In Vitro: A stock solution containing 4.4 mg/mL of macropa-NCS was prepared in 0.1 M pH 9.1 NaHCO3 buffer containing 0.154 M NaCl and was stored at -80 °C. To a portion of Tmab in saline (74 μL) were added macropa-NCS (52 μL) and NaHCO3 buffer (266 μL), so that the final concentrations of Tmab and macropa-NCS were 5.1 mg/mL and 0.59 mg/mL, respectively. Macropa-NCS was estimated to be in 16-fold molar excess to Tmab based on a molecular weight of 1045.76 g/mol for macropa-NCS (tetra-TFA salt).