DELIVERY OF MIRNA TO BREAST CANCER CELLS THROUGH EXOSOMES RELEASED FROM BONE MARROW STROMA AND MESENCHYMAL STEM CELLS

Breast cancer (BC) shows preference for bone marrow (BM) where the cells (BCCs) can adapt dormancy. This is consistent with BC resurgence from BM after >10 years of remission. It is unlikely that the BCC selects the BM for homing. Rather, we believe that BCCs enter the cavity and then use the functions of endogenous BM cells for their survival. This innovative concept plans to examine microRNA (miRNA)-containing exosomes, released from endogenous BM cells, into a subset of BCCs, consequently facilitating cell cycle quiescence. Cell cycle quiescence of BCCs with stroma can be partly explained by the formation of gap junctional intercellular communication (GJIC) to allow for exchange in miRNA. The concept proposes that miRNA containing exosomes, released from BM stroma and mesenchymal stem cells (MSCs), enter BCCs as a method to transfer miRNAs. Exosomes are small (50-90 nM) membrane vesicles that are released from one cell and then enter into another cell through receptor-ligand interaction or endocytosis. This study focuses on a subset of BCCs that expresses the stem cell gene, Oct4, referred to as Oct4(+) BCCs. The hypothesis states that GJIC between Oct4(+) BCCs and stroma or MSCs establishes close interaction to facilitate the transfer of exosomes released from stroma and/or MSCs. The exosomes containing miR-222 and miR-223 cause the Oct4(+) BCCs to adapt a dormant phenotype. In Aim 1, we will determine the levels of miRNA-222 and miR-223 in exosomes released from stroma, MSCs, Oct4(+) BCCs, and Oct4(-) BCCs. We will investigate if the amounts of exosomes released from stroma, MSCs, and BCC subsets are different after they are placed in co-cultures with each other and whether the changes correlate with miR-222 and miR-223 levels. In Aim 2, we plan to determine if GJIC is required for the entry of the MSC/stroma-released endosomes into Oct4(+) BCCs, and to study if miRNA-222 and miR-223 within the exosomes are sufficient to transition the Oct4(-) BCCs to cell cycle quiescence, and also investigates their contribution in the quiescent phenotype in the Oct4(+) BCCs. Overall, this grant is highly significant in light of the BM remaining as a major clinical problem. The BM is a major site of BC resurgence even after more than 10 years of remission. Additionally, this concept is relevant to BC in other regions since MSCs can home to the area of the cancer where they form tumor stroma.