Soluble fms‐like tyrosine kinase‐1‐enriched exosomes suppress the growth of small cell lung cancer by inhibiting endothelial cell migration

BACKGROUND: Previous studies have reported that soluble fms‐like tyrosine kinase‐1 (sFlt‐1) possesses anti‐tumor effects by inhibiting angiogenesis in many cancers. Exosomes can be engineered as delivery vehicles for transferring functional biomolecules, such as proteins, lipids, and nucleic acids (DNA, mRNA, and miRNA) to target cells to affect inflammation, apoptosis, and angiogenesis. The purpose of this study was to investigate whether exosomes can function as efficient carriers of sFlt‐1 in vitro and in vivo, to play a role in SCLC therapy. METHODS: We adopted three different methods: TEM, NTA and western blot analysis to characterize the cell‐derived exosomes from NCI‐H69 SCLC cell line and normal bronchial epithelial BEAS‐2B cell line. we next explored the effects of these exosomes on HUVE cell proliferation and migration in vitro.To verify sFlt‐1‐loaded exosomes suppress the tumor growth in vivo,we established subcutaneous xenografts in nude mice using the NCI‐H69 cell line. RESULTS: We observed that NCI‐H69‐exo significantly increased human umbilical vein endothelial cells (HUVEC) migration compared to BEAS‐2B‐exo in vitro and in vivo. sFlt‐1 protein expression was statistically higher in BEAS‐2B‐exo than NCI‐H69‐exo. sFlt‐1 protein or sFlt‐1‐enriched exosomes can inhibit the migration of HUVECs. Furthermore, sFlt‐1‐enriched exosomes exhibited higher inhibition efficacy on pro‐angiogenesis of NCI‐H69‐exo in comparison with the same concentration of sFlt‐1 protein. Intriguingly, sFlt‐1‐loaded exosomes showed marked anti‐tumor activity by inhibiting the growth of NCI‐H69 tumor xenografts. CD31 staining revealed that sFlt‐1‐loaded exosomes significantly reduced the vascular density of experimental mice. sFlt‐1‐loaded exosomes markedly induced tumor apoptosis and inhibited tumor cell proliferation in mice. CONCLUSION: Exosomes from a SCLC cell line contain low levels of sFlt‐1 and significantly increased the migration of HUVECs. SFlt‐1‐enriched exosomes can inhibit NCI‐H69‐exo‐induced HUVEC migration. Exosomes enriched in sFlt‐1 have the potential to be effective therapeutic agents for SCLC.