BRCA1-methylated triple negative breast cancers previously exposed to neoadjuvant chemotherapy form RAD51 foci and respond poorly to olaparib

Carolina Velazquez; Esin Orhan; Imene Tabet; Lise Fenou; Béatrice Orsetti; José Adélaïde; Arnaud Guille; Simon Thézénas; Evelyne Crapez; Pierre-Emmanuel Colombo; Max Chaffanet; Daniel Birnbaum; Claude Sardet; William Jacot; Charles Theillet

doi:10.3389/fonc.2023.1125021

BRCA1-methylated triple negative breast cancers previously exposed to neoadjuvant chemotherapy form RAD51 foci and respond poorly to olaparib

Front Oncol. 2023 Mar 17:13:1125021. doi: 10.3389/fonc.2023.1125021. eCollection 2023.

Authors

Carolina Velazquez¹, Esin Orhan¹, Imene Tabet¹, Lise Fenou¹, Béatrice Orsetti¹, José Adélaïde², Arnaud Guille², Simon Thézénas³, Evelyne Crapez⁴, Pierre-Emmanuel Colombo^{1

5}, Max Chaffanet², Daniel Birnbaum², Claude Sardet¹, William Jacot^{1

6}, Charles Theillet¹

Affiliations

¹ Institut de Recherche en Cancérologie de Montpellier, IRCM U1194, Montpellier University, INSERM, ICM, CNRS, Montpellier, France.
² Centre de Recherche en Cancérologie de Marseille, CRCM UMR1068, Aix-Marseille University, IPC, CNRS, Marseille, France.
³ Biometry Unit, Institut du Cancer de Montpellier, Montpellier, France.
⁴ Unité de Recherche Translationnelle, Institut du Cancer de Montpellier, Montpellier, France.
⁵ Oncological Surgery, Institut du Cancer de Montpellier, Montpellier, France.
⁶ Clinical Oncology, Institut du Cancer de Montpellier, Montpellier, France.

Abstract

Background: About 15% of Triple-Negative-Breast-Cancer (TNBC) present silencing of the BRCA1 promoter methylation and are assumed to be Homologous Recombination Deficient (HRD). BRCA1-methylated (BRCA1-Me) TNBC could, thus, be eligible to treatment based on PARP-inhibitors or Platinum salts. However, their actual HRD status is discussed, as these tumors are suspected to develop resistance after chemotherapy exposure.

Methods: We interrogated the sensitivity to olaparib vs. carboplatin of 8 TNBC Patient-Derived Xenografts (PDX) models. Four PDX corresponded to BRCA1-Me, of which 3 were previously exposed to NeoAdjuvant-Chemotherapy (NACT). The remaining PDX models corresponded to two BRCA1-mutated (BRCA1-Mut) and two BRCA1-wild type PDX that were respectively included as positive and negative controls. The HRD status of our PDX models was assessed using both genomic signatures and the functional BRCA1 and RAD51 nuclear foci formation assay. To assess HR restoration associated with olaparib resistance, we studied pairs of BRCA1 deficient cell lines and their resistant subclones.

Results: The 3 BRCA1-Me PDX that had been exposed to NACT responded poorly to olaparib, likewise BRCA1-WT PDX. Contrastingly, 3 treatment-naïve BRCA1-deficient PDX (1 BRCA1-Me and 2 BRCA1-mutated) responded to olaparib. Noticeably, the three olaparib-responsive PDX scored negative for BRCA1- and RAD51-foci, whereas all non-responsive PDX models, including the 3 NACT-exposed BRCA1-Me PDX, scored positive for RAD51-foci. This suggested HRD in olaparib responsive PDX, while non-responsive models were HR proficient. These results were consistent with observations in cell lines showing a significant increase of RAD51-foci in olaparib-resistant subclones compared with sensitive parental cells, suggesting HR restoration in these models.

Conclusion: Our results thus support the notion that the actual HRD status of BRCA1-Me TNBC, especially if previously exposed to chemotherapy, may be questioned and should be verified using the BRCA1- and RAD51-foci assay.

Keywords: BRCA1 methylation; HRD (homologous recombination deficiency); RAD51; TNBC; nuclear foci.

Grants and funding

The authors declare that this study received funding from Astra-zeneca (contract # 2018-02069). The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article, or the decision to submit it for publication. This work also benefited from the following financial support: Institut National du Cancer PRTK-2017 MODUREPOIS, Ligue Nationale Contre le Cancer ‘Comité régional Occitanie-Est’ 2021-R22031FF and the SIRIC Montpellier Cancer Grant INCa-DGOS-Inserm_12553.