Silva, GSales-Dias, JCasal, DAlves, SDomenici, GBarreto, CMatos, CLemos, AMatias, AKucheryava, KFerreira, AMoita, MRBraga, SBrito, CCabral, MGCasalou, CBarral, DSousa, PVideira, PBandeiras, TBarbas, A2021-10-132021-10-132021Cancers (Basel). 2021 Aug 13;13(16):4074.http://hdl.handle.net/10400.17/3881The Notch-signaling ligand DLL1 has emerged as an important player and promising therapeutic target in breast cancer (BC). DLL1-induced Notch activation promotes tumor cell proliferation, survival, migration, angiogenesis and BC stem cell maintenance. In BC, DLL1 overexpression is associated with poor prognosis, particularly in estrogen receptor-positive (ER+) subtypes. Directed therapy in early and advanced BC has dramatically changed the natural course of ER+ BC; however, relapse is a major clinical issue, and new therapeutic strategies are needed. Here, we report the development and characterization of a novel monoclonal antibody specific to DLL1. Using phage display technology, we selected an anti-DLL1 antibody fragment, which was converted into a full human IgG1 (Dl1.72). The Dl1.72 antibody exhibited DLL1 specificity and affinity in the low nanomolar range and significantly impaired DLL1-Notch signaling and expression of Notch target genes in ER+ BC cells. Functionally, in vitro treatment with Dl1.72 reduced MCF-7 cell proliferation, migration, mammosphere formation and endothelial tube formation. In vivo, Dl1.72 significantly inhibited tumor growth, reducing both tumor cell proliferation and liver metastases in a xenograft mouse model, without apparent toxicity. These findings suggest that anti-DLL1 Dl1.72 could be an attractive agent against ER+ BC, warranting further preclinical investigation.engHSJ ANPATDLL1ER+ Breast CancerNotch SignalingAngiogenesisCell ProliferationMonoclonal AntibodyTumor Growth.journal article10.3390/cancers13164074.