CD9 Upregulation-Decreased CCL21 Secretion in Mesenchymal Stem Cells Reduces Cancer Cell Migration

Tetraspanin CD9 is widely expressed on various cell types, such as cancer cells and mesenchymal stem cells (MSCs), and/or cell-released exosomes. It has been reported that exosomal CD9 plays an important role in intercellular communications involved in cancer cell migration and metastasis. However, reports on the effect of the CD9 of MSCs or MSC-derived exosomes on cancer cell migration are still lacking. In this study, using a transwell migration assay, we found that both dextran-coated iron oxide nanoparticles (dex-IO NPs) and ionomycin stimulated exosomal CD9 expression in human MSCs (hMSCs); however, hMSCs could not deliver them to melanoma cells to affect cell migration. Interestingly, a reduced migration of melanoma cell line was observed when the ionomycin-incubated hMSC-conditioned media but not dex-IO NP-labeled hMSC-conditioned media were in the bottom chamber. In addition, we found that dex-IO NPs decreased cellular CD9 expression in hMSCs but ionomycin increased this. Simultaneously, we found that ionomycin suppressed the expression and secretion of the chemokine CCL21 in hMSCs. The silencing of CD9 demonstrated an inhibitory role of cellular CD9 in CCL21 expression in hMSCs, suggesting that ionomycin could upregulate cellular CD9 to decrease CCL21 expression and secretion of hMSCs, which would reduce the migration of B16F10, A549 and U87MG cancer cell lines due to chemoattraction reduction of CCL21. The present study not only highlights the important role of bone marrow-derived hMSCs' CD9-mediated CCL21 regulation in cancer bone metastasis but also suggests a new distinct pharmaceutical strategy for prevention or/and therapy of cancer metastasis.

Novel DNA Aptamers Against CCL21 Protein: Characterization and Biomedical Applications for Targeted Drug Delivery to T Cell-Rich Zones

The chemokine (C-C motif) ligand 21 (CCL21) is a cytokine that attracts CCR7-positive cells to the T cell (paracortical) zone of lymph nodes by directional migration of these cells along the CCL21 gradient. In this article, we sought to mimic this chemotactic mechanism, by identifying a novel aptamer that binds CCL21 with high affinity. In vitro selection of DNA aptamers was performed by the Systematic Evolution of Ligands by Exponential Enrichment. Quantitative polymerase chain reaction (qPCR) and enzyme-linked oligonucleotide assay were used to screen for high-affinity aptamers against human and mouse CCL21 protein, respectively. Three such aptamers were identified. Surface plasmon resonance showed equilibrium dissociation constant (K_d) for these three aptamers in the nano to picomolar range. Cytotoxicity assays showed <10% toxicity in HEK293 and HL-60 cells. Last, in vivo biodistribution was successfully performed and CCL21 chemokine-binding aptamers were quantified within the draining lymph nodes and spleen using qPCR. Fluorescence microscopy revealed that one of the aptamers showed significantly higher presence in the paracortex than the control aptamer. The use of anti-CCL21 aptamers to mimic the chemotaxis mechanism thus represents a promising approach to achieve targeted delivery of drugs to the T cell-rich zones of the lymph node. This may be important for the treatment of HIV infection and the eradication of HIV reservoirs.