MC-Val-Cit-PAB

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.

Antibody-drug conjugate (ADC) is a novel class of therapeutics for cancer target therapy. This study assessed antitumor activity of ADC with an antimitotic agent, monomethyl auristatin E (MMAE) and a humanized monoclonal anti-HER2 antibody, hertuzumab, in gastric cancer. The efficacy of hertuzumab-MC-Val-Cit-PAB-MMAE (hertuzumab-vcMMAE) on human epidermal growth factor receptor 2 (HER2) positive human gastric cancer cells, NCI-N87, was evaluated in vitro and in vivo. The cytotoxicity of hertuzumab was significantly enhanced after conjugation with MMAE. Compared to trastuzumab, hertuzumab had a higher affinity to HER2 and had more potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro. After conjugation with MMAE, the binding specificity for HER2 was not affected. Furthermore, the internalization of hertuzumab-vcMMAE in HER2 positive gastric cancer cells was verified. Although the conjugation of hertuzumab and MMAE decreased the ADCC effect, the overall cytotoxicity was dramatically increased in HER2 positive gastric cancer cells. In vitro data on this hertuzumab-vcMMAE has exerted much stronger antitumor activity compared to trastuzumab-DM1 in HER2 positive gastric cancer cells.