Design, Synthesis, and Biological Evaluations of Novel Thiazolo[4,5-d]pyrimidine Corticotropin Releasing Factor (CRF) Receptor Antagonists as Potential Treatments for Stress Related Disorders and Congenital Adrenal Hyperplasia (CAH).

Corticotropin-releasing factor (CRF) is a key neuropeptide hormone that is secreted from the hypothalamus. It is the master hormone of the HPA axis, which orchestrates the physiological and behavioral responses to stress. Many disorders, including anxiety, depression, addiction relapse, and others, are related to over-activation of this system. Thus, new molecules that may interfere with CRF receptor binding may be of value to treat neuropsychiatric stress-related disorders. Also, CRF1R antagonists have recently emerged as potential treatment options for congenital adrenal hyperplasia. Previously, several series of CRF1 receptor antagonists were developed by our group. In continuation of our efforts in this direction, herein we report the synthesis and biological evaluation of a new series of CRF1R antagonists. Representative compounds were evaluated for their binding affinities compared to antalarmin. Four compounds (2, 5, 20, and 21) showed log IC50 values of -8.22, -7.95, -8.04, and -7.88, respectively, compared to -7.78 for antalarmin. This result indicates that these four compounds are superior to antalarmin by 2.5, 1.4, 1.7, and 1.25 times, respectively. It is worth mentioning that compound 2, in terms of IC50, is among the best CRF1R antagonists ever developed in the last 40 years. The in silico physicochemical properties of the lead compounds showed good drug-like properties. Thus, further research in this direction may lead to better and safer CRF receptor antagonists that may have clinical applications, particularly for stress-related disorders and the treatment of congenital adrenal hyperplasia.

Evaluation of Rhenium and Technetium-99m Complexes Bearing Quinazoline Derivatives as Potential EGFR Agents.

Τhe Epidermal Growth Factor Receptor tyrosine kinase inhibitor (EGFR-TKI) 6-amino-4-[(3-bromophenyl) amino]quinazoline was derivatized with 6-bromohexanoyl-chloride and coupled with the tridentate chelating agents N-(2-pyridylmethyl) aminoethyl acetic acid (PAMA) and L(+)-cysteine bearing the donor atom set NNO and SNO, respectively. The rhenium precursors ReBr(CO)5 and fac-[NEt4]2[ReBr3(CO)3] were used for the preparation of the Re complexes fac-[Re(NNO)(CO)3] (5a) and fac-[Re(SNO)(CO)3] (7a) which were characterized by NMR and IR spectroscopies. Subsequently, the new potential EGFR inhibitors were labeled with the fac-[99mTc(CO)3]+ core in high yield and radiochemical purity (>90%) by ligand exchange reaction using the fac-[99mTc][Tc(OH2)3(CO)3]+ precursor. The radiolabeled complexes were characterized by comparative HPLC analysis with the analogous rhenium (Re) complexes as references. In vitro studies in the A431 cell lines showed that both ligands and Re complexes inhibit A431 cell growth. Complex 5a demonstrated the highest potency (IC50 = 8.85 ± 2.62 µM) and was further assessed for its capacity to inhibit EGFR autophosphorylation, presenting an IC50 value of 26.11 nM. Biodistribution studies of the 99mTc complexes in healthy mice showed high in vivo stability for both complexes and fast blood and soft tissue clearance with excretion occurring via the hepatobiliary system.

Synthesis and preclinical evaluation of rhenium and technetium-99m "4 + 1" mixed-ligand complexes bearing quinazoline derivatives as potential EGFR imaging agents.

Epidermal growth factor receptors (EGFR) of tyrosine kinase (TK) have shown high expression levels in most cancers and are considered a promising target for cancer diagnosis and therapy. Expanding the investigation for novel targeted radiopharmaceuticals, an EGFR inhibitor such as 4-aminoquinazoline derivatives along with a radionuclide such as technetium-99m (99mTc) could be ideal. Thus, we report herein the synthesis, characterization, and biological evaluation of new "4 + 1" mixed-ligand ReIII- and 99mTcIII-complexes of the general formula [99mTc][Tc(NS3)(CN-R)] bearing tris(2-mercaptoethyl)-amine (NS3) as the tetradentate tripodal ligand and a series of isocyanide derivatives (CN-R) of tyrosine kinase inhibitor (3-bromophenyl)quinazoline-4,6-diamine as the monodentate ligand. The quinazoline isocyanide derivatives 4a-d were prepared in two steps and reacted with the [Re(NS3)PMe2Ph] precursor leading to the final complexes 5a-d in high yield. All compounds were characterized by elemental analysis, IR, and NMR spectroscopies. In vitro studies, for their potency to inhibit the cell growth, using intact A431 cells indicate that the quinazoline derivatives 4a-d and the Re complexes 5a-d significantly inhibit the A431 cell growth. In addition, the EGFR autophosphorylation study of complex 5b shows an IC50 value in the nanomolar range. The corresponding "4 + 1" 99mTc-complexes 6a-d were prepared by employing the [99mTc]TcEDTA intermediate and the appropriate monodentate 4a-d in a two-step synthetic procedure with a radiochemical yield (RCY) from 63 to 77 % and a radiochemical purity (RCP) > 99 % after HPLC purification. Their structures have been established by HPLC comparative studies using the well-characterized Re-complexes 5a-d as reference. All 99mTc-complexes remain stable for at least 6 h, and their logD7.4 values confirmed their anticipated lipophilic character. Biodistribution studies in healthy Swiss albino mice of 99mTc-complexes showed hepatobiliary excretion and initial fast blood clearance. Complex 6b was also tested in Albino SCID mice bearing A431 tumors and showed rapid tumor uptake at 5 min (2.80 % ID/g) with a moderate tumor/muscle ratio (2.06) at 4 h p.i. The results encourage further investigation for this type of 99mTc-complexes as single-photon emission computed tomography (SPECT) radio agents for imaging tumors overexpressing EGFR.

Effective Labeling of Amine Pharmacophores through the Employment of 2,3-Pyrazinedicarboxylic Anhydride and the Generation of fac-[M(CO)3(PyA)P] and cis-trans-[M(CO)2(PyA)P2] Complexes (PyA = Pyrazine-2-carboxylate, P = Phosphine, M = Re, 99mTc).

The fac-[M(CO)3(PyA)(P)] and cis-trans-[M(CO)2(PyA)(P)2] neutral complexes (M is Re or 99mTc), based on the mixed ligand strategy with pyrazine-2-carboxylic acid (PyAH) as the bidentate N,O and triphenylphosphine as the monodentate P ligand, are presented. Through the employment of the anhydride of pyrazine-2,3-dicarboxylic acid (PyDA), the PyAH scaffold was conveniently derivatized with the model bioactive amine 1-(2-methoxyphenyl)piperazine, the active part of the 5-HT1A antagonist WAY100635. Reaction of either PyAH or the pharmacophore-bearing PyAH ligand (L1H) with fac-[M(CO)3]+ core in water yielded the intermediate fac-[M(CO)3(PyA)(H2O)] complexes. The labile aqua ligand was easily replaced by PPh3 to yield the fac-[Re(CO)3(PyA)(PPh3)] complexes, while in toluene under reflux, the cis-trans-[Re(CO)2(PyA)(PPh3)2] complexes were obtained. The latter complexes were alternatively obtained from mer-[Re(CO)3(PPh3)2Cl] by refluxing with the PyA ligand in toluene. The analogous 99mTc complexes were synthesized quantitatively, showing excellent stability in competition studies. The methodology described herein represents a practical procedure for the effective integration of the fac-[M(CO)3]+ core with amine-bearing biologically active compounds for diagnosis/therapy.

Synthesis and evaluation of new mixed "2 + 1" Re, 99mTc and 186Re tricarbonyl dithiocarbamate complexes with different monodentate ligands.

A series of "2 + 1" mixed ligand tricarbonyl complexes of the general formula fac-[Re/99mTc/186Re(CO)3(DDTC)(L)] containing diethyldithiocarbamate (DDTC) as a monoanionic bidentate ligand and a series of monodentate ligands L was synthesized, characterized and evaluated. The impact of ligand L on the radiochemical yield (RCY) and biodistribution of the final compounds was also investigated. DDTC and the appropriate L ligand [cyclohexyl isocyanide (cisc), tert-butyl isocyanide (tbi), triphenylphosphine (PPh3), methyldiphenylphosphine (PPh2Me), triphenylarsine (AsPh3), imidazole (im), and 4-aminopyridine (4AP)] readily reacted in equimolar amounts with the [Et4N]2[Re(CO)3Br3] precursor to afford fac-[Re(CO)3(DDTC)(cisc)], Re1, fac-[Re(CO)3(DDTC)(tbi)], Re2, fac-[Re(CO)3(DDTC)(PPh3)], Re3, fac-[Re(CO)3(DDTC)(PPh2Me)], Re4, fac-[Re(CO)3(DDTC)(AsPh3)], Re5, fac-[Re(CO)3(DDTC)(im)], Re6 and fac-[Re(CO)3(DDTC)(4AP)], Re7, complexes in high yields (>80%). All Re complexes were fully characterized by IR, NMR, and in addition Re4, Re5, and Re7 with X-ray crystallography. Analogous reactions as performed with Re were subsequently explored on the 99mTc and 186Re-tracer levels using the corresponding fac-[99mTc/186Re(CO)3(H2O)3]+ precursor. Complexes 99mTc1 - 99mTc5, 186Re1 and 186Re3 were obtained in high radiochemical yield (>91%), while the complexes 99mTc6, 99mTc7 and 186Re7 formed with radiochemical yields of 55%, 28%, and 75%, respectively. The 99mTc and 186Re-complexes were characterized by comparative HPLC analysis using the analogous Re complexes. During histidine and cysteine challenge experiments at 37 °C through 6 h, complexes 99mTc1 - 99mTc5 remained > 92% stable, while complexes 99mTc6 and 99mTc7 remained only 8% stable through 3 h. Similar studies for 186Re-complexes showed that 186Re1 and 186Re3 remained > 95% stable for up to 48 h, while 186Re7 had decreased to 7% after 3 h. LogD7.4 data of 99mTc1 - 99mTc5, 186Re1, and 186Re3 complexes, which ranged from 2.59 to 3.39, suggested high lipophilicity. Biodistribution studies in healthy Swiss albino mice showed hepatobiliary excretion for 99mTc1, 99mTc2, and 99mTc4, fast blood clearance for 99mTc4, while high liver uptake and retention for 99mTc3 and 99mTc5 were measured. Moreover, 99mTc2 showed high accumulation in the lungs with sustained retention (52.80% ID/g at 4 h p.i.) and significant brain uptake at 2 min p.i. (1.89% ID/g). The study showed the great influence of monodentate ligand in the synthesis and biodistribution of the mixed ligand complexes.

Comparative Study of a Series of 99mTc(CO)3 Mannosylated Dextran Derivatives for Sentinel Lymph Node Detection.

Sentinel lymph node detection (SLND) is rapidly entering common practice in the management of patients with tumors. The introduction of mannose molecules to 99mTc-labeled dextrans, so far, showed that the sentinel node could trap these agents due to their recognition by the mannose receptors of lymph node macrophages. The current study aimed to synthesize, characterize, and biologically evaluate a series of mannosylated dextran derivatives labeled with 99mTc for potential use in SLND. The compounds were designed to have a dextran with a molecular weight of 10-500 kDa as a backbone, S-derivatized cysteines, efficient SNO chelators, and mannose moieties for binding to mannose receptors. They were successfully synthesized, thoroughly characterized using NMR techniques, and labeled with the fac-[99mTc(CO)3]+ synthon. Labeling with high yields and radiochemical purities was achieved with all derivatives. In vivo biodistribution and imaging studies demonstrated high uptake in the first lymph node and low uptakes in the following node and confirmed the ability to visualize the SLN. Among the compounds studied, 99mTc-D75CM demonstrated the most attractive biological features, and in combination with the high radiochemical yield and stability of the compound, its further evaluation as a new radiopharmaceutical for sentinel lymph node detection was justified.

Synthesis, characterization and evaluation of 68Ga labelled monomeric and dimeric quinazoline derivatives of the HBED-CC chelator targeting the epidermal growth factor receptor.

Tyrosine kinase (TK) receptors including epidermal growth factor receptors (EGFRs) are known to be overexpressed in a wide variety of solid tumors associated with poor prognosis. The HBED-CC chelator N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid 1 was coupled via one or both its propionic acid moieties with the quinazoline EGFR-TK inhibiting pharmacophore 4-amino-N-(4-((3-bromophenyl)amino)quinazolin-6-yl)butanamide 3 resulting in either a monomeric 4 or a dimeric 5 species. Ligands 4 and 5 reacted with Ga3+ generating the corresponding complexes Ga4 and Ga5. Both ligands and complexes were characterized with mass spectrometry and NMR spectroscopy and evaluated in vitro with MTT assays in A431 cells, where they showed IC50 values in the range 51.6 to 68.8 µM. Labeling of ligands 4 and 5 with the PET radionuclide 68Ga was quantitative and resulted in tracers [68Ga]Ga4 and [68Ga]Ga5 with radiochemical purities greater than 98%, which were also characterised by comparative RP-HPLC studies with Ga4 and Ga5 respectively. Radiotracers [68Ga]Ga4 and [68Ga]Ga5 were stable (intact tracer over 98%) in the reaction mixture (120 min) and in human serum (30 min). Both tracers were evaluated in vivo with biodistribution experiments in SCID mice bearing A431 tumors presenting tumor uptake of 1.34 for [68Ga]Ga4 and 1.01 %ID/g for [68Ga]Ga5 at 5 min, which was slightly decreased at 60 min p.i. and then remained stable until 120 min p.i. To the best of our knowledge, this is the first report of monomeric and dimeric quinazoline conjugates with the chelator HBED-CC, which can serve as a basis for further development of EGFR-TKI targeting tracers.

Electrospray ionization study of tricarbonyl fac-[Re(CO)3 (PO)(X)]-type complexes: influence of ancillary co-ligands in the release of carbon monoxide.

RATIONALE: fac-[Re(CO)3 (PO)(X)]-type complexes (PO = chelated bidentate tertiary phosphine (1-), X = various neutral, mono-dentate ligands) represent a class of compounds that meets the synthetic criteria for the preparation of potential carbon monoxide (CO) release molecules (CORMs) for medicinal application. The aim of our investigation was to achieve qualitative information whether the nature of the ancillary X ligand might influence the release of CO. METHODS: The release of CO has been investigated by means of product ion spectrometry of electrospray ionization (ESI)-generated [M + H]+ species, produced by multiple collisional experiments, using an ion trap mass spectrometer. RESULTS: Tandem mass spectrometry applied to the protonated species [Re(CO)3 (PO)(X) + H]+ of seven complexes (those including X = OH2 (1), isonitrile (2, 3), imidazole (4), pyridine (5) and phosphine (6, 7)) shows initial loss of coordinated water (1) or pyridine (5), whereas the majority of investigated entries display initial, sequential release of CO groups. The energetics of CO release have been investigated by breakdown curves for selected collisionally activated decomposition processes involving CO, and compared with those involving X groups. CONCLUSIONS: The nature of the co-ligand X drives the primary loss in the MSn processes of [Re(CO)3 (PO)(X) + H]+ compounds. When X = solvent, the energetics of these decompositions follow the trend H2 O < MeOH < CO. In each case, loss of CO is a favored fragmentation route with associated energies following the trend: N-py ≤ P-phosphine < C-isonitrile. Overall, MSn pathways indicate that [Re(PO)] (Re with chelated PO phosphine) constitutes the residual moiety. This behavior indicates that the presence of a functionalized phosphine is essential for a sequential, controlled release of CO.

Dicarbonyl cis-[M(CO)2(N,O)(C)(P)] (M = Re, 99mTc) Complexes with a New [2 + 1 + 1] Donor Atom Combination.

The synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO)2(quin)(cisc)(PPh3)] complex, 4, where quin is the deprotonated quinaldic acid, cisc is cyclohexyl isocyanide, and PPh3 is triphenylphosphine, is presented. The synthesis of 4 proceeds in three steps. In the first, the intermediate fac-[Re(CO)3(quin)(H2O)] aqua complex 2 is generated from the fac-[NEt4]2[Re(CO)3Br3] precursor, together with the brominated products fac-[Re(CO)3(quinH)(Br)] 1a and fac-[NEt4][Re(CO)3(quin)(Br)] 1b, in low yield. In the following step, replacement of the aqua ligand of complex 2 by the monodentate isocyanide ligand leads to the formation of fac-[Re(CO)3(quin)(cisc)], 3. In the third step replacement of the species trans to the isocyanide carbonyl group of 3 by a phosphine generates complex 4. The Re complexes 2-4 were prepared in high yield and fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography. At the technetium-99m (99mTc) tracer level, the analogous complexes 3' and 4' were produced in high radiochemical purity, characterized by comparative reverse phase high-performance liquid chromatography and showed high resistance to transchelation by histidine or cysteine. This new [N,O][C][P] donor atom combination with the cis-[M(CO)2]+ core (M = Re, 99mTc) is a promising scaffold for the development of novel diagnostic and therapeutic targeted radiopharmaceuticals.

Rhenium(I) Tricarbonyl Complexes with (2-Hydroxyphenyl)diphenylphosphine as PO Bidentate Ligand.

In the present work, we investigated potential means to obtain neutral tricarbonyl mixed-ligand fac-[M(CO)3L1L2] complexes (M = Re, 99mTc) containing the (2-hydroxyphenyl)diphenylphosphine (POH) bidentate ligand (L1H) and a series of monodentate ligands (L2). First, fac-[Re(CO)3(PO)(H2O)], 1, was synthesized by reaction of POH and [Et4N]2[Re(CO)3Br3] in equimolar amounts in MeOH at room temperature. Interestingly, with excess of POH this reaction afforded fac-[Re(CO)3(PO)(POH)], 2, with POH operating both as a bidentate and as a monodentate ligand. Owing to the presence of the labile aqua ligand, which can be readily replaced by various monodentate ligands, 1 was further used as a precursor to generate a small library of the desired fac-[M(CO)3L1L2] complexes. Specifically, by reaction of triphenylphosphine (PPh3), imidazole (im), pyridine (py), cyclohexyl isocyanide (cisc), and tert-butyl isocyanide (tbi), the following products were readily obtained in excellent yields (92%-95%): fac-[Re(CO)3(PO)(PPh3)], 3, fac-[Re(CO)3(PO)(im)], 4, fac-[Re(CO)3(PO)(py)], 5, fac-[Re(CO)3(PO)(cisc)], 6, and fac-[Re(CO)3(PO)(tbi)], 7. All compounds were fully characterized by elemental analysis, IR and NMR spectroscopies, and electrospray ionization(+) mass spectrometry. Their solid-state structure was elucidated by X-ray crystallography. Of considerable interest is the fact that the corresponding 2'-7' were easily accessible at the 99mTc-tracer level in quantitative yields after reaction of POH and the respective monodentate ligand L2 with fac-[99mTc(CO)3(H2O)3]+ in aqueous MeOH, as verified by comparative chromatographic methods adopting dual photo- and radiometric detection modes. The high stability displayed by all 99mTc complexes during histidine and cysteine challenge assays underscored the suitability of the fac-[M(CO)3(PO)L2] system for radiopharmaceutical development purposes.

Development and Pharmacological Evaluation of New Bone-Targeted (99m)Tc-Radiolabeled Bisphosphonates.

A novel bisphosphonate, 1-(3-aminopropylamino)ethane-1,1-diyldiphosphonic acid (3), was coupled to the tridentate chelators di-2-picolylamine, 2-picolylamine-N-acetic acid, iminodiacetic acid, 3-((2-aminoethyl)thio)-3-(1H-imidazol-4-yl)propanoic acid, and 2-((2-carboxyethyl)thio)-3-(1H-imidazol-4-yl)propanoic acid to form ligands 6, 9, 11, 15, and 19, respectively. Organometallic complexes of the general formula [Re/(99m)Tc(CO)3(κ(3)-L)] were synthesized, where L denotes ligand 6, 9, 11, 15, or 19. The rhenium complexes were prepared at the macroscopic level and characterized by spectroscopic methods. The technetium-99m organometallic complexes were synthesized in high yield and were identified by comparative reversed-phase HPLC with their Re analogues. The (99m)Tc tracers were stable in vitro and exhibited binding to hydroxyapatite. In biodistribution studies, all of the (99m)Tc complexes exhibited high bone uptake superior to that of 25, which is the directly (99m)Tc-labeled bisphosphonate 3, and comparable to that of (99m)Tc-methylene diphosphonate ((99m)Tc-MDP). The tracers [(99m)Tc(CO)3(6)] (26), [(99m)Tc(CO)3(9)] (27), [(99m)Tc(CO)3(11)] (28), and [(99m)Tc(CO)3(15)] (29) exhibited higher bone/blood ratios than (99m)Tc-MDP. 26 had the highest bone uptake at 1 h p.i. The new bisphosphonates showed no substantial growth inhibitory capacity in PC-3, Saos-2, and MCF-7 established cancer cell lines at low concentrations. Incubation of 26 with the same cancer cell lines indicated a rapid and saturated uptake. The promising properties of 26-29 indicate their potential for use as bone-imaging agents.

New labeled derivatives of the neuroprotective peptide colivelin: synthesis, characterization, and first in vitro and in vivo applications.

Colivelin (CL), first reported in 2005, is the most potent member of the humanin family of neuroprotective peptides with in vitro and in vivo rescuing action against insults associated with Alzheimer's disease (AD). The objective of the present work is the design, synthesis and characterization of specific CL derivatives that can be used as molecular probes in the investigation of the unknown mechanism of CL action. Within this framework, three CL derivatives bearing suitable tags, i.e., the fluorescent moiety FITC, the streptavidin-counterpart biotinyl-group, and the (99m)Tc-radiometal chelating unit dimethylGly-Ser-Cys, were developed and subsequently applied in biological evaluation experiments. Specifically, the FITC-labeled derivative of CL was used in confocal microscopy, where specific binding at the periphery of F11 cells was observed; the biotin-labeled derivative of CL was used in an in-house developed ELISA-type assay, where specific and concentration-dependent binding with the ß-amyloid peptide of AD was shown; finally, the (99m)Tc-radiolabeled derivative of CL was used in in vivo biodistribution studies in healthy Swiss Albino mice, where 0.58% of the radioactivity administered was measured in the mouse brain 2min after injection. The above first successful applications of the CL probes demonstrate their potential to contribute in the field of neuroprotective peptides.

Injection site radioactivity of (99m)Tc-labeled mannosylated dextran for sentinel lymph node mapping.

The high and persistent radioactivity at the injection site hinders the accuracy and expansion of sentinel lymph node (SLN) mapping. We investigated the mechanism underlying the undesirable radioactivity after subcutaneous injection of (99m)Tc-labeled mannosylated dextran ((99m)Tc(CO)3-DCM20), a SLN mapping agent targeting mannose receptors on macrophages and dendritic cells, in a mouse model. Biodistribution studies were performed 1 h after subcutaneous injection of (99m)Tc(CO)3-DCM20 from the rear footpad of mice in the presence of varying molar amounts of DCM20 or DC15, a modified dextran without mannose. Biodistribution studies were also conducted after subcutaneous injection of [(125)I]radioiodinated mannosyl-neoglycoalbumin ((125)I-NMA) from the rear footpad. The distribution of fluorescence-labeled DCM20 and DC15 at the injection site was also compared 1 h after subcutaneous injection by immunofluorescent histochemistry. The radioactivity levels of (99m)Tc(CO)3-DCM20 at the injection site and popliteal lymph node, a SLN in this model, decreased with an increase in the molar amounts of DCM20, whereas no significant changes in biodistribution were observed after injection of (99m)Tc(CO)3-DCM20 with varying molar amounts of DC15. (125)I-NMA exhibited rapid elimination of radioactivity from both the popliteal lymph node and the injection site. The fluorescence-labeled DCM20 colocalized well with CD68-positive cells such as macrophages and dendritic cells at the injection site. While partial colocalization was observed between DC15 and CD68-positive cells, the signal intensity was very weak. These findings suggest that specific binding of (99m)Tc(CO)3-DCM20 to the mannose receptor on macrophages and dendritic cells would be responsible for the sustained radioactivity levels at the injection site. These results also imply that discriminated blockage of (99m)Tc(CO)3-DCM20 binding to mannose receptors at the injection sites would reduce the radioactivity at the injection site.

Synthesis and Evaluation of 99mTc(CO)3 Complexes with Ciprofloxacin Dithiocarbamate for Infection Imaging.

Background: The accurate diagnosis of bacterial infections remains a critical challenge in clinical practice. Traditional imaging modalities like computed tomography (CT) and magnetic resonance imaging (MRI) often fail to distinguish bacterial infections from sterile inflammation. Nuclear medicine, such as technetium-99m (99mTc) radiopharmaceuticals, offers a promising alternative due to its ideal characteristics. Methods: This study explores the development of [2 + 1] mixed-ligand 99mTc-labeled ciprofloxacin dithiocarbamate (Cip-DTC) complexes combined with various phosphine ligands, including triphenylphosphine (PPh3), tris(4-methoxyphenyl)phosphine (TMPP), methyl(diphenyl)phosphine (MePPh2), dimethylphenylphosphine (DMPP), and 1,3,5-triaza-7-phosphaadamantane (ADAP). The characterization of 99mTc-complexes was conducted using rhenium analogs as structural models to ensure similar coordination. Results: Stability studies demonstrated the high integrity (97-98%) of the complexes under various conditions, including cysteine and histidine challenges. Lipophilicity studies indicated that complexes with higher logD7.4 values (1.6-2.7) exhibited enhanced tissue penetration and prolonged circulation. Biodistribution studies in Swiss Albino mice with induced infections and aseptic inflammation revealed distinct patterns. Specifically, the complex fac-[99mTc(CO)3(Cip-DTC)(PPh3)] (2') showed high infected/normal muscle ratios (4.62 at 120 min), while the complex fac-[99mTc(CO)3(Cip-DTC)(TMPP)] (3') demonstrated delayed but effective targeting (infected/normal muscle ratio of 3.32 at 120 min). Conclusions: These findings highlight the potential of 99mTc-labeled complexes as effective radiopharmaceuticals for the differential diagnosis of bacterial infections, advancing nuclear medicine diagnostics. Future studies will focus on optimizing molecular weight, lipophilicity, and stability to further enhance the diagnostic specificity and clinical utility of these radiopharmaceuticals.

Synthesis and characterization of fac-[M(CO)3(P)(OO)] and cis-trans-[M(CO)2(P)2(OO)] complexes (M = Re, (99m)Tc) with acetylacetone and curcumin as OO donor bidentate ligands.

The synthesis and characterization of neutral mixed ligand complexes fac-[M(CO)3(P)(OO)] and cis-trans-[M(CO)2(P)2(OO)] (M = Re, (99m)Tc), with deprotonated acetylacetone or curcumin as the OO donor bidentate ligands and a phosphine (triphenylphosphine or methyldiphenylphosphine) as the monodentate P ligand, is described. The complexes were synthesized through the corresponding fac-[M(CO)3(H2O)(OO)] (M = Re, (99m)Tc) intermediate aqua complex. In the presence of phosphine, replacement of the H2O molecule of the intermediate complex at room temperature generates the neutral tricarbonyl monophosphine fac-[Re(CO)3(P)(OO)] complex, while under reflux conditions further replacement of the trans to the phosphine carbonyl generates the new stable dicarbonyl bisphosphine complex cis-trans-[Re(CO)2(P)2(OO)]. The Re complexes were fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography showing a distorted octahedral geometry around Re. Both the monophosphine and the bisphosphine complexes of curcumin show selective binding to ß-amyloid plaques of Alzheimer's disease. At the (99m)Tc tracer level, the same type of complexes, fac-[(99m)Tc(CO)3(P)(OO)] and cis-trans-[(99m)Tc(CO)2(P)2(OO)], are formed introducing new donor combinations for (99m)Tc(I). Overall, ß-diketonate and phosphine constitute a versatile ligand combination for Re(I) and (99m)Tc(I), and the successful employment of the multipotent curcumin as ß-diketone provides a solid example of the pharmacological potential of this system.

Radiochemical and radiobiological assessment of a pyridyl-S-cysteine functionalized bombesin derivative labeled with the (99m)Tc(CO)3(+) core.

Bombesin is a neuropeptide widely studied due to its ability to target various types of cancers. Technetium-99m on the other hand is ideal for diagnostic tumor targeting. The aim of the present study is the investigation of the coupling of the ligand (S)-(2-(2'-pyridyl)ethyl)-d,l-cysteine with the BN-peptide Gln-Arg-Leu-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Met(CONH2) through the spacer aminohexanoic acidand the labeling of the resulting derivative MBN with the synthon [M(CO)3(H2O)3](+) (M=(99m)Tc, Re). The peptide was synthesized according to the SPPS method, purified and characterized by ESI-MS. The new (99m)Tc-labeled biomolecule was stable in vitro, showed high affinity for the human GRP receptor expressed in PC3 cells and the rate of internalization was found to be time-dependent tissue distribution of the radiopeptide was evaluated in normal mice and in prostate cancer experimental models and significant radioactivity uptake was observed in the pancreas of normal mice as well as in PC3 tumors. Dynamic studies of the radiopeptide showed satisfactory tumor images.

Design, synthesis, structural optimization, SAR, in silico prediction of physicochemical properties and pharmacological evaluation of novel & potent thiazolo[4,5-d]pyrimidine corticotropin releasing factor (CRF) receptor antagonists.

Corticotropin-releasing factor (CRF) is a 41-amino-acid neuropeptide secreted from the hypothalamus and is the main regulator of the hypothalamus-pituitary-adrenocortical (HPA) axis. CRF is the master hormone which modulates physiological and behavioral responses to stress. Many disorders including anxiety, depression, addictive disorders and others are related to over activation of the CRF system. This suggests that new molecules which can interfere with CRF binding to its receptors may be potential candidates for neuropsychiatric drugs to treat stress-related disorders. Previously, three series of pyrimidine and fused pyrimidine CRF1 receptor antagonists were synthesized by our group and specific binding assays, competitive binding studies and determination of the ability to antagonize the agonist-stimulated accumulation of cAMP (the second messenger for CRF receptors) were reported. In continuation of our efforts in this direction, in the current manuscript, we report the synthesis & biological evaluation of a new series of CRF1 receptor antagonists. Seven compounds showed promising binding affinity with the best two compounds (compounds 6 & 43) displaying a superior binding affinity to all of our previous compounds. Compounds 6 & 43 have only 4 times and 2 times less binding affinity than the standard CRF antagonist antalarmin, respectively. Thus, our two best lead compounds (compound 6 & 43) can be considered potent CRF receptor antagonists with binding affinity of 41.0 & 19.2 nM versus 9.7 nM for antalarmin.

Synthesis and Characterization of Novel [2 + 1] Tricarbonyl Rhenium Complexes with the Hydrophilic Phosphine Ligands PTA and CAP.

In the pursuit of hydrophilic model fac-[Re(CO)3]+ complexes for (radio) pharmaceutical applications, six novel [2 + 1] mixed-ligand complexes of the general type fac-[Re(CO)3(bid)P] were synthesized and characterized, where bid is a bidentate ligand bearing either (N, O) or (S, S') donor atom sets and P is the hydrophilic phosphine 1,3,5-triaza-7-phosphoadamantane (PTA) or its macrocyclic homologue 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP). The (N, O) ligands used in this study were picolinic and quinaldic acid, while the (S, S') ligand was diethyldithiocarbamate. The complexes were synthesized in generally high yields and purity and the characterization was performed by spectroscopic methods, IR, NMR, and elemental analysis. Detailed X-ray crystallographic study of molecular packing by using Hirshfeld analysis tools revealed a plethora of intermolecular interactions such as hydrogen bond, π⋯π, C-H⋯π, and carbonyl-carbonyl interactions. To our knowledge, the CAP complexes reported herein are the first example of [2 + 1] mixed-ligand fac-[Re(CO)3]+ complexes with CAP. The new complexes might have the potential to serve as platforms for the design of target-specific complexes with favorable pharmacokinetics.

Curcumin as the OO bidentate ligand in "2 + 1" complexes with the [M(CO)3]+ (M = Re, 99mTc) tricarbonyl core for radiodiagnostic applications.

The synthesis and characterization of "2 + 1" complexes of the [M(CO)(3)](+) (M = Re, (99m)Tc) core with the ß-diketones acetylacetone (complexes 2, 8) and curcumin (complexes 5, 10 and 6, 11) as bidentate OO ligands, and imidazole or isocyanocyclohexane as monodentate ligands is reported. The complexes were synthesized by reacting the [NEt(4)](2)[Re(CO)(3)Br(3)] precursor with the ß-diketone to generate the intermediate aqua complex fac-Re(CO)(3)(OO)(H(2)O) that was isolated and characterized, followed by replacement of the labile water by the monodentate ligand. All complexes were characterized by mass spectrometry, NMR and IR spectroscopies, and elemental analysis. In the case of complex 2, bearing imidazole as the monodentate ligand, X-ray analysis was possible. The chemistry was successfully transferred at (99m)Tc tracer level. The curcumin complexes 5 and 6, as well as their intermediate aqua complex 4, that bear potential for radiopharmaceutical applications due to the wide spectrum of pharmacological activity of curcumin, were successfully tested for selective staining of ß-amyloid plaques of Alzheimer's disease. The fact that the complexes maintain the affinity of the mother compound curcumin for ß-amyloid plaques prompts for further exploration of their chemistry and biological properties as radioimaging probes.

Synthesis and In Vitro Evaluation of Gold Nanoparticles Functionalized with Thiol Ligands for Robust Radiolabeling with 99mTc.

Radiolabeled gold nanoparticles (AuNPs) have been widely used for cancer diagnosis and therapy over recent decades. In this study, we focused on the development and in vitro evaluation of four new Au nanoconjugates radiolabeled with technetium-99m (99mTc) via thiol-bearing ligands attached to the NP surface. More specifically, AuNPs of two different sizes (2 nm and 20 nm, referred to as Au(2) and Au(20), respectively) were functionalized with two bifunctional thiol ligands (referred to as L1H and L2H). The shape, size, and morphology of both bare and ligand-bearing AuNPs were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. In vitro cytotoxicity was assessed in 4T1 murine mammary cancer cells. The AuNPs were successfully radiolabeled with 99mTc-carbonyls at high radiochemical purity (>95%) and showed excellent in vitro stability in competition studies with cysteine and histidine. Moreover, lipophilicity studies were performed in order to determine the lipophilicity of the radiolabeled conjugates, while a hemolysis assay was performed to investigate the biocompatibility of the bare and functionalized AuNPs. We have shown that the functionalized AuNPs developed in this study lead to stable radiolabeled nanoconstructs with the potential to be applied in multimodality imaging or for in vivo tracking of drug-carrying AuNPs.