TSPO and cancer: Although PK11195 exhibits high-affinity binding to TSPO with a reported binding affinity of 9.3 nM (Selleri et al. 2001), its therapeutic anti-parasitic effects (Dzierszinski et al. 2002, Bouyer et al. 2011) and cytotoxic effects on a variety of cancer cell types (Shoukrun et al. 2008) have been shown to occur only at elevated (micromolar) concentrations.