Abstract 2655: Anti-CD19 antibody-drug conjugate therapy in B cell non-Hodgkin lymphoma
Authors: Saito Chieko , Bi Chengfeng , Fu Kai 
Published: June 2023

Abstract
Previously, we have shown that overexpression of Polo-like kinase (PLK)-1 is associated with poor clinical outcomes in patients with aggressive B cell lymphomas. PLK-1 selective inhibitor, Volasertib (BI 6727), has a potent anti-tumor effect in aggressive B cell lymphomas. Unfortunately, Volasertib was withdrawn in Phase III clinical trials due to severe myelosuppression. In this study, we developed a Volasertib antibody-drug conjugate (V-ADC) using -CD19 antibody Inebilizumab to increase the targeting specificity for B-cell lymphoma cells and minimize the side effects of Volasertib. However, we found that V-ADC treatment exhibited little cytotoxic effects, comparing to free Volasertib treatment in Z138 cells, a mantle cell lymphoma (MCL) cell line. We hypothesized that the expression level/density of CD19 on B-lymphoma cells as well as its gene mutations may affect V-ADC binding affinity required for its endocytosis. We, therefore, established Z138 cell lines with overexpression of either wild-type (WT) or mutant (Mut) CD19. The cell viability at 48h post 10nM V-ADC treatment was determined to be 90%, 61%, and 69% in parent, WT, and Mut CD19-overexpressing Z138 cells, respectively. In comparison, the cell viability with 10nM free volasertib treatment ranged from 3-30% in these cell lines. Therefore, other factors, in addition to CD19 expression, may have also played an important role in V-ADC induced cytotoxicity. Upon endocytosis, the V-ADC will enter the endolysosome where cathepsin, a lysosomal enzyme, cleaves the linker between Volasertib and Inebilizumab and releases free Volasertib into the cells. Our previous works have shown that a starvation condition (culture media with 1% FBS) increased lysosomal cathepsin activity, comparing to the culture media with 10% FBS. Herein, we found that upon treatment with 10nM V-ADC, CD19-overexpressing Z138 cells cultured in media with 1% FBS exhibited markedly increased apoptotic cell death comparing to cells in media with 10% FBS (64% vs 41%, respectively). Furthermore, WT and Mut CD19-overexpressing Z138 cells exhibited 2.8- and 2.4-folds of apoptotic cell death compared to control Z138 cells at 48h post 10nM V-ADC treatment with 1% FBS. The cell apoptosis occurred via upregulation of caspase 3, but not caspase 9, with induction of cleavage of poly (ADP-ribose) polymerase (PARP) and reduction of mitochondria membrane potential. In conclusion, starvation and lysosomal cathepsin activation increased V-ADC-induced apoptotic cell death in CD19 overexpression Z138 cell lines. We are actively investigating the in vivo therapeutic effects of V-ADC in patient-derived xenograft (PDX) animal models of MCL and other aggressive B-cell lymphomas.
Citation Format: Chieko Saito, Chengfeng Bi, Kai Fu. Anti-CD19 antibody-drug conjugate therapy in B cell non-Hodgkin lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2655.