Improvement in radiolabelling proteins with the 99mTc‐tricarbonyl‐core [99mTc(CO)3]+, by thiol‐derivatization with iminothiolane: application to γ‐globulins and annexin V

The aim of this study was to improve the radiolabelling of proteins with the ^99mTc‐tricarbonyl‐[Tc(I)(CO)₃]⁺ core by introducing thiol groups to their structure. To achieve this goal, γ‐globulins and annexin V were derivatized with mercaptobutyrimidyl groups (MBG) after reaction with 2‐iminothiolane. The optimal conditions permitted attachment of an average of 3.3 thiol groups on γ‐globulins and 1.0 to annexin V. The radiolabelling assays were carried out by incubating 3.2 nmol of either γ‐globulin‐SH or unmodified γ‐globulin with 60 MBq ^99mTc‐tricarbonyl produced from an Isolink^® kit (Mallinckrodt) under different reaction conditions. Results clearly showed that the introduction of three MBG could double the radiolabelling yields to more than 90% in a short time (30 mn, 37°C). Such results would never have been reached with unmodified γ‐globulins alone. Under the same conditions when using 1–2 nmol derivatized annexin V, the average radiolabelling yield was 55% against 19% with the unmodified protein. The ^99mTc‐tricarbonyl‐conjugates were challenged with cysteine or histidine and showed good stability. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis,characterization and pre‐clinical evaluation of 99mTc‐tricarbonyl complexes as potential myocardial perfusion imaging agents

Myocardial perfusion imaging is an established Nuclear Medicine investigation. Current myocardial perfusion imaging agents sestamibi and tetrofosmin have number of drawbacks; low heart uptake coupled with uptake into the surrounding tissues leads to a poorer image quality. There is a need for continued research into designing and evaluating potentially superior myocardial imaging agents. Tri‐carbonyl‐technetium and rhenium complexes were prepared by combination with mono‐dentate and bi‐dentate ligands. Complexes were characterized by HPLC, MAS, nuclear magnetic resonance, infrared, single‐crystal X‐ray diffraction and partition coefficient determinations. ^99mTc(CO)₃ complexes were administered intravenously to Sprague Dawley rats, and tissue distribution studies were carried out at 15 min and 1 h p.i. Radiochemical purity was assessed as >90%. 1‐10‐phenanthroline, 2,2′‐bipyridine and imidazole complexes gave the highest heart uptake. The percentage injected dose per gram (n = 3) at 1 h for 1‐10‐phenanthroline/imidazole was blood 0.21 ± 0.01, heart 1.12 ± 0.11, kidney 3.61 ± 1.13, liver 0.62 ± 0.06, lung 0.28 ± 0.12, spleen 0.24 ± 0.05, small intestine contents 1.87 ± 0.92; and for 2,2′‐bipyridine /imidazole was blood 0.23 ± 0.02, heart 1.07 ± 0.18, kidney 3.31 ± 1.28, liver 0.56 ± 0.09, lung 0.14 ± 0.02, spleen 0.2 ± 0.1, small intestine content 1.05 ± 0.48. Further investigation to evaluate more complexes based on 1,10‐phenanthroline, 2,2′‐bipyridine and imidazole derivatives could potentially lead to agents with an increased heart uptake and faster clearance from the liver and gastrointestinal tract.     

Evaluation of 99mTc‐immunoglobulins for imaging infection in the rat

Three immunoglobulin molecules were evaluated as infection imaging agents in a rat model of S. aureas infection: ^99mTc‐infliximab, ^99mTc‐human immunoglobulin (HIG) and ^99mTc‐rat immunoglobulin (RIG). Infliximab is a chimeric monoclonal antibody specific for human tumour necrosis factor alpha (TNFα). ^99mTc‐HIG was chosen as an exogenous protein and ^99mTc‐RIG as an endogenous marker. Each immunoglobulin was treated with 2‐mercaptoethanol and the reduced antibody was isolated by size exclusion chromatography. In combination with Sn^II‐methylenediphosphonic acid, cold kit formulations were prepared. Native and reduced infliximab were tested for rat TNFα binding ability in vitro. A focal intramuscular infection of S. aureus (1 × 10⁸ colony forming units) was induced in the left thigh muscle of rats, that developed for 24 h. In separate experiments each tracer was administered by intravenous injection, then whole body scintigraphic imaging and biodistribution studies were performed at 1 and 4 h later. ^99mTc‐infliximab, ^99mTc‐HIG and ^99mTc‐RIG were prepared with ?95% radiochemical purity from stable cold kits. Results from the organ assay gave infected (target) to non‐infected (control) muscle ratios for ^99mTc‐infliximab as 5.7±0.8, 7.1±1.2, ^99mTc‐HIG gave 3.1±1.1, 7.8±1.2, and ^99mTc‐RIG 7.9±0.3, 12.5±1.5 at 1 and 4 h, respectively. Infliximab and Sn^II‐infliximab did not bind to rat TNFα by the in vitro assay. Although lacking specific affinity for TNFα, ^99mTc‐infliximab accumulated at infectious sites in vivo. ^99mTc‐infliximab gave similar infection uptake ratios to ^99mTc‐HIG at 1 and 4 h, but these proteins were inferior in comparison to ^99mTc‐RIG, and is likely to be due to increased clearance associated with the foreign protein structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of 99mTc‐labeled organo‐germanium nanoparticles and their in vivo study as a spleen imaging agent

^99mTc‐Labeled organo‐germanium nanoparticles ranging in size from 60 to 80 nm were newly developed for a spleen imaging agent. The radiolabeled nanoparticles were prepared with a high labeling efficiency (over 99%) and they also showed an excellent stability at room temperature for 6 h. The biodistribution data of the nanoparticles injected into rats via intravenous routes showed a notably higher accumulation in the spleen when compared to other reticuloendothelial system organs. Gamma image of the rabbits obtained after an intravenous injection of the nanoparticles revealed a localization of the radioactivity mainly in the spleen and the liver. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and biological evaluation of a series of 99mTc‐labeled diphosphonates as novel radiotracers with improved bone imaging

Three radiolabeled diphosphonates, ^99mTc‐labeled 1‐hydroxy‐3‐(2‐propyl‐1H‐imidazol‐1‐yl)propane‐1,1‐diyldiphosphonic acid (PIPrDP), 1‐hydroxy‐4‐(2‐propyl‐1H‐imidazol‐1‐yl)butane‐1,1‐diyldiphosphonic acid (PIBDP), and 1‐hydroxy‐5‐(2‐propyl‐1H‐imidazol‐1‐yl)pentane‐1,1‐diyldiphosphonic acid (PIPeDP), have been designed and synthesized with good chemical yields and high radiochemical purity. Their in vitro and in vivo biological properties were investigated and compared. All radiotracers evaluated in mice showed substantial retention in bone (8.42 ± 0.53, 9.08 ± 0.65, and 10.3 ± 0.61 ID%/g, respectively) at 1 h post‐injection and had rapid clearance in blood (1.9484, 1.3666, and 0.7704 ID%/g/min, respectively). ^99mTc‐PIBDP has the highest uptake ratio of bone‐to‐soft tissue at 1 h post‐injection among the three radiotracers. The results indicate that ^99mTc‐PIBDP is the most promising bone imaging agent. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and biodistribution of novel 99mTc‐nitrido methylpiperidine dithioformate derivatives as potential brain imaging agents

Three dithioformate ligands with methyl substituted on the piperidine rings, potassium 1‐(2‐methylpiperidine‐1‐yl)‐dithioformate (2‐mp), potassium 1‐(3‐methylpiperidine‐1‐yl)‐dithioformate (3‐mp) and potassium 1‐(4‐methylpiperidine‐1‐yl)‐dithioformate (4‐mp) were synthesized. The corresponding ^99mTc‐nitrido complexes were prepared in high yield (>95%) through the [^99mTcN] intermediate and characterized by thin layer chromatography and high‐performance liquid chromatography. All the neutral ^99mTc‐nitrido complexes were stable under physiological conditions and lipophilic with log P values between 1.40 and 1.58. In vivo biodistribution results showed that all the ^99mTc‐nitrido complexes displayed high brain uptakes and long retention times. Among them, ^99mTcN‐4mp, demonstrated the best properties for brain imaging with the brain uptake 3.40±0.24, 3.22±0.31, 2.72±0.28 and 2.22±0.18% ID/g at 5, 30, 60 and 120 min p.i., respectively. Moreover, the influence of stereochemistry of the ^99mTcN complexes with methyl substitution on ortho, meta and para positions on piperidine ring on the biodistribution properties were investigated with B3LYP/6‐31G*(LANL2DZ for Tc) method using the Gaussian 03 program package. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and evaluation of a 99mTc‐labeled tubulin‐binding agent for tumor imaging

Cholchicine and its derivatives are very potent tubulin‐binding compounds and can be used as a potential tumor targeting agents. In this study, colchicine was labeled with ^99mTc via hydrazinonicotinic acid (HYNIC) and was investigated further. HYNIC/cholchicine was synthesized and labeling with ^99mTc was performed at 95 °C for 15 min and radiochemical analysis included HPLC method. The stability of radiconjugate was checked in the presence of human serum at 37 °C up to 24 h. Biodistribution was studied in breast tumor‐bearing mice. Labeling yield of 95.8 ± 0.54% was obtained corresponding to a specific activity of 54 MBq/µmol. Radioconjugate showed good stability in the presence of human serum. Biodistribution studies in tumor‐bearing mice showed that ^99mTc/HYNIC/colchicine conjugate accumulated in tumor with good uptake (3.17 ± 0.14% g/g at 1 h post‐injection). The radioconjugate was cleared fast from normal organs and showed clearance through urinary and hepatobiliary systems with accumulation of activity in kidneys and intestine. This radioconjugate may be useful to assess the presence of tumor by imaging.     

Synthesis and preliminary biological evaluation of a 99mTc‐labeled hypericin derivative as a necrosis avid imaging agent

Mono‐[¹²³I]iodohypericin and mono‐[¹²³I]iodohypericin monocarboxylic acid are iodine‐123‐labeled hypericin derivatives which have shown great promise in preclinical studies as necrosis avid imaging agents in animal models of infarction. In view of the more attractive properties of a ^99mTc‐labeled hypericin derivative, we have synthesized a conjugate of protohypericin monocarboxylic acid with S‐benzoylmercaptoacetyldiglycyl‐diaminopentane in an overall yield of 15%. The conjugate was labeled with technetium‐99m by exchange labeling at pH 10 in a labeling yield of 95% followed by photocyclization to yield ^99mTc‐mercaptoacetyldiglycyl‐1,5‐diaminopentylene hypericincarboxamide (^99mTc‐13). The negatively charged ^99mTc‐13 complex was purified by reversed phase high‐pressure liquid chromatography and the log P_7.4 was determined to be 2.36. In normal NMRI mice, the complex showed slow hepatobiliary clearance while plasma clearance was rapid. The tracer was evaluated in rats with reperfused hepatic infarction by ex vivo autoradiography, gamma counting and histochemical techniques. Unlike the radioiodinated hypericin derivatives, the new tracer agent did not show preferential uptake in necrotic tissue on autoradiography and gamma counting techniques. Conjugation of hypericin with a ^99mTc‐chelate, resulting in a change in size, charge and lipophilicity, had a profound effect on the necrosis avidity of the tracer agent. The results show that ^99mTc‐13 is not suitable for imaging necrosis. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and pharmacological evaluation of 99mTc‐labeled imidazolyl‐containing diphosphonic acid as a novel bone imaging agent

In order to develop a superior bone imaging agent, a new radiotracer ^99mTc‐1‐hydroxy‐5‐(2‐butyl‐1H‐imidazol‐1‐yl)pentane‐1,1‐diyldiphosphonic acid (BIPeDP) was designed and prepared with good radiochemical yield and stability. The biodistribution in mice shows that ^99mTc‐BIPeDP has high specificity in the skeleton with the maximum uptake of 17.30 ± 0.14 injected dose per gram at 60 min. Kinetics of blood clearance shows that the distribution half‐life (T_1/2α) and elimination half‐life (T_1/2β) of ^99mTc‐BIPeDP are 3.7 and 49.7 min, respectively. An excellent image can be obtained at 1‐h post‐injection with the single photon emission computed tomography bone scanning, which is clearer and quicker than ^99mTc‐zoledronic acid, ^99mTc‐1‐hydroxy‐5‐(1H‐imidazol‐1‐yl)pentane‐1,1‐diyldiphosphonic acid, and ^99mTc‐methylenediphosphonic acid All results indicate that ^99mTc‐BIPeDP holds great potential as a novel promising bone imaging agent. Copyright © 2013 John Wiley & Sons, Ltd.     

99mTc‐tricabonyl labeling of ofloxacin and its biological evaluation in Staphylococcus aureus as an infection imaging agent

Even in recent decades, one of the major causes of death and unhealthiness in the whole world is infection and inflammation. The use of radiopharmaceuticals is a powerful tool in managing the patients with infectious diseases. In this study, ofloxacin as a second‐generation fluoroquinolone has been labeled with [^99mTc(CO)₃(H₂O)₃]⁺ core to formulate a suitable infection imaging agent. Ofloxacin was radiolabeled with ^99mTc using carbonyl core. Radioligand chemical analysis involved HPLC methods. Radioconjugate stability and lipophilicity were determined. Binding with Staphylococcus aureus and biodistribution in infected mice for labeled compound were studied. The radioligand was characterized by HPLC, and its radiochemical purity was more than 90%. In vitro stability studies have shown the complex was stable at least 6 h after labeling at room temperature. The n‐octanol/water partition coefficient experiment exhibited logP = 1.52 ± 0.21 for ^99mTc(CO)₃‐ofloxacin. The complex showed specific binding to S. aureus. Biodistribution results showed that radioligand had high accumulation in the infected muscle in a mice (T/NT = 2.02 ± 0.12 at 4 h postinjection). On the basis of stability and infection site uptake ratio, suitability of this complex as a radiotracer for imaging of infections is recognized.     

99mTc‐labeled rHuEpo for imaging of the erythropoietin receptor in tumors

To analyze erythropoietin receptor (EpoR) status in tumors, recombinant human erythropoietin (rHuEpo) was labeled with ^99mTc by ^99mTc‐centered 1‐pot synthesis, resulting in high radiochemical purity, stability, and biological activity. Both in vitro cell culture experiments and biodistribution studies of normal rats demonstrated successful EpoR targeting. The biodistribution of labeled rHuEpo in a NCI‐H1975 xenograft model showed tumor accumulation (tumor‐to‐muscle ratio, 4.27 ± 1.77), confirming the expression of active EpoR in tumors. Thus, as a novel single positron emission computerized tomography tracer for the imaging of EpoR expression in vivo, ^99mTc‐rHuEpo is effective for exploring the role of EpoR in cancer growth, metastasis and angiogenesis.     

99mTc‐labeled NGR‐chlorambucil conjugate, 99mTc‐HYNIC‐CLB‐c(NGR) for targeted chemotherapy and molecular imaging

Targeted delivery of chemotherapeutic drug at the tumor site enhances the efficacy with minimum systemic exposure. Towards this, drugs conjugated with peptides having affinity towards a particular molecular target are recognized as affective agents for targeted chemotherapy. Thus, in the present study, tumor‐homing asparagine‐glycine‐arginine (NGR) peptide ligand was conjugated to DNA alkylating nitrogen mustard, chlorambucil (CLB). The peptide‐drug conjugate (PDC), CLB‐c(NGR), was radiolabeled with ^99mTc‐HYNIC core to trace its pharmacokinetics and biodistribution pattern. In vitro cell‐binding studies of ^99mTc‐HYNIC‐CLB‐c(NGR) were conducted in murine melanoma B16F10 cells. The cytotoxicity studies conducted by incubation of the peptide/drug/PDC with B16F10 cells demonstrated enhanced cytotoxic effect of PDC in comparison to either the peptide or the drug alone. In vivo biodistribution studies in C57BL6 mice bearing melanoma tumor showed maximum tumor uptake at 30 minutes pi (2.45 ± 0.28% ID/g), which reduced to 0.77 ± 0.1% ID /g at 3 hours pi. The radiotracer being hydrophilic cleared rapidly from the heart, lungs, liver, and muscle. The tumor‐to‐blood and tumor‐to‐muscle ratios improved with time. This study opens avenues for conjugation of other targeting peptides with the drug CLB for enhanced toxicity at the diseased site.     

Synthesis, 99mTc‐labeling,and preliminary biological evaluation of DTPA‐melphalan conjugates

Melphalan (MFL) is a typical nitrogen mustard for the treatment of many types of cancer. For the purpose to develop novel ^99mTc‐labeled tumor imaging agents with SPECT, MFL was directly labeled by ^99mTc using diethylene triamine pentacetate acid (DTPA) as bifunctional chelating agent. The novel ligands were successfully synthesized by conjugation of DTPA to MFL to get monosubstituted DTPA‐MFL and bis‐substituted DTPA‐2MFL. Radiolabeling was performed in high yield to get ^99mTc‐DTPA‐MFL and ^99mTc‐DTPA‐2MFL, respectively, which were hydrophilic and stable at room temperature. The high initial tumor uptake with retention, good tumor/muscle ratios, and satisfactory scintigraphic images suggested the potential of ^99mTc‐DTPA‐MFL and ^99mTc‐DTPA‐2MFL for tumor imaging. However, the slow normal tissue clearance would be a great obstacle. Further modification on the linker and/or ^99mTc‐chelate to improve the tumor targeting efficacy and in vivo kinetic profiles is currently in progress.     

Red blood cells labelling with 99mTc‐d,l‐HMPAO: an alternative method for specific cases

The effectiveness of the classic methods for red blood cells (RBCs) labelling with ^99mTc has been demonstrated in nuclear medicine. However, nuclear physicians have found, in certain circumstances, this diagnostic technique fails and poor quality images are obtained. In this work we report on an alternative method that is of useful in these occasions, for in vitro labelling RBCs with ^99mTc‐d,l‐HMPAO complex. The study shows a high and reproducible labelling efficiency (94.14±0.38), using low amount of tin. The RBCs were isolated from plasma and other interfering blood cells before adding ^99mTc‐d,l‐HMPAO. The tracer was retained and the elution rate from RBCs was low (less than 6% after 120 min). The preclinical results indicate that this new method could be a good alternative to the standard classic methods for specific cases. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and preclinical pharmacological evaluation of 99mTc‐TEDP as a novel bone imaging agent

The detection of bone metastasis in early stages requires the development of high‐affinity bone imaging radiopharmaceuticals for the improvement of the diagnostic accuracy of routine bone scanning and effective management of these medical cases. This study aimed to provide a convenient synthesis of 1‐thioethylidene‐l,l‐disodiumphosphonate (TEDP) and an improved preparation of its ^99mTc‐TEDP complex. The results showed that the radiochemical purity of ^99mTc‐TEDP was found to be 95 ± 2% and that its stability was up to 6 h. Biodistribution study showed high and long uptake of ^99mTc‐TEDP in bone starting from 15 min (39 ± 4 ID/g) to 3 h (53 ± 2.4 ID/g) showing high affinity of ^99mTc‐TEDP complex to bones. This research could introduce a novel radiopharmaceutical that could be used in scanning body bones starting from 15 min between injection of ^99mTc‐TEDP and bone imaging, minimizing the burden on patients in terms of the total length of the examination and the dose of radiation absorbed and showing high specificity and efficacy in bone scintigraphy.     

Evaluation of a 99mTc‐labelled meso‐bisphenylporphyrin as a tumour image agent

Porphyrins are excellent agents for photodynamic treatment of various types of cancer and also good metal chelators that form highly stable metallo‐complexes with different radionuclides. Therefore, radiolabelled porphyrins could also be potentially used as tumour imaging agents. In this context, the aim of this work was the radiolabelling of meso‐bis[3,4‐bis(carboxymethyleneoxy)phenyl]porphyrin, 2CPP, with Technetium‐99 m (^99mTc) and the evaluation of its radiochemical and biological properties in vitro and in vivo. The labelling procedure was optimized resulting in an efficiency of 92.52 ± 0.48%. The complex ^99mTC‐2CPP remained stable for more than 4 h. The biodistribution showed that ^99mTc‐2CPP is eliminated by gastrointestinal and urinary pathways. The tumour/muscle ratio increases over time, being 3.33 ± 1.22 and 3.55 ± 1.29 in WiDr‐bearing tumours mice and in H1299‐bearing tumours mice, respectively, 6 h post‐injection, showing the tumour specificity of the ^99mTc‐2CPP complex. The favourable tumour/muscle ratio of ^99mTc‐2CPP shows that this complex could potentially be used as tumour imaging agent. Moreover, it could be used to follow the progression or regression of tumours before, during and after the radiotherapy, chemotherapy and photodynamic therapy. Copyright © 2014 John Wiley & Sons, Ltd.     

Quality control methods for 99mTc‐labeled exogenous natural surfactant (99mTc‐ENS)

To standardize the quality control for ^99mTc‐ENS, the following methods were studied: (1) physical properties and pH, (2) radiochemical purity (chromatographic studies on Whatman‐1 paper, or instant thin‐layer chromatography and solvent extraction using different solvents and (3) rat biodistribution studies by intratracheal injection. The tolerance limits were fixed for each method. The radiopharmaceutical stability was also evaluated. The results showed that ^99mTc‐ENS was a white suspension with a pH between 4.0 and 6.0. The limit for radiochemical impurities in Whatman‐1 paper/acetone was fixed at lower than 2% and the established limit for the organic aliquot in cyclohexane extraction was greater than 2%. In the biodistribution studies, the limits for activity concentration were fixed at greater than 90% for lungs, less than 9% for the gastrointestinal system and less than 1% for the sum of the other organs studied. After a storage time of 6 h at room temperature or in a refrigerator, ^99mTc‐ENS physical properties and pH, radiochemical and biodistribution results were within the established values. In conclusion, the quality control methods for ^99mTc‐ENS are tests on physical properties and pH, radiochemical purity by Whatman‐1 paper/acetone chromatography and cyclohexane extraction and biodistribution studies in rats. The stability of this radiopharmaceutical is at least 6 h at room temperature. Copyright © 2003 John Wiley & Sons, Ltd.     

Labelling of ceftriaxone with 99mTc and its bio‐evaluation as an infection imaging agent

Differentiation of bacterial and sterile inflammation will have a significant impact on the current clinical practice. Ceftriaxone (CTRX) was labelled with ^99mTc and assessed for its ability to depict infection on scintigraphy. Stoichiometry was performed to optimize labelling parameters. Stability and bacterial binding was verified and biodistribution pattern was seen in normal, infected/inflamed animal models. ^99mTc‐CTRX prepared at pH 7 with stannous chloride of 50 µg, ligand of 30 mg, and boiling for 10 min gave labelling yield of 96.2 ± 0.2% with good stability. In vitro binding was higher for Escherichia coli than Staphylococcus aureus. Biodistribution in normal rats showed high uptake in hepatobiliary system, gut and urinary system. In animal models induced with infection or inflammation, lesion to normal ratios at 4 h were 2.36 ± 0.21, 12.66 ± 1.44 and 1.40 ± 0.01 with S. aureus infection, E. coli infection and turpentine oil inflammation, respectively. Infection specificity especially for E. coli was also confirmed on scintigraphic findings. Ceftriaxone can be labelled with ^99mTc with high labelling yield at pH compatible with that of blood. Our preparation has shown stability in vitro and in human serum, and binds preferentially with bacteria. ^99mTc‐CTRX scintigraphy can be used to delineate sites of active infection and to differentiate infection and inflammation.     

99mTc‐anti‐epidermal growth factor receptor nanobody for tumor imaging

Nanobodies are important biomolecules for tumor targeting. In this study, we synthesized and labeled anti‐epidermal growth factor receptor (EGFR) nanobody OA‐cb6 with ^99mTc(CO)₃⁺ and evaluated its characteristics for targeting the EGFR in the A431 human epidermal carcinoma cell line. Nanobody radiolabeling was achieved with high yield and radiochemical purity, and the radioconjugate was stable. Biodistribution results in nude mice exhibited a favorable tumor‐to‐muscle ratio at 4‐hr postinjection, and tumor location was visualized at 4 hr after injection of radiolabeled nanobody. Our result showed that the OA‐cb6‐^99mTc‐tricarbonyl radiolabeled nanobody is a promising radiolabeled biomolecule for tumor imaging in cancers with high EGFR overexpression.     

Synthesis and preliminary biological evaluation of a 99mTc‐chlorambucil derivative as a potential tumor imaging agent

Technetium‐99m‐based radiopharmaceuticals have been used widely as diagnostic agents in the nuclear medicine. Chlorambucil (CLB) as one typical alkylating drug exhibits excellent inhibition effects against many human malignancies. To develop and explore a novel potential imaging agent for early diagnosis of tumors, tricarbonyl technetium‐99m and rhenium complexes on the basis of the tridentate ligand dipicolylamine (DPA) bound to the chlorambucil pharmacophore were designed and synthesized: ^99mTc‐DPA‐CLB ( 3 ) and Re‐DPA‐CLB ( 4 ). The high performance liquid chromatography analyses showed that the retention time of 3 and 4 was 13.5 and 13.6 minutes, respectively. Radiolabeling efficiency of the ^99mTc‐DPA‐CLB tracer was 97%, and the radiochemical purity was larger than 95% after 6 hours stored in phosphate buffered saline or human serum as observed by thin layer chromatography and high performance liquid chromatography. Biodistribution studies in a mouse model of breast cancer showed ^99mTc‐DPA‐CLB exhibited a favorable tumor affinity. The radiotracer cleared quickly in the first hour via hepatobiliary and renal routes of excretion, resulted in a very low background at 4 hours post injection (p.i.). It had moderate uptake ratios of tumor to blood and tumor to muscle. These results suggested ^99mTc‐DPA‐CLB might be a promising SPECT imaging agent for tumor diagnosis.