Synthesis and biodistribution of a novel 99mTc complex of HYNIC-conjugated metronidazole as a potential tumor hypoxia imaging agent

Radioiodination and in vivo assessment of the potential of newly synthesized pyrrolizine-5-carboxamides derivative in tumor model

Recently, pyrrolizine derivatives have been reported to possess numerous anticancer activities. In a previous study, (EZ)-6-((4-chlorobenzylidene)-amino)-7-cyano-N-(p-tolyl)-2,3-dihydro-1H-pyrrolizine carboxamide (EZPCA) compound was synthesized and the cytotoxic activity of EZPCA toward COX-2 enzyme (overexpressed in cancer cells) was reported. In order to assess the suitability of this compound as a promising pilot structure for in vivo applications, EZPCA was radiolabeled with radioiodine-131 (¹³¹I) and various factors affecting radiolabeling process were studied. Quality control studies of [¹³¹I]iodo-EZPCA were performed using paper chromatography and HPLC was used as a co-chromatographic technique for confirming the radiochemical yield. Biodistribution studies of [¹³¹I]iodo-EZPCA were undertaken in normal and tumor bearing mice. The radiochemical yield percentage of [¹³¹I]iodo-EZPCA was 94.20 ± 0.12%. The biodistribution results showed evident tumor uptake of [¹³¹I]iodo-EZPCA with promising target/non-target (T/NT) ratios. As a conclusion, these data suggest that [¹³¹I]iodo-EZPCA had high binding efficiency, high tumor uptake and sufficient stability to be used be used in diagnostic studies.

Synthesis and bioevaluation of radioiodinated nitroimidazole hypoxia imaging agents by one-pot click reaction

Eight radioiodinated 2-nitroimidazole derivatives for use as hypoxia imaging agents were synthesized by one-pot click reaction using four azides, two alkynes, and [¹³¹I]iodide ions and evaluated by hypoxic cellular uptake and biodistribution experiments. The results suggested that radiotracers with suitable partition coefficients (log P: -0.2-1.2) were more likely to have higher hypoxic cellular uptake. Among these eight molecules, [¹³¹I]15 ([¹³¹I]-(5-iodo-1-(2-(2-(2-nitro-1H-imidazol-1-yl)ethoxy)ethyl)-4-((2-nitro-1H-imidazol-1-yl)methyl)-1H-1,2,3-triazole)) had a suitable log P (0.05 ± 0.03) and contained two 2-nitroimidazole groups. The hypoxic/aerobic cellular uptake ratio of [¹³¹I]15 was 4.4 ± 0.5, and the tumor/blood (T/B) and tumor/muscle (T/M) ratios were 2.03 ± 0.45 and 6.82 ± 1.70, respectively. These results suggested that [¹³¹I]15 was a potential hypoxia imaging agent.

Radioiodination and biological distribution of a new s-triazine derivative for tumor uptake evaluation

A newly synthesized s-triazine derivative 1,1',1″-(((1,3,5-triazine-2,4,6-triyl) tris (azanediyl)) tris (benzene-4,1-diyl))tris (ethan-1-one), (1), was synthesized as a part of an ongoing research for development of novel s-triazine-based radiopharmaceuticals. In-vitro cell viability assay against different human cancer cell lines showed very promising inhibitory activity of the synthesized compound. This finding encouraged the radioiodination of 1 to study the degree of its localization in tumor site for evaluating the possibility of its use as a tumor imaging agent. The biodistribution study showed good localization of the radioiodinated derivative 2 at tumor site following i.v. administration in solid tumor-bearing mice. Finally, in a trial to understand the mechanism of the anticancer effect exerted by 1, a target prediction study and a docking study were performed. The results of the first study showed that focal adhesion kinase is a possible target for compound 1 and the docking study confirmed successful binding of both compound 1 and its radioiodinated derivative 2 to the binding site of focal adhesion kinase. As a conclusion, the results of this study suggest that, compound 2 could be used as a potential agent for tumor imaging after preclinical trials.

In vivo click reaction between Tc-99m-labeled azadibenzocyclooctyne-MAMA and 2-nitroimidazole-azide for tumor hypoxia targeting

The bioactivity of nitroimidazole in Tc-99m-labeled 2-nitroimidazole, a traditional solid tumor hypoxia-imaging agent for single photon emission computed tomography (SPECT), is reduced by the presence of large ligand and metallic radionuclide, exhibiting lower tumor-to-nontumor ratios. In an effort to solve this general problem, a pretargeting strategy based on click chemistry (strain-promoted cyclooctyne-azide cycloaddition) was applied. The functional click synthons were synthesized as pretargeting components: an azide group linked to 2-nitroimidazole (2NIM-Az) serves for tumor hypoxia-targeting and azadibenzocyclooctyne conjugated with monoamine monoamide dithiol ligand (AM) functions as radiolabeling and binding group to azides in vivo. 2NIM-triazole-MAMA was obtained from in vitro click reaction with a reaction rate constant of 0.98M(-1)s(-1). AM and 2NIM-triazole-MAMA were radiolabeled with Tc-99m. The hypoxia-pretargeting biodistribution was studied in Kunming mice bearing S180 tumor; (99m)Tc-AM and (99m)Tc-triazole-2NIM were used as blank control and conventional control. Compared to the control groups, the pretargeting experiment exhibits the best radio-uptake and retention in tumor, with higher tumor-to-muscle and tumor-to-blood ratios (up to 8.55 and 1.44 at 8h post-(99m)Tc-complex-injection, respectively). To some extent, the pretargeting strategy protects the bioactivity of nitroimidazole and therefore provides an innovative approach for the development of tumor hypoxia-SPECT imaging agents.

tert-ButylN-{[5-(5-oxohexanamido)pyridin-2-yl]amino}carbamate

In the crystal structure of the title compound, C₁₆H₂₄N₄O₄, mol­ecules are linked by N—H⋯O hydrogen bonds between the carbonyl groups of the carbamoyl and amido functional groups and the amino groups, and by N—H⋯N hydrogen bonds between the amino group and the pyridine ring, forming two-dimensional networks parallel to the ab plane.

⁹⁹mTc/Re complexes bearing bisnitroimidazole or mononitroimidazole as potential bioreductive markers for tumor: synthesis, physicochemical characterization and biological evaluation

Four monoamine-monoamide dithiol (MAMA) ligands containing two or one nitroimidazole moieties were synthesized and labeled with (99m)Tc (labeling yield > 95%). The proposed structures of (99m)Tc-complexes are identified by comparison with analogous Re-MAMA complexes. (99m)Tc-MAMA complexes show better physicochemical characters than (99m)TcO-(PnAO-1-(2-nitroimidazole)). Reduction potentials of nitro groups of the rhenium complexes are within the range for bioreductive compounds. As expected, biodistribution studies demonstrate that the 2-nitroimidazole complex shows better tumor-to-tissue ratios than 4-nitroimidazole analog for mononitroimidazole complexes, but not for MAMA-bisnitroimidazoles due to higher lipophilicity. Both the bisnitroimidazole compounds show rapider excretion, lower background activity in liver and higher tumor-to-tissue ratios than the mononitroimidazoles. Better biodistribution characteristic makes both the MAMA-bisnitroimidazole complexes, especially (99m)Tc-15, be potential tumor hypoxia marker.