After upscaling the conjugation and purification ofpeptibodyC19-PEG4-vcMMAE, its interaction with FGFR1 wasstudied by SPR, showing slightly weaker affinity (Kd = 110 nM) compared to unconjugated peptibodyC19, whichmay be a result of steric hindrance caused by MMAE and PEG chains.Despite reduced affinity, cytotoxicity assays showed a specificityof PepF-PEG4vcMMAE toward lung cancer cells overexpressingFGFR1, leaving cells lacking the receptor unaffected. The gene discussed is FGFR1; the disease is lung cancer.