Abstract 1902: The comparative superiority of a bispecific antibody targeting alpha v and alpha 5 integrins is uniquely characterized by induced degradation of integrins (2019)

Background: Bispecific antibody blockade of alpha v and alpha 5 integrins (BsAbαvα5) resulted in superior anti-tumor activity in prostate cancer cells over monospecific αv (MsAbαv) and α5 blockade (MsAbα5), singly or in combination. We sought to define a molecular basis for this observation.Methods: We examined the comparative impact of monospecific and bispecific antibody strategies on membrane-specific and cellular expression of integrins as well as their transcription, translation and degradation fate in integrin av/a5+ prostate cancer cells (VCAP, C4-2b, DU-145 and PC-3). These dynamic changes were assessed in the context of functional studies including tumor-stromal interactions and downstream signaling.Results: With MsAbαv or MsAbα5 therapy, alone or in combination, upregulation of target integrin and/or the alternative integrin was observed which suggested both autoregulation as well as a cross-regulation among the target integrins. However, with BsAbαvα5 therapy, either a block in upregulation of target integrin/s or a marked decrease in cellular integrin expression was noted. Unexpectedly, these dynamic changes in cellular integrin expression with the BsAbαvα5 were retained up to 72 hours after antibody exposure with recovery of integrin expression in viable cells noted by 7 days. In cells recovered at 48-72 hours, a marked decrease in clonogenicity, adhesion and migration was observed. Flow cytometry indicated persistent membrane loss of integrin expression at 48-72 hours confirming that the impact of the BsAbαvα5 is not related to altered subcellular integrin trafficking alone. QRT-PCR studies did not identify upregulation of integrin transcription to account for upregulated integrin expression. Blockade of protein translation with cycloheximide failed to abrogate the differential impact of MsAbs or BsAbαvα5 on integrin expression. However, lysosomal inhibition with chloroquine blocked the downregulation of integrin expression with BsAbαvα5 therapy. Variable effects on downstream signaling in the Akt and MAPK pathway observed across cell types contrasted with consistent functional impairment of tumor-stromal interactions.Conclusions: BsAbαvα5 therapy uniquely induces lysosomal degradation of target integrins compared to MsAbs, alone or in combination. Cellular depletion of integrin expression serves as a pharmacodynamic marker of BsAbαvα5activity. By contrast, upregulated cellular expression secondary to MsAb therapy is likely secondary to a block in both integrin degradation and membrane recycling within the endosomal/lysosomal pathway. These observations provide additional insight into the mechanistic impact of the BsAbαvα5 as well as a pharmacodynamic method for monitoring in vivo activity.Citation Format: Raghav Joshi, Wenying Ren, Paul Mathew. The comparative superiority of a bispecific antibody targeting alpha v and alpha 5 integrins is uniquely characterized by induced degradation of integrins [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1902.