Rituximab-drug Conjugate Incorporating Auristatin E via A Quaternary Ammonium Linker Inducing Potent Antitumor Activity Against Non-Hodgkin’s B-cells

Abstract

Background: Rituximab represents a drug used for standard Non-Hodgkin’s B-cell lymphoma therapy; however, it displays limited clinical efficacy. Antibody-drug conjugate (ADC) is one of the potential strategies to increase the antitumor activity of an antibody, with improved cytotoxicity directly resulting from the delivery of a molecular warhead. Currently, the warhead monomethyl auristatin E (MMAE) has been widely applied in the study of ADCs, conjugated to a carbamate-based linker (MC-VC-PABC). However, the hydrophobic drug-linker (MC-VC-PABC-MMAE) may lead to ADC aggregation, ultimately resulting in decreased activity. Objective: In this study, we developed a hydrophilic drug-linker MC-VC-PABQ-AE linked to rituximab.. If the replacement of the tertiary amine in AE for a secondary amine in MMAE represents a characteristic modification, the change of antitumor activity of two corresponding anti-CD20 ADC is unknown, requiring further verification. Method: The structural elucidation of MC-VC-PAB-AE was displayed by high-resolution mass spectra. The average drug antibody ratio (DAR) of rituximab-VC-AE/MMAE ADCs was performed by HIC-HPLC. The cell cycle arrest analysis of two ADCs was detected by flow cytometry, and the antitumor activity of two ADCs was evaluated in vitro against Ramos and Daudi cells. Results: The average drug antibody ratio (DAR) of two ADCs was approximately 4.0. The activities of rituximab-VC-AE could be increased in CD20 positive B-lymphoma cell lines, most notably due to the higher cell viability inhibitory rates and apoptosis rates compared to rituximab-VC-MMAE. Conclusions: A hydrophilicity linker of ADC was developed and studied. Rituximab-VC-AE may potentially be used against CD20-positive cells, and the therapeutic efficacy and safety bring about further investigations.