Abstract P5-06-02: Ex vivo CSC assays for personalized testing of drug susceptibility in advanced breast cancer

In the developing area of personalized medicine, targeted therapies are mainly based on genomic characterization of each tumor, and is currently proposed as promising strategies for advanced breast cancer (ABC). Despite the promises of advanced genome sequencing, many patients still fail therapy, resulting in disease progression, recurrence, and metastases. Cancer stem cells (CSCs) concept illustrates the non-genetic intrinsic resistance, recapitulates tumor heterogeneity that creates hierarchically organized tumor tissues where a subpopulation of self-renewing cancer stem cells (CSCs) sustains the long- term clonal maintenance of the neoplasm. Evidences indicate that CSCs survive many commonly employed cancer therapeutics. Patient-derived tumor xenograft (PDXs) models recapitulate tumor complexity and heterogeneity at cellular and molecular level.

We aimed to specifically address the therapeutic sensitivity in ABC, by using an ex vivo assay based on PDX prospective collection, fully characterized for genomic alterations.

In this work, we aim at defining for each tumor the best therapy to target breast cancer intratumor heterogeneity, the CSC component. For that, we defined a panel of 44 FDA-approved compounds used for cancer treatment, including breast and other types of cancer, cancer stem cell drugs, chemo or targeted therapies. For each drug, we screened the differential sensitivity of the bulk tumor cells and the CSC components for 12 PDX models using an ex vivo screening approach on short term culture. To assess intra tumor heterogeneity, we set up an original dual strategy: for the bulk cells, an ex vivo assay based on IC50, and for breast CSC component a miniaturized Aldefluor assay. First, we demonstrate that bulk cells and CSCs sensitivity may be dissociated for the same drug in the same PDX models. Then, we observed that whereas bulk cell sensitivity may be correlated to tumor genomic abnormalities, CSC drug sensitivity seems not to follow the rule.CSC are selectively sensitive to specific compounds. We are exploring the pathways that sustain this selective sensitivity in the CSCs components. We are currently identifying targets using mass spectrometry in CSCs and bulk cells.Then, we validated the hits predicted from ex vivo screening assays by in vivo treatment of using PDX models for the selected drugs, and in a patient with ABC.

In that work, we demonstrated that CSCs display different sensitivity profiles than bulk cells to the same agents, irrespective to their genomic background and are identifying the CSC specific targets. Here, we propose a new model of precision medicine based on ex vivo CSC assays for personalized testing of drug susceptibility in advanced breast cancer.

Citation Format: Charafe-Jauffret E, Wicinski J, Cabaud O, Lopez M, Audebert S, Adelaide J, Chaffanet M, Guille A, Goncalves A, Bertucci F, Birnbaum D, Ginestier C. Ex vivo CSC assays for personalized testing of drug susceptibility in advanced breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-06-02.

Abstract P5-03-01: Cancer stem cells predict engraftment and poor prognosis of primary breast tumors

Breast cancer is a major health problem and heterogeneity of the disease has been considered as a strong limitation to find the best therapies to cure cancer, overcome recurrences and metastases. The establishment of models that reflect tumor biology and metastatic progression is critical to develop successful new therapeutic strategies. In the breast, orthotopic xenografts currently appear as the best models to study tumor growth, metastasis and develop tools for prognosis prediction. Furthermore, mouse transplant assays have been used to assess cancer stem cell (CSC) activity and demonstrate that leukemia and many solid tumors are organized along a hierarchical model.

Despite the promise of the CSC model sustained by mouse transplantation assays, the clinical relevance of xenografts studies to identify determinants of stemness able to influence clinical outcome remains challenging. In breast cancer, transcriptional programs from functionally validated CSC populations remain to be deciphered.

Here, we report the establishment of a bank of primary breast tumor-derived xenografts (xenobank). We showed that the xenografts retain the main features of primary tumors, that engraftment is correlated with the presence of CSC in tumors, and that engraftment in the mouse is able to predict prognosis in patients. This suggests that CSCs may govern breast cancer prognosis. We established the gene expression profiles of functionally validated ALDEFLUOR-positive CSC populations (breast CSC-GES) and demonstrated their clinical relevance. Among 2609 patients with breast cancers, we validated that he expression of the breast CSC-GES is correlated with poor outcome and metastasis in uni-and multivariate analysis (5-year MFS was 70% CI95 [67–74] in the breast CSC-positive class and 80% (CI95 [77–83]) in the breast CSC-negative class (p = 5.5E−04 with log-rank test). Furthermore, we identified a core of 19 genes commonly expressed in breast CSC, murine embryonic, neural and hematopoietic stem cells programs and demonstrated for each gene its ability to modulate breast CSC population, being implicated in self-renewing or differentiation programs. We found that the core of genes in common between four stem cell gene expression studies (CE-BCSC-3SC) displayed an adverse prognostic impact for patients with breast cancer. The core contained genes implicated in oxidative phosphorylation, detoxification, lipid metabolism, and genomic stability, and these shared determinants of stemness influenced clinical outcome.

Thus, we show ed that CSCs from orthotopically engrafted primary breast tumors have clinical and biological relevance. This functionally validated CSC population is highly correlated with survival and express genes governing main stem cell functions, substantiating a major prediction of the CSC model and opening further promises for new CSC therapies using valid preclinical models.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-03-01.