Cancer immunotherapies, such as immune checkpoint inhibitors (ICIs), are effective against many types of cancer. However, these treatments don’t work well for some tumors, including ovarian cancer (OC).
MIT researchers have now designed polymer-coated nanoparticles (NPs) that can deliver the immune-stimulating molecule IL-12 directly to ovarian tumors. Preclinical studies showed that when given alongside immune checkpoint inhibitor therapy, IL-12 helped the immune system launch an attack on cancer cells. Working with a mouse model of ovarian cancer, the researchers demonstrated that the combination treatment could eliminate metastatic tumors in more than 80% of animals. When the mice were later injected with more cancer cells to simulate tumor recurrence, their immune cells remembered the tumor proteins and cleared them again.
“What’s really exciting is that we’re able to deliver IL-12 directly in the tumor space,” said Paula Hammond, PhD, an MIT Institute Professor, MIT’s vice provost for faculty, and a member of the Koch Institute for Integrative Cancer Research. “And because of the way that this nanomaterial is designed to allow IL-12 to be borne on the surfaces of the cancer cells, we have essentially tricked the cancer into stimulating immune cells to arm themselves against that cancer.”
Hammond and Darrell Irvine, PhD, a professor of immunology and microbiology at the Scripps Research Institute, are senior authors of the team’s published report in Nature Materials,” titled “IL-12-releasing nanoparticles for effective immunotherapy of metastatic ovarian cancer,” in which the authors stated, “These findings demonstrate the potential of ‘target-and-release’ NP designs to effectively concentrate cytokine in disseminated OC lesions and promote robust antitumor immunity.”
Study first author Ivan Pires, PhD, is currently a postdoc at Brigham and Women’s Hospital. Most tumors express and secrete proteins that suppress immune cells, creating a tumor microenvironment (TME) in which the immune response is weakened. One of the main players that can kill tumor cells are T cells, but they get sidelined or blocked by the cancer cells and are unable to attack the tumor. Checkpoint inhibitors are an FDA-approved treatment designed to take those brakes off the immune system by removing the immune-suppressing proteins so that T cells can mount an attack on tumor cells.
For some cancers, including some types of melanoma and lung cancer, removing the brakes is enough to provoke the immune system into attacking cancer cells. However, ovarian tumors have many ways to suppress the immune system, so checkpoint inhibitors alone usually aren’t enough to launch an immune response. “Immunotherapies such as immune checkpoint inhibitors are effective in treating several advanced cancers, but these treatments have had limited success in metastatic ovarian cancer,” the authors wrote.
“The problem with ovarian cancer is no one is hitting the gas. So, even if you take off the brakes, nothing happens,” Pires commented. IL-12 offers one way to “hit the gas,” by supercharging T cells and other immune cells. However, the large doses of IL-12 required to get a strong response can produce side effects due to generalized inflammation, such as flu-like symptoms (fever, fatigue, GI issues, headaches, and fatigue), as well as more severe complications such as liver toxicity and cytokine release syndrome—which can be so severe they may even lead to death.
So while immunostimulatory agents such as cytokines and costimulatory antibodies may have the potential to overcome the current limitations of immunotherapy for OC patients, which include poor baseline lymphocyte infiltration and an immunosuppressive TME “… the systemic administration of these therapeutics is severely constrained by dose-limiting toxicities,” the researchers added.
In a 2022 study Hammond’s lab developed nanoparticles that could deliver IL-12 directly to tumor cells, which allows larger doses to be given while avoiding the side effects seen when the drug is injected. However, they found that these NPs tended to release their payload all at once after reaching the tumor, which hindered their ability to generate a strong T cell response.
In mouse OC models, the administration of these liposomal LbL (layer-by-layer) NPs carrying IL-12 did show reduced toxicity over systemic IL-12 dosing, but “only modest therapeutic efficacy,” the researchers stated. “We hypothesized that the non-covalent nickel–histidine interaction used to tether IL-12 to these particles was very short-lived in vivo, leading to the premature release of cytokine before uptake in tumors.”
The particles consist of liposomes with IL-12 molecules tethered to the surface. For their newly reported study the researchers modified the particles so that IL-12 would be released more gradually, over about a week. They achieved this by using a different chemical linker to attach IL-12 to the particles. “With our current technology, we optimize that chemistry such that there’s a more controlled release rate, and that allowed us to have better efficacy,” Pires said.
They used a linker called maleimide to attach IL-12 to the liposomes. This linker is more stable than the one they used in the previous generation of particles, which was susceptible to being cleaved by proteins in the body, leading to premature release.
To make sure that the particles get to the right place, the researchers coat them with a layer of a polymer called poly-L-glutamate (PLE), which helps the particles directly target ovarian tumor cells. Once they reach the tumors, they bind to the cancer cell surfaces, where they gradually release their payload and activate nearby T cells.
In tests in mice, the researchers showed that the IL-12-carrying particles could effectively recruit and stimulate T cells that attack tumors. The cancer models used for these studies are metastatic, so tumors developed not only in the ovaries but throughout the peritoneal cavity, which includes the surface of the intestines, liver, pancreas, and other organs. Tumors could even be seen in the lung tissues.
First, the researchers tested the IL-12 nanoparticles on their own, and they showed that this treatment eliminated tumors in about 30% of the mice. They also found a significant increase in the number of T cells that accumulated in the tumor environment.
Then, the researchers gave the particles to mice along with checkpoint inhibitors. More than 80% of the mice that received this dual treatment were cured. The results were positive even when the researchers used models of ovarian cancer that are highly resistant to immunotherapy or to the chemotherapy drugs usually used for ovarian cancer.
“When combined with immune checkpoint inhibitors (ICIs), a striking response and survival rate could be observed in immunologically ‘cold’ OC mouse models,” they wrote. “We demonstrate that optimized LbL IL-12 NPs are non-toxic, elicit strong systemic antitumor immunity, drive remodeling of the TME and strongly sensitize ovarian tumors to ICI therapy.” Patients with ovarian cancer are usually treated with surgery followed by chemotherapy. While this may be initially effective, cancer cells that remain after surgery are often able to grow into new tumors. Establishing an immune memory of the tumor proteins could help to prevent that kind of recurrence.
In this study, when the researchers injected tumor cells into the cured mice five months after the initial treatment, the immune system was still able to recognize and kill the cells. “We don’t see the cancer cells being able to develop again in that same mouse, meaning that we do have an immune memory developed in those animals,” Pires said. In their paper, the team commented in summary, “Combining tumor targeting with localized cytokine dissemination in the TME significantly improves the efficacy of this immunotherapy against metastatic OC. Importantly, optimized LbL NPs exhibited strong synergy with checkpoint blockade, the current gold standard for cancer immunotherapy in the clinic.”
The researchers are now working with MIT’s Deshpande Center for Technological Innovation to spin out a company that they hope could further develop the nanoparticle technology. In a study published earlier this year, Hammond’s lab reported a new manufacturing approach that should enable large-scale production of this type of nanoparticle.
