Structure-Activity Relationships of Bis-Intercalating Peptides and Their Application as Antibody-Drug Conjugate Payloads

Synthetic analogs based on the DNA bis-intercalatingnatural productpeptides sandramycin and quinaldopeptin were investigated as antibodydrug conjugate (ADC) payloads. Synthesis, biophysical characterization,and in vitro potency of 34 new analogs are described.Conjugation of an initial drug-linker derived from a novel bis-intercalatingpeptide produced an ADC that was hydrophobic and prone to aggregation.Two strategies were employed to improve ADC physiochemical properties:addition of a solubilizing group in the linker and the use of an enzymaticallycleavable hydrophilic mask on the payload itself. All ADCs showedpotent in vitro cytotoxicity in high antigen expressingcells; however, masked ADCs were less potent than payload matchedunmasked ADCs in lower antigen expressing cell lines. Two pilot in vivo studies were conducted using stochastically conjugatedDAR4 anti-FR alpha ADCs, which showed toxicity even at low doses,and site-specific conjugated (THIOMAB) DAR2 anti-cMet ADCs that werewell tolerated and highly efficacious.