Generation of Novel Diagnostic and Therapeutic Exosomes to Detect and Deplete Protumorigenic M2 Macrophage

Exosomes are now the most widely studied extracellular vesicles that are produced in the cell. Exosomes have a natural ability to carry functional biomolecules, such as small RNAs, DNAs, and proteins, in their lumen. Indeed, exosomes can be developed to express targeting antibodies or peptides on their surface for the delivery of specific targeted therapeutics. This property makes exosomes attractive for use in drug delivery and molecular diagnosis. Moreover, exosomes can be attached to nanoparticles and used for high precision imaging. Exosomes are now considered an important component in liquid biopsy assessments, which are useful for detecting cancers, including lung cancer. Several studies are currently underway to develop methods of exploiting exosomes for use as efficient drug delivery vehicles and to develop novel diagnostic modalities.

The few successes recorded in the use of targeted therapies for the treatment of solid tumors has influenced the extension of cancer treatment strategies to include other cell types in the tumor microenvironment apart from the tumor cell alone. An increase in the infiltration of tumor-associated macrophages (TAMs) has been associated with poor survival and tumor stage. Therefore, engineering exosomes that will bind specifically to TAMs receptors will allow for the development of therapies that target TAMS and not normal macrophages. In the absence of major histocompatibility complex and complement, the non-phagocytic mechanism by which leucocytes (effector cells) can kill antibody-coated target cells is referred to as Antibody-dependent cell-mediated cytotoxicity (ADCC). This mechanism has found application in the clinical context following the successful use of a monoclonal antibody in the treatment of various diseases. Antibodies serve as a connection between the effector cell Fc receptors (FcR) and the target antigen on the cell to be killed. There is no evidence of studies conducted to engineer targeted exosomes to induce ADCC.

Scientists from Augusta University: Dr. Mohammad Harun Rashid, Dr. Thaiz Borin, Dr. Roxan Ara, Dr. Ahmet Alptekin, Dr. Yutao Liu, and led by Professor Ali Arbab determined the in vivo distribution of M2 macrophages using novel engineered exosomes. Their findings showed M2 macrophage depletion by the engineered exosomes both in vitro and in vivo. The work is published in the Advanced Therapeutics journal.

The research team tracked the accumulation of rhodamine-labeled precision peptide in CD206-positive macrophages in the lungs, spleen, and tumor, which demonstrated their specificity. Then, they engineered exosomes targeted at CD206-Positive M2 Macrophages. When viewed under transmission electron microscopy, the engineered exosomes were round in size with no deformity. The exosomes were attached and incorporated by the CD206-positive macrophages in vitro. However, treatment with anti-CD206 peptide attenuated the binding of the engineered exosomes. The authors used fluorescence microscopy to visualize the co-localization of engineered exosomes with the CD206-positive M2 macrophages, a demonstration of the ability of the targeting potential of the engineered exosomes in vivo.  A significant accumulation of exosomes was observed in the tumor, lung, and spleen of mice injected with ¹¹¹In-oxine-labeled M2-targeting exosomes with noticeable localization in the lymph nodes and bones. Treatment with Clophosome-A (depletes more than 90% macrophages) reduced the accumulation of targeted exosomes. Similarly, the tumor, lung, and spleen of animals injected with ¹¹¹In-oxine-labeled M2-targeting exosomes showed substantially decreased radioactivity. Furthermore, Augusta University scientists successfully conjugated engineered exosomes with the Fc portion of mouse IgG2b to induce ADDC and showed strong cytotoxic effects on TAMs in vitro. When the research team used therapeutic IgG2b exosome resulted in a dose-dependent decrease in M2 macrophage with no effect on the T cell population. Moreover, treatment with engineered therapeutic exosomes caused a slower tumor growth in treated mice and prolonged their survival.

In summary, this study conducted is important and showed that exosomes can be engineered to be used in diagnosis, monitoring, and preventing the growth and metastasis of tumors to improve survival. The study will pave the way for the translational application of exosome-based theranostics.