Auger electrons
Auger electrons are exciting forms of radioactivity. In theory, if you can specifically attach them to cancer cells, they will irradiate only the cells you want. This truly is the holy grail in radiotherapy: to target diseased cells with radiation and not affect healthy tissues. Work with Auger electron emitters so far, including Tc-99m, I-123, In-111, Ga-67, and Tl-201, have all shown the ability to damage the DNA of cancer cells, but only when attached to the cancer cells.
Example 1. Auger electron-emitter thallium-201 is an extremely effective anticancer radionuclide
Thallium-201 (201Tl), a gamma-emitting radionuclide used in myocardial perfusion scintigraphy, decays by electron capture, releasing around 37 Auger and Coster–Kronig electrons per decay. Here, we show that adding thallium-201 to cancer cells leads to complete cytotoxic effect, which is specific as it can be blocked by the presence of competing potassium K+. From Osytek et al. 2021.
Example 2. SPECT imaging and Auger electron-emitting radionuclide Tc-99m can be used for anti-cancer therapy in vitro
Technetium-99m causes toxicity to breast cancer only when internalised into cells, with survival fraction decreasing with increasing amounts radioactivity (MBq/mL). Decayed technetium-99m was not toxic to cells. From Costa et al. 2021
Example 3. Ga-67 emits Auger electrons and can be used for targeted cancer radiotherapy
This image shows radioactive element and Auger electron-emitter Ga-67 located irradiating around one breast cancer cell. The radioactivity was targeted to this cell by attaching Ga-67 to trastuzumab, an antibody that binds the Her2 receptor on certain breast cancer cells. In this paper, Ga-67-trastuzumab was shown to be able to kill these breast cancer cells, only when Ga-67 was located within/on the cell itself.
Example 4. Auger electrons need to be close to the DNA to cause damage to cancer cells
Radioactive epidermal growth factor (EGF), labelled with Auger electron-emitter In-111, causes damage to the DNA (yH2AX foci/cell). This is further enhanced when compounds such as 5-aza and SAHA are used to open up the DNA enabling better access of the radioactivity to all parts of the DNA. This led to more cancer cell killing also. From Terry and Vallis 2012.