title: Imaging Mass Spectrometry Revealed the Accumulation Characteristics of the 2-Nitroimidazole-Based Agent "Pimonidazole" in Hypoxia.
abstract: Hypoxia, or low oxygen concentration, is a key factor promoting tumor progression and angiogenesis and resistance of cancer to radiotherapy and chemotherapy. 2-Nitroimidazole-based agents have been widely used in pathological and nuclear medicine examinations to detect hypoxic regions in tumors; in particular, pimonidazole is used for histochemical staining of hypoxic regions. It is considered to accumulate in hypoxic cells via covalent binding with macromolecules or by forming reductive metabolites after reduction of its nitro group. However, the detailed mechanism of its accumulation remains unknown. In this study, we investigated the accumulation mechanism of pimonidazole in hypoxic tumor tissues in a mouse model by mass spectrometric analyses including imaging mass spectrometry (IMS). Pimonidazole and its reductive metabolites were observed in the tumor tissues. However, their locations in the tumor sections were not similar to the positively stained areas in pimonidazole-immunohistochemistry, an area considered hypoxic. The glutathione conjugate of reduced pimonidazole, a low-molecular-weight metabolite of pimonidazole, was found in tumor tissues by LC-MS analysis, and our IMS study determined that the intratumor localization of the glutathione conjugate was consistent with the area positively immunostained for pimonidazole. We also found complementary localization of the glutathione conjugate and reduced glutathione (GSH), implying that formation of the glutathione conjugate occurred in the tumor tissue. These results suggest that in hypoxic tumor cells, pimonidazole is reduced at its nitro group, followed by conjugation with GSH.
authors: Shionogi Innovation Center for Drug Discovery, Discovery Research Laboratory for Innovative Frontier Medicines, Shionogi & Co., Ltd., Sapporo, Japan.
authors: Yukiko
authors: Y
authors: Masaki
authors: Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.|Central Institute of Isotope Science, Hokkaido University, Sapporo, Japan.
authors: Yoichi
authors: Y
authors: Shimizu
authors: Shionogi Innovation Center for Drug Discovery, Discovery Research Laboratory for Innovative Frontier Medicines, Shionogi & Co., Ltd., Sapporo, Japan.
authors: Takeshi
authors: T
authors: Yoshioka
authors: Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors: Fei
authors: F
authors: Feng
authors: Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors: Songji
authors: S
authors: Zhao
authors: Shionogi Innovation Center for Drug Discovery, Discovery Research Laboratory for Innovative Frontier Medicines, Shionogi & Co., Ltd., Sapporo, Japan.
authors: Kenichi
authors: K
authors: Higashino
authors: Shionogi Innovation Center for Drug Discovery, Discovery Research Laboratory for Innovative Frontier Medicines, Shionogi & Co., Ltd., Sapporo, Japan.
authors: Yoshito
authors: Y
authors: Numata
authors: Central Institute of Isotope Science, Hokkaido University, Sapporo, Japan.|Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors: Yuji
authors: Y
authors: Kuge
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D009593:Nitroimidazoles / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D009593:Nitroimidazoles; C033815:pimonidazole; D005978:Glutathione