Positron emission tomography (PET) is the process of injecting a radioactive dye into a human’s so that when it decays positrons (positive electrons) are emitted which can be used to learn about what might have gone wrong in the body. Often the dye is in fact glucose with the radioactive component attached so it will easily be absorbed into the blood and transferred around the body to the locations of interest. One of the other options is to use a metal ion as many of these are also required by the body and so accepted willingly. This study is looking primarily at copper (Cu) and the possibility of using it as the radioactive dye.
Copper is required in respiration, blood transport, clotting, hormone production and just general cell growth. Almost all cells in the human body have evolved some way of accumulating copper and so there is good potential for a tracer made from it. The protein responsible for the transportation of copper is called the high affinity copper uptake protein (CTR1). Since cancer cells are so eager to grow, cancers such as skin, lung, prostate and liver have all been shown to have a high abundance of CTR1. This vulnerability is what the researchers are hoping to exploit in their work. Luckily there is a range of radioisotopes to choose from: Cu-60 through to 64 and Cu-67. We want out positron radiation but also an isotope that will decay quite quickly so the patient isn’t left spewing radiation for years to come.
Cu-60 has a half life of 23.4 minutes, Cu-61 takes 3.32 hours and Cu-62 back down to 9.76 minutes; so these three are the choices at a glance. But the actual focus of the study was Cu-64, half life 12.7 hours, with 18% of the decays being β+; 38% being β–; and the final decays just being electron capture. Copper chloride (CuCl2) containing Cu-64 has been used before for PET scans but since the tumours seem to prefer the uptake of Cu(I) over Cu(II), the reduction to CuCl was necessary before the viability was evaluated. It was found that CuCl was indeed collected in melanoma cells at much greater quantities that CuCl2, but the imaging results were unfortunately unimproved as an oxidation reaction occurred in the living sample so improvements to the stability of Cu(I) still need to be worked on before it can be used as a radioactive tracer.
Paper links: Pilot Study of 64Cu(I) for PET Imaging of Melanoma