Synthesis and in vivo biodistribution of BPA-Gd-DTPA complex as a potential MRI contrast carrier for neutron capture therapy

p-boronophenylalanine (BPA) conjugated Gd-DTPA complex (3) was synthesized from the active methyne compound 6, the allylic carbonate 7, and BPA by the palladium-catalyzed allylation reaction followed by the DCC coupling reaction. The in vivo biodistribution of complex 3 was evaluated by prompt gamma-ray analysis and alpha-autoradiography using the tumor-bearing rats. High accumulation of gadolinium was observed in the kidney and the %ID values were 0.17 and 0.088 at 20 and 60 min after injection of 3, respectively. The accumulation was also observed in the tumor and the %ID values were 0.010 and 0.0025 at 20 and 60 min after injection, respectively. The visualization experiment of boron distribution in the tumor-bearing rat by alpha-autoradiography indicates that boron was accumulated in the tumor and the intestines at 20 min after injection.     

Synthesis and physicochemical characterization of Gd-DTPA-B(sLex)A, a new MRI contrast agent targeted to inflammation

A new magnetic resonance imaging (MRI) contrast agent designed to mimic sialyl Lewis X (sLeX) and to target inflammation has been synthesized and characterized. The evolution of its proton longitudinal relaxivity as a function of the magnetic field (NMRD) and temperature has been studied. The exchange rate of the water coordinated to the metal has been assessed by oxygen-17 relaxometry. The transmetalation by zinc(II) ions and the noncovalent binding to human serum albumin have been evaluated. The results show no limitation by the residence time of the coordinated water molecule above room temperature, a higher stability of the complex versus transmetalation by zinc(II) ions than a parent complex, the clinically used Gd-DTPA-BMA, and negligible interaction with human serum albumin.     

Synthesis and characterization of poly(L-glutamic acid) gadolinium chelate: a new biodegradable MRI contrast agent

Most currently evaluated macromolecular contrast agents for magnetic resonance imaging (MRI) are not biodegradable. The goal of this study is to synthesize and characterize poly(l-glutamic acid) (PG) gadolinium chelates as biodegradable blood-pool MRI contrast agents. Two PG chelates of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) were synthesized through the use of difunctional and monofunctional DTPA precursors. The conjugates were characterized with regard to molecular weight and molecular weight distribution, gadolinium content, relaxivity, and degradability. Distributions of the polymeric MRI contrast agents in various organs were determined by intravenous injection of (111)In-labeled polymers into mice bearing murine breast tumors. MRI scans were performed at 1.5 T in mice after bolus injection of the polymeric chelates. PG-Hex-DTPA-Gd, obtained from aminohexyl-substituted PG and DTPA-dianhydride, was partially cross-linked and was undegradable in the presence of cathepsin B. On the other hand, PG-Bz-DTPA-Gd synthesized directly from PG and monofunctional p-aminobenzyl-DTPA(acetic acid-tert-butyl ester) was a linear polymer and was degradable. The relaxivities of the polymers at 1.5 T were 3-8 times as great as that of Gd-DTPA. Both polymers had high blood concentrations and were primarily accumulated in the kidney. However, PG-Bz-DTPA-Gd was gradually cleared from the body and had significantly less retention in the blood, the spleen, and the kidney. MRI with PG-Bz-DTPA-Gd in mice showed enhanced vascular contrast at up to 2 h after the contrast agent injection. The ability of PG-Bz-DTPA-Gd to be degraded and cleared from the body makes it a favorable macromolecular MRI contrast agent.     

Synthesis and visualization of a membrane-permeable MRI contrast agent

The study of in vivo developmental events has undergone significant advances with the advent of biological molecular imaging techniques such as computer enhanced light microscopy imaging, positron emission tomography (PET), micro-CT, and magnetic resonance imaging (MRI). MRI has proven to be a particularly powerful tool in clinical and biological settings. Images can be acquired of opaque living animals, with the benefit of tracking events of extended periods of time on the same specimen. Contrast agents are routinely used to enhance regions, tissues, and cells that are magnetically similar but histologically distinct. A principal barrier to the development of MR contrast agents for investigating developmental biological questions is the ability to deliver the agent across cellular membranes. As part of our research, we are investigating a number of small molecules that facilitate transport of charged and uncharged species across cell membranes. Here we describe the synthesis and testing of a Gd(III)-based MR contrast agent conjugated to polyarginine that is able to permeate cell membranes. We confirmed cellular uptake of the agent using two-photon laser microscopy to visualize a Eu(III) derivative of the contrast agent in cell culture, and verified this uptake by T₁ analysis of the Gd(III) agent in cells.Abbreviations DOTA 1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid - DOTA(tris-t-Bu ester) 1,4,7,10-tetraazacyclododecane-1,4,7-tris(acetic acid-tert-butyl ester)-10-acetic acid - DO3A(tris-t-Bu ester) 1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane - MRI magnetic resonance imaging - PET positron emission tomography - TPLM two-photon laser microscopy     

Sesamol as a potential radioprotective agent: in vitro studies

Protection against radiation-induced DNA strand breaks is an important aspect in the design and development of a radioprotector. In this study, the radioprotective efficacy of sesamol, a natural antioxidant, was investigated in aqueous solution of plasmid DNA (pBR322) and compared with that of melatonin, a known antioxidant-based radioprotector. Thermal denaturation studies on irradiated calf thymus DNA were also carried out with sesamol and melatonin. Sesamol demonstrated greater radioprotective efficacy in both plasmid DNA and calf thymus DNA. To assess the radical scavenging capacity of sesamol and melatonin, 2-deoxyribose degradation, DPPH and ABTS assays were performed. Sesamol exhibited more scavenging capacity compared to melatonin. In vitro studies with V79 cells showed that sesamol is 20 times more potent than melatonin. It is proposed that the greater radioprotective efficacy of sesamol could be due to its greater capacity for scavenging of free radicals compared to melatonin. The results will be helpful in understanding the mechanisms and development of sesamol as a radioprotector.     

A gadolinium(III) complex of a carboxylic-phosphorus acid derivative of diethylenetriamine covalently bound to inulin, a potential macromolecular MRI contrast agent

A novel conjugate of a polysaccharide and a Gd(III) chelate with potential as contrast agent for magnetic resonance imaging (MRI) was synthesized. The structure of the chelate was derived from H5DTPA by replacing the central pendant arm by a phosphinic acid functional group, which was covalently bound to the polysaccharide inulin. On the average, each monosaccharide unit of the inulin was attached to approximately one (0.9) chelate moiety. The average molecular weight is 23110 and the average number of Gd3+ ions per molecule is 24. The ligand binds the Gd3+ ion in an octadentate fashion via three nitrogen atoms, four carboxylate oxygen atoms, and one P-O oxygen atom, and its first coordination sphere is completed by a water molecule. This compound shows promising properties for application as a contrast agent for MRI thanks to a favorable residence lifetime of this water molecule (170 ns at 298 K), a relatively long rotational correlation time (866 ps at 298 K), and the presence of two water molecules in the second coordination sphere of the Gd3+ ion. Furthermore, its stability toward transmetalation with Zn(II) is as high as that of the clinically used [Gd(DTPA)(H2O)]2-.     

Synthesis and evaluation of Gd-DTPA-labeled arabinogalactans as potential MRI contrast agents

Arabinogalactan derivatives conjugated with gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) by ethylenediamine (Gd-DTPA-CMAG-A2) or hexylamine (Gd-DTPA-CMAG-A6) have been synthesized and characterized by means of Fourier transform infrared spectra (FTIR), 13C nuclear magnetic resonance (13C NMR), size exclusion chromatography (SEC), and inductively coupled plasma atomic emission spectrometry (ICP-AES). Relaxivity studies showed that arabinogalactan-bound complexes possessed higher relaxation effectiveness compared with the clinically used Gd-DTPA, and the influence of the spacer arm lengths on the T1 relaxivities was studied. Their stability was investigated by competition study with Ca2+, EDTA, and DTPA. MR imaging of Wistar rats showed remarkable enhancement in rat liver and kidney after i.v. injection of Gd-DTPA-CMAG-A2 (0.079+/-0.002 mmol/kg Gd3+): The mean percentage enhancement of the liver parenchyma and kidney was 38.7+/-6.4% and 69.4+/-4.4% at 10-30 min. Our preliminary in vivo and in vitro study indicates that the arabinogalactan-bound complexes are potential liver-specific contrast agents for MRI.     

Synthesis and characterization of novel natural product-Gd(III) MRI contrast agent conjugates

Several novel gadolinium chelates conjugated with paclitaxel, colchicine and thyroxine have been prepared as MRI contrast agents targeted to tubulin and thyroxine-binding globulin, respectively.     

GdDO3NI,a nitroimidazole-based T 1 MRI contrast agent for imaging tumor hypoxia in vivo

Tumor hypoxia is known to affect sensitivity to radiotherapy and promote development of metastases; therefore, the ability to image tumor hypoxia in vivo could provide useful prognostic information and help tailor therapy. We previously demonstrated in vitro evidence for selective accumulation of a gadolinium tetraazacyclododecanetetraacetic acid monoamide conjugate of 2-nitroimidazole (GdDO3NI), a magnetic resonance imaging T ₁-shortening agent, in hypoxic cells grown in tissue culture. We now report evidence for accumulation of GdDO3NI in hypoxic tumor tissue in vivo. Our data show that GdDO3NI accumulated significantly (p < 0.05) in the central, poorly perfused regions of rat prostate adenocarcinoma AT1 tumors (threefold higher concentration than for the control agent) and showed better clearance from well-perfused regions and complete clearance from the surrounding muscle tissue. Inductively coupled plasma mass spectroscopy confirmed that more GdDO3NI than control agent was retained in the central region and that more GdDO3NI was retained in the central region than at the periphery. These results show the utility of GdDO3NI to image tumor hypoxia and highlight the potential of GdDO3NI for application to image-guided interventions for radiation therapy or hypoxia-activated chemotherapy.     

Some physicochemical properties of the gadolinium-DTPA complex, a contrast agent for MRI

The physicochemical characteristics of a good contrast agent for NMR are met by the gadolinium-DTPA complex. Measurements of density, viscosity and osmotic pressure of solutions to be injected are reported. A short survey of the results of X-ray analysis of the di-sodium-Gd-DTPA is given.     

In vivo MR detection of vascular endothelial injury using a new class of MRI contrast agent

A new class of dye-based MRI contrast agents, EB-DTPA-Gd, was designed and synthesized. The contrast agent was found to accumulate at the site of endothelial injury when the reagent was applied to isolated porcine blood vessels or in an ex vivo experiment using rat. In vivo MR detection of vascular endothelial injury was also successful in rat with its common carotid artery injured by balloon treatment. These results indicate that EB-DTPA-Gd is potentially useful for the diagnosis of vascular diseases.     

Synthesis, characterization, and cytotoxicity in vitro of the complex [Mn (Hptc) (phen) (OH)] n

AimsA bridging ligand 2,4,6-pyridine tricarboxylic acid (H₃ptc) and its manganese(II) complex [Mn(Hptc)(phen)(OH)]n(Hptc = 2,4,6-pyridine tricarboxylic acid, phen = 1,10-phenanthroline) have been synthesized and characterized.Main methodsThe interaction with DNA (HeLa and KB) was carried out by fluorescence spectrum and gel electrophoresis assay. In vitro apoptosis assay and cytotoxicity assay detect the manganese (II) complex interaction with cancer cells.Key findingsFluorescence spectrum demonstrated the ability of the complexes to interact with DNA in an intercalative mode. Gel electrophoresis assay exhibited more effective DNA-cleavage activity. In vitro apoptosis assay of the complexes were examined on HeLa and KB cells, exhibited cytotoxic specificity and a significant cancer cell inhibitory rate.SignificanceThe complex may be a latent antitumor agent as a result of its unique interaction mode with DNA and cancer cells inhibition effect.     

Synthesis and biodistribution of a novel (99m)TcN complex of ciprofloxacin dithiocarbamate as a potential agent for infection imaging

The ciprofloxacin dithiocarbamate (CPFXDTC) was synthesized and radiolabeled with [(99m)TcN](2+) intermediate to form the (99m)TcN-CPFXDTC complex in high yield (>95%). No decomposition of the complex at room temperature was observed over a period of 6 h. Its partition coefficient indicated that it was a good lipophilic complex. The bacterial binding assay studies showed (99m)TcN-CPFXDTC had a better binding affinity as compared with (99m)Tc-ciprofloxacin. Biodistribution results in induced infection mice showed (99m)TcN-CPFXDTC had higher uptake at the sites of infection and better abscess/blood ratio than that of (99m)Tc-ciprofloxacin, suggesting (99m)TcN-CPFXDTC would be a novel potential infection imaging agent.     

Bis(3-hydroxy-4-pyridinone)-EDTA derivative as a potential therapeutic Al-chelating agent. Synthesis, solution studies and biological assays

The 3-hydroxy-4-pyridinones are chelating agents of current interest due to their high affinity for hard metal ions and potential clinical applications as metal-decorporation agents. A new bis-(3-hydroxy-4-pyridinone) derivative of EDTA have been developed, and herein we describe the results of solution studies to determine the protonation constants and the partition coefficient. Biodistribution studies, performed with 67Ga-overload mice, showed rapid clearance of the radiotracer from the body, thus indicating that the new ligand should be a quite effective agent for the in vivo aluminium removal.     

In Vivo evaluation of a PAMAM-cystamine-(Gd-DO3A) conjugate as a biodegradable macromolecular MRI contrast agent

Macromolecular Gd(III) chelates are superior magnetic resonance imaging (MRI) contrast agents for blood pool and tumor imaging. However, their clinical development is limited by the safety concerns related to the slow excretion and long-term gadolinium tissue accumulation. A generation 6 PAMAM Gd(III) chelate conjugate with a cleavable disulfide spacer, PAMAM-G6-cystamine-(Gd-DO3A), was prepared as a biodegradable macromolecular MRI contrast agent with rapid excretion from the body. T(1) and T(2) relaxivities of the contrast agent were 11.6 and 13.3 mM(-1)sec(-1) at 3T, respectively. Blood pool and tumor contrast enhancement of the agent were evaluated in female nude mice bearing MDA-MB-231 human breast carcinoma xenografts with a nondegradable conjugate PAMAM-G6-(Gd-DO3A) as a control. PAMAM-G6-cystamine-(Gd-DO3A) resulted in significant contrast enhancement in the blood for about 5 mins, and Gd-DO3A was released from the conjugate and rapidly excreted via renal filtration after the disulfide spacer was cleaved. The nondegradable control had much longer blood circulation and excreted more slowly from the body. PAMAM-G6-cystamine-(Gd-DO3A) also resulted in more prominent tumor contrast enhancement than the control. However, PAMAM-G6-cystamine-(Gd-DO3A) demonstrated high toxicity due to the intrinsic toxicity of PAMAM dendrimers. In conclusion, although PAMAM-G6-cystamine-(Gd-DO3A) showed some advantages compared with the nondegradable control, PAMAM dendrimers are not suitable carriers for biodegradable macromolecular MRI contrast agents, due to their high toxicity.     

Design,synthesis, and in vitro evaluation of a binary targeting MRI contrast agent for imaging tumor cells

A binary targeting vector that consists of peptide sequences of Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) motifs has been designed and synthesized using solid-phase peptide synthesis procedure. The vector is then coupled with Gd-DOTA to work as a targeting contrast agent (CA1) for magnetic resonance imaging of human lung adenocarcinoma cells A549. Its longitudinal relaxivity is measured to be 7.55 mM^?1 s^?1 in aqueous solution at a magnetic field of 11.7 T, which is higher than that of Magnevist (4.25 mM^?1 s^?1) in the same conditions. The cell experiment shows, at the same concentration, uptake quantity of CA1 by A549 is much more than Magnevist and also superior over CA2 (a single targeting contrast agent contains only RGD). The uptake can be blocked by the targetable peptide containing RGD or NGR without coupling Gd. To summarize, CA1 has very good ability to target A549 and higher relaxivity than that of Magnevist. So CA1 is promising MRI contrast agent for high-resolution MR molecular imaging of human lung adenocarcinoma A549 cells.     

Synthesis and evaluation of Al18F-NODA complex conjugated 2-(4-aminophenyl)benzothiazole as a potential tumor imaging agent

The objective of the study was to prepare and evaluate a ¹⁸F-radiolabled tracer (Al¹⁸F-5), derivated from the antitumor agent 2-(4-aminophenyl)benzothiazole, as a PET probe for tumor imaging. Al¹⁸F-5 was successfully prepared with approx. 40% radiochemical yield in aqueous phase. In in vitro cell uptake experiments and competition assay, Al¹⁸F-5 displayed good tumor-binding ability and specificity in HeLa cells (24.7 ± 0.9% ID/10⁶ cells, IC₅₀ = 63.8 ± 13.6 nM) and MCF-7 cells (6.8 ± 0.3% ID/10⁶ cells, IC₅₀ = 331.1 ± 33.7 nM). The nonradioactive compound, Al¹⁹F-5, visibly marked HeLa cells and MCF-7 cells but did not stain HEB cells in florescent staining, which further indicated the tumor-binding ability of Al¹⁸F-5. In in vivo PET imaging, HeLa and MCF-7 tumors were clearly delineated by specific accumulation of Al¹⁸F-5 in model mice. In biodistribution study, Al¹⁸F-5 exhibited good tumor uptake (4.66 ± 0.13% ID/g and 3.69 ± 0.56% ID/g, respectively), moderate tumor-to-muscle ratio (3.38 and 2.48, respectively) at 1 h post injection, which were in a good consistency with the results of PET imaging. In conclusion, Al¹⁸F-5 might be developed as a candidate PET probe for tumor imaging, though additional optimizations are still needed to improve pharmacokinetics in vivo.     

Synthesis, cytotoxicity, and structure-activity relationship (SAR) studies of andrographolide analogues as anti-cancer agent

A series of analogues of andrographolide, prepared through chemo-selective functionalization at C14 hydroxy, have been evaluated for in vitro cytotoxicities against human leukemic cell lines. Two of the analogues (6a, 9b) exhibited significant potency. Preliminary studies on structure-activity relationship (SAR) revealed that the α-alkylidene-γ-butyrolactone moiety of andrographolide played a major role in the activity profile. The structures of the analogues were established through spectroscopic and analytical data.     

In vitro and in vivo evaluation of cis-methyl-phencyclidine (cis-MPCP) as a potential antagonist of phencyclidine (PCP)

In four preparations/tests (isolated nerve, venticular strip, rotarod, and mouse acute lethality), cis-N-phenyl-4-methylcyclohexyl piperidine (cis-MPCP) was consistently less active than PCP and trans-MPCP. As expected, cis-MPCP, at 10^?4M, which did not depress the action potential evoked on frog sciatic nerves, reduced by half both the nerve block and prolongation of relative refractory period caused by PCP. However, cis-MPCP at 10^?6M, which by itself had little effect, failed to reduce the positive inotropic effect of PCP on the field-stimulated rat ventricular strip. Cis-MPCP also failed to decrease the ataxic effect of 6 mg/kg PCP (ED80) in the mouse rotarod test. Finally, at a dose that was neither ataxic nor lethal to mice (20 mg/kg), cis-MPCP failed to reduce the 24-hour LD₅₀ of PCP. These data suggest that the actions of PCP are mediated through a multiple receptor system.