Fig. 6. Selection of drug for the generation of the hLRG1-targeting ADC. (a) Structure of N₃-PEG₃-vc-PABC-MMAE; (b) SPAAC ‘click’ functionalisation (the pre-click strategy) reaction between the strained alkyne bearing PD 1 and azide-linked MMAE to form PD 4. (c) LCMS analysis of PD 1 (662 Da); (d) N₃-PEG₃-vc-PABC-MMAE (1353 Da) and (e) pre-click reaction of PD 1 with N₃-PEG₃-vc-PABC-MMAE showing formation of PD 4 (2015 Da) and complete consumption of PD 1.