Highly Potent, Anthracycline-based Antibody-Drug Conjugates Generated by Enzymatic, Site-specific Conjugation

Antibody-drug conjugates (ADC) are highly potent and specific antitumor drugs, combining the specific targeting of mAbs with the potency of small-molecule toxic payloads. ADCs generated by conventional chemical conjugation yield heterogeneous mixtures with variable pharmacokinetics, stability, safety, and efficacy profiles. To address these issues, numerous site-specific conjugation technologies are currently being developed allowing the manufacturing of homogeneous ADCs with predetermined drug-to-antibody ratios. Here, we used sortase-mediated antibody conjugation (SMAC) technology to generate homogeneous ADCs based on a derivative of the highly potent anthracycline toxin PNU-159682 and a noncleavable peptide linker, using the anti-HER2 antibody trastuzumab (part of Kadcyla) and the anti-CD30 antibody cAC10 (part of Adcetris). Characterization of the resulting ADCs in vitro and in vivo showed that they were highly stable and exhibited potencies exceeding those of ADCs based on conventional tubulin-targeting payloads, such as Kadcyla and Adcetris. The data presented here suggest that such novel and highly potent ADC formats may help to increase the number of targets available to ADC approaches, by reducing the threshold levels of target expression required. Mol Cancer Ther; 16(5); 879-92. ©2017 AACR.