Resolving the micro-heterogeneity and structural integrity of monoclonal antibodies by hybrid mass spectrometric approaches

For therapeutic monoclonal antibodies (mAbs), detailed analysis of the structural integrity and heterogeneity, which results from multiple types of post-translational modifications (PTMs), is relevant to various processes, including product characterization, storage stability and quality control. Despite the recent rapid development of new bioanalytical techniques, it is still challenging to completely characterize the proteoform profile of a mAb. As a nearly indispensable tool in mAb analysis, mass spectrometry (MS) provides unique structural information at multiple levels. Here, we tested a hybrid strategy for the comprehensive characterization of micro-heterogeneity by integrating 2 state-of-the-art MS-based approaches, high-resolution native MS and targeted glycan profiling, to perform complementary analysis at the intact protein level and released glycan level, respectively. We compared the performance of these methods using samples of engineered half-body IgG4s and a panel of mAbs approved for human use. The glycosylation characterization data derived from these approaches were found to be mutually consistent in composition profiling, and complementary in identification and relative-quantitation of low-abundant uncommon glycoforms. In addition, multiple other sources of micro-heterogeneity, such as glycation, lack of glycosylation, and loss of light chains, could be detected by this approach, and the contribution of multiple types of modifications to the overall micro-heterogeneity could be assessed using our superposition algorithm. Our data demonstrate that the hybrid strategy allows reliable and thorough characterization of mAbs, revealing product characteristics that would easily be missed if only a single approach were used.     

Prenyltransferases Regulate CD20 Protein Levels and Influence Anti-CD20 Monoclonal Antibody-mediated Activation of Complement-dependent Cytotoxicity

Anti-CD20 monoclonal antibodies (mAbs) are successfully used in the management of non-Hodgkin lymphomas and chronic lymphocytic leukemia. We have reported previously that statins induce conformational changes in CD20 molecules and impair rituximab-mediated complement-dependent cytotoxicity. Here we investigated in more detail the influence of farnesyltransferase inhibitors (FTIs) on CD20 expression and antitumor activity of anti-CD20 mAbs. Among all FTIs studied, L-744,832 had the most significant influence on CD20 levels. It significantly increased rituximab-mediated complement-dependent cytotoxicity against primary tumor cells isolated from patients with non-Hodgkin lymphomas or chronic lymphocytic leukemia and increased CD20 expression in the majority of primary lymphoma/leukemia cells. Incubation of Raji cells with L-744,832 led to up-regulation of CD20 at mRNA and protein levels. Chromatin immunoprecipitation assay revealed that inhibition of farnesyltransferase activity was associated with increased binding of PU.1 and Oct-2 to the CD20 promoter sequences. These studies indicate that CD20 expression can be modulated by FTIs. The combination of FTIs with anti-CD20 mAbs is a promising therapeutic approach, and its efficacy should be examined in patients with B-cell tumors.