Abstract
[(123)I]β-methyl-p-iodophenyl-pentadecanoic acid ([(123)I]BMIPP), which is used for nuclear medicine imaging of myocardial fatty acid metabolism, accumulates in cancer cells. However, the mechanism of accumulation remains unknown. Therefore, this study aimed to elucidate the accumulation and accumulation mechanism of [(123)I]BMIPP in cancer cells. We compared the accumulation of [(123)I]BMIPP in cancer cells with that of [(18)F]FDG and found that [(123)I]BMIPP was a much higher accumulation than [(18)F]FDG. The accumulation of [(123)I]BMIPP was evaluated in the presence of sulfosuccinimidyl oleate (SSO), a CD36 inhibitor, and lipofermata, a fatty acid transport protein (FATP) inhibitor, under low-temperature conditions and in the presence of etomoxir, a carnitine palmitoyl transferase I (CPT1) inhibitor. The results showed that [(123)I]BMIPP accumulation was decreased in the presence of SSO and lipofermata in H441, LS180, and DLD-1 cells, suggesting that FATPs and CD36 are involved in [(123)I]BMIPP uptake in cancer cells. [(123)I]BMIPP accumulation in all cancer cell lines was significantly decreased at 4 °C compared to that at 37 °C and increased in the presence of etomoxir in all cancer cell lines, suggesting that the accumulation of [(123)I]BMIPP in cancer cells is metabolically dependent. In a biological distribution study conducted using tumor-bearing mice transplanted with LS180 cells, [(123)I]BMIPP highly accumulated in not only LS180 cells but also normal tissues and organs (including blood and muscle). The tumor-to-intestine or large intestine ratios of [(123)I]BMIPP were similar to those of [(18)F]FDG, and the tumor-to-large-intestine ratios exceeded 1.0 during 30 min after [(123)I]BMIPP administration in the in vivo study. [(123)I]BMIPP is taken up by cancer cells via CD36 and FATP and incorporated into mitochondria via CPT1. Therefore, [(123)I]BMIPP may be useful for imaging cancers with activated fatty acid metabolism, such as colon cancer. However, the development of novel imaging radiotracers based on the chemical structure analog of [(123)I]BMIPP is needed.