INTRODUCTION: A growing body of evidence suggests that increased expression of the vascular endothelial growth factor (VEGF) co-receptor Neuropilin-2 (NRP2) is associated with aggressive breast cancers and that VEGF/NRP2 signaling contributes to clinical resistance to chemotherapy and tumor recurrence, making NRP2 a promising therapeutic target. A major limitation that has hampered the development of such a therapy, however, has been the lack of availability of high-quality anti-human NRP2 monoclonal antibodies (mAbs) that specifically block VEGF/NRP2 signaling.

aTyr has generated a panel of high-quality, anti-human NRP2 mAbs that have the potential to be developed for the clinical management of diseases that involve NRP2 signaling. Among them, ATYR2810 has been characterized to bind to the b1 domain of NRP2 that encompasses the VEGF binding sites. It completely blocks the binding of VEGF to NRP2, and VEGF-induced NRP2/VEGFR dimerization. Importantly, ATYR2810 had no effect on Semaphorin 3F (Sema3F) induced NRP2/PlexinA1 dimerization, demonstrating its specificity for blocking the VEGF/NRP2 pathway. We have shown that ATYR2810, but not a Sema3F-blocking mAb has tumor-inhibitory effects on triple negative breast cancer (TNBC) cell lines or patient-derived organoids.

RESULTS: We further evaluated the efficacy of ATYR2810 in combination with standard-of-care therapeutics including Cisplatin and Bevacizumab (anti-VEGF-A blocking antibody). In in vitro 3D methylcellulose colony formation assays, ATYR2810 sensitized TNBC cells to Cisplatin or Bevacizumab and considerably reduced colony formation in combination with these treatments. In an in vivo TNBC xenograft cancer model (MDA-MB-231), ATYR2810 augmented the anti-tumor effects of Cisplatin or Bevacizumab. To explore the underlying molecular mechanism, we performed gene expression profiling with samples treated by ATYR2810 alone and the combo therapy with Cisplatin or Bevacizumab. A number of gene markers of cancer stem cells (CSC) and/or epithelial-mesenchymal transition (EMT) were found to be down-regulated by ATYR2810 treatment in TNBC patient-derived organoids, including a key EMT transcription factor ZEB1. We also confirmed the reduction of ZEB1 protein expression by ATYR2810 treatment in TNBC cells.

CONCLUSIONS: These results demonstrate the efficacy of ATYR2810 in combination with standard-of-care therapeutics in in vitro and in vivo TNBC models, and suggest its activity is mediated through inhibiting both EMT and cellular dedifferentiation that renders tumors more sensitive to the treatment regimes. The targeting of VEGF/NRP2 signaling by ATYR2810 may provide a new therapeutic option, and lead to the identification of new treatment biomarkers, which could offer improved efficacy and reduced toxicity in aggressive breast cancers.

Citation Format: Zhiwen Xu, Christoph Burkart, Hira L. Goel, Justin Rahman, Clara Polizzi, Matt Seikkula, Luke Burman, Arthur M. Mercurio, Leslie A. Nangle. A domain-specific antibody to NRP2 down-regulated epithelial-mesenchymal transition genes and enhanced efficacy of standard-of-care therapeutics for aggressive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB095.