A developed antibody-drug conjugate rituximab-vcMMAE shows a potent cytotoxic activity against CD20-positive cell line

Rituximab is a chimeric monoclonal antibody directed against B-lymphocyte specific antigen CD20, which is used for the treatment of B-cell malignancies. However, the effectiveness of rituximab is limited partly due to treatment resistance. The aim of this study was to develop rituximab-based antibody drug conjugate (ADC) to enhance rituximab activity. In this study, monomethyl auristatin E (MMAE) was covalently conjugated to dithiothreitol -reduced rituximab via a valine-citrulline peptide linker (rituximab-vcMMAE). The conjugates were then characterized by using nonreducing sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) and cell-based enzyme-linked immunosorbent assay (ELISA). The cytotoxic activity of the ADC was evaluated against Raji (human B-cell lymphoma; CD20-positive) and MOLT-4 (T lymphoblast; acute lymphoblastic leukemia; CD20-negative) cell lines. In addition, the colony formation assay was used to identify the propagation ability of ADC-treated cells in vitro. Results from nonreducing SDS-PAGE revealed various species of rituximab-MC-Val-Cit-PABC-MMAE (rituximab-vcMMAE), as compared with unconjugated rituximab. The binding capacity of rituximab-vcMMAE to the CD20-positive cell was similar to that of the parental rituximab. Most importantly, our results revealed that rituximab-vcMMAE was highly potent against the CD20-positive cell line, but not against the CD20-negative cell. At the same time, rituximab-vcMMAE was able to inhibit colony formation in CD20-positive cells. These data indicate that rituximab-vcMMAE may be a highly effective and selective therapy for the treatment of B-cell lymphoma.