Dexamethasone promotes breast cancer stem cells in obese and not lean mice

Abstract

Obesity is highly prevalent in breast cancer patients and is associated with increased recurrence and breast cancer-specific mortality. Glucocorticoids (GC) are used as an adjuvant in cancer treatment and are associated with promoting breast cancer metastasis through activation of stemness-related pathways. Therefore, we utilized the synergetic allograft E0771 breast cancer model to investigate if treatment with GCs had differential effects on promoting cancer stem cells in lean and diet-induced obese mice. Indeed, both lean mice treated with dexamethasone and obese mice with no treatment had no effect on the ex vivo colony-forming ability, mammosphere formation, or aldehyde dehydrogenase (ALDH) bright subpopulation. However, treatment of obese mice with dexamethasone resulted in a significant increase in ex vivo colony formation, mammosphere formation, ALDH bright subpopulation, and expression of pluripotency transcription factors. GC transcriptionally regulated genes were not altered in the dexamethasone-treated groups compared to treatment controls. In summary, these results provide initial evidence that obesity presents a higher risk of GC-induced cancer stemness via non-genomic GC signaling which is of potential translational significance.

Keywords: breast cancer; cancer stem cells; glucocorticoids; obesity; tumour initiating cells.

FIGURE 1

High fat diet and dexamethasone does not alter tumor growth but promotes ex vivo mammosphere and colony formation. (A) Overview of experimental design. Female C57BL/6N mice were fed a normal chow diet (n = 17) or high fat diet (HFD) for 12 weeks (n = 11). E0771 murine tumor cells were implanted into the mammary fat pad and mice were randomly allocated no treatment or dexamethasone (0.1 mg/kg) in the drinking water for 5 out of 7 days for 3 weeks. Tumors were excised for ex vivo analysis. (B) Weight of mice following 12 weeks of normal chow diet or HFD. (C) Tumor growth rate of mice in the following treatment groups; normal chow diet and no treatment (n = 10), normal chow diet and dexamethasone (n = 7), HFD and no treatment (n = 6), HFD and dexamethasone (n = 5). (D) Expression of mRNA Cd31 within excised E0771 tumors following normal diet or HFD and treatment with dexamethasone. (E) Ex vivo colony‐forming ability and (F) Mammosphere formation following different diets or treatment with dexamethasone. Data points are mean ± SEM. n ≥ 3. *p < .05; **p < .01 (one‐way ANOVA or two‐tailed Student t‐test)

FIGURE 2

High fat diet and dexamethasone promotes an ALDH⁺ bright subpopulation and pluripotency transcription factors. (A, B) Ex vivo analysis of an ALDH bright subpopulation of cells in excised E0771 tumors from mice fed either a normal or high fat diet and/or treated with dexamethasone (0.1 mg/kg) in the drinking water for 5 out of 7 days for 3 weeks. Expression of mRNA (C) Sox2 and Nanog, (D) Ror1 and Wnt5a and (E) Nr3cl1 and Fkbp51 from excised E0771 tumors following normal diet or HFD and treatment with dexamethasone. Data points are mean ± SEM. n ≥ 3. *p < .05; **p < .01 (one‐way ANOVA or two‐tailed Student's t‐test). SSC, side scatter