64Cu-Labeled 1,1’-{1,4-phenylenebis(methylene)}-bis{1,4,8,11-tetraaza-cyclotetradecane}

Excerpt

The chemokine receptor 4 (CXCR4) and its ligand, the stromal cell–derived factor-1 (SDF-1 or CXCL12), are known to play a major role in the migration of progenitor cells during embryonic development of the central nervous, cardiovascular, and the hematopoietic systems (1, 2). In addition, this receptor–ligand pair has a function in the development, progression, and spread of various cancers (3), and the CXCR4 acts as a co-receptor to facilitate entry of the human immunodeficiency virus (HIV) into CD4⁺ cells (4). It has also been suggested that CXCR4 and SDF-1 participate in the pathogenesis of neurodegenerative and inflammatory conditions (5). Because of its role in the development of cancer and HIV infections, a variety of CXCR4 inhibitors, including 1,1’-{1,4-phenylenebis(methylene)}-bis{1,4,8,11-tetraaza-cyclotetradecane} (AMD3100), have been evaluated for the treatment of these ailments (6, 7).

Some imaging studies have also been performed on CXCR4 (8, 9). Technetium (^99mTc)-labeled SDF-1 was shown to be a suitable probe to quantify CXCR4 levels under in vivo conditions and could be used to determine changes in CXCR4 expression in different tissue under various pathological and physiological conditions (8). An indium (¹¹¹In)-labeled CXCR4 antagonist, [¹¹¹In]-Ac-TZ14011, was developed for the imaging of CXCR4 expression in xenograft tumors in mice, and Hanaoka et al. used single-photon emission computed tomography to investigate the biodistribution of [¹¹¹In]-Ac-TZ14011 in mice (9). However, the labeled compound showed a low accumulation in the tumors (<1% of the injected dose/gram tissue (% ID/g)), and a high accumulation was reported in the liver (19.3% ID/g), kidneys (29.5% ID/g), and the spleen (5.83% ID/g). These results indicated that [¹¹¹In]-Ac-TZ14011 was suitable for the imaging of CXCR4, although it lacked tumor specificity and the high accumulation of radioactivity in the liver and kidneys showed that this radiochemical was not suitable for the imaging of tumors in these organs.

In an effort to develop a superior CXCR4 imaging agent, AMD3100 was labeled with radioactive copper (⁶⁴Cu) to produce [⁶⁴Cu]-AMD3100, and it was evaluated as a positron emission tomography imaging agent by Jacobson et al. (10). The investigators also studied the biodistribution of [⁶⁴Cu]-AMD3100 in normal mice.