A team led by researchers at Washington State University (WSU) has developed a nanoparticle technology to deliver cell-killing drugs to shut down the overactive immune response that can cause damage or death in diseases like stroke and sepsis without affecting other cell types or compromising the immune system.
In a study published in Science Advances, the researchers outlined the technology that allows the nanoparticles to target neutrophils that drive dangerous inflammatory reactions while leaving beneficial neutrophils alone. That’s a challenge that previous efforts have not been able to overcome.
"Scientists have started realizing that neutrophils – which were always seen as the 'good guys' for the key role they play in our immune system – are actually also contributing to the pathology of all kinds of diseases," said the study's senior author, Zhenjia Wang, an associate professor in the WSU College of Pharmacy and Pharmaceutical Sciences.
“Neutrophils form the defensive line to protect the body. They migrate to infected tissue and remove pathogens. That’s the good part,” Wang told BioWorld. “If you get viral pneumonia, an appropriate amount of neutrophils will respond and they will help you heal.”
Controlling rogue neutrophils
But sometimes the neutrophils get carried away and cause serious problems. “In sepsis, for instance, the neutrophils are overactivated and they cannot distinguish between infection and healthy tissue,” he explained. The excessive response can cause tissue damage to the heart, lungs and other organs. Patients who have severe sepsis or septic shock have a 40% to 60% mortality rate.
The same overreaction contributes to the neurologic damage in ischemic stroke, Wang noted. Stroke has historically been viewed as a vascular disease, but recent studies have demonstrated that inflammation and immune response play a critical role in the acute and long-term damage to the brain following ischemic stroke.
In stroke, microglial activation triggers production of pro-inflammatory cytokines and a rush of lymphocytes and macrophages to the injured brain tissue. The overresponse can kill cells in the area around the stroke core after reperfusion, extending the neurological damage.
No therapies have yet been developed to mute the immune response. In fact, no new therapies for stroke have been developed since tissue plasminogen activator therapy, more than 20 years ago.
Wang said he thinks the nanoparticles could change that. “Ischemic stroke is our next model. We can control when inflammation happens and when we release nanoparticles. It’s an easy model to demonstrate our concept,” he said.
Targeting drug delivery
Neutrophils comprise up to 70% of the body’s white blood cells, so killing all of them is not an option. Ordinarily, they migrate from the bone marrow where they are produced into the bloodstream. They then typically circulate for eight to 20 hours before returning to the bone marrow to die. Inflammation caused by infection or trauma can extend their lifecycle and increase the number of neutrophils in circulation at one time, making it more likely that some will accumulate in and damage healthy tissue.
"Neutrophils don't know who the enemies are," Wang said. "They just attack, releasing all kinds of harmful proteins in the bloodstream. They will kill bacteria, but they will also kill healthy tissue in the body at the same time."
The researchers found that Fc-gamma receptors found on the surface of all neutrophils are only activated in inflammatory neutrophils. Using albumin, a protein found in the bloodstream, they developed nanoparticles that attach to the activated Fc-gamma receptors. As a result, the nanoparticles ignore the resting, beneficial neutrophils and seek out the activated, inflammatory ones. The activated neutrophils internalize the nanoparticles.
The nanoparticles carry the cancer drug doxorubicin. The bond between the nanoparticle and the drug releases when exposed to the acid of the neutrophil’s interior, but remains intact in the alkaline environment of the bloodstream. The doxorubicin triggers cell apoptosis.
The paper showed that the nanoparticles increased survival in sepsis and reduced neurological damage from stroke in mice. "Our experiment found that our doxorubicin albumin nanoparticles can decrease the lifespan of harmful neutrophils in the bloodstream," Wang said. "More importantly, we also found that our nanoparticles don't inhibit the neutrophils' function in the bone marrow."
The study also demonstrated that the low dose of doxorubicin used, about 5% of the amount typically required for cancer treatment, was safe. “We didn’t see any toxicity in major organs,” Wang said, “and doxorubicin is well-tolerated compared to other drugs.”
While the team is focused on acute inflammation applications now, Wang noted that the technology may also be able to address chronic inflammatory diseases such as rheumatoid arthritis and atherosclerosis in the future. “Nanotechnology is very powerful and can circulate for a longer time with one injection, so it could be used for chronic disease. We are working on this direction,” he said.
The team hopes to demonstrate that the nanoparticles can be internalized by human neutrophils next. “After addressing those questions, we’ll find a partner to quickly develop commercialization of the technology,” Wang said.