Pancreatic ductal adenocarcinoma (PDAC) is known for its resistance to gemcitabine, which acts to inhibit cell growth by termination of DNA replication. Tumor-associated macrophages (TAM) were recently shown to contribute to gemcitabine resistance; however, the exact mechanism of this process is still unclear. Using a genetic mouse model of PDAC and electron microscopy analysis, we show that TAM communicate with the tumor microenvironment via secretion of approximately 90 nm vesicles, which are selectively internalized by cancer cells. Transfection of artificial dsDNA (barcode fragment) to murine peritoneal macrophages and injection to mice bearing PDAC tumors revealed a 4-log higher concentration of the barcode fragment in primary tumors and in liver metastasis than in normal tissue. These macrophage-derived exosomes (MDE) significantly decreased the sensitivity of PDAC cells to gemcitabine, in vitro and in vivo. This effect was mediated by the transfer of miR-365 in MDE. miR-365 impaired activation of gemcitabine by upregulation of the triphospho-nucleotide pool in cancer cells and the induction of the enzyme cytidine deaminase; the latter inactivates gemcitabine. Adoptive transfer of miR-365 in TAM induced gemcitabine resistance in PDAC-bearing mice, whereas immune transfer of the miR-365 antagonist recovered the sensitivity to gemcitabine. Mice deficient of Rab27 a/b genes, which lack exosomal secretion, responded significantly better to gemcitabine than did wildtype. These results identify MDE as key regulators of gemcitabine resistance in PDAC and demonstrate that blocking miR-365 can potentiate gemcitabine response. Significance: Harnessing macrophage-derived exosomes as conveyers of antagomiRs augments the effect of chemotherapy against cancer, opening new therapeutic options against malignancies where resistance to nucleotide analogs remains an obstacle to overcome. Cancer Res; 78(18); 5287–99. ©2018 AACR.

BACKGROUND: The impact of lymph node metastases on prognosis in patients with oral cavity squamous cell carcinoma (OSCC) has been well recognized. However, accurate stratification of risk for recurrence among patients with lymph node metastases is difficult based on the existing staging systems. In the current study, the utility of lymph node density (LND) was evaluated as an alternative method for predicting survival.METHODS: Three hundred eighty‐six patients who underwent neck dissection were included. The median follow‐up was 67 months. Five‐year overall survival (OS), disease‐specific survival (DSS), and locoregional failure (LRF) rates were calculated using the Kaplan‐Meier method. LND (number of positive lymph nodes/total number of excised lymph nodes) and tumor‐node‐metastasis (TNM) staging variables were subjected to multivariate analysis.RESULTS: Using the median (LND = 0.06) as the cutoff point, LND was found to be significantly associated with outcome. For patients with LND ≤0.06, the OS was 58 percent versus 28 percent for patients with LND >0.06 (P < .001). Similarly, the DSS for patients with LND ≤0.06 was 65 percent and was 34 percent for those with LND >0.06 (P < .001). On univariate analysis, pathologic T and N classification, extracapsular spread, and LND were found to be significant predictors of outcome (P < .001). However, on multivariate analysis, LND remained the only independent predictor of OS (P = .02; hazards ratio, 2.0), DSS (P = .02; hazards ratio, 2.3), and LRF (P = .005; hazards ratio, 4.1). LND was also found to be the only significant predictor of outcome in patients receiving adjuvant radiotherapy (P < .05). Within individual subgroups of pN1 or pN2 patients, LND reliably stratified patients according to their risk of failure (P < .05).CONCLUSIONS: After surgery for OSCC, pathologic evaluation of the neck using LND was found to reliably stratify the risk of disease recurrence and survival. Cancer 2009. © 2009 American Cancer Society.

Extracellular vesicles (EVs) are heterogamous lipid bilayer-enclosed membranous structures secreted by cells. They are comprised of apoptotic bodies, microvesicles, and exosomes, and carry a range of nucleic acids and proteins that are necessary for cell-to-cell communication via interaction on the cells surface. They initiate intracellular signaling pathways or the transference of cargo molecules, which elicit pleiotropic responses in recipient cells in physiological processes, as well as pathological processes, such as cancer. It is therefore important to understand the molecular means by which EVs are taken up into cells. Accordingly, this review summarizes the underlying mechanisms involved in EV targeting and uptake. The primary method of entry by EVs appears to be endocytosis, where clathrin-mediated, caveolae-dependent, macropinocytotic, phagocytotic, and lipid raft-mediated uptake have been variously described as being prevalent. EV uptake mechanisms may depend on proteins and lipids found on the surfaces of both vesicles and target cells. As EVs have been shown to contribute to cancer growth and progression, further exploration and targeting of the gateways utilized by EVs to internalize into tumor cells may assist in the prevention or deceleration of cancer pathogenesis.