by histofluorescence, while the dorsally located cells seldom visualized. Since these populations of TH-positive cells appear to only partially express the catecholaminergic phenotype, these cells may provide a model in which factors regulating the expression of neurotransmitter phenotypes can be examined in neurons of the developing CNS.
Animals↗
Analysis of the change in number of serotonergic neurons in the chick spinal cord during embryonic development.
The existence of serotonin (5-HT)-containing neurons in the spinal cord of the chick embryo was examined by anti-5-HT immunocytochemistry. The first immunoreactive cells were observed in embryos at 7 days of incubation (E7) and were initially located within the floor plate of the early spinal cord. By E9, immunostained cells occurred throughout the length of the spinal cord and were frequently encountered in most transverse sections of the cord. When examined at later embryonic ages of E12, 17 and at hatching (E21 or 22), the 5-HT cells became progressively more difficult to find with the advancing age of the embryos. To determine if this population of spinal cord 5-HT neurons actually diminished during development, a detailed quantitative analysis was undertaken to estimate the number of 5-HT cells in the cord of chick embryos at different ages. The results of this investigation demonstrated that the size of the 5-HT neuronal population rose rapidly from E7 and plateaued (at approximately 3500 neurons) between E9 and E12. As anticipated, the number of 5-HT cells at E17 decreased at all cord levels. Surprisingly, however, the number of spinal cord 5-HT neurons at hatching increased (depending on the cord level) either back to, or above, the counts estimated for the earlier ages of E9 and E12. Therefore, cells expressing the 5-HT phenotype in the spinal cord of the chick embryo persist throughout the period of embryonic development, rather than appear transiently.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Regional cerebral uptake and retention of 99mTc-tetramethyl- and pentamethyl-propyleneamine oxime chelates.
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Animals↗
Cerebral uptake and retention of 99Tcm-hexamethylpropyleneamine oxime (99Tcm-HM-PAO).
A new radiopharmaceutical, 99Tcm-hexamethylpropyleneamine oxime (99Tcm-HM-PAO) is described. This agent displays considerable promise for imaging cerebral blood flow. In studies in rats and one human volunteer, 99Tcm-HM-PAO demonstrates good brain uptake, prolonged retention of activity in the brain, and slow regional redistribution. These properties suggest that this new radiopharmaceutical is ideal for single photon emission tomographic (SPECT) imaging of cerebral blood flow.
Animals↗
99mTc-propylene amine oxime (99mTc-PnAO); a potential brain radiopharmaceutical.
Propylene amine oxime (PnAO) forms a neutral lipid soluble complex with 99mTc. 99mTc-PnAO can be prepared by simple reduction of 99mTc-pertechnetate with stannous ion in the presence of excess PnAO in saline at or near neutral pH. This agent will passively penetrate biological membranes including the intact blood-brain barrier (BBB) as evidenced by the high brain uptake observed shortly after IV injection. The first-pass extraction efficiency in baboons was estimated to be 80% at normal blood flow. This agent or a derivatized form of 99mTc-PnAO may be useful in assessment of regional cerebral blood flow (rCBF) in humans.
Animals↗
A neutral lipophilic complex of 99mTc with a multidentate amine oxime.
Propylene amine oxime, 3,3'-(1,3-propanediyldiimino)bis(3-methyl-2-butanone)dioxime, (PnAO) forms a neutral lipophilic complex with 99mTc in greater than 95% yield at room temperature at pH 5-10. The complex can be prepared with generator produced 99mTc using 10(-5) M SnC4H4O6 as the reducing agent at ligand concentrations as low as 3 X 10(-5) M. It is stable in saline solutions for as long as 24 h. [99mTc]PnAO may be useful as an imaging agent which passively diffuses across the blood brain barrier.
Brain↗
The behavior of neutral amine oxime chelates labelled with Tc at tracer level.
Neutral 99mTc-chelates were formed with propylene amine oxime, 3,3'-(1,3-propanediyldiimino)bis-(3-methyl-2-butanone)-dioxime and other PnAO analogues. Even though the other amine oxime ligands form neutral chelates with 99mTc, the stability, lipophilic and the brain uptake characteristics are less desirable than [99mTc]-PnAO. These results demonstrate that slight modifications in the amine oxime ligand backbone produces significant effects on the chemical and biological behavior of the [99mTc]dioxime chelates.
Animals↗
Biodistribution of lipophilic 99mTc complexes of cyclam derivatives.
Several n-alkyl-cyclam derivatives were synthesized which form stable single component cationic chelates with 99mTc. These results suggest that the cyclam moiety in these derivatives complexes 99mTc in the same manner as the underivatized macrocycle. Biodistribution studies in mice show that all of these chelates are cleared from circulation by both the kidneys and liver. The ratio and rates of clearance by these organ systems is related to lipid solubility. None of the lypophilic-cationic-99mTc agents show any significant myocardial uptake. Also, these chelates show no significant ability to penetrate the blood-brain-barrier.
Animals↗
Radionuclide evaluation of acute gastrointestinal bleeding. Case reports.
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Acute Disease↗
Synthesis, characterization, and labeling with 99mTc/188Re of peptide conjugates containing a dithia-bisphosphine chelating agent.
Radiolabeling of small receptor-avid peptides at specific predetermined chelation sites with radioactive metals has been an effective approach for production of target-specific radiopharmaceuticals for diagnosis and therapy of diseases. Among various electron-donating groups found on chelator frameworks, phosphines are unique because they display versatile coordination chemistry with a wide range of transition metals. We have recently reported the utility of a dithia-bis(hydroxymethyl)phosphine-based (P2S2) bifunctional chelating agent (BFCA) containing air-stable primary phosphine groups to form 99mTc-labeled receptor-avid peptides by the preconjugation approach. Here we report a novel strategy for labeling small peptides with both 99mTc and 188Re using the P2S2-COOH (6,8-bis[3-(bis(hydroxymethyl)phosphanyl)propylsulfanyl]octanoic acid) BFCA by a postconjugation radiolabeling approach. The first step in this approach involves the coupling of the corresponding (PH2)2S2-COOH intermediate to the N-terminus of the peptide(s). Formylation of P-H bonds with aqueous formaldehyde in the presence of HCl in ethanol affords the corresponding (hydroxymethyl)phosphine-P2S2-peptide conjugates in the form of an oxidatively stable phosphonium salt. The P2S2-peptide conjugates are generated (where the PH2 groups are converted to P(CH2OH)2 groups) by treatment of the P2S2-peptide phosphonium salt(s) with 1 M sodium bicarbonate solution at pH 8.5. Complexation of BFCA conjugates with 99mTc is achieved by direct reduction with Sn(II) tartarate to yield the 99mTc-P2S2-peptide conjugate in near quantitative yields. Complexation of the BFCA conjugates with 188Re is achieved by transchelation with 188Re citrate in yields of >/=90%. In this study, (PH2)2S2-COOH BFCA was conjugated to model peptides. The glycineglycine ethyl ester (GlyGlyOEt)-(PH2)2S2-COOH BFCA conjugate was converted to the hydroxymethylene phosphine form and complexed with 99mTc to produce the 99mTcO2-P2S2-GlyGlyOEt conjugate 8 in RCPs of >/=95%. This singular 99mTc product is stable over 24 h in aqueous solution as confirmed by HPLC. Identical retention times of the 99mTcO2-P2S2-GlyGlyOEt complex and its cold rhenium analogue (ReO2-P2S2-GlyGlyOEt) on HPLC indicates similarity in structures at the macroscopic and the tracer levels. The utility of this postconjugation strategy was further demonstrated by synthesizing a P2S2-D-Lys6-LHRH conjugate and producing its corresponding 99mTc complex in RCPs of >/=88%. Finally, the P2S2-5-Ava-BBN[7-14]NH2 bombesin (BBN) analogue was synthesized, the PH2 groups converted to P(CH2OH)2 groups and subsequently labeled with 188Re to yield a 188Re-labeled bombesin analogue with a RCP of >/=90%. The biological integrity of this conjugate was demonstrated in both in vitro and in vivo. The results of this investigation demonstrate that the (PH2)2S2-COOH BFCA can be conveniently used as a precursor for labeling small receptor-avid peptides with diagnostic (99mTc) and therapeutic (188Re) radionuclides via the postconjugation approach in high yields.
3T3 Cells↗
99mTc-labeling and in vivo studies of a bombesin analogue with a novel water-soluble dithiadiphosphine-based bifunctional chelating agent.
Recent progress in the synthesis of water-soluble phosphine ligand systems and their corresponding 99mTc complexes prompted the development of a new bifunctional chelating agent (BFCA) based on a tetradentate dithiadiphosphine framework (P2S2-COOH). The detailed synthesis of this new BFCA is described here. The corresponding 99mTc complex, 99mTc-P2S2-COOH, can be formed in >95% yield. To demonstrate the potential of this chelate to efficiently label peptides, 99mTc-P2S2-COOH was coupled to the N-terminal region of the truncated nine-amino acid bombesin analogue, 5-Ava-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH2 [BBN(7-14)], to form 99mTc-P2S2-BBN(7-14). Conjugation to the peptide was performed in borate buffer (pH 8.5) by applying the prelabeling approach in yields of >60%. In competitive binding assays, using Swiss 3T3 mouse fibroblast cells against [125I-Tyr4]bombesin, Re-P2S2-BBN(7-14) exhibited an IC50 value of 0.8 +/- 0.4 nM. The pharmacokinetic studies of 99mTc-P2S2-BBN(7-14) and its ability to target tissue expressing gastrin-releasing peptide (GRP) receptors were performed in normal mice. The 99mTc-P2S2-BBN(7-14) exhibited fast and efficient clearance from the blood pool (0.6 +/- 0.1% ID, 4 h postinjection) and excretion through the renal and hepatobiliary pathways (56.4 +/- 8.2 and 28.1 +/- 7.9% ID, 4 h postinjection, respectively). Significant uptake in the pancreas was observed (pancreatic acini cells express bombesin/GRP receptors), producing pancreas:blood and pancreas:muscle ratios of ca. 22 and 80, respectively, at 4 h postinjection.
3T3 Cells↗
Synthesis and in vitro evaluation of an 111In-labeled ST-peptide enterotoxin (ST) analogue for specific targeting of guanylin receptors on human colonic cancers.
BACKGROUND: Human colonic cancer cells are known to express guanylate cyclase C (GC-C) receptors for guanylin and uroguanylin. E. coli ST is a peptide with high metabolic stability that specifically binds to GC-C receptors. An in vitro evaluation of a new synthetic indium-111 labeled ST conjugate for specific targeting of human colonic cancers that express GC-C receptors was performed. MATERIALS AND METHODS: A DOTA conjugated ST analogue DOTA-NCS-6-Ahx-Phe19-ST[1-19] (DOTA-NCS-ST) was synthesized and labeled with indium-111. The non-radioactive indium analogue (In-DOTA-NCS-ST) was also prepared in macroscopic quantities. 111In-DOTA-NCS-ST was produced as a single species (>80% RCP) and purified by HPLC. Human colon cancer CaCO-2 and T-84 cells were used to evaluate the in vitro IC50 values for GC-C receptor binding and determine the cell uptake and retention of radioactivity. RESULTS: The DOTA-NCS-ST and In-DOTA-NCS-ST conjugates exhibit high in vitro binding affinity for GC-C receptors with IC50 values <10 nM. The in vitro cell binding studies with the 111In-DOTA-NCS-ST conjugate demonstrated that 111In-label ST internalizes in human colon cancer cells and exhibits long-term retention. CONCLUSION: The combination of radiolabeling efficacy and specific in vitro cell uptake and retention suggests that the DOTA-NCS-ST construct holds potential for the development of diagnostic or therapeutic radiopharmaceuticals labeled with trivalent radiometals for specific targeting of human colonic cancers.
Amino Acid Sequence↗
Evaluation of alkylated derivatives of 99mTc-propylene amine oxime (99mTc-PnAO).
Several lipophilic di-alkylated derivatives of propylene amine oxime (PnAO were complexed to 99mTc. Assessment of the 99mTc-PnAO derivatives included biodistribution and qualitative autoradiography. All of the derivatives studied penetrated the intact blood-brain-barrier, with the 99mTc-dibutyl-PnAO complex exhibiting the lowest initial brain uptake while the 99mTc-diethyl-PnAO and the 99mTc-dipropyl-PnAO complexes possessing nearly identical initial brain uptake as compared to 99mTcPnAO. Qualitative autoradiographs revealed significant loss of image resolution with extended time post injection indicative of rapid radiopharmaceutical washout. Although increasing alkyl chain length did not enhance initial brain uptake, the data demonstrates that limited modification of the PnAO ligand structure can be performed without decreasing cerebral uptake of the respective 99mTc complex.
Animals↗
Formation of a stable 99mTc-tri-hydrazidophosphine oxide (99mTc-THP) chelate.
Atri-hydrazidophosphine oxide (THP) ligand was synthesized and used to complex 99mTc in high yield (> 95%) by Sn(II) reduction of 99mTcO4-. 99mTc-THP has excellent stability in both 0.9% acqueous NaCl at neutral pH and in human serum at 37 degrees C. Biodistribution studies indicate minimal organ specificity and no significant in vivo release of 99mTcO4-. The ease of 99mTc complexation with THP and the high stability of 99mTc-THP suggests that this ligand may be used as a basis for the development of new imaging agents.
Animals↗