<P> Cu - ATSM (diacetyl - bis (N4 - methylthiosemicarbazone)) has been shown to increase the survival time of tumor - bearing animals with no acute toxicity . Areas of low oxygen retention have been shown to be resistant to radiotherapy because hypoxia reduces the lethal effects of ionizing radiation . Cu was believed to kill these cells because of its unique decay properties . In this experiment, animal models having colorectal tumors with and without induced hypoxia were administered Cu - ATSM . Cu - ATSM is preferentially taken up by hypoxic cells over normoxic cells . The results demonstrated that this compound increased survival of the tumor bearing hamsters compared with controls . In the control groups, death due to tumor burden occurred within 20 days weeks while animals with a dose greater than 6 mCi of the radioisotope tumor growth was inhibited and survival increased to 135 days in 50% of animals . The results also suggested that multiple doses and a single dose of 10 mCi were equally effective while the multiple dose regimen is safer for non-target tissue . </P> <P> Radiotherapy of cancer cells using Cu can be applied in medical research and clinical practice . The advantages of radiotherapy with beta emitters of this energy are that there is enough to do substantial damage to the target cells but the mean range in tissue is less than a millimeter so non target tissues are unlikely to be harmed . In addition, Cu is a positron emitter making it a viable PET imaging radionuclide which can give real time images of the physiological processes in the system . These abilities in conjunction enable accurate monitoring of drug distribution and biokinetics simultaneously . Radiotherapeutic efficacy of copper - 64 depends highly upon the radioligand delivery to the target cells, so the development of bifunctional chelates is central to development of Cu's potential as a radiopharmaceutical . </P>

How many protons neutrons and electrons in copper-64