Dynamic Role of Exosome microRNAs in Cancer Cell Signaling and Their Emerging Role as Noninvasive Biomarkers

SIMPLE SUMMARY: Exosomes are vesicles that vary between 40 and 150 nm in diameter and are secreted by cells. These carry miRNAs that have various roles in intercellular signaling. They have different biological functions and are unique to the secreting cell. This provides information about the state of the cell and its involvement in pathological processes such as cancer. Exosomes play an important role in cancer signaling since they have both pro- and antitumor functions. In addition, they can render cells sensitive or resistant to chemotherapeutic agents. Exosomal miRNAs play an important role in promoting tumor growth and metastasis by altering the signaling pathway and promoting angiogenesis. They increase the metastatic ability of cancer cells by increasing the secretion of matrix metalloproteinases, which degrade the extracellular matrix, thereby allowing cells to spread to different parts of the body. The level of miRNAs in exosomes can be used to identify the cancer stage and grade, which eliminates the need for invasive cancer biopsies. Since exosomes can cross the blood–brain barrier, they are an excellent choice for drug delivery. As exosomes are isolated from the cells or biological fluids of the patient, their use minimizes the risk of infection and inflammation. A better understanding of exosomes and their cargoes can be exploited in the development of cancer therapeutics. ABSTRACT: Exosomes are extracellular vesicles that originate from endosomes and are released by all cells irrespective of their origin or type. They play an important role in cell communication and can act in an autocrine, endocrine, or paracrine fashion. They are 40–150 nm in diameter and have a similar composition to the cell of origin. An exosome released by a particular cell is unique since it carries information about the state of the cell in pathological conditions such as cancer. miRNAs carried by cancer-derived exosomes play a multifaceted role by taking part in cell proliferation, invasion, metastasis, epithelial–mesenchymal transition, angiogenesis, apoptosis, and immune evasion. Depending on the type of miRNA that it carries as its cargo, it can render cells chemo- or radiosensitive or resistant and can also act as a tumor suppressor. Since the composition of exosomes is affected by the cellular state, stress, and changes in the environment, they can be used as diagnostic or prognostic biomarkers. Their unique ability to cross biological barriers makes them an excellent choice as vehicles for drug delivery. Because of their easy availability and stability, they can be used to replace cancer biopsies, which are invasive and expensive. Exosomes can also be used to follow the progression of diseases and monitor treatment strategies. A better understanding of the roles and functions of exosomal miRNA can be used to develop noninvasive, innovative, and novel treatments for cancer.