Sylvie Maubant

Transcriptome analysis of Wnt3a-treated triple-negative breast cancer cells.

The canonical Wnt/β-catenin pathway is activated in triple-negative breast cancer (TNBC). The activation of this pathway leads to the expression of specific target genes depending on the cell/tissue context. Here, we analyzed the transcriptome of two different TNBC cell lines to define a comprehensive list of Wnt target genes. The treatment of cells with Wnt3a for 6h up-regulated the expression (fold change > 1.3) of 59 genes in MDA-MB-468 cells and 241 genes in HCC38 cells. Thirty genes were common to both cell lines. Beta-catenin may also be a transcriptional repressor and we found that 18 and 166 genes were down-regulated in response to Wnt3a treatment for 6h in MDA-MB-468 and HCC38 cells, respectively, of which six were common to both cell lines. Only half of the activated and the repressed transcripts have been previously described as Wnt target genes. Therefore, our study reveals 137 novel genes that may be positively regulated by Wnt3a and 104 novel genes that may be negatively regulated by Wnt3a. These genes are involved in the Wnt pathway itself, and also in TGFβ, p53 and Hedgehog pathways. Thorough characterization of these novel potential Wnt target genes may reveal new regulators of the canonical Wnt pathway. The comparison of our list of Wnt target genes with those published in other cellular contexts confirms the notion that Wnt target genes are tissue-, cell line- and treatment-specific. Genes up-regulated in Wnt3a-stimulated cell lines were more strongly expressed in TNBC than in luminal A breast cancer samples. These genes were also overexpressed, but to a much lesser extent, in HER2+ and luminal B tumors. We identified 72 Wnt target genes higher expressed in TNBCs (17 with a fold change >1.3) which may reflect the chronic activation of the canonical Wnt pathway that occurs in TNBC tumors.

Abstract 2764: The depletion of LRP5, unlike that of LRP6, promotes apoptosis in triple-negative breast cancer cells, making it an interesting therapeutic target

Treatment of patients with triple-negative breast cancers (TNBCs) remains a major challenge for oncologists and alternative treatments to conventional chemotherapies are needed to improve their survival. The Wnt/beta-catenin signaling, recently reported to be activated in TNBCs, may represent an interesting pathway to target. We report that both LRP5 and LRP6 Wnt coreceptors are more strongly expressed in TNBCs than in other breast tumor subtypes. As very few studies have explored potential differences between LRP5 and LRP6, we investigated the effects of modulating specifically LRP5 or LRP6 expression on Wnt signaling, cell viability and tumorigenesis in HCC38 and MDA-MB-468 TNBC cells. We found that these two cell lines are more similar to TNBC biopsy specimens in terms of Wnt pathway gene expression profiles than any other tested cell line. Unlike LRP5, LRP6 was involved in activating the canonical Wnt pathway in response to Wnt3a. LRP5 knockdown induced caspase-dependent apoptosis, whereas LRP6 knockdown had no such effect. Importantly, LRP5-depleted cells were more sensitive to conventional chemotherapy than cells depleted of LRP6. The knockdown of LRP5 or LRP6 decreased tumorigenesis both in vitro and in vivo. Overall, these data suggest that the LRP5 and LRP6 coreceptors have different functions in TNBCs, with LRP5 playing a preponderant role in survival control. Our data suggest that both LRP5 and LRP6 are potential treatment targets in TNBCs, but that LRP5 may be the most useful target, given the impact of its depletion on cell survival as well as on the response to anti-cancer drugs. Citation Format: Sylvie Maubant, Virginie Maire, Bruno Tesson, Fariba Nemati, David Gentien, Berengere Marty-Prouvost, Stephane Depil, Francisco Cruzalegui, Gordon Tucker, Sergio Roman-Roman, Thierry Dubois. The depletion of LRP5, unlike that of LRP6, promotes apoptosis in triple-negative breast cancer cells, making it an interesting therapeutic target. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2764. doi:10.1158/1538-7445.AM2014-2764

Abstract B233: The depletion of LRP5, unlike that of LRP6, promotes apoptosis in triple-negative breast cancer cells, making it an interesting therapeutic target.

Introduction. Treatment of patients with triple-negative breast cancers (TNBCs) remains a major challenge for oncologists. Although they respond well to the current therapeutic strategies based on conventional chemotherapies, they represent a large proportion of breast cancer death due to a high recurrence rate. Alternative treatments are needed to improve survival of these patients. The Wnt/beta-catenin signaling, recently reported to be activated in TNBCs, may represent an interesting pathway to target. Methods. We analyzed mRNA, DNA and protein levels for the LRP5 and LRP6 Wnt coreceptors in our cohort of breast tumor biopsy specimens. We then identified which TNBC cell lines display the most similarity to TNBC tumors regarding the Wnt pathway status using a centroid approach. We investigated the effects of modulating LRP5 or LRP6 expression on Wnt signaling, cell viability and apoptosis. We evaluated the potential therapeutic value of targeting LRP5 and LRP6 in TNBCs, by performing depletion experiments and treating cells with a mixture of doxorubicin/cyclophosphamide. We also examined whether the depletion of LRP5 or LRP6 had an impact on tumorigenicicy in vitro, in soft-agar assays, and in vivo, in xenograft models. Results. Gene expression analyses revealed that both LRP5 and LRP6 Wnt coreceptors were more strongly expressed in TNBCs than in other breast tumor subtypes. HCC38 and MDA-MB-468 TNBC cells were more similar to TNBC biopsy specimens in terms of Wnt pathway gene expression profiles than any other tested cell line. Unlike LRP5, LRP6 was involved in activating the canonical Wnt pathway in response to Wnt3a. LRP5 knockdown induced caspase-dependent apoptosis, whereas LRP6 knockdown had no such effect. LRP5-depleted cells were also more sensitive to conventional chemotherapy than cells depleted of LRP6. The knockdown of LRP5 or LRP6 decreased tumorigenesis both in vitro and in vivo. Conclusions. These data indicate that the LRP5 and LRP6 have different functions in TNBCs, with LRP5 playing a preponderant role in survival control. Our data suggest that both coreceptors are potential treatment targets in TNBCs, but that LRP5 may be the most useful target, given the impact of its depletion on cell survival and the response to anti-cancer drugs. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B233. Citation Format: Sylvie Maubant, Virginie Maire, Bruno Tesson, Fariba Nemati, Aurelie Dumont, David Gentien, Berengere Marty-Prouvost, Guillem Rigaill, Leanne De Koning, Anne Vincent-Salomon, Emmanuel Barillot, Didier Decaudin, Alain Pierre, Stephane Depil, Francisco Cruzalegui, Gordon C. Tucker, Sergio Roman-Roman, Thierry Dubois. The depletion of LRP5, unlike that of LRP6, promotes apoptosis in triple-negative breast cancer cells, making it an interesting therapeutic target. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B233.

LRP5 regulates the expression of STK40, a new potential target in triple-negative breast cancers

Triple-negative breast cancers (TNBCs) account for a large proportion of breast cancer deaths, due to the high rate of recurrence from residual, resistant tumor cells. New treatments are needed, to bypass chemoresistance and improve survival. The WNT pathway, which is activated in TNBCs, has been identified as an attractive pathway for treatment targeting. We analyzed expression of the WNT coreceptors LRP5 and LRP6 in human breast cancer samples. As previously described, LRP6 was overexpressed in TNBCs. However, we also showed, for the first time, that LRP5 was overexpressed in TNBCs too. The knockdown of LRP5 or LRP6 decreased tumorigenesis in vitro and in vivo, identifying both receptors as potential treatment targets in TNBC. The apoptotic effect of LRP5 knockdown was more robust than that of LRP6 depletion. We analyzed and compared the transcriptomes of cells depleted of LRP5 or LRP6, to identify genes specifically deregulated by LRP5 potentially implicated in cell death. We identified serine/threonine kinase 40 (STK40) as one of two genes specifically downregulated soon after LRP5 depletion. STK40 was found to be overexpressed in TNBCs, relative to other breast cancer subtypes, and in various other tumor types. STK40 depletion decreased cell viability and colony formation, and induced the apoptosis of TNBC cells. In addition, STK40 knockdown impaired growth in an anchorage-independent manner in vitro and slowed tumor growth in vivo. These findings identify the largely uncharacterized putative protein kinase STK40 as a novel candidate treatment target for TNBC.

Abstract 2669: Antitumor activity of the CMP-001 (TLR9 agonist) alone or combined with immune modulators in syngeneic tumor models

Targeted blockade of checkpoint inhibitors such as CTLA-4 or PD-1 with antagonist monoclonal antibodies (mAbs) has shown impressive and durable clinical responses in patients with advanced cancer. An alternative strategy to boost anti-tumor immunity is to promote T cell activation through co-stimulatory receptors such as OX40 and 4-1BB. OX40 is of particular interest as treatment with an activating anti-OX40 mAb augments T cell differentiation and cytolytic function leading to enhanced anti-tumor immunity. However, each of these agents benefits only a subset of patients, highlighting the critical need for more effective combinatorial therapeutic strategies. Toll-like receptor 9 (TLR9) agonist CpG oligodeoxynucleotides (ODN) are candidates to promote an anti-tumor immune response. CMP-001, a CpG-A ODN formulated within a virus-like particle, is designed to activate TLR9 (the receptor for CpG-A) in tumor-associated plasmacytoid dendritic cells (pDC) within the tumor or tumor-draining lymph nodes. Resting or immature pDC promote tumor growth, but when activated by CpG-A, the resulting mature pDC promote a robust anti-tumor immune response. Activation of pDC causes secretion of very large quantities of type I interferons, increased expression of costimulatory molecules, and recruitment and activation of other DC subsets to enhance tumor antigen presentation to T cells, culminating in the generation of effective anti-tumor T cell responses. The preclinical efficacy of intratumorally administered CMP-001 alone or in combination with an intraperitoneally administered PD-1 antagonist and/or an OX40 agonist was examined and assessed in a variety of syngeneic tumor models: CT-26 colon tumor model, MBT-2 bladder tumor model, RenCa kidney tumor model, 4T1 breast tumor model and LLC-1 lung tumor model. Tumors were implanted into left and right flanks while only one tumor was injected with CMP-001. In addition to body weight and overall survival, tumor volume was monitored on both flanks to assess direct and abscopal/systemic anti-tumor activity. Some discrepancies were observed between evaluated syngeneic tumor models with non-responders (LLC-1, 4T1) and responders (CT-26, MBT-2, RenCa). The most efficacious results were registered in the CT-26 model. Each therapeutic yielded weak activity as a single agent, which improved when combined with another treatment modality. The best therapeutic efficacy was obtained with the combination of all three agents resulting in cures of both treated and untreated CT-26 tumors in 40% of the mice. The median survival time was increased for these animals compared to those treated with only vehicle or one or two immune modulators (50 vs 18 vs 21 or 23-28 days, respectively). Similar results were generated in the MBT-2 model (and to a less extent in RenCa model) though no complete response was recorded. These data support the clinical investigation of these combinations in cancer patients Citation Format: Francis Bichat, Sylvie Maubant, Jean-Francois Mirjolet, Philippe Slos, Arthur M. Krieg, Aaron Morris. Antitumor activity of the CMP-001 (TLR9 agonist) alone or combined with immune modulators in syngeneic tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2669. doi:10.1158/1538-7445.AM2017-2669

Abstract 328: Antitumor activity of the oncolytic peptide LTX-315 in syngeneic tumor models

Cationic antimicrobial peptides (CAPs) are naturally occurring molecules found in a number of species as a defense mechanism for eukaryotic cells against pathogens and are an integral part of the innate immune system. CAPs have a broad spectrum of activities including antimicrobial and anticancer while being less cytotoxic toward non-malignant cells. The potential therapeutic application against cancer has spawned an interest in developing oncolytic agents that display a new mode of action to overcome the potential drug resistance associated with other current therapeutics. The anticancer effects of CAPs are still under investigation, but several peptides have already exhibited a promising potential with cytotoxic activities against a broad spectrum of tumor cells. Oncolytic peptides exert their activity through either a membranolytic mode of action or an interaction with intracellular targets, or a combination of both. LTX-315 (K-K-W-W-K-K-W-Dip-K-NH2), a novel oncolytic peptide developed by Lytix Biopharma AS has the potential to adopt an amphipathic helical coil structure. In vitro studies have demonstrated that it was highly effective against both drug-resistant and drug-sensitive cancer cells from several organ origins, with lower toxicity toward normal cells. LTX-315 was designed for intratumoral treatment of transdermal lesions. Previously, LTX-315 has been shown to induce complete regression of B16 melanomas and long lasting antitumor immune responses. Histological analyses of treated tumors revealed extensive hemorrhagic necrosis and infiltration of CD3+ T cells. Moreover, mRNA levels of inflammatory cytokines such as IL1β, IL6 and IL18 were found to be increased in the tumor tissue after LTX-315 treatment. The treatment did also prevent lung metastasis in mice re-challenged with B16F1 cells intravenously. Due to its oncolytic mode of action, LTX-315 induces immunogenic cell death through the release of danger-associated molecular pattern molecules and tumor antigens. Recently, we have demonstrated that when subcutaneously established EMT-6 tumors (inoculated into both flanks of the animal) were treated intratumorally with LTX-315, an antitumor response was observed with a T/C ratio of 17% 19 days post start of treatment. Furthermore, an abscopal effect of LTX-315 on the untreated tumor was also reported but only when it was combined with anti-PD-L1 antibody. At the end of study, 50% of mice that had received the combination therapy were still alive vs 30% and 40% in the groups treated with LTX-315 or anti-PD-L1 antibody alone, respectively. In conclusion, LTX-315 seems to be an ideal combinations partner for immune checkpoint inhibitors. Citation Format: Ketil Andre Camilio, Baldur Sveinbjornsson, Sylvie Maubant, Guillaume Serin, Jean-Francois Mirjolet, Francis Bichat, Oystein Rekdal. Antitumor activity of the oncolytic peptide LTX-315 in syngeneic tumor models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 328.

Abstract B93: Tumor infiltrating lymphocytes as a biomarker of response for CTLA-4 targeting therapies

Immunotherapy based on monoclonal antibodies (mAbs) targeting cancer cells is now developed as a valid approach to treat cancer. Suppressive mechanisms in immune responses normally play a critical role in maintaining immune homeostasis. However, these suppressive mechanisms are also considered as one of the main reasons for the failure of cancer immunotherapies because they induce peripheral tolerance of tumor-specific immune responses and allow tumor growth. Regulatory T cells have been revealed as the most important population of immune suppressors, and their depletion has been reported to enhance antitumor immune responses. CTLA-4 was reported as a critical target for regulatory T cell function and thus blockade of CTLA 4 mediated signals has been suggested as a possible strategy to treat cancers. The first anti-CTLA-4 human mAb, ipilimumab, was approved in 2011 by the FDA for use in metastatic melanoma. Success for ipilimumab was reported in a large phase III clinical trial involving patients with metastatic melanoma, who had undergone previous failed treatment. Mice obtained from Charles River (France) were orthotopically or subcutaneously injected with syngenic tumor cell lines. They received repeated intraperitoneal injections of antibody directed against CTLA-4. During the course of the experiment, animals were terminated under anesthesia when they displayed significant signs of physiological changes. Animal housing and experimental procedures were performed according to the French and European Regulations and NRC Guide for the Care and Use of Laboratory Animals. Animal facility is authorized by the French authorities (Agreement N°B21231011EA). The tumor and tumor draining lymph nodes were collected for subsequent FACS analysis to study the immune response in mice. Cells suspensions were prepared from tissues either by mechanistic dissociation or by enzymatic digestion. The antigens associated antibodies used for FACS analyses were CD45, CD3 and CD8 for effector T cell lymphocytes, and were CD45, CD3, CD4, FoxP3 and CD25 for regulatory T cell lymphocytes. The stained cells were analyzed with a LSR II flow cytometer (BD Biosciences) equipped with 3 excitation lasers at wavelengths 405, 488 and 633nm. In CT26 and EMT6 models, an increase in T effector vs T regulator infiltrating immune cells ratio was observed for responding mice treated with CTLA-4 mAb. In 4T1 model, no ratio change was observed for mice treated with CTLA-4 mAb. Pending new generation of humanized mouse models, the growing interest in immunology as a cancer therapy shows the limitation of conventional xenograft models in immunodeficient animals. A more effective approach is the use of syngeneic mouse models. We here report on syngenic tumor models our capacity to identify biomarkers of response to CTLA-4 targeting therapies using detailed analysis of tumor immune infiltrating cells. Citation Format: MARC HILLAIRET DE BOISFERON, FRANCIS BICHAT, CAROLINE MIGNARD, XAVIER TIZON, DAMIEN FRANCE, SYLVIE MAUBANT, Jean-Francois Mirjolet. Tumor infiltrating lymphocytes as a biomarker of response for CTLA-4 targeting therapies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B93.

Abstract B94: Efficacy of PD-1 - PD-L1 pathway disruptors in syngeneic models

Immune checkpoint modulators, such as antibodies targeting CTLA-4 or PD-1, are now being approved for treatment of patients with unresectable or metastatic melanoma and advanced squamous non-small cell lung cancer (NSCLC) who have progressed on or after platinum-based chemotherapy. Efficacy was also evidenced on other tumor types (renal cell carcinoma, bladder, Hodgkin lymphoma, colorectal carcinoma (CRC) ⋯). However, there is still needs to identify predictive biomarkers of response in order to select patients who will benefit from treatments. PD-L1 expression was proposed to be a good candidate for NSCLC, even if PD-L1 expression is a difficult parameter due to its expression on both tumor cells and immune cells as well as technical challenges to use immunohistochemical detection. The dynamic of the immune system as well as the site and time where interactions between tumor cells and immune cells take place, increase the complexity of having a solid biomarker identified. In addition, for other pathologies like colorectal carcinoma, genomic biomarkers were evidenced. For example, CRC patients with mismatch repair (MMR) deficiencies have an objective response rate of 62% compared with 0% in patients with MMR-proficient tumors. We propose here the use of syngeneic models to address mechanism of action and biomarker related questions for agent targeting PD-1 / PD-L1 axis. Syngeneic model systems remain one of the only options to analyse physiologically relevant interactions between tumor and immune cells. Up to now, eight models were characterized for response to either PD-1 and/or PD-L1 targeting antibodies. Among them, 4T1, LLC and Renca were identified as non-responders and B16-F10, CT-26, EMT-6, MBT-2 identified as partial responders. Most of the time, targeting PD-1 is more effective than targeting PD-L1, even if there is exception (e.g. B16-F10). Attempting to identify key parameters that could help us understand efficacy of PD-1 /PD-L1 axis disruptors, intratumoral immune infiltrate was analyzed in depth using flow cytometry: regulatory T cells (Treg), effector T cells (Teff), M-MDSCs, G-MDSCs, TAMs were phenotyped and quantified. In contrast to CTLA-4 targeting therapy, where Teff/Treg ratio was correlated to treatment efficacy, this is not the case for PD-1 or PD-L1 targeting therapies. It is now hypothesized that a more complex signature (e.g. detailed phenotype of CD8 positive T cells, tumor neoantigen expression⋯) will be needed to identify valuable biomarkers of response. Preliminary results using syngeneic models, both subcutaneously or orthotopically engrafted with tumors, will be presented. Citation Format: MARC HILLAIRET DE BOISFERON, Francis Bichat, CAROLINE MIGNARD, XAVIER TIZON, DAMIEN FRANCE, SYLVIE MAUBANT, Jean-Francois Mirjolet. Efficacy of PD-1 - PD-L1 pathway disruptors in syngeneic models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B94.

Abstract 41: The Wnt3a targetome in triple-negative breast cancer cell lines

The canonical Wnt/beta-catenin pathway has been shown to be activated in triple-negative breast cancer (TNBC). The activation of this pathway leads to the expression of specific target genes depending on the cell/tissue context. Here, we analyzed the transcriptome of two different TNBC cell lines to define a comprehensive list of Wnt target genes. The treatment of cells with Wnt3a for 6h up-regulated the expression (fold change > 1.3) of 59 genes in MDA-MB-468 cells and 241 genes in HCC38 cells. Thirty genes were common to both cell lines. Beta-catenin may also be a transcriptional repressor and we found that 18 and 166 genes were down-regulated in response to Wnt3a treatment for 6h in MDA-MB-468 and HCC38 cells, respectively, of which six were common to both cell lines. Only half of the activated and the repressed transcripts have been previously described as Wnt target genes. Therefore, our study reveals 137 novel genes that may be positively regulated by Wnt3a and 104 novel genes that may be negatively regulated by Wnt3a. These genes are involved in the Wnt pathway itself, and also in TGF-beta, p53 and Hedgehog pathways. Thorough characterization of these novel potential Wnt target genes may reveal new regulators of the canonical Wnt pathway. The comparison of our list of Wnt target genes with those published in other cellular contexts confirms the notion that Wnt target genes are tissue-, cell line- and treatment-specific. Genes up-regulated in Wnt3a-stimulated cell lines were more strongly expressed in TNBC than in luminal A breast cancer samples. These genes were also overexpressed, but to a much lesser extent, in HER2+ and luminal B tumors. We identified 72 Wnt target genes higher expressed in TNBCs (17 with a fold change >1.3) which may reflect the chronic activation of the canonical Wnt pathway that occurs in TNBC tumors. Citation Format: Sylvie Maubant, Bruno Tesson, Virginie Maire, Mengliang Ye, Guillem Rigaill, David Gentien, Francisco Cruzalegui, Gordon C. Tucker, Sergio Roman-Roman, Thierry Dubois. The Wnt3a targetome in triple-negative breast cancer cell lines. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 41. doi:10.1158/1538-7445.AM2015-41

Abstract 4373: LRP5: a potential therapeutic target in triple-negative breast cancer.

Background: Triple-negative breast cancer (TNBC) is associated with poor prognosis, only partial response to chemotherapy and lack of clinically established targeted therapies [1]. A deregulation of the Wnt signaling pathway has been described in breast cancers, particularly in TNBC [2–6]. Low-density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6) serve as Wnt co-receptors for the canonical beta-catenin pathway. An overexpression of LRP6 has been reported to enhance Wnt signaling favoring in vitro cell proliferation and in vivo mammary gland hyperplasia and tumor growth [5,7,8]. LRP6 has been claimed to be a potential TNBC therapeutic target [5]. Material and Methods: RNA microarray analysis and reverse phase protein array were performed on 154 samples including biopsies of the various subclasses of breast cancer. MDA-MB-468 and HCC38 cell lines were defined as the most representative in vitro models of the Wnt pathway status found in TNBC biopsies. In order to study the functions of LRP5 or LRP6 in TNBC, we examined in these cell lines the effects of their depletions using RNAi technology on tumorigenesis and on the Wnt3a-induced signaling pathway. Results: Our transcriptomic and proteomic data revealed that both LRP5 and LRP6 are overexpressed in TNBC compared to the other breast cancer subtypes i.e. HER2+/ER-, luminal A and luminal B. Our in vitro studies indicated that the transcriptional activity of beta-catenin/Tcf was strongly reduced when LRP6 was silenced and to a lesser extend when LRP5 was depleted. In accordance with these results, the expression of AXIN2 and other newly identified Wnt target genes, was mainly down-regulated in cells silenced for LRP6. LRP5 and LRP6 knockdown impaired colony formation in soft agar and weakly decreased the number of mammospheres. The inhibition of cell viability observed after LRP5 depletion was the consequence of a programmed cell death as revealed by the increase of annexin V-positive cells, the activation of initiator and effector caspases (8,9,3/7) and the cleavage of poly(ADP-ribose) polymerase. On the contrary, LRP6 depletion inhibited cell viability without promoting apoptosis as reported by others [5]. Conclusions: Altogether our data demonstrate that in TNBC cell lines, LRP5 or LRP6 silencing has an impact on Wnt signaling, cancer stem cell-like activity, tumorigenic properties and cell viability. Most importantly, LRP5 silencing promotes apoptosis, suggesting that LRP5 could represent a promising therapeutic candidate to target in TNBC. Citation Format: Sylvie Maubant, Virginie Maire, Bruno Tesson, David Gentien, Berengere Marty-Prouvost, Francisco Cruzalegui, Stephane Depil, Gordon C. Tucker, Sergio Roman-Roman, Thierry Dubois. LRP5: a potential therapeutic target in triple-negative breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4373. doi:10.1158/1538-7445.AM2013-4373