Inhibition of mTOR downregulates expression of DNA repair proteins and is highly efficient against BRCA2-mutated breast cancer in combination to PARP inhibition

Rania El Botty,Bérengère Ouine,Franck Assayag,Sophie Leboucher,Sophie Vacher,Sophie Chateau-Joubert,Charles Fouillade,Jean-Luc Servely,Leanne De Koning,Elisabetta Marangoni,Aurélie Cartier,Rana Hatem,Ivan Bièche,Florence Coussy,Paul Cottu

doi:10.18632/oncotarget.25640

Abstract

Breast cancer is a complex disease in which each patient could present several genetic alterations that are therapeutically relevant in cancers. Here we explored the therapeutic benefit of combining PARP and mTOR inhibitors in a context of DNA repair deficiency and PI3K pathway activation.The combination of everolimus and olaparib was tested in BRCA2-mutated patient-derived xenografts (PDX) carrying alterations in the PI3K/AKT/mTOR pathway. An RPPA analysis of different signalling pathways was performed in untreated and treated xenografts.Everolimus and olaparib showed marked anti-tumor activities in the monotherapy setting and high efficacy when given in combination with 100% of mice showing tumor regressions. The fraction of P-H2AX positive cells was increased in both monotherapy arms and strongly increased in the combination setting. Everolimus given as monotherapy resulted in downregulation of different proteins involved in DNA damage repair, including FANCD2, RAD50 and SUV39H1. In the combination setting, expression of these proteins was almost completely abolished, suggesting convergence of PARP and mTOR in downregulation of DNA damage repair components.In conclusion, our results suggest that combining mTOR and DNA repair inhibition could be a successful strategy to treat a subset of breast cancer with BRCA2 mutation and alterations in the PI3K/AKT/mTOR pathway.

Highlights

Current treatment options for breast cancer are moving toward potent targeted therapies in general well tolerated and that can be tailored to an individual patient’s tumor
To test whether the combination of DNA repair and mTOR inhibitors could be a relevant therapeutic strategy in tumors with genomic alterations in DNA repair and PI3K/AKT/mTOR pathway, we treat a patient-derived xenografts (PDX) model established from a BRCA2 mutated breast cancer (HBCx22 TamR) with the Parp inhibitor olaparib combined to the mTOR inhibitor everolimus
This PDX model has been established from an ER+ primary breast cancer [12] and has been rendered resistant to tamoxifen in mice, through long-term in vivo treatment and re-engraftment of xenograft that showed acquired resistance to tamoxifen, as previously described [13]

Summary

Introduction

Current treatment options for breast cancer are moving toward potent targeted therapies in general well tolerated and that can be tailored to an individual patient’s tumor. Among them are tyrosine kinase inhibitors directed at a number of targets (HER1, HER2, HER3, IGF receptor [IGFR], C-MET, FGF receptor [FGFR]), inhibitors of intracellular signaling pathways (PI3K, AKT, mammalian target of rapamycin [mTOR]), angiogenesis inhibitors and agents that interfere with DNA repair [5]. Some of these agents have shown remarkable activity and have become part of the standard of care in patients with breast cancer (exemplified by the anti-HER2 agents trastuzumab and lapatinib). Others have been recently approved for the treatment of specific breast cancer subtypes, such as the mTOR inhibitor everolimus in advanced luminal breast cancer and the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib in metastatic breast cancer with germline BRCA1 or BRCA2 mutations [6,7,8,9]

Methods

Results

Conclusion