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.     

Synthesis and biological evaluation of a novel 99mTc cyclopentadienyl tricarbonyl complex ([(Cp-R)99mTc(CO)3]) for sigma-2 receptor tumor imaging

We report the design, synthesis and biological evaluation of a novel ^99mTc 4-(4-cyclohexylpiperazine-1-yl)-butan-1-one-1-cyclopentadienyltricarbonyl technetium ([^99mTc]5) as a potential SPECT tracer for imaging of σ₂ receptors in tumors. [^99mTc]5 was prepared in 25 ± 5% isolated radiochemical yield with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the ferrocene precursor 2b (4-(4-cyclohexylpiperazine-1-yl)-1-ferrocenylbutan-1-one). The corresponding Re-complex 4 and the ferrocenyl complex 2b showed relatively high affinity towards σ₂ receptors in in vitro competition binding assay (K_i values of 4 and 2b were 64.4 ± 18.5 nM and 43.6 ± 21.3 nM, respectively) and moderate to high selectivity versus σ₁ receptors (K_iσ₁/K_iσ₂ ratios were 12.5 and 95.5, respectively). The log D value of [^99mTc]5 was determined to be 2.52 ± 0.33. Biodistribution studies in mice revealed comparably high initial brain uptake of [^99mTc]5 and slow washout. Administration of haloperidol 5 min prior to injection of [^99mTc]5 significantly reduced the radiotracer uptake in brain, heart, lung, and spleen by 40–50% at 2 h p.i.. Moreover, [^99mTc]5 showed high uptake in C6 glioma cell lines (8.6%) after incubation for 1 h. Blocking with haloperidol to compete with [^99mTc]5 significantly reduced the cell uptake. Preliminary blocking study in C6-brain-tumor bearing rats showed that [^99mTc]5 binds to σ receptors in the brain-tumor specifically. These results are encouraging for further exploration of ^99mTc-labeled probes for σ₂ receptor tumor imaging in vivo.     

Synthesis and biological evaluation of a novel 99mTc labeled 2-nitroimidazole derivative as a potential agent for imaging tumor hypoxia

Tumor hypoxia plays a major role in reducing the efficacy of therapeutic modalities like chemotherapy and radiation therapy in combating cancer. In order to target hypoxic tissues, a tripeptide ligand having a 2-nitroimidazole moiety, as a bioreductive species, was synthesized. The latter was radiolabeled with ^99mTc for imaging hypoxic regions of tumors and was characterized by means of its rhenium analogue. The biodistribution and scintigraphic image of the corresponding ^99mTc-complex showed accumulation in tumor and these results suggest that it could be a marker for imaging tumor hypoxia.     

Synthesis and biological evaluation of a novel 99mTc nitrido radiopharmaceutical with deoxyglucose dithiocarbamate,showing tumor uptake

The deoxyglucose dithiocarbamate (DGDTC) was synthesized and radiolabelled with [^99mTcN]²⁺ intermediate to form the ^99mTcN–DGDTC complex. The radiochemical purity of the ^99mTcN–DGDTC complex was over 90%, as measured by TLC and by HPLC, without any notable decomposition at room temperature over a period of 6 h. The partition coefficient and electrophoresis results indicated that this complex was hydrophilic and neutral. The biodistribution of ^99mTcN–DGDTC in mice bearing S 180 tumor showed that the complex accumulated in the tumor with high uptake and good retention. The tumor/blood and tumor/muscle ratios increased with time and reached 2.32 and 1.68 at 4 h post-injection, suggesting it would be a promising candidate for tumor imaging.     

Synthesis and in vitro/in vivo evaluation of novel 99mTc(CO)3-folates

Novel organometallic 99mTc(I)-folate derivatives have been synthesized and evaluated in vitro and in vivo in order to assess the influence of the overall charge of the radioconjugates and the spacer entity on the affinity and pharmacokinetic profile. Folic acid has been functionalized at the gamma-carboxylate group of the glutamate moiety with (i) a hydrophilic diethoxyethyl spacer bearing a picolylamine monoacetic acid chelate, (ii) a hexyl spacer bearing an iminodiacetic acid chelate, and (iii) a hexyl spacer with a bis(pyridylmethyl)amine chelating system. Coordination of the 99mTc(CO)3-core resulted in neutral complex 21, anionic complex 22, and cationic complex 23 in excellent yields (>90%) at ligand concentrations of 10(-4) M. Complexes 21-23 were HPLC purified for in vitro and in vivo experiments. In the case of 23, separation from the unlabeled folate analogue was incomplete, leading to low specific activity and, hence, significantly inferior in vivo uptake in folate-receptor-positive (FR-positive) organs and tissues (tumors and kidneys). Time dependent in vivo studies were performed in female, athymic nude mice bearing subcutaneous FR-positive human KB cell xenografts at 1, 4, and 24 h post injection (p.i.) of the radiotracers. Tumor uptake ranged between 1.9-2.7% ID/g, 4 h p.i. and 1.6-2.2% ID/g, 24 h p.i. for 21 and 22, and 0.9% ID/g, 4 h p.i. and 1.1% ID/g, 24 h p.i. for 23. Blood clearance was fast for all derivatives (< or =0.2% ID/g 1 h p.i.). Significant fractions of radioactivity were found in nontargeted and FR-negative organs and tissues (particularly in the liver and the intestines/intestinal contents) at early time points p.i. Coadministration of folic acid reduced radioactivity in FR-positive tissues and organs to background levels. In conclusion, overall charge and the nature of the spacer entity seemed to have a relatively minor influence on receptor affinity and the in vivo pharmacokinetic profile of the tested radiofolates.     

Synthesis and biological properties of the lipophilic technetium-99m complex 99mTc(acac)3

In the development of technetium-99m radiopharmaceuticals for the evaluation of regional cerebral perfusion, one series of complexes that has remained unexplored is the neutral lipophilic tris complexes formed with β-diketonato ligands. The prototype complex of this series, tris(2,4-pentanedionato) technetium(III), has been prepared via a new synthetic route and chemically characterized using ⁹⁹Tc and the biodistribution of the no-carrier-added ^99mTc complex has been determined. The ^99mTc complex was found to be distributed throughout the body with persistant high blood levels indicative of a high degree of protein binding. The primary route of excretion was the hepatobiliary system as indicated by the appearance of ^99mTc in the gut and feces at longer sample times post-injection. Although this complex was not retained by the brain, it does provide a starting point from which a more effective agent might be developed.     

Synthesis, metal complexation and biological evaluation of a novel semi-rigid bifunctional chelating agent for 99mTc labelling

A novel bifunctional chelating agent bearing an aromatic ring has been synthesised and characterised. This ligand formed well-defined oxorhenium complexes. The analogous 99mTcO-complex was obtained in an excellent yield with high radiochemical purity (>95%). The biodistribution of the 99mTc-complex after intravenous injection studied in normal rats showed that the activity was excreted mainly via renal-urinary pathway indicating its use for labelling peptides with 99mTc.     

Preparation and biodistribution of a 99mTc tricarbonyl complex with deoxyglucose dithiocarbamate as a tumor imaging agent for SPECT

The deoxyglucose dithiocarbamate (DGDTC) was successfully labeled with the ^99mTc(CO)₃ core to provide the corresponding ^99mTc(CO)₃–DGDTC complex in good yields. The radiochemical purity of the ^99mTc(CO)₃–DGDTC complex was over 90%, as measured by high performance liquid chromatography (HPLC). The complex possessed good stability in saline at room temperature and in mouse plasma at 37 °C. Its partition coefficient result indicated that it was a hydrophilic complex. The electrophoresis results showed the complex was neutral. The biodistribution of ^99mTc(CO)₃–DGDTC in mice bearing S 180 tumor showed that the complex clearly accumulated in tumor, exhibiting high tumor/blood and tumor/muscle ratios and good tumor retention. Single photon emission computed tomography (SPECT) image studies showed there was a visible uptake in tumor sites, suggesting ^99mTc(CO)₃–DGDTC could be considered as a potential tumor imaging agent.     

Synthesis, characterization, and evaluation of a novel 99mTc(CO)3 pyrazolyl conjugate of a peptide nucleic acid sequence

The 16-mer peptide nucleic acid sequence H-A GAT CAT GCC CGG CAT-Lys-NH₂ (1), which is complementary to the translation start region of the N-myc oncogene messenger RNA, was synthesized and conjugated to a pyrazolyl diamine bifunctional chelator (pz). The novel conjugate pz-A GAT CAT GCC CGG CAT-Lys-NH₂ (2) was labeled with technetium tricarbonyl, yielding quantitatively the complex fac-[^99mTc(CO)₃(κ³-pz-A GAT CAT GCC CGG CAT-Lys-NH₂)]²⁺ (4). Complex 4 was obtained with high radiochemical purity and high specific activity, revealing high stability in human serum and in cell culture medium. The identity of 4 was confirmed by comparing its reversed-phase high performance liquid chromatography profile with that of the rhenium analog fac-[Re(CO)₃(κ³-pz-A GAT CAT GCC CGG CAT-Lys-NH₂)]²⁺ (3), prepared by conjugation of fac-[Re(CO)₃(3,5-Me₂pz(CH₂)₂N((CH₂)₃COOH)(CH₂)₂NH₂)]⁺ to 1, using solid-phase techniques. UV melting experiments of 1 and 3 with the complementary DNA sequence led to the formation of stable duplexes, indicating that the conjugation of 1 to the pyrazolyl chelator and to the metal fragment fac-[M(CO)₃]⁺ did not affect the recognition of the complementary sequence as well as the duplex stability. For a first screening, SH-SY5Y human neuroblastoma cells, which express N-myc, were treated with 4. The results show that 4 internalizes (7% of the activity goes into the cells, after 4 h at 37 °C), presenting also a relatively high cellular retention (only 40% of internalized activity is released from the cells after 5 h). An erratum to this article can be found at     

Evaluation of 99mTc(CO)3 complex of 2-methyl-5-nitroimidazole as an agent for targeting tumor hypoxia

An iminodiacetic acid (IDA) derivative of 2-methyl-5-nitroimidazole was synthesized as a carrier molecule for radiolabeling with the gamma emitting radioisotope, 99mTc, for imaging hypoxic regions of tumors. The ligand was synthesized in excellent yield and labeled using freshly prepared [99mTc(CO)3(H2O)3]+ intermediate. A complexation yield of over 95% could be achieved under mild conditions using a ligand concentration of 1 mg/mL [ approximately 3 x 10(-3)M]. The complex was characterized by HPLC and its stability in human serum was studied. Biodistribution studies performed in Swiss mice bearing fibrosarcoma tumor showed maximum accumulation in the tumor to the extent of approximately 0.52 % ID/g at 30 min post-injection (pi). The major clearance of the complex was through the hepatobiliary route. The complex showed tumor/muscle ratio of 1.75 at 30 min pi, which significantly increased to 17 at 180 min pi. However, the tumor/blood ratio was below one throughout the period of study, which could be due to slow clearance of the complex from blood.     

In vitro and in vivo evaluation of a novel 99mTc(CO)3-pyrazolyl conjugate of cyclo-(Arg-Gly-Asp-d-Tyr-Lys)

Radiolabeled peptides containing the Arg-Gly-Asp amino acid sequence (single letter code = RGD) have been studied extensively to target integrin receptors upregulated on tumor cells and neovasculature. Integrins are cell surface transmembrane glycoproteins that exist as alphabeta heterodimers. The alphavbeta3 integrin is known to be overexpressed in many tumor types and is expressed at lower levels in normal tissues. Furthermore, alphavbeta3 and alphavbeta5 subtypes are expressed in neovasculature during angiogenesis. Thus, there is some impetus to image angiogenesis and tumor formation in vivo using RGD-based peptide targeting vectors. In this study, we report the design and development of a new cyclic RGD analogue cyclo-[Arg-Gly-Asp-d-Tyr-Lys(PZ)] (PZ = 3,5-Me2-pz(CH2)2N((CH2)3COOH)(CH2)2NH2) that can be radiolabeled with the [99mTc(CO)3(H2O)3]+ metal aquaion. Radiochemical evaluation of this new conjugate in vitro indicated a facile radiosynthesis of the new 99mTc-RGD conjugate with high radiolabeling yields (>or=95%) and high specific activities. In vitro internalization and blocking assays in alphavbeta3 receptor-positive, human M21 melanoma cancer cells showed the ability of this conjugate to target the integrin receptor with high specificity and selectivity. In vivo pharmacokinetic studies in normal CF-1 mice showed rapid clearance from blood with excretion primarily via/through the renal-urinary system. In vivo accumulation of radioactivity in mice bearing either alphavbeta3 receptor-positive or negative human melanoma tumors showed receptor specific uptake of tracer with accumulations of 2.50 +/- 0.29 and 0.71 +/- 0.08% ID/g in alphavbeta3 integrin positive (M21) and negative (M21L) tumors at 1 h postinjection (p.i.), respectively.     

A 99mTc(I)-postlabeled high affinity bombesin analogue as a potential tumor imaging agent

The overexpression of neuropeptide receptors observed in many cancers provides an attractive target for tumor imaging and therapy. Bombesin is a peptide exhibiting a high affinity for the gastrin releasing peptide (GRP) receptor, which is overexpressed by a variety of tumors such as breast or prostate cancer. In the present study, we have evaluated if the bombesin analogue [N(alpha)-histidinyl acetate]bombesin(7-14), radiolabeled with the novel [99mTc(OH(2))(3)(CO)(3)]+, has the potential to be used as a diagnostic radiopharmaceutical. Receptor saturation studies, carried out on the GRP receptor-expressing PC-3 human prostate cancer cell line, revealed for [99mTc(CO)(3)-N(alpha)-histidinyl acetate]bombesin(7-14) K(d) values in the subnanomolar range. Competitive binding assays, using the cold rhenium(I)-labeled analogue as a surrogate for the 99mTc-conjugate, also showed high affinity binding. Incubation of the radioconjugate with PC-3 cells resulted in a rapid temperature- and time-dependent specific internalization. At 37 degrees C more than 70% was internalized within the first 15 min and remained constant up to 2 h. Despite the weak proteolytic stability of [99mTc(CO)(3)-N(alpha)-histidinyl acetate]bombesin(7-14) in vitro, biodistribution studies, performed in PC-3 tumor-bearing mice, showed low uptake in the tumor (0.89 +/- 0.27% ID/g 30 min pi) but high uptake into the pancreas (7.11 +/- 3.93% ID/g 30 min pi), a GRP receptor-positive organ. Blockade experiment (coinjection of 300 microg bombesin/mouse with the radioligand) showed specificity of the uptake. Despite the low tumor uptake, tumor-to-blood ratios of 2.0 and 2.7 and tumor-to-muscle ratios of 8.9 and 8.0 were obtained at 30 min and 1.5 h postinjection, respectively. The promising results merit the future in vivo investigation of 99mTc/188Re-tricarbonyl-labeled bombesin analogues.     

Synthesis and biological evaluation of novel benzodioxinocarbazoles (BDCZs) as potential anticancer agents

We report the efficient synthesis and biological evaluation of new benzodioxinoindolocarbazoles heterocycles (BDCZs) designed as potential anticancer agents. Indolic substitution and maleimide variations were performed to design a new library of BDCZs and their cytotoxicity were evaluated on two representative cancer cell lines. Several derivatives have shown a marked cytotoxicity with IC₅₀ values in the nanomolar range. Results are reported in this Letter.     

Synthesis and biological evaluation of 99mTc, Re-monoamine-monoamide conjugated to 2-(4-aminophenyl)benzothiazole as potential probes for beta-amyloid plaques in the brain

The benzothiazole aniline (BTA) conjugated with monoamine-monoamide (MAMA) was synthesized and then labeled with (99m)Tc. Its corresponding rhenium analogue was synthesized, and the fluorescent staining was performed in brain sections of both Tg mouse and Alzheimer's disease (AD) patient. The fluorescent rhenium complex Re-MAMA-BTA selectively bound to the amyloid aggregates in the brain sections of both APP Tg mouse and AD patient. The analogous (99m)Tc-MAMA-BTA complex could enter the normal mouse brain with high initial uptake. These results are encouraging for further exploration of their derivatives as imaging agents for Abeta plaques in the brain.     

Biological evaluation of glucose and deoxyglucose derivatives radiolabeled with [99mTc(CO)3(H2O)3]+ core as potential melanoma imaging agents

Glucose 9 and 2-deoxyglucose 10 were successfully synthesized and radiolabeled with [(99m)Tc(CO)(3)(H(2)0)(3)](+) intermediate in high yield. The complexes were characterized by HPLC and its stability with histidine over time was challenged. Cell uptake and biodistribution studies in melanoma-bearing C57BL/6 mice were performed. Both compounds showed accumulation in tumor tissue with high tumor-to-muscle ratios. Thus, D-glucose- and D-2-deoxyglucose-(99m)Tc complex could be considered as agents for melanoma diagnosis.     

Synthesis and biological evaluation of dithiocarbamate esters of parthenolide as potential anti-acute myelogenous leukaemia agents

A series of dithiocarbamate esters of parthenolide (PTL) was designed, synthesised, and evaluated for their anti- acute myelogenous leukaemia (AML) activities. The most promising compound 7l showed greatly improved potency against AML progenitor cell line KG1a with IC₅₀ value of 0.7?μM, and the efficacy was 8.7-folds comparing to that of PTL (IC₅₀?=?6.1?μM). Compound 7l induced apoptosis of total primary human AML cells and leukaemia stem cell (LSCs) of primary AML cells while sparing normal cells. Furthermore, 7l suppressed the colony formation of primary human leukaemia cells. Moreover, compound 12, the salt form of 7l, prolonged the lifespan of mice in two patient-derived xenograft models and had no observable toxicity. The preliminary molecular mechanism study revealed that 7l-mediated apoptosis is associated with mitogen-activated protein kinase signal pathway. On the basis of these investigations, we propose that 12 might be a promising drug candidate for ultimate discovery of anti-LSCs drug.     

A novel [99mTc[triple bond]N]2+ complex of metronidazole xanthate as a potential agent for targeting hypoxia

A xanthate derivative (L) at the pendant hydroxy group of metronidazole, a nitroimidazole known to possess affinity for hypoxic tumors, has been used as the carrier molecule for targeted delivery of the gamma-emitting radioisotope 99mTc to tumors. The xanthate residues (S2(-)) from two molecules of this ligand (L) were used for chelation with the [99mTcN]2+ intermediate to form a square pyramidal and neutral [99mTcN/L2] complex in >95% yield using a low ligand concentration of 1 mg/mL (approximately 3 x 10(-3) M). Biodistribution studies carried out in Swiss mice bearing fibrosarcoma tumor showed selective accumulation of the injected activity in the tumor (1.44 +/- 0.26% per gram 1 h pi) with major clearance through hepatobiliary route. The complex showed high tumor/muscle ratio (2.15 and 3.35 at 1 and 3 h post-injection, respectively) and tumor/blood ratio, which were comparable to hypoxia targeting agents 99mTc-BMS181321 and 99mTc-BRU59-21 reported earlier.     

Synthesis and biological evaluation of polyhydroxylated oxindole derivatives as potential antileishmanial agent

The devastating appearance of numerous drug-unresponsive strains of Leishmania donovani and severe toxic side effects of conventional antileishmanial therapy necessitates the search for novel leads, to treat visceral leishmaniasis efficiently. The current study deals with the synthesis and biological evaluation of a unique C-5 functionalized oxindole based polyphenol to ascertain its activities against L. donovani infection, in vitro. The polyhydroxylated oxindole derivative (1) was generated by coupling styrene derivatives with 5-bromo bis-arylidene oxindole using Heck coupling reaction. The synthesized molecule 1 was tested for its antileishmanial activity using both promastigote and amastigote stages of L. donovani. Molecule 1 showed promising anti-promastigote and anti-amastigote activities with IC₅₀ values 15?µM and 1?µM, respectively, with no cytotoxicity towards host splenocytes. The results revealed that this compound induced parasite death by promoting oxidative stress, thereby triggering apoptosis.     

Synthesis and preliminary biological evaluation of the 99mTc labeled nitrobenzoimidazole and nitrotriazole as tumor hypoxia markers

1-(3-1,2,4-Nitrotriazole-1-yl)-propanhydroxyiminoamide and 1-(6-nitrobenzoimidazole-1-yl)-propanhydroxyiminoamide were synthesized and radiolabeled with (99m)Tc. The (99m)Tc labeled complexes continuously accumulated in hypoxic murine sarcoma S180 cells in vitro but not in aerobic cells. Biodistribution results in mice bearing S180 tumor indicated that the tracers could localize in tumor and eliminate from it slowly. These results suggested that the (99m)Tc labeled nitrobenzoimidazole and nitrotriazole might be the novel tumor hypoxia markers.     

Synthesis and biological evaluation of novel benzoxazinyl-oxazolidinones as potential antibacterial agents

A number of benzoxazinyl-oxazolidinones bearing 3-trizolylmethyl or 3-carboxamide side chain were designed and synthesized with the aim to develop antibacterial agents with improved properties. In vitro antibacterial activities of these novel compounds were evaluated against a panel of resistant and susceptible Gram-positive bacteria. Most analogues bearing 3-trizolylmethyl showed good to moderate antibacterial activities. Compound 12a exhibited a fourfold increase in activity compared with linezolid against all the tested strains, which was identified to be a promising antibacterial agent for further evaluation.