Exosomes: A Promising Factor Involved in Cancer Hypoxic Microenvironments

As a significant tumor feature, hypoxia can trigger cancer adaptive processes, induce malignant phenotype development, and promote drug resistance. Previous studies demonstrated that exosomes are critical during these procedures. Exosomes are small vesicles formed in vesicular bodies in the endosomal network. These small vesicles are mainly involved in the transport of bioactive molecules between cells. Exosomes are also involved in the mediation of some cellular communications depending on derived donor cells; thus, recipient cells undergo phenotypic changes. Furthermore, hypoxia can remarkably stimulate exosomal secretion; for instance, nucleic acids and proteins as transmission signals in exosomes in a tumor microenvironment are involved in various functions, such as inducing intratumoral heterogeneity, altering immunological responses, producing cancer-associated fibroblasts, and promoting angiogenesis and metastasis. Moreover, exosome contents resemble those of a donor cell; this finding indicates that exosomes may also be regarded as suitable biomarkers of hypoxia status. Therefore, exosomes can be used to facilitate diagnosis and prognosis with minimal invasive procedures. Further studies on exosomes in cancer may provide new therapeutic strategies.