American Association for Cancer Research
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Supplementary Figure 2 from PI3K Inhibition Impairs BRCA1/2 Expression and Sensitizes BRCA-Proficient Triple-Negative Breast Cancer to PARP Inhibition

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journal contribution
posted on 2023-04-03, 20:22 authored by Yasir H. Ibrahim, Celina García-García, Violeta Serra, Lei He, Kristine Torres-Lockhart, Aleix Prat, Pilar Anton, Patricia Cozar, Marta Guzmán, Judit Grueso, Olga Rodríguez, Maria Teresa Calvo, Claudia Aura, Orland Díez, Isabel T. Rubio, José Pérez, Jordi Rodón, Javier Cortés, Leif W. Ellisen, Maurizio Scaltriti, José Baselga

PDF file - 208K, PI3K blockade suppresses BRCA1/2 transcription



PARP inhibitors are active in tumors with defects in DNA homologous recombination (HR) due to BRCA1/2 mutations. The phosphoinositide 3-kinase (PI3K) signaling pathway preserves HR steady state. We hypothesized that in BRCA-proficient triple-negative breast cancer (TNBC), PI3K inhibition would result in HR impairment and subsequent sensitization to PARP inhibitors. We show in TNBC cells that PI3K inhibition leads to DNA damage, downregulation of BRCA1/2, gain in poly-ADP-ribosylation, and subsequent sensitization to PARP inhibition. In TNBC patient–derived primary tumor xenografts, dual PI3K and PARP inhibition with BKM120 and olaparib reduced the growth of tumors displaying BRCA1/2 downregulation following PI3K inhibition. PI3K-mediated BRCA downregulation was accompanied by extracellular signal–regulated kinase (ERK) phosphorylation. Overexpression of an active form of MEK1 resulted in ERK activation and downregulation of BRCA1, whereas the MEK inhibitor AZD6244 increased BRCA1/2 expression and reversed the effects of MEK1. We subsequently identified that the ETS1 transcription factor was involved in the ERK-dependent BRCA1/2 downregulation and that knockdown of ETS1 led to increased BRCA1/2 expression, limiting the sensitivity to combined BKM120 and olaparib in 3-dimensional culture.Significance: Treatment options are limited for patients with TNBCs. PARP inhibitors have clinical activity restricted to a small subgroup of patients with BRCA mutations. Here, we show that PI3K blockade results in HR impairment and sensitization to PARP inhibition in TNBCs without BRCA mutations, providing a rationale to combine PI3K and PARP inhibitors in this indication. Our findings could greatly expand the number of patients with breast cancer that would benefit from therapy with PARP inhibitors. On the basis of our findings, a clinical trial with BKM120 and olaparib is being initiated in patients with TNBCs. Cancer Discov; 2(11); 1036–47. ©2012 AACR.Read the Commentary on this article by Rehman et al., p. 982.This article is highlighted in the In This Issue feature, p. 961