*4.2. Radiotracer Synthesis and Formulation*

[ <sup>11</sup>C]Tariquidar was synthesized as described previously [51]. For i.v. injection, [11C]tariquidar was formulated in sterile aqueous saline containing 0.01 % (*w*/*v*) Tween 80 to an approximate concentration of 370 MBq/mL. Radiochemical purity, as determined by radio-high performance liquid chromatography, was greater than 98%, and molar activity at the end of synthesis was >100 GBq/µmol.

[ <sup>11</sup>C]Erlotinib was synthesized following established procedures [52] with a radiochemical purity of >98% and a molar activity of >100 GBq/µmol at end of synthesis. For administration into mice, [ <sup>11</sup>C]erlotinb was formulated in 0.1 mM hydrochloric acid in sterile aqueous saline solution to yield a concentration of approximately 370 MBq/mL.
