Introduction: MiRNAs are aberrantly expressed in both the circulation and tissue of patients with breast tumours, however little is currently known about the relationship between circulating and tissue miRNAs. The aim of this study was to quantify circulating and tumour tissue miRNA expression in a murine model of breast cancer and identify novel circulating markers of disease progression.

Materials and Methods: Athymic nude mice (n = 20) received either a mammary fat pad (n = 8, MFP), or subcutaneous (n = 7, SC) injection of MDA-MB-231 cells. Controls received no tumour cells (n = 5). Tumour volume was monitored weekly and blood sampling performed at weeks 1, 3 and 6 following tumour induction (total n=60). Animals were sacrificed at week 6 and tumour tissue (n = 15), lungs (n = 20) and enlarged lymph nodes (n = 3) harvested. RNA were extracted from all samples (n = 98) and relative expression of miRNAs previously associated with tumour progression were quantified using RQ-RCR. A microRNA array was also preformed comparing animals with early (weeks 1, n=5) versus late (week 6, n=5) disease and results were analysed using RQ-PCR in all blood samples (n = 60). Reverse transcription for the relevant targets and endogenous controls was carried out and expression was quantified using RQ-PCR.

Results:MiR-10b expression was significantly higher in MFP compared to SC tumours (p < 0.05), with the highest levels in diseased lymph nodes (p < 0.05). MiR-10b was undetectable in the circulation. MiR-221 expression was significantly increased in tumour tissue (p < 0.001). MiR-195 and miR-497 were significantly decreased in tumour tissue (p < 0.05), and also in the circulation of animals 3 weeks following tumour induction (p < 0.05). At both tissue and circulating level, a significant correlation was observed between miR-497 and miR-195 (r = 0.61, p < 0.001; r = 0.41, p < 0.01 respectively). Microarray analysis revealed the level of 47 miRs to be significantly changed between week 1 and week 6 as disease progressed in a murine model, 10 of which (miR A-J) were significantly altered and internally validated within the murine model.

Conclusions: This study highlights the importance of miRNAs in breast cancer, with each displaying distinct roles in circulation and tissue. Novel circulating miRNAs which have never previously been associated with breast cancer have been identified, with quantification of circulating levels in breast cancer patients currently ongoing.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-05-09.