A novel [99mTcN]2+ complex of metronidazole xanthate as a potential agent for targeting hypoxia

Approaches for the discovery of cinnamic acid derivatives with anticancer potential

INTRODUCTION

Cinnamic acid is a privileged scaffold for the design of biologically active compounds with putative anticancer potential, following different synthetic methodologies and procedures. Since there is a need for the production of potent anticancer, cinnamate moiety can significantly contribute in the design of new and more active anticancer agents.

AREAS COVERED

In this review, the authors provide a review on the synthetic approaches for the discovery of cinnamic acid derivatives with anticancer potential. Results from molecular simulations, hybridization, and chemical derivatization along with biological experiments in vitro and structural activity relationships are given, described, and discussed by the authors. Information for the mechanism of action is taken from original literature sources.

EXPERT OPINION

The authors suggest that (i) numerous areas of biology-pharmacology need to be considered: selectivity, in vivo studies, toxicity and drug-likeness, the mechanism of action in animals and humans, development of more efficient assays for various cancer types; (ii) hybridization techniques outbalance in the discovery and production of compounds with higher activity and greater selectivity; (iii) repositioning offers new anticancer cinnamic agents.

Recent Developments in PET and SPECT Radiotracers as Radiopharmaceuticals for Hypoxia Tumors

Hypoxia, a deficiency in the levels of oxygen, is a common feature of most solid tumors and induces many characteristics of cancer. Hypoxia is associated with metastases and strong resistance to radio- and chemotherapy, and can decrease the accuracy of cancer prognosis. Non-invasive imaging methods such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) using hypoxia-targeting radiopharmaceuticals have been used for the detection and therapy of tumor hypoxia. Nitroimidazoles are bioreducible moieties that can be selectively reduced under hypoxic conditions covalently bind to intracellular macromolecules, and are trapped within hypoxic cells and tissues. Recently, there has been a strong motivation to develop PET and SPECT radiotracers as radiopharmaceuticals containing nitroimidazole moieties for the visualization and treatment of hypoxic tumors. In this review, we summarize the development of some novel PET and SPECT radiotracers as radiopharmaceuticals containing nitroimidazoles, as well as their physicochemical properties, in vitro cellular uptake values, in vivo biodistribution, and PET/SPECT imaging results.

Functionalized Ultrasmall Iron Oxide Nanoparticles for T1-Weighted Magnetic Resonance Imaging of Tumor Hypoxia

Hypoxia is a common biological condition in many malignant solid tumors that plays an imperative role in regulating tumor growth and impacting the treatment’s therapeutic effect. Therefore, the hypoxia assessment is of great significance in predicting tumor development and evaluating its prognosis. Among the plenty of existing tumor diagnosis techniques, magnetic resonance imaging (MRI) offers certain distinctive features, such as being free of ionizing radiation and providing images with a high spatial resolution. In this study, we develop a fluorescent traceable and hypoxia-sensitive T₁-weighted MRI probe (Fe₃O₄-Met-Cy5.5) via conjugating notable hypoxia-sensitive metronidazole moiety and Cy5.5 dye with ultrasmall iron oxide (Fe₃O₄) nanoparticles. The results of in vitro and in vivo experiments show that Fe₃O₄-Met-Cy5.5 has excellent performance in relaxivity, biocompatibility, and hypoxia specificity. More importantly, the obvious signal enhancement in hypoxic areas indicates that the probe has great feasibility for sensing tumor hypoxia via T₁-weighted MRI. These promising results may unlock the potential of Fe₃O₄ nanoparticles as T₁-weighted contrast agents for the development of clinical hypoxia probes.

Radiolabeling and evaluation of a novel [99mTcN]2+ complex with deferoxamine dithiocarbamate as a potential agent for bacterial infection imaging

In order to find a ^99mTc-labeled deferoxamine radiotracer for bacterial infection imaging, deferoxamine dithiocarbamate (DFODTC) was successfully synthesized and it was radiolabeled with [^99mTcN]²⁺ core to prepare the ^99mTcN(DFODTC)₂ complex. ^99mTcN(DFODTC)₂ was obtained with high radiochemical purity without further purification. The complex was lipophilic and exhibited good in vitro stability. According to the result of bacterial binding study, the binding of ^99mTcN(DFODTC)₂ to bacteria was specific. Biodistribution in mice study indicated that ^99mTcN(DFODTC)₂ had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses at 120 min after injection, which showed that the radiotracer could differentiate between bacterial infection and sterile inflammation. SPECT/CT images showed that there was a clear accumulation in infection sites, suggesting that ^99mTcN(DFODTC)₂ could be a potential bacterial infection imaging radiotracer.

Synthesis and evaluation of [99mTcN]2+ core and [99mTcO]3+ core labeled complexes with 4-nitroimidazole xanthate derivative for tumor hypoxia imaging

A 4-nitroimidazole xanthate ligand (NMXT) was synthesized and radiolabeled with [^99mTcN]²⁺ core and [^99mTcO]³⁺ core to obtain ^99mTcN-NMXT and ^99mTcO-NMXT, respectively. The two ^99mTc-complexes were prepared with high radiochemical purity and had good stability. The partition coefficient results indicated both of them were hydrophilic, and cellular uptake studies showed they exhibited good hypoxic selectivity. From the biodistribution study results, ^99mTcO-NMXT showed more favourable tumor uptake (1.73 ± 0.14 ID%/g) and higher tumor/muscle ratio (7.01 ± 0.16) than ^99mTcN-NMXT at 4 h post-injection. Single photon emission computed tomography (SPECT) imaging study of ^99mTcO-NMXT showed there was a visible accumulation in tumor site, suggesting it would be a promising candidate as a tumor hypoxia imaging agent.

Clinical imaging of hypoxia: Current status and future directions

Tissue hypoxia is a key feature of many important causes of morbidity and mortality. In pathologies such as stroke, peripheral vascular disease and ischaemic heart disease, hypoxia is largely a consequence of low blood flow induced ischaemia, hence perfusion imaging is often used as a surrogate for hypoxia to guide clinical diagnosis and treatment. Importantly, ischaemia and hypoxia are not synonymous conditions as it is not universally true that well perfused tissues are normoxic or that poorly perfused tissues are hypoxic. In pathologies such as cancer, for instance, perfusion imaging and oxygen concentration are less well correlated, and oxygen concentration is independently correlated to radiotherapy response and overall treatment outcomes. In addition, the progression of many diseases is intricately related to maladaptive responses to the hypoxia itself. Thus there is potentially great clinical and scientific utility in direct measurements of tissue oxygenation. Despite this, imaging assessment of hypoxia in patients is rarely performed in clinical settings. This review summarises some of the current methods used to clinically evaluate hypoxia, the barriers to the routine use of these methods and the newer agents and techniques being explored for the assessment of hypoxia in pathological processes.

Post-functionalization of platinum–NHC complexes by oxime ligation for ligand targeted therapy

Carbonyl condensation reactions have been used for accessing N-heterocyclic carbene (NHC) platinum bioconjugate complexes.

[Preparation of (99m)Tc-EDTA-MN and Its Bioimaging in Mouse]

BACKGROUND AND OBJECTIVE

Hypoxia is an important biological characteristics of solid tumor, it is not sensitive to radiotherapy and chemotherapy for which is the presence of hypoxic cell, thus increasing their resistance to conventional radiotherapy and chemotherapy, therefore, the detection of hypoxia degree of tumor tissue is of great significance. The hypoxia imaging of nuclear medicine can reflect the degree of tissue hypoxia, which can selectively retained on the hypoxic cells or tissues, including nitroimidazole and non nitroimidazole; the nitroimidazole is widely and deeply researched as hypoxic celles developer in China and abroad at present. The research about application of radionuclide labelled technique has clinical application value to develop the hypoxia imaging agent EDTA-MN complexes which was labeled. To study the feasibility of (99m)Tc by direct labeling method, the radiochemical properties evaluation of (99m)Tc-EDTA-MN, and observe the distribution characteristics of (99m)Tc radiolabeled EDTA-MN in the xenograft lung cancer nude mice bearing non-small cell lung cancer cell (A549), and provide experimental evidence for its further research and application.

METHODS

The radiolabeling of EDTA-MN with (99m)Tc was performed with direct labeling method, respectively, on the reaction dosage (10 mg, 5 mg, 2 mg), stannous chloride dosage (8 mg/mL, 4 mg/mL, 2 mg/mL), mark system pH (2, 4, 5, 6) one by one test, using orthogonal design analysis, to find the optimal labeling conditions. Labelling rate, radiochemical purity, lipid-water partition coefficient and in vitro stability in normal saline (NS) were determined by TLC and HPLC, and the preliminary study on the distribution of (99m)Tc-EDTA-MN in nude mice.

RESULTS

The labeling rate of 99mTc-EDTA-MN with the best labeling conditions was (84.11±2.83)%, and the radiochemical purity was higher than 90% by HPLC purification, without any notable decomposition at room temperature over a period of 12 h. The partition coefficient was lgP=-3.05, indicated that this complex was hydrophilic. At 3 h post-injection, the imaging of (99m)Tc-EDTA-MN in nude mice bearing non-small cell lung cancer cell showed that more radioactive gathered in bladder at 0.5 h, the transplanted tumor was clearly imaged at 1 h post-injection, during whole imaging radioactive in other tissues and organs was low. The radioactivity of tumor uptake by using of ROI technology were (88.14±11.59), (123.17±9.06), (98.08±14.40) and (79.87±10.57) at 0.5, 1, 2, 3 h post-injection, and the ratio of T/NT of tumor and liver area were (1.95±0.19), (3.58±0.78), (3.95±0.39) and (5.01±0.28), respectively. (99m)Tc-EDTA-MN could be quickly cleared from the blood in mice primarily through the kidneys, and the radioactivity in other tissues and organs remained low.

CONCLUSIONS

(99m)Tc-EDTA-MN can be easily prepared and labeled compound with high labeling rate and stability, it appears to be suitable for further experiments requirement in vivo and in vitro application.

Synthesis and biodistribution of novel 99mTc labeled 4-nitroimidazole dithiocarbamate complexes as potential agents to target tumor hypoxia

^99mTcO-N4IPDTC was prepared from a kit without the need for purification and would be a promising hypoxia imaging agent.

Novel metronidazole-sulfonamide derivatives as potent and selective carbonic anhydrase inhibitors: design, synthesis and biology analysis

Metronidazole–sulfonamide derivatives, a new class of human carbonic anhydrase inhibitors (hCA), were designed, synthesized, isolated, and evaluated for their ability to inhibit the enzymatic activity of the isozymes hCA II and hCA IX.

Synthesis, radiolabeling and biological evaluation of propylene amine oxime complexes containing nitrotriazoles as hypoxia markers

Two propylene amine oxime (PnAO) complexes, 1, containing a 3-nitro-1,2,4-triazole and 2, containing two 3-nitro-1,2,4-triazoles, were synthesized and radiolabeled with (99m)Tc in high labeling yields. Cellular uptakes of (99m)Tc-1 and (99m)Tc-2 were tested using a S180 cells line. Under anoxic conditions, the cellular uptakes of (99m)Tc-1 and (99m)Tc-2 were 33.7 ± 0.2% and 35.0 ± 0.7% at 4 h, whereas the normoxic uptakes of the two complexes were 6.0 ± 1.6% and 4.6 ± 0.9%, respectively. Both (99m)Tc-1 and (99m)Tc-2 displayed significant anoxic/normoxic differentials. The cellular uptakes were highly dependent on oxygen and temperature. Biodistribution studies revealed that both (99m)Tc-1 and (99m)Tc-2 showed a selective localization in tumor and slow clearance from it. At 4 h, the tumor-to-muscle ratios (T/M) were 3.79 for (99m)Tc-1 and 4.58 for (99m)Tc-2. These results suggested that (99m)Tc-labeled PnAO complexes (99m)Tc-1 and (99m)Tc-2 might serve as novel hypoxia markers. By introducing a second nitrotriazole redox center, the hypoxic accumulation of the marker was slightly enhanced.

Synthesis and evaluation of a novel (99m)Tc-labeled bioreductive probe for tumor hypoxia imaging

Tumor hypoxia is closely associated with the malignant progression and/or the high metastatic ability of tumors and often induces resistance to chemo- and/or radiotherapy. Thus, the detection and evaluation of hypoxia is important for the optimization of cancer therapy. We designed a novel (99m)Tc-labeled probe for tumor hypoxia imaging that utilizes bioreductive reactions in hypoxic cells. This probe, which contains a 4-nitrobenzyl ester group, is reduced in hypoxic cells to produce a corresponding carboxylate anion that cannot penetrate cell membranes because of its hydrophilicity and negative charge; therefore, it is expected to be trapped inside hypoxic cells. Based on this unique strategy, we synthesized the Technetium-99m ((99m)Tc)-labeled probe (99m)Tc-SD32. The uptake of (99m)Tc-SD32 in tumor cells was investigated under normoxic and hypoxic conditions. (99m)Tc-SD32 showed sufficient accumulation and good retention in hypoxic cells. In addition, we demonstrated that (99m)Tc-SD32 was subjected to bioreduction in hypoxic cells and was trapped as the corresponding carboxylate anion. These results indicated that (99m)Tc-SD32 would be a promising agent for in vivo hypoxia imaging.

Metronidazole acid acyl sulfonamide: a novel class of anticancer agents and potential EGFR tyrosine kinase inhibitors

A series of novel metronidazole derivatives were recently reported as potent anticancer agents targeting EGFR and HER-2 by our group [Qian, Y.; Zhang, H. J.; Zhang, H.; Xu, C.; Zhao, J.; Zhu, H. L. Bioorg. Med. Chem.2010, 18, 4991]. Based on the previous results, we designed and synthesized a new series of metronidazole acid acyl sulfonamide derivatives and a new series of phenylacetyl benzenesulfonamide derivatives and their anticancer activities were evaluated as potential EGFR and HER-2 kinase inhibitors. Among all the compounds, compound 12 displayed the most potent inhibitory activity EGFR and HER-2 (IC(50)=0.39 μM for EGFR and IC(50)=1.53 μM for HER-2) and it also showed the most potent growth inhibitory activity against A549 and B16-F10 cancer cell line in vitro, with an IC(50) value of 1.26 μg/mL for A549 and 0.35 μg/mL for B16-F10. Docking simulation was further performed to position compound 12 into the EGFR active site to determine the probable binding model.

Synthesis, molecular modeling, and biological evaluation of cinnamic acid metronidazole ester derivatives as novel anticancer agents

A series of novel cinnamic acid metronidazole ester derivatives have been designed and synthesized, and their biological activities were also evaluated as potential EGFR and HER-2 kinase inhibitors. Compound 3h showed the most potent biological activity (IC50=0.62 microM for EGFR and IC50=2.15 microM for HER-2). Docking simulation was performed to position compound 3h into the EGFR active site to determine the probable binding model. Antiproliferative assay results demonstrated that some of these compounds possessed good antiproliferative activity against MCF-7. Compound 3h with potent inhibitory activity in tumor growth inhibition may be a potential anticancer agent.

Synthesis of a novel 99mTc nitrido radiopharmaceutical with isopropyl xanthate, showing brain uptake

In the present study, isopropyl xanthate (IPXT) ligand was labeled with the [(99m)Tc triple bond N](2+) core successfully to obtain the (99m)TcN(IPXT)(2) complex with high radiochemical purity. No decomposition of the complex at room temperature was observed over a period of 6h. Its partition coefficient indicated that it was a good lipophilic complex. The electrophoresis results showed that the complex was neutral. Biodistribution in mice demonstrated that the complex accumulated in the brain with high uptake and good retention. The brain uptake (ID%/g) was 1.95, 1.58 and 1.86 at 5-, 30- and 60-min post-injection, respectively. As compared with other reported (99m)TcN-xanthates, the (99m)TcN(IPXT)(2) complex showed higher brain uptake and better brain retention, suggesting potential usefulness of the complex as a brain perfusion imaging agent.

Metronidazole-flavonoid derivatives as anti-Helicobacter pylori agents with potent inhibitory activity against HPE-induced interleukin-8 production by AGS cells

Three series of metronidazole-flavonoid derivatives were generated and evaluated for antimicrobial activity against H. pylori. Among these compounds, high anti-H. pylori activities were observed in isoflavones derivatives 4-7, 19, and 20 but exhibited no inhibitory activity against other sorts of bacteria and fungi, for example, Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli, Pseudomonas fluorescence, and Aspergillus niger. Genistein derivative 6 with the potent activity (MIC=0.39 microg mL(-1)) was >50-fold more than metronidazole, and comparable to the positive control amoxicillin. Additionally, compound 6 can significantly attenuate the increase in interleukin-8 (IL-8) levels in the AGS cells stimulated by H. pylori water extract (HPE) at concentrations of 15, 30, and 60 micromol L(-1), which did not show any effects on the cell viability.

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.

Design and evaluation of “3 + 1” mixed ligand oxorhenium and oxotechnetium complexes bearing a nitroaromatic group with potential application in nuclear medicine oncology

The synthesis and evaluation of a series of oxotechnetium and oxorhenium complexes containing a nitroaromatic moiety as potential radiopharmaceuticals for targeting tumour hypoxia is presented. 99mTc labelling was performed in high yield (>85%) and radiochemical purity (>90%). Their structure was corroborated by means of the rhenium complexes. Reduction potentials were in the range for bioreducible compounds. 99mTc complexes III-VI were selected for "in vivo" experiments in view of the results of cytotoxicity studies. Biodistribution in normal animals was characterized by high initial blood, lung and liver uptake, fast blood and soft tissue depuration and preferential excretion via the hepatobiliary system. Initial tumour uptake was moderate but tumour/muscle ratios for complexes III and IV, were favourable at all time points. Although the results are encouraging further development is still necessary in order to achieve higher tumour uptake and lower gastrointestinal activity.