Sílvia Cufí 1,2 , Bruna Corominas-Faja 1,2 , Alejandro Vazquez-Martin 1,2 , Cristina Oliveras-Ferraros 1,2 , Joan Dorca 2,3 , Joaquim Bosch-Barrera 2,3 , Begoña Martin-Castillo 2,4 , Javier A. Menendez 1,2 1 Translational Research Laboratory, Catalan Institute of Oncology (ICO), Girona, Spain 2 Girona Biomedical Research Institute (IDIBGi), Girona, Spain 3 Medical Oncology, Catalan Institute of Oncology (ICO), Girona, Spain 4 Clinical Research Unit, Catalan Institute of Oncology (ICO), Girona, Spain Received: April 27, 2012, Accepted: April 28, 2012, Published: May 4, 2012, Keywords: Metformin, trastuzumab, HER2, cancer stem cells, breast cancer Correspondence: Javier A. Menendez, email: // // Abstract Trastuzumab-refractory breast cancer stem cells (CSCs) could also explain the high rate of primary resistance to single-agent trastuzumab in HER2 gene-amplified breast cancer patients. The identification of agents with strong selective toxicity for trastuzumab-resistant breast CSCs may have tremendous relevance for how HER2+ breast cancer patients should be treated. Using the human breast cancer cell line JIMT-1, which was established from the pleural metastasis of a patient who was clinically resistant to trastuzumab ab initio , we examined whether preferential killing of the putative CD44 + CD24 -/low breast CSC population might be sufficient to overcome primary resistance to trastuzumab in vivo . Because recent studies have shown that the anti-diabetic biguanide metformin can exert antitumor effects by targeted killing of CSC-like cells, we explored whether metformin’s ability to preferentially kill breast cancer initiating CD44 + CD24 -/low cells may have the potential to sensitize JIMT-1 xenograft mouse models to trastuzumab. Upon isolation for breast cancer initiating CD44 + CD24 -/low cells by employing magnetic activated cell sorting, we observed the kinetics of metformin-induced killing drastically varied among CSC and non-CSC subpopulations. Metformin’s cell killing effect increased dramatically by more than 10-fold in CD44 + CD24 -/low breast CSC cells compared to non-CD44 + CD24 -/low immunophenotypes. While seven-weeks treatment length with trastuzumab likewise failed to reduce tumor growth of JIMT-1 xenografts, systemic treatment with metformin as single agent resulted in a significant two-fold reduction in tumor volume. When trastuzumab was combined with concurrent metformin, tumor volume decreased sharply by more than four-fold. Given that metformin-induced preferential killing of breast cancer initiating CD44 + CD24 -/low subpopulations is sufficient to overcome in vivo primary resistance to trastuzumab, the incorporation of metformin into trastuzumab-based regimens may provide a valuable strategy for treatment of HER2+ breast cancer patients.
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Cufí et al. (2012) studied this question.