Macrophages are white blood cells that play a large role in immunity, including in the context of cancer. Not all macrophages behave similarly, and they can be influenced towards different sub-types. At one end of the spectrum, M1-like macrophages are pro-inflammatory, anti-tumor cells that defend the body from threats through phagocytosis. On the other extreme are M2-like macrophages that are great at repairing damaged tissue, but their anti-inflammatory phenotype can end up helping tumors progress, metastasize, and resist chemotherapy by suppressing immune recognition of the tumor. Because tumor associated macrophages (TAMs) tend to be M2-like, researchers have previously tried to deplete or activate TAMs in an attempt to halt their pro-tumor activities. However, these attempts often resulted in off-target toxicities because of their effects on other cells. The laboratory of Dr. Matthias Stephan (Clinical Research Division) used nanoparticles that target macrophages and reprogram them from M2-like to M1-like. The results of this study were recently published in the journal Nature Communications.
Because TAMs express high amounts of a mannose receptor, also called CD206, on their surface, the researchers coated the surface of the nanoparticles with Di-mannose. CD206 on the TAMs can bind to the Di-mannose on the nanoparticles and the TAMs can phagocytose the nanoparticles. This way, the nanoparticles target the TAMs and other CD206 expressing cells such as dendritic cells while not affecting other cells. The researchers used cationic polymers in the core of the nanoparticles to surround the center of the nanoparticles, the anionic mRNA, the key to reprogramming TAMs. Once phagocytosed, the nanoparticles release the mRNA into the cells. The cells then transiently express the genes encoded by the mRNA. In this application, the mRNA in the nanoparticles encodes transcription factors that polarize macrophages to the M1-like phenotype. The researchers found that these transcription factors were upregulated in transfected macrophages for five days, after which they returned to baseline levels.
They next tested the nanoparticles in a mouse model of ovarian cancer. In this model, ovarian tumors establish themselves throughout the abdominal cavity. After intraperitoneal administration of the nanoparticles, the researchers found that 40% of the mice cleared the tumors. Using flow cytometry, the investigators found a marked increase in frequency of M1-like macrophages in the peritoneum, while the proportion of M2-like macrophages dropped. They also found lymphocyte migration and infiltration into the tumor cells, suggesting that reprogrammed TAMs recruited the lymphocytes, which may be helpful in eliminating the tumors.
In untreated cancer, monocytes and macrophages can help establish metastases. The authors investigated whether the nanoparticles that reprogram macrophages can aid in the treatment of metastatic tumors. They tested the nanoparticles in a mouse model of melanoma where metastases have disseminated systemically. The authors found that mice treated with nanoparticles had reduced metastases and tumor burden in the lungs, and improved survival.
Encouragingly, the authors found that these treatments indicated the targeted nanoparticles were safe in these models at the doses they used. They noted only minor increases in serum cytokines in these experiments, normal liver and kidney function, and no evidence of off-target toxicity. “This immunotherapy could enable physicians to obviate suppressive tumors while avoiding systemic treatments that disrupt immune homeostasis,” said Dr. Fan Zhang, the lead author on the paper and post-doctoral research fellow in the Stephan lab. The Stephan lab will next work with the Nanotechnology Characterization Laboratory at the National Cancer Institute in preparation for a first-in-human clinical trial to test the nanoparticles in chemo-resistant ovarian carcinoma patients.
This work was supported by the Bezos Family Foundation, the Experimental Histopathology Shared Resource of the Fred Hutchinson/UW Cancer Consortium, the National Science Foundation, the American Cancer Society, and the American Brain Tumor Association.
Fred Hutch/UW Cancer Consortium members Drs. Eric Holland and Matthias Stephan contributed to this research.
Zhang F, Parayath NN, Ene CI, Stephan SB, Koehne AL, Coon ME, Holland EC, Stephan MT. Genetic programming of macrophages to perform anti-tumor functions using targeted mRNA nanocarriers. Nat Commun. 2019 Sep 3;10(1):3974. doi: 10.1038/s41467-019-11911-5.