Injectable Protein-Like Polymers Protect Rodent Heart After Myocardial Infarction

Scientists at Northwestern University and at the University of California San Diego have developed a potent injectable therapy that the results of rodent studies showed can protect the heart from damage after a heart attack.

The therapeutic approach comprises specially designed polymers that act like proteins. These protein-like polymers (PLPs) “grab” onto regulatory proteins, which blunt the body’s natural healing process, in heart tissue. With those proteins out of the way, the healing proteins are free to do their job—preventing stress and inflammation. After demonstrating success in cell culture, the scientists tested their new therapy in a rat model of myocardial infarction (MI). Following a single, low-dose intravenous injection, the animals experienced decreased inflammation and cell death along with improved cardiac function and increased growth of new blood vessels.

“Heart disease remains the leading cause of death worldwide, with heart attacks accounting for many of those deaths,” said Nathan Gianneschi, PhD, the Jacob and Rosaline Cohn Professor of Chemistry at Northwestern’s Weinberg College of Arts and Sciences, a professor of materials science and engineering and of biomedical engineering at the McCormick School of Engineering and a professor of pharmacology at Feinberg School of Medicine. “Despite this startling regularity, there is relatively little that can be done to change the course of the subsequent progression to heart failure. Our work introduces an entirely new type of therapy capable of addressing previously ‘undruggable’ targets within the cells. It offers a promising strategy to change the course of this devastating disease.”

“Preventing heart failure after a heart attack is still a major unmet clinical need,” added Karen Christman, PhD, a Professor in the Shu Chien-Gene Lay Department of Bioengineering at the UC San Diego Jacobs School of Engineering. “The goal of this therapy is to intervene very soon after someone suffers a heart attack to keep them from ultimately going into heart failure.”

Research leads Gianneschi and Christman are co-senior authors of the researchers’ published paper in Advanced Materials, titled “Protein-Like Polymers Targeting Keap1/Nrf2 as Therapeutics for Myocardial Infarction,” in which they concluded, “These results have broad implications not only for MI but also for other oxidative stress-driven diseases and conditions.”

Centers for Disease Control and Prevention figures indicate that in the US, 6.7 million people over the age of 20 years have heart failure (HF), which occurs when the heart is unable to pump enough blood to the rest of the body, the authors wrote. “… a staggering 52.6% of those with HF will die within 5 years.” The most significant cause of heart failure is a myocardial infarction, which affects more than 800,000 Americans each year, the team added. “These statistics highlight the need for the development of therapeutics to help prevent progression to HF following MI.”

When a person suffers a heart attack, their heart muscle often becomes damaged due to a lack of oxygen and increased oxidative stress. This damage can lead to inflammation and scarring, which eventually weakens the heart and causes heart failure. Although current treatments exist to restore blood flow, these methods do not fully prevent the long-term damage that leads to heart failure over time. “… despite tremendous clinical need, treatment options focusing on preventing and repairing the damage caused by acute cardiac ischemic events are lacking,” the investigators stated.

To address this unmet need, the research team focused on the interaction between two proteins, Keap1 and Nrf2. While Nrf2 protects heart cells from stress and inflammation, Keap1 physically binds to Nrf2, regulating its function. This prevents Nrf2 from entering the cell’s nucleus, where it can activate protective genes.

“Based on past biological studies, Nrf2 has been shown to have a positive effect on heart health following heart attack,” Gianneschi said. “We wanted to see if boosting Nrf2 could act to help the body heal itself after a heart attack.” The authors also noted, “Although small molecules targeting Keap1/Nrf2 have been developed and are used clinically for other diseases, these inhibitors face significant challenges with off-target effects, owing to the non-specific targeting of Keap1.”

Gianneschi and colleagues had previously developed the PLP platform, in which nanoscale precision polymers mimic proteins to act like artificial antibodies. Once inside cells, they effectively grab biological targets. For their newly reported study Gianneschi, Christman and colleagues engineered a PLP with multiple arms that mimic a part of the Nrf2 protein that typically binds to Keap1, and this newly engineered PLP can grab onto Keap1 and inhibit the Keap1/Nrf2 protein-protein interaction.

Because it has many arms, the PLP binds strongly to Keap1, preventing it from interacting with Nrf2. With Keap1 out of the way, Nrf2 can then move into the heart cell’s nucleus to exert its protective effects.

The researchers then conducted laboratory tests on heart muscle cells to evaluate effectiveness of the Keap1-inhibiting PLPs. Results from their experiments showed that the PLPs—even at very low concentrations—successfully protected cells from damage caused by oxidative stress. Testing their approach in vivo, the team administered a single dose of PLP intravenously in a small animal model of heart attack. “The challenge was whether, despite activity in vitro, an intracellular protein–protein interaction could be targeted following an intravenous injection in the rat MI model,” they wrote.

The researchers say this novel PLP platform represents a significant advancement in therapeutic development, offering a new tool to tackle challenging biological targets where traditional approaches have fallen short. Gianneschi is scientific founder of Northwestern spin-out company Grove Biopharma, which is commercializing the PLP platform. With Grove Biopharma, researchers are developing PLPs to target protein-protein interactions in various diseases, with an initial focus on cancer and neurodegenerative diseases.

“Proteins are the molecular machines that drive all essential cellular function, and dysregulated intracellular protein-protein interactions are the cause of many human diseases,” Gianneschi said. “Existing drug modalities are either unable to penetrate cells or cannot effectively engage these large disease target domains. We are looking at these challenges through a new lens, and I am excited to continue collaborating with the Grove team to help advance this new modality to the clinic.”

In their paper the team acknowledged that future studies will be needed to evaluate optimal timing for inducing and maintaining the Nrf2 pathway, and to investigate multi-dosing of Keap1i-PLP to optimize the Nrf2-mediated response. “Though Keap1i-PLPs as they stand did not provide complete resolution of the pathologic changes induced by MI, there is now precedent for utility as adjunctive therapies in the acute setting, especially in the case of procedures that result in reperfusion of ischemic tissues where oxidative stress is of abundance, as demonstrated by other biomaterials targeting oxidative stress in MI,” the authors concluded. “For example, targeting the Keap1/Nrf2 via the PLP platform could be done for treating ischemia-reperfusion injury in other organs, such as in the kidney and liver.”