In vitro and in vivo antiproliferative activity of metformin on stem-like cells isolated from spontaneous canine mammary carcinomas: translational implications for human tumors

Abstract

BackgroundCancer stem cells (CSCs) are considered the cell subpopulation responsible for breast cancer (BC) initiation, growth, and relapse. CSCs are identified as self-renewing and tumor-initiating cells, conferring resistance to chemo- and radio-therapy to several neoplasias. Nowadays, th (about 10mM)e pharmacological targeting of CSCs is considered an ineludible therapeutic goal. The antidiabetic drug metformin was reported to suppress in vitro and in vivo CSC survival in different tumors and, in particular, in BC preclinical models. However, few studies are available on primary CSC cultures derived from human postsurgical BC samples, likely because of the limited amount of tissue available after surgery. In this context, comparative oncology is acquiring a relevant role in cancer research, allowing the analysis of larger samples from spontaneous pet tumors that represent optimal models for human cancer.MethodsIsolation of primary canine mammary carcinoma (CMC) cells and enrichment in stem-like cell was carried out from fresh tumor specimens by culturing cells in stem-permissive conditions. Phenotypic and functional characterization of CMC-derived stem cells was performed in vitro, by assessment of self-renewal, long-lasting proliferation, marker expression, and drug sensitivity, and in vivo, by tumorigenicity experiments. Corresponding cultures of differentiated CMC cells were used as internal reference. Metformin efficacy on CMC stem cell viability was analyzed both in vitro and in vivo.ResultsWe identified a subpopulation of CMC cells showing human breast CSC features, including expression of specific markers (i.e. CD44, CXCR4), growth as mammospheres, and tumor-initiation in mice. These cells show resistance to doxorubicin but were highly sensitive to metformin in vitro. Finally, in vivo metformin administration significantly impaired CMC growth in NOD-SCID mice, associated with a significant depletion of CSCs.ConclusionsSimilarly to the human counterpart, CMCs contain stem-like subpopulations representing, in a comparative oncology context, a valuable translational model for human BC, and, in particular, to predict the efficacy of antitumor drugs. Moreover, metformin represents a potential CSC-selective drug for BC, as effective (neo-)adjuvant therapy to eradicate CSC in mammary carcinomas of humans and animals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1235-8) contains supplementary material, which is available to authorized users.

The impact of melatonin and carbon ion irradiation on cancer stem cells

“…A number of studies demonstrated the existence of stem cells in canine and human breast cancer cell lines [83][84][85][86][87][88][89]. The study of Dontu and colleagues demonstrated that the stemness of tumor cells is assessed in vitro by their capability to produce mammospheres [90].…”

Identification and characterization of cancer stem cells in canine mammary tumors

“…The same cells were resistant to radiation doses of 1–5 Gy and exhibited a reduced loss of colony formation ability. Increased resistance to doxorubicin and no response to paclitaxel treatment were also observed by three other groups [27, 31, 35]. Barbieri et al [31] did not observe any reduction in cell viability, even at the highest concentrations (5–10 µM) of the drugs.…”

“…Increased resistance to doxorubicin and no response to paclitaxel treatment were also observed by three other groups [27, 31, 35]. Barbieri et al [31] did not observe any reduction in cell viability, even at the highest concentrations (5–10 µM) of the drugs. Discordance between results obtained using cell lines and spheres derived from tumor samples might be explained by possible different gene expressions and cellular properties that occur during the process of immortalization [24].…”

“…In one study, the anti-diabetic drug metformin was shown to specifically inhibit the viability of CSC [31]. The IC 50 concentration after treatment for 48 h varied between samples, resulting in a mean value of ~10 mM.…”

Drug-repositioning opportunities for cancer therapy: novel molecular targets for known compounds

“…Metformin effects have been evaluated in preclinical studies on different solid tumor models, including breast [89,90], endometrial [91], pancreatic [70], lung [92], prostate [93], head and neck [94] carcinomas, glioma and neuroblastoma [95][96][97], and blood malignancies [98][99][100].…”