Preparation of an Ultrahigh-DAR PDL1 monoclonal antibody-polymeric-SN38 conjugate for precise colon cancer therapy

Antibody-drug conjugates (ADCs) are the most potent active tumor-targeting agents used clinically. However, the preparation of ADCs with high drug-to-antibody ratios (DARs) remains a major challenge. Herein, a Fab-nondestructive SN38-loaded antibody-polymeric-drug conjugate (APDC), aPDL1-NPLG-SN38, was prepared that had a DAR as high as 72 for the first time, by increased numbers of payload binding sites via the carboxyl groups of poly (l-glutamic acid) (PLG). The bonding of Fc-III-4C peptide with PLG-graft-mPEG/SN38 (Fc-NPLG-SN38) was achieved using a click reaction between azide and DBCO groups. The aPDL1-NPLG-SN38 conjugate was then synthesized by the high-affinity interaction between the Fc-III-4C peptide in Fc-NPLG-SN38 and the crystallizable fragment (Fc) of PDL1 monoclonal antibody (aPDL1). This approach avoided the potential deleterious effects on the Fab structure of the monoclonal antibody. The aqueous environment used in its preparation helped maintain monoclonal antibody recognition capability. Through the specific recognition by aPDL1 of PDL1 that is highly expressed on MC38 tumors, the accumulation of aPDL1-NPLG-SN38 in the tumors was 2.8-fold greater than achieved with IgG-NPLG-SN38 that had no active tumor-targeting capability. aPDL1-NPLG-SN38 exhibited excellent therapeutic properties in both medium-sized and large MC38 tumor animal models. The present study provides the details of a novel preparation strategy for SN38-loaded ADCs having a high DAR.