The study has two innovative aspects: the discovery of a new therapeutic target and the development of an effective nanocarrier for the selective delivery of immunotherapy and chemotherapy drugs.

Researchers have developed cancer-fighting nanoparticles that can deliver innovative chemoimmunotherapy.

According to a new study published in the journal Nature Nanotechnology, researchers at the University of Pittsburgh have developed cancer-fighting nanoparticles that simultaneously deliver chemotherapy and a novel immunotherapy.

The new immunotherapy, which silences a gene involved in immunosuppression, has been shown to be effective in shrinking tumors in mouse models of colon and pancreatic cancer when combined with chemotherapy and packaged into nanoparticles.

“There are two innovative aspects of our study: the discovery of a new therapeutic target and a new nanocarrier that is very effective in selective delivery of immunotherapy and chemotherapeutic drugs,” said senior author Song Li, M.D., Ph.D., professor of pharmaceutical sciences in the Pitt School of Pharmacy and UPMC Hillman Cancer Center investigator. “I’m excited about this research because it’s highly translational. We don’t know yet whether our approach works in patients, but our findings suggest that there is a lot of potential.”

Electron microscopy image of nanoparticles containing the chemotherapy drug FuOXP and novel immunotherapy of siRNA that blocks expression of Xkr8. Credit: Chen et al., 2022, Nature Nanotechnology, 10.1038/s41565-022-01266-2

Chemotherapy is a pillar of cancer treatment, but residual cancer cells can persist and cause tumor relapse. This process involves a lipid called phosphatidylserine (PS), which is usually found inside the tumor cell membrane’s inner layer but migrates to the cell surface in response to chemotherapy drugs. On the surface, PS acts as an immunosuppressant, protecting the remaining cancer cells from the immune system.

The Pitt researchers found that treatment with chemotherapy drugs fluorouracil and oxoplatin (FuOXP)

led to increased levels of Xkr8, a protein that controls the distribution of PS on the cell membrane. This finding suggested that blocking Xkr8 would prevent cancer cells from shunting PS to the cell surface, allowing immune cells to mop up cancer cells that lingered after chemotherapy.

Proposed strategy for how chemotherapy FuOXP can lead to immunosuppression (left side of image) in tumors but a novel immunotherapy that blocks expression of a protein called Xkr8 can reactivate the immune system (right side of image). The new study found that FuOXP led to increased levels of Xkr8, a protein that redistributes PS to the cell surface, resulting in immunosuppression due to more T-regulatory cells and tumor-promoting M2 macrophages. However, when the researchers blocked the expression of Xkr8 with siRNA, PS remained within the cell membrane’s inner layer, enhancing the immune system by boosting the numbers of tumor-fighting T cells, M1 macrophages, and dendritic cells. Credit: Chen et al., 2022, Nature Nanotechnology, 10.1038/s41565-022-01266-2

In an independent study that was recently published in Cell Reports, Yi-Nan Gong, Ph.D., assistant professor of immunology at Pitt, also identified Xkr8 as a novel therapeutic target to boost anti-tumor immune response.

Li and his team designed snippets of genetic code called short interference RNA (siRNA), which shuts down the production of specific proteins — in this case, Xkr8. After packaging siRNA and FuOXP together into dual-action nanoparticles, the next step was targeting them to tumors.

Song Li, M.D., Ph.D., professor of pharmaceutical sciences in the Pitt School of Pharmacy and UPMC Hillman Cancer Center investigator. Credit: Jan Shaw

Nanoparticles are typically too large to cross intact blood vessels in healthy tissue, but they can reach cancer cells because tumors sometimes have poorly developed vessels with holes that allow them passage. But this tumor-targeting approach is limited because many human tumors do not have large enough holes for nanoparticles to pass through.

“Like a ferry carrying people from one side of the river to the other, we wanted to develop a mechanism that allows nanoparticles to cross intact blood vessels without relying on holes,” said Li.

To develop such a ferry, the researchers decorated the surface of the nanoparticles with chondroitin sulfate and PEG. These compounds help the nanoparticles target tumors and avoid healthy tissue by binding to cell receptors common on both tumor blood vessels and tumor cells and prolonging the length of time they remain in the bloodstream.

FuOXP siRNA Nanoparticles and Mouse Colon Cancer Cells

Fluorescence microscopy image showing FuOXP-siRNA nanoparticles (red) effectively taken up by mouse colon cancer cells. Cell nuclei appear as blue circles. Credit: Chen et al., 2022, Nature Nanotechnology, 10.1038/s41565-022-01266-2

When injected into mice, about 10% of the nanoparticles made their way to their tumor — a significant improvement over most other nanocarrier platforms. A previous analysis of published research found that, on average, only 0.7% of nanoparticle doses reach their target.

The dual-action nanoparticles dramatically reduced the migration of immunosuppressing PS to the cell surface compared to nanoparticles containing the chemodrug FuOXP alone.

Next, the researchers tested their platform in mouse models of colon and pancreatic cancer. Animals treated with nanoparticles containing both FuOXP and siRNA had better tumor microenvironments with more cancer-fighting T cells and fewer immunosuppressive regulatory T cells than animals that received placebo or FuOXP doses.

As a result, mice that received the siRNA-FuOXP nanoparticles showed a dramatic decrease in tumor size compared to animals that received those carrying just one therapy.

According to Li, the study also pointed to the potential of combining the FuOXP-siRNA nanoparticles with another type of immunotherapy called checkpoint inhibitors. Immune checkpoints such as PD-1 act like brakes on the immune system, but checkpoint inhibitors work to release the brakes and help immune cells to fight cancer.

The researchers found that FuOXP nanoparticles with or without siRNA increased PD-1 expression. But when they added a PD-1 inhibitor drug, the combination therapy had drastic improvements in tumor growth and survival in mice.

With their sights set on translating their novel therapy to the clinic, the team is now looking to validate their findings with additional experiments and further evaluate potential side effects.