A comparison of serum miRNAs influencing metastatic growth of EMT6 vs 4THM tumor cells in wild-type and CD200R1KO mice

We investigated whether miRNAs in exosomes from EMT6 or 4THM tumor-bearing mice played a role in regulating inflammatory cytokine expression and/or metastasis in WT mice injected with EMT6 and/or 4THM tumor cells. EMT6 tumors in BALB/c CD200R1KO mice resolve following surgical resection of localized tumor and immunization with irradiated EMT6 cells along with CpG as adjuvant. Wild-type (WT) animals treated in the same fashion develop pulmonary and liver metastases within 20 days of surgery. DLNs from CD200R1KO mice contain no tumor cells detectable at limiting dilution. In contrast, 4THM tumor cells injected into CD200R1KO show increased metastasis compared with WT mice. Transfer of serum exosomes from 4THM tumor-bearing mice to WT animals increased metastasis of EMT6 tumors, an effect attenuated by anti-IL-6 antibody. We compared miRNA expression in exosomes from the serum of 4THM/EMT6 WT or CD200R1KO tumor-bearing mice, and the effects of antagomirs to miRNAs on tumor growth. Complex changes in miRNA expression were observed in the isolated exosomes. Some miRNAs, including miR155, have been reported to potentiate inflammatory responses and augment inflammatory cytokine expression. Expression of miR155 increased in exosomes from 4THM relative to EMT6 tumor bearers, and antagomirs to miR155 attenuated tumor growth and metastasis, and improved survival, following infusion into WT mice. Antagomirs to the miR205 family were thought to affect metastasis by targeting epithelial-to-mesenchymal transition (EMT), increased growth and metastasis in both 4THM and EMT6 tumor-bearing mice, and decreased survival, with some modulation of inflammatory cytokine production. Multiple pathways are implicated in differential metastasis of EMT6/4THM, and targeting these may have clinical utility in human breast cancer.