Anti-nicastrin monoclonal antibodies elicit pleiotropic anti-tumour pharmacological effects in invasive breast cancer cells

The goal of targeted cancer therapies is to specifically block oncogenic signalling, thus maximising efficacy, while reducing side-effects to patients. The gamma-secretase(GS) complex is an attractive therapeutic target in haematological malignancies and solid tumourswith major pharmaceutical activity to identify optimal inhibitors. Within GS, nicastrin(NCSTN) offers an opportunity for therapeutic intervention using blocking monoclonal antibodies (mAbs). Here we explore the role of anti- nicastrinmonoclonal antibodies, which we have developed as specific, multi-faceted inhibitors of proliferation and invasive traits of triple-negative breast cancercells. We use 3D in vitro proliferation and invasion assays as well as an orthotopic and tail vail injection triple-negative breast cancerin vivo xenograft model systems. RNAScope assessed nicastrinin patient samples. Anti-NCSTN mAb clone-2H6 demonstrated a superior anti-tumour efficacy than clone-10C11 and the RO4929097 small molecule GS inhibitor, acting by inhibiting GS enzymatic activity and Notch signalling in vitro and in vivo. Confirming clinical relevance of nicastrinas a target, we report evidence of increased NCSTN mRNA levels by RNA in situ hybridization (RNAScope) in a large cohort of oestrogen receptornegative breast cancers, conferring independent prognostic significance for disease-free survival, in multivariate analysis. We demonstrate here that targeting NCSTN using specific mAbs may represent a novel mode of treatment for invasive triple-negative breast cancer, for which there are few targeted therapeutic options. Furthermore, we propose that measuring NCSTN in patient samples using RNAScope technology may serve as companion diagnosticfor anti-NCSTN therapy in the clinic.