Figure 1.

Chemical structure and relative folate receptor binding affinity of EC2629. (a) Module 1 (in black) is the tumor-targeting ligand, folic acid. Module 2 (in blue) is a hydrophilic peptidic-PEG spacer. Module 3 (in green) is a bio-cleavable, self-immolative protected disulfide-based linker system. Module 4 (in red) is a pro-PBD which when released after disulfide reduction forms the PBD dimer agent, EC2491. (b) KB cells were incubated for 1 h at 37 °C with 100 nmol/L [³H]-FA in the presence of increasing competitor concentrations. open circle, FA; filled circle, EC2629 and cell associated ³H measured. Points, average CPM of three wells; bars, standard deviation (s.d.).