Azomycin

Synthesis and Biological Evaluation of Iodoglucoazomycin (I-GAZ), an Azomycin-Glucose Adduct with Putative Applications in Diagnostic Imaging and Radiotherapy of Hypoxic Tumors.[Pubmed:27377671]

ChemMedChem. 2016 Aug 5;11(15):1638-45.

IodoglucoAzomycin (I-GAZ; N-(2-iodo-3-(6-O-glucosyl)propyl)-2-nitroimidazole), a non-glycosidic nitroimidazole-6-O-glucose adduct, was synthesized, radioiodinated, and evaluated as a substrate of glucose transporter 1 (GLUT1) for radiotheranostic (therapy+diagnostic) management of hypoxic tumors. Nucleophilic iodination of the nosylate synthon of I-GAZ followed by deprotection afforded I-GAZ in 74 % overall yield. I-GAZ was radioiodinated via 'exchange' labeling using [(123/131) I]iodide (50-70 % RCY) and then purified by Sep-Pak (>96 % RCP). [(131) I]I-GAZ was stable in 2 % ethanolic solution in sterile water for 14 days when stored at 5 degrees C. In cell culture, I-GAZ was found to be nontoxic to EMT-6 cells at concentrations <0.5 mm, and weakly radiosensitizing (SER 1.1 at 10 % survival of EMT-6 cells; 1.2 at 0.1 % survival in MCF-7 cells). The hypoxic/normoxic uptake ratio of [(123) I]I-GAZ in EMT-6 cells was 1.46 at 2 h, and under normoxic conditions the uptake of [(123) I]I-GAZ by EMT-6 cells was unaltered in the presence of 5 mm glucose. The biodistribution of [(131) I]I-GAZ in EMT-6 tumor-bearing Balb/c mice demonstrated rapid clearance from blood and extensive renal and hepatic excretion. Tumor/blood and tumor/muscle ratios reached approximately 3 and 8, respectively, at 4 h post-injection. Regression analysis of the first order polynomial plots of the blood and tumor radioactivity concentrations supported a perfusion-excretion model with low hypoxia-dependent binding. [(131) I]I-GAZ was found to be stable in vivo, and did not deiodinate.

beta -[¹⁸F]Fluoro Azomycin Arabinoside (beta -[¹⁸F]FAZA): Synthesis, Radiofluorination and Preliminary PET Imaging of Murine A431 Tumors.[Pubmed:28294075]

Curr Radiopharm. 2017;10(2):93-101.

BACKGROUND: 1-alpha-D-(5-Deoxy-5-[18F]fluoroarabinofuranosyl)-2-nitroimidazole([18F] FAZA) is a PET radiotracer that demonstrates excellent potential in imaging regional hypoxia, and is clinically used in diagnosing a wide range of solid tumors in cancer patients. [18F]FAZA, however, is radiofluorinated in only moderate recovered radiochemical yield (rRCY, ~12%). It is postulated that the relative stability of the C1' beta-anomeric bond at C5' will make 1-beta-D-(5-fluoro-5-deoxyarabinofuranosyl)-2-nitroimidazole (beta-FAZA), the beta-conformer of FAZA, an attractive candidate for clinical hypoxia imaging. OBJECTIVES: The principle goals were to synthesize beta-FAZA and beta-Ac2TsAZA, the radiofluorination precursor, to establish the radiofluorination chemistry leading to beta-[18F]FAZA, and to investigate the biodistribution of beta-[18F]FAZA in an animal tumor-bearing model using PET imaging. METHODS: The appropriately-protected furanose sugar was coupled with 2-nitroimidazole to afford 1-beta-D-(2,3-di-O-acetylarabinofuranosyl)-2-nitroimidazole (beta-Ac2AZA). Fluorination of beta-Ac2AZA with DAST, followed by alkaline hydrolysis, afforded beta-FAZA (21%). The radiolabeling synthon, 1-beta-D-(5-O-toluenesulfonyl-2,3-di-O-acetylarabinofuranosyl)-2-nitroimidazole (beta-Ac2TsAZA), on radiofluorination using the 18F/K222 complex under various reaction conditions, followed by base-catalyzed deacetylation, afforded beta-[18F]FAZA. beta-[18F]FAZA was radiochemically stable for at least 8 h when stored in aqueous ethanol (8%) at 22 degrees C. A preliminary PET imaging-based biodistribution study of beta-[18F]FAZA was performed in A431 tumor-bearing nude mice. RESULTS: beta-FAZA and beta-Ac2TsAZA were synthesized in satisfactory yield. Radiochemistry of [18F]FAZA was established. PET images showed strong uptake in hypoxic regions of the tumor. CONCLUSION: The synthesis of beta-FAZA and beta-[18F]FAZA are reported. Radiofluorination of beta-Ac2TsAZA and the deprotection of beta-Ac2[18F]FAZA were facile, but led to a more complex mixture of radiofluorinated by-products than observed with the corresponding precursor of alpha-[18F]FAZA. PET images were indicative of hypoxia-selective accumulation of beta-[18F]FAZA in tumor.

In vitro and in vivo evaluation of [(18)F]F-GAZ, a novel oxygen-mimetic azomycin-glucose conjugate, for imaging hypoxic tumor.[Pubmed:22746267]

Cancer Biother Radiopharm. 2012 Oct;27(8):473-80.

Several F-18-labeled 2-nitroimidazole (Azomycin) derivatives have been proposed for imaging hypoxia using positron emission tomography (PET). Their cell penetration is based on passive diffusion, which limits their intracellular concentration maxima. The purpose of this study was to investigate the uptake of N-(2-[(18)F]fluoro-3-(6-O-glucosyl)propyl-Azomycin ([(18)F]F-GAZ), a new Azomycin-glucose conjugate, in vitro and in vivo. [(18)F]F-GAZ was synthesized from its tetraacetyl nosylate precursor by nucleophilic radiofluorination. [(18)F]F-GAZ was evaluated in vivo in EMT-6 tumor-bearing Balb/C mice utilizing the PET and biodistribution analysis. In vitro uptake of [(18)F]FDG by EMT-6 cells was measured in the presence of unlabeled F-GAZ, 2-FDG, and D-glucose. [(18)F]F-GAZ was rapidly cleared from all tissues, including the blood pool and kidneys, with ultimate accumulation in the urinary bladder. Uptake of tracer doses of [(18)F]F-GAZ into EMT-6 tumors was fast, reaching a standardized uptake value of 0.66+/-0.05 within 5-6 minutes postinjection (p.i.), and decreased to 0.24+/-0.04 by 60 minutes p.i. (n=6). A tumor-muscle ratio of 1.87+/-0.18 was observed after 60 minutes. Total uptake of [(18)F]F-GAZ in tumors (60 minutes) amounted to 1.25%+/-0.15% ID/g versus 0.61%+/-0.14% ID/g (n=4) in muscle. Similar biodistribution and excretion were observed using carrier-added (100 mg/kg) doses of F-GAZ. In vitro, D-glucose and unlabeled 2-FDG were two orders of magnitude more potent than F-GAZ as competitive inhibitors of [(18)F]FDG uptake into EMT-6 cells. Besides its interaction with glucose transporters, F-GAZ seems to be not transported in the presence of glucose. Furthermore, [(18)F]F-GAZ is unlikely to be effective as a hypoxia imaging agent. The low in vivo toxicity and substantial retention in tumor observed at high doses of F-GAZ do provide rationale for further testing as a radiosensitizer for external beam radiation therapy of radioresistant, hypoxic tumors.

[(18)F]Fluoro-azomycin-2 -deoxy-beta-d-ribofuranoside - A new imaging agent for tumor hypoxia in comparison with [(18)F]FAZA.[Pubmed:27693670]

Nucl Med Biol. 2016 Dec;43(12):759-769.

INTRODUCTION: Radiolabeled 2-nitroimidazoles (Azomycins) are a prominent class of biomarkers for PET imaging of hypoxia. [(18)F]Fluoro-Azomycin-alpha-arabinoside ([(18)F]FAZA) - already in clinical use - may be seen as alpha-configuration nucleoside, but enters cells only via diffusion and is not transported by cellular nucleoside transporters. To enhance image contrast in comparison to [(18)F]FAZA our objective was to (18)F-radiolabel an Azomycin-2 -deoxyriboside with beta-configuration ([(18)F]FAZDR, [(18)F]-beta-8) to mimic nucleosides more closely and comparatively evaluate it versus [(18)F]FAZA. METHODS: Precursor and cold standards for [(18)F]FAZDR were synthesized from methyl 2-deoxy-d-ribofuranosides alpha- and beta-1 in 6 steps yielding precursors alpha- and beta-5. beta-5 was radiolabeled in a GE TRACERlab FXF-N synthesizer in DMSO and deprotected with NH4OH to give [(18)F]FAZDR ([(18)F]-beta-8). [(18)F]FAZA or [(18)F]FAZDR was injected in BALB/c mice bearing CT26 colon carcinoma xenografts, PET scans (10min) were performed after 1, 2 and 3h post injection (p.i.). On a subset of mice injected with [(18)F]FAZDR, we analyzed biodistribution. RESULTS: [(18)F]FAZDR was obtained in non-corrected yields of 10.9+/-2.4% (9.1+/-2.2GBq, n=4) 60min EOB, with radiochemical purity >98% and specific activity >50GBq/mumol. Small animal PET imaging showed a decrease in uptake over time for both [(18)F]FAZDR (1h p.i.: 0.56+/-0.22% ID/cc, 3h: 0.17+/-0.08% ID/cc, n=9) and [(18)F]FAZA (1h: 1.95+/-0.59% ID/cc, 3h: 0.87+/-0.55% ID/cc), whereas T/M ratios were significantly higher for [(18)F]FAZDR at 1h (2.76) compared to [(18)F]FAZA (1.69, P<0.001), 3h p.i. ratios showed no significant difference. Moreover, [(18)F]FAZDR showed an inverse correlation between tracer uptake in carcinomas and oxygen breathing, while muscle tissue uptake was not affected by switching from air to oxygen. CONCLUSIONS: First PET imaging results with [(18)F]FAZDR showed advantages over [(18)F]FAZA regarding higher tumor contrast at earlier time points p.i. Availability of precursor and cold fluoro standard together with high output radiosynthesis will allow for a more detailed quantitative evaluation of [(18)F]FAZDR, especially with regard to mechanistic studies whether active transport processes are involved, compared to passive diffusion as observed for [(18)F]FAZA.