A 99mTc-Labeled Misonidazole Analogue: Step Toward a 99mTc-Alternative to [18F]Fluromisonidazole for Detecting Tumor Hypoxia

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.

Hypoxia-activated nanomedicines for effective cancer therapy

Hypoxia, a common characteristic in solid tumors, is found in phenotypically aggressive cancers that display resistance to typical cancer interventions. Due to its important role in tumor progression, tumor hypoxia has been considered as a primary target for cancer diagnosis and treatment. An advantage of hypoxia-activated nanomedicines is that they are inactive in normoxic cells. In hypoxic tumor tissues and cells, these nanomedicines undergo reduction by activated enzymes (usually through 1 or 2 electron oxidoreductases) to produce cytotoxic substances. In this review, we will focus on approaches to design nanomedicines that take advantage of tumor hypoxia. These approaches include: i) inhibitors of hypoxia-associated signaling pathways; ii) prodrugs activated by hypoxia; iii) nanocarriers responsive to hypoxia, and iv) bacteria mediated hypoxia targeting therapy. These strategies have guided and will continue to guide nanoparticle design in the near future. These strategies have the potential to overcome tumor heterogeneity to improve the efficiency of radiotherapy, chemotherapy and diagnosis.

Hypoxia-active nanoparticles used in tumor theranostic

Hypoxia is a hallmark of malignant tumors and often correlates with increasing tumor aggressiveness and poor treatment outcomes. Therefore, early diagnosis and effective killing of hypoxic tumor cells are crucial for successful tumor control. There has been a surge of interdisciplinary research aimed at developing functional molecules and nanomaterials that can be used to noninvasively image and efficiently treat hypoxic tumors. These mainly include hypoxia-active nanoparticles, anti-hypoxia agents, and agents that target biomarkers of tumor hypoxia. Hypoxia-active nanoparticles have been intensively investigated and have demonstrated advanced effects on targeting tumor hypoxia. In this review, we present an overview of the reports published to date on hypoxia-activated prodrugs and their nanoparticle forms used in tumor-targeted therapy. Hypoxia-responsive nanoparticles are inactive during blood circulation and normal physiological conditions but are activated by hypoxia once they extravasate into the hypoxic tumor microenvironment. Their use can enhance the efficiency of tumor chemotherapy, radiotherapy, fluorescence and photoacoustic intensity, and other imaging and therapeutic strategies. By targeting the broad habitats of tumors, rather than tumor-specific receptors, this strategy has the potential to overcome the problem of tumor heterogeneity and could be used to design diagnostic and therapeutic nanoparticles for a broad range of solid tumors.

Novel 99mTc labelled complexes with 2-nitroimidazole isocyanide: design, synthesis and evaluation as potential tumor hypoxia imaging agents

Radiolabelled 2-nitroimidazoles have been used for imaging hypoxia. With the aim of developing novel 99mTc radiotracers for imaging hypoxia, four novel 2-nitroimidazole isocyanide derivatives (2a, 2b, 2c, and 2d) were synthesized and radiolabelling was carried out for preparing their corresponding 99mTc complexes. These 99mTc complexes were stable in vitro and could exhibit good hypoxic selectivity. The partition coefficient results indicated that they were hydrophilic, and an evaluation of biodistribution in mice bearing S180 tumors indicated that all of the complexes could accumulate in the tumors. Among them, 99mTc-2c exhibited the highest tumor uptake and tumor/blood and tumor/muscle ratios at 2 h post-injection. Further, single photon emission computed tomography (SPECT) imaging studies indicated clear accumulation in tumors, suggesting that 99mTc-2c was a promising candidate for hypoxia imaging.

Toward hypoxia-selective rhenium and technetium tricarbonyl complexes

With the aim of preparing hypoxia-selective imaging and therapeutic agents, technetium(I) and rhenium(I) tricarbonyl complexes with pyridylhydrazone, dipyridylamine, and pyridylaminocarboxylate ligands containing nitrobenzyl or nitroimidazole functional groups have been prepared. The rhenium tricarbonyl complexes were synthesized with short reaction times using microwave irradiation. Rhenium tricarbonyl complexes with deprotonated p-nitrophenyl pyridylhydrazone ligands are luminescent, and this has been used to track their uptake in HeLa cells using confocal fluorescent microscopy. Selected rhenium tricarbonyl complexes displayed higher uptake in hypoxic cells when compared to normoxic cells. A (99m)Tc tricarbonyl complex with a dipyridylamine ligand bearing a nitroimidazole functional group is stable in human serum and was shown to localize in a human renal cell carcinoma (RCC; SK-RC-52) tumor in a mouse.