Retinoic Acid Sensitivity of Triple-Negative Breast-Cancer Cells Characterized by Constitutive Activation of the NOTCH1 Pathway: The Role of RARβ

Abstract

Background: All-trans retinoic-acid (ATRA) is a promising agent in the personalized treatment/chemo-prevention of breast-cancer. Triple-negative breast-cancer (TNBC) accounts for 15-20% of all mammary tumours and share common features such as a high proliferation index and a basal-like gene expression signature. In spite of this, TNBC is very heterogeneous and lacks effective therapeutic strategies.Methods: We profile eighteen TNBC breast-cancer cell-lines for their sensitivity to the anti-proliferative action of ATRA. In addition, we perform RNA-sequencing studies in two of the most sensitive cell-lines exposed to ATRA, a γ-secretase inhibitor and combinations thereof. Results: The only three TNBC cell-lines (HCC-1599, MB-157 and MDA-MB-157) endowed with ATRA-sensitivity are characterized by constitutive activation of the NOTCH1 γ-secretase product, N1ICD and we identify the associated genetic aberrations of the NOTCH1-gene. N1ICD expression renders HCC-1599, MB-157 and MDA-MB-157 cells sensitive not only to ATRA, but also to γ-secretase inhibitors, like DAPT [N-(N-(3,5-difluorophenacetyl)-L-alanyl)-S-phenylglycine-t-butyl-ester] and PF-03084014. The anti-proliferative action of ATRA and γ-secretase inhibitors is complementary, as combinations of ATRA and DAPT or PF-03084014 cause synergistic effects. This synergism is confirmed in mouse xenografts of HCC-1599 cells. RNA-sequencing studies performed in HCC-1599 and MB-157 cells exposed to ATRA and DAPT demonstrate that the two compounds act on common gene-sets, some of which belong to the NOTCH1 pathway. ATRA inhibits the growth of HCC-1599, MB-157 and MDA-MB-157 cells via RARα, which up-regulates several retinoid target-genes, including RARβ. RARβ induction is observed only in HCC-1599, MB-157 and MDA-MB-157 cells, as the other TNBC cell-lines lack ATRA-dependent stimulation of the retinoid-receptor. RARβ is a key determinant of ATRA anti-proliferative activity, as its silencing suppresses the effects exerted by the retinoid. Conclusions: We demonstrate that ATRA exerts a significant anti-tumor action in TNBC cells characterized by constitutive NOTCH1 activation. We show that ATRA enhances the anti-tumor activity of γ-secretase inhibitors in an additive/synergistic manner. We support the idea that ATRA anti-proliferative activity is mediated by the Retinoid-Acid-Receptor-β (RARβ). The present study represents the basis for the design of clinical trials on the efficacy of combinations between ATRA and γ-secretase inhibitors in the treatment of patients affected by a specific subtype of TNBC.

The Notch Signaling Pathway Contributes to Angiogenesis and Tumor Immunity in Breast Cancer

“… 146 TNBC is sensitive to PF-03084014, and the Notch inhibitor PF-03084014 combined with the AKT inhibitor MK-2206 or NF-κB inhibitor can have a significant inhibitory impact on TNBC. 147 , 148 NMK-T-057 triggers autophagic apoptosis in BC cells by restraining γ-secretase-mediated activation of Notch signaling. 149 …”

“…MK-2206 or NF-κB inhibitor can have a significant inhibitory impact on TNBC 147,148. NMK-T-057 triggers autophagic apoptosis in BC cells by restraining γ-secretase-mediated activation of Notch signaling.…”