Despite recent therapeutic advances that have doubled the median survival time of patients with multiple myeloma (MM), intratumor genetic heterogeneity contributes to disease progression and emergence of drug resistance. MicroRNAs (miRs), are noncoding small RNAs that play important roles in the regulation of gene expression, and have been implicated in cancer progression and drug resistance. We investigated the role of the miR-221-222 family in dexamethasone(Dex)-induced drug resistance in MM using the isogenic cell lines, MM1R and MM1S, which represent models of resistance and sensitivity, respectively. Analysis of array comparative genome hybridization (aCGH) data revealed gain of chromosome X regions at band p11.3, wherein the miR-221-222 resides, in resistant MM1R cells but not in sensitive MM1S cells. DNA copy number gains in MM1R cells were associated with increased miR-221-222 expression and downregulation of p53-upregulated modulator of apoptosis (PUMA) as a likely pro-apoptotic target. We confirmed PUMA mRNA as a direct target of miR-221-222 in MM1S and MM1R cells by both gain- and loss- of function studies. In addition, miR-221-222 treatment rendered MM1S cells resistant to Dex, whereas anti-miR-221-222 partially restored the Dex sensitivity of MM1R cells. These studies have uncovered a role for miR-221-222 in MM drug resistance, and suggest a potential therapeutic role for inhibitors of miR-221-222 binding to PUMA mRNA as a means of overcoming Dex resistance in patients. The clinical utility of this approach is predicated on the ability of anti-sense miR-221-222 to increase survival while reducing tumor burden, and is strongly supported by the metastatic propensity of MM1R cells in preclinical mouse xenograft models of MM. Moreover, our observation of increased levels of miR-221-222 with decreased PUMA expression in MM cells from patients at relapse versus untreated controls suggests an even broader role for miR-221-222 in drug resistance, and provides a rationale for the targeting of miR-221-222 as a means of improving patient outcomes.

The tumor-promoting chemokine CCL5 has been implicated in malignant transformation of breast epithelial cells, with studies to date focusing mainly on basal-type breast cancers. In this study, we investigated the consequences of CCL5 deletion in the MMTV-PyMT transgenic mouse model of luminal breast cancer. In this model, primary tumor burden and pulmonary metastases were reduced significantly in CCL5-deficient subjects, an effect found to be associated with a deficit of Th2 (IL4+CD4+ T) cells. Mechanistic investigations revealed that CCL5 activates CCR3, a highly expressed chemokine on CD4+ T cells, and also boosts Gfi1 expression to promote the differentiation of Th2 cells which enhance the pro-metastatic activity of tumor-associated myeloid cells. Clinically, polarization towards this immunosuppressive Th2 phenotype was also evident in patients with advanced luminal breast cancer. Thus, our findings showed that CCL5/CCR3 signaling promotes metastasis by inducing Th2 polarization of CD4+ T cells, with implications for prognosis and immunotherapy of luminal breast cancer.

When cancer patients need help, they are often surprised to find that long-trusted friends have disappeared.

Studies have shown that the use of oral contraceptives lowers the risk for endometrial cancer, and now a new study has found that the protection continues for many years after women stop using them.

Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. TNBC is characterized by reduced expression of metastasis suppressors such as Raf kinase inhibitory protein (RKIP), which inhibits tumor invasiveness. Mechanisms by which metastasis suppressors alter tumor cells are well characterized; however, their ability to regulate the tumor microenvironment and the importance of such regulation to metastasis suppression are incompletely understood. Here, we use species-specific RNA sequencing to show that RKIP expression in tumors markedly reduces the number and metastatic potential of infiltrating tumor-associated macrophages (TAM). TAMs isolated from nonmetastatic RKIP+ tumors, relative to metastatic RKIP− tumors, exhibit a reduced ability to drive tumor cell invasion and decreased secretion of prometastatic factors, including PRGN, and shed TNFR2. RKIP regulates TAM recruitment by blocking HMGA2, resulting in reduced expression of numerous macrophage chemotactic factors, including CCL5. CCL5 overexpression in RKIP+ tumors restores recruitment of prometastatic TAMs and intravasation, whereas treatment with the CCL5 receptor antagonist Maraviroc reduces TAM infiltration. These results highlight the importance of RKIP as a regulator of TAM recruitment through chemokines such as CCL5. The clinical significance of these interactions is underscored by our demonstration that a signature comprised of RKIP signaling and prometastatic TAM factors strikingly separates TNBC patients based on survival outcome. Collectively, our findings identify TAMs as a previously unsuspected mechanism by which the metastasis-suppressor RKIP regulates tumor invasiveness, and further suggest that TNBC patients with decreased RKIP activity and increased TAM infiltration may respond to macrophage-based therapeutics. Cancer Res; 75(19); 1–11. ©2015 AACR.