Abstract 2907: Exosome secretion is an inheritable property of cancer cells: Single-cell profiling of exosome secretion

Decades of research on exosomes, nano-sized vesicles secreted by cells, have revealed novel roles of these vesicles in the formation of pre-metastasis niches that enhances the migration of tumor cells to those sites. Paradoxically, more recent work has suggested that these tumor-derived exosomes can also have an immunostimulatory role, depending on the model studied. The rate of secretion of exosomes by single cells is likely heterogeneous, and a deep profiling of the secretion capacity of individual tumor cells has been largely unexplored. We have developed a high-throughput single-cell methodology to quantify the dynamic secretion of exosomes from single cells using a modified immunoassay and sought to define: (a) heterogeneity among individual cells within the tumor cell population, and (b) the nature of the cells secreting exosomes within a tumor cell population. In order to investigate these, we chose to study models of triple negative breast cancer: the metastatic tumor lines, 4T1 (mouse) and MDA-MB-231(human); and the non-metastatic lines 67NR (mouse) and MCF7 (human). Our method revealed that MDA-MB-231 single cells secreted exosomes at a rate, ~2 fold higher than MCF7 cells. Surprisingly, the non-metastatic 67NR cells showed a higher secretion rate (~1.5 fold) than metastatic 4T1 cells. Next, we performed single-cell RNA-seq on 67NR and 4T1 single cells. Consistent with our single-cell exosomal profiling results, 67NR cells were significantly (p-value Since our in vitro results clearly demonstrated that the secretor clonal cell lines had a higher frequency of exosome secreting single cells, we sought to define the in vivo relevance of these results. Consistent with the hypothesis that the exosomes from 67NR are immune-stimulatory, injection of the secretor clones into Balb/c mice led to lack of primary tumor formation (2/15 mice had tumors) whereas the injection of the non-secretor clones led to tumor formation in 7/15 mice. In aggregate, our results show that the higher rate of secretion of exosomes from non-metastatic cells can facilitate tumor rejection in vivo. We are currently performing in vitro studies with the 67NR and MDA-MB-231 exosomes to study their impact on immune cells. Citation Format: Mohsen Fathi, Robiya Joseph, Melisa Martinez-Paniagua, Jay R Adolacion, Xingyue An, Ankit Mahendra, Konrad Gabrusiewicz, Sujash Chatterjee, Sendurai A. Mani, Navin Varadarajan. Exosome secretion is an inheritable property of cancer cells: Single-cell profiling of exosome secretion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2907.