Therapeutics, Targets, and Chemical Biology Polo-like Kinase 1: A Potential Therapeutic Option in Combination with Conventional Chemotherapy for the Management of Patients with Triple-Negative Breast Cancer Virginie Maire 1,3,4 , Fariba N emati 1,3,5 , Marion Richardson 1,3,4,6 , Anne Vincent-Salomon 1,6,7 , Bruno Tesson 1,3,4,8,9 , Guillem Rigaill 1,2,3,4,8,9 , El eonore Gravier 1,3,8,9,10 ,B ereng ere Marty-Prouvost 1,3,4 , Leanne De Koning 1,3,4,12 , Guillaume Lang 1,3,5 , David Gentien 1,3,13 , Aur elie Dumont 1,3,4 , Emmanuel Barillot 1,8,9 , Elisabetta Marangoni 1,3,5 , Didier Decaudin 1,3,5,11 , Sergio Roman-Roman 1,3 , Alain Pierr e 14 , Francisco Cruzalegui 14 , St ephane Depil 14 , Gordon C. Tucker 14 , and Thierry Dubois 1,3,4 Abstract Breast cancers are composed of molecularly distinct subtypes with different clinical outcomes and responses to therapy. To discover potential therapeutic targets for the poor prognosis-associated triple-negative breast cancer (TNBC), gene expression profiling was carried out on a cohort of 130 breast cancer samples. Polo-like kinase 1 (PLK1) was found to be significantly overexpressed in TNBC compared with the other breast cancer subtypes. High PLK1 expression was confirmed by reverse phase protein and tissue microarrays. In triple-negative cell lines, RNAi-mediated PLK1 depletion or inhibition of PLK1 activity with a small molecule (BI-2536) induced an increase in phosphorylated H2AX, G 2 –M arrest, and apoptosis. A soft-agar colony assay showed that PLK1 silencing impaired clonogenic potential of TNBC cell lines. When cells were grown in extracellular matrix gels (Matrigel), and exposed to BI-2536, apoptosis was observed specifically in TNBC cancerous cells, and not in a normal cell line. When administrated as a single agent, the PLK1 inhibitor significantly impaired tumor growth in vivo in two xenografts models established from biopsies of patients with TNBC. Most importantly, the administration of BI-2536, in combination with doxorubicin þ cyclophosphamide chemotherapy, led to a faster complete response compared with the chemotherapy treatment alone and prevented relapse, which is the major risk associated with TNBC. Altogether, our observations suggest PLK1 inhibition as an attractive therapeutic approach, in association with conventional chemotherapy, for the management of patients with TNBC. Cancer Res; 73(2); 813–23. Ó2012 AACR. Introduction Breast cancer is a heterogeneous disease with different subgroups characterized by specific clinical outcomes and responses to therapy (1). Triple-negative breast cancers (TNBC) are characterized by a lack of expression of estrogen and progesterone receptors (ER/PR) and a lack of HER2 over- expression (2). TNBCs account for 15% of breast cancers and are associated with African-American ethnicity, younger age, and poorer outcome when compared with the other breast can- cer subtypes: luminal A (LA), luminal B (LB), and HER2þ/ER (HER2; ref. 2). TNBC show a high rate of TP53 mutation (3), are associated with a "BRCAness" phenotype (4), and are highly proliferative, genetically unstable, poorly differentiated, and often grade 3 carcinomas (5). In contrast to HER2 and luminal carcinomas, which can be treated with targeted therapy such as anti-HER2 monoclonal antibodies or hormonal therapies, respectively, there is no available targeted therapy for patients with TNBC who are managed exclusively with conventional chemotherapy. Although they show high rates of objective initial response, the majority of patients do not display a complete response and have a poorer prognosis than those within other breast tumor subgroups due to high rates of recurrence (6). Because of this unfavorable prognosis and the lack of targeted therapy, there is currently an intensive search for identifying therapeutic targets for TNBC (7). Polo-like kinase 1 (PLK1) is the best-characterized member of the human PLK family (PLK1-5) of serine/threonine protein kinases, which is involved in various functions such as mitotic entry, spindle assembly, and DNA damage response (8). In Authors' Affiliations: 1 Institut Curie, Centre de Recherche; 2 AgroParis- Tech/INRA UMR MIA 518, Paris; 3 Translational Research Department; 4 Breast Cancer Biology Group; 5 Laboratory of Preclinical Investigation; 6 Tumor Biology Department, Institut Curie Hospital; 7 INSERM U830; 8 INSERM U900; 9 Mines ParisTech, Fontainebleau; 10 Departments of Bio- statistics and 11 Medical Oncology; 12 Reverse Phase Protein Array Plat- form; 13 Platform of Molecular Biology Facilities; and 14 Oncology Research and Development Unit, Institut de Recherches SERVIER, Croissy-sur- Seine, France Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Author: Thierry Dubois, D epartement de Recherche Translationnelle, Equipe "Biologie du Cancer du Sein", Centre de Recherche, Institut Curie, 26 rue d'Ulm, Paris 75248, France. Phone: 0033-0153-197416; Fax: 0033-0153-194130; E-mail: thierry.dubois@curie.fr doi: 10.1158/0008-5472.CAN-12-2633 Ó2012 American Association for Cancer Research. Cancer Research www.aacrjournals.org 813 Downloaded from http://aacrjournals.org/cancerres/article-pdf/73/2/813/2695699/813.pdf by guest on 30 January 2023