Despite advances in the field of nuclear medicine, the imaging of bacterial infections has remained a challenge. The existing reagents suffer from poor sensitivity and specificity. In this study we investigate the potential of a novel PET (positron emission tomography) tracer that overcomes these limitations.Methods6-[18F]-fluoromaltose was synthesized. Its behavior in vitro was evaluated in bacterial and mammalian cultures. Detailed pharmacokinetic and biodistribution profiles for the tracer were obtained from a murine model.Results6-[18F]-fluoromaltose is taken up by multiple strains of pathogenic bacteria. It is not taken up by mammalian cancer cell lines. 6-[18F]-fluoromaltose is retained in infected muscles in a murine model of bacterial myositis. It does not accumulate in inflamed tissue.ConclusionWe have shown that 6-[18F]-fluoromaltose can be used to image bacterial infection in vivo with high specificity. We believe that this class of agents will have a significant impact on the clinical management of patients.

Purpose To develop novel positron emission tomography (PET) agents for visualization and therapy monitoring of bacterial infections. Procedures It is known that maltose and maltodextrins are energy sources for bacteria. Hence, 18F-labelled maltose derivatives could be a valuable tool for imaging bacterial infections. We have developed methods to synthesize 4-O-(α-D-glucopyranosyl)-6-deoxy-6-[18F]fluoro-D-glucopyranoside (6-[18F]fluoromaltose) and 4-O-(α-D-glucopyranosyl)-1-deoxy-1-[18F]fluoro-D-glucopyranoside (1-[18F]fluoromaltose) as bacterial infection PET imaging agents. 6-[18F]fluoromaltose was prepared from precursor 1,2,3-tri-O-acetyl-4-O-(2′,3′,-di-O-acetyl-4′,6′-benzylidene-α-D-glucopyranosyl)-6-deoxy-6-nosyl-D-glucopranoside (5). The synthesis involved the radio-fluorination of 5 followed by acidic and basic hydrolysis to give 6-[18F]fluoromaltose. In an analogous procedure, 1-[18F]fluoromaltose was synthesized from 2,3, 6-tri-O-acetyl-4-O-(2′,3′,4′,6-tetra-O-acetyl-α-D-glucopyranosyl)-1-deoxy-1-O-triflyl-D-glucopranoside (9). Stability of 6-[18F]fluoromaltose in phosphate-buffered saline (PBS) and human and mouse serum at 37 °C was determined. Escherichia coli uptake of 6-[18F]fluoromaltose was examined. Results A reliable synthesis of 1- and 6-[18F]fluoromaltose has been accomplished with 4–6 and 5–8 % radiochemical yields, respectively (decay-corrected with 95 % radiochemical purity). 6-[18F]fluoromaltose was sufficiently stable over the time span needed for PET studies (~96 % intact compound after 1-h and ~65 % after 2-h incubation in serum). Bacterial uptake experiments indicated that E. coli transports 6-[18F]fluoromaltose. Competition assays showed that the uptake of 6-[18F]fluoromaltose was completely blocked by co-incubation with 1 mM of the natural substrate maltose. Conclusion We have successfully synthesized 1- and 6-[18F]fluoromaltose via direct fluorination of appropriate protected maltose precursors. Bacterial uptake experiments in E. coli and stability studies suggest a possible application of 6-[18F]fluoromaltose as a new PET imaging agent for visualization and monitoring of bacterial infections.

Targeting tumor vasculature is an emerging strategy in cancer treatment. Promising results have been shown in preclinical studies when vascular disrupting agents (VDAs) are used in combination with other anticancer therapies. Because radiation therapy with concurrent cisplatin or cetuximab has become standard treatment for patients with locally advanced head and neck squamous cell carcinoma (HNSCC), we investigated whether the VDA ombrabulin (AVE8062) could improve the antitumor activity of radiation plus cisplatin and radiation plus cetuximab combinations. HNSCC HEP2 or FaDu tumor bearing mice were treated with ombrabulin, cisplatin, cetuximab, local radiation therapy or combinations of these treatments. Ombrabulin attenuated tumor growth of HEP2 and FaDu xenografts compared to control tumors. A more pronounced tumor growth delay and tumor regression were induced when ombrabulin was added to local irradiation, cisplatin or cetuximab in FaDu tumors compared to single agent treatments. Finally, triple agent therapies combining ombrabulin, irradiation, and either cisplatin or cetuximab were more effective than double combination treatment regimens and increased tumor growth delay in both HEP2 and FaDu tumor models. Of note, complete tumor regression was achieved in FaDu tumor model for the triple combination including platinum. Immunohistochemistry on FaDu tumors demonstrated a specificity of ombrabulin towards intratumoral vessels, in contrast to peritumoral vasculature. Our results provide a rationale for the use of ombrabulin in combination with two standard treatment regimens that are concurrent cisplatin-based chemoradiation and cetuximab plus ionizing radiation therapies, for the treatment of HNSCC.

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