Researchers are shining a light on cancer cells' energy centers - literally - to damage these power sources and trigger widespread cancer cell death.
In a new study, scientists combined strategies to deliver energy-disrupting gene therapy using nanoparticles manufactured to zero in only on cancer cells. Experiments showed the targeted therapy is effective at shrinking glioblastoma brain tumors and aggressive breast cancer tumors in mice.
The research team overcame a significant challenge to break up structures inside these cellular energy centers, called mitochondria, with a technique that induces light-activated electrical currents inside the cell. They named the technology mLumiOpto.
"We disrupt the membrane so mitochondria cannot work functionally to produce energy or work as a signaling hub. This causes programmed cell death followed by DNA damage - our investigations showed these two mechanisms are involved and kill the cancer cells," said co-lead author Lufang Zhou, professor of biomedical engineering and surgery at The Ohio State University. "This is how the technology works by design."
Zhou collaborated on the research with co-lead author X. Margaret Liu, professor of chemical and biomolecular engineering at Ohio State, who developed the particles used to precisely deliver the gene therapy to cancer cells. Zhou and Liu are also both investigators in The Ohio State University Comprehensive Cancer Center.
The study appears in the December issue of the journal Cancer Research.
Mitochondria, the primary producers of energy that fuels cell functions, have been considered an attractive anti-cancer therapeutic target for years, but their impermeable inner membrane complicates these efforts. Zhou's lab cracked the code five years ago by figuring out how to exploit the inner membrane's vulnerability - an electrical charge differential that keeps its structure intact and functions on track.
"Previous attempts to use a pharmaceutical reagent against mitochondria targeted specific pathways of activity in cancer cells," he said. "Our approach targets mitochondria directly, using external genes to activate a process that kills cells. That's an advantage, and we've shown we can get a very good result in killing different types of cancer cells."
Zhou's earlier cell studies showed the mitochondrial inner membrane could be disrupted by a protein that creates electrical currents, and researchers activated that light-induced protein with a laser. In this new work, the team created an internal source of light - key to translating the technology for clinical use.
The strategy involves delivering genetic information for two types of molecules: a light-sensitive protein known as CoChR that can produce positively charged currents, and a bioluminescence-emitting enzyme. Packed into an altered virus particle and delivered to cancer cells, the proteins are produced as their genes are expressed in mitochondria. A follow-up injection of a specific chemical turns on the enzyme's light to activate CoChR, which leads to mitochondrial collapse.
The other half of the battle is ensuring this therapy does not interfere with normal cells.
Liu's lab specializes in targeted anti-cancer therapy development. The foundation for the delivery system in this work is the well-characterized adeno-associated virus (AAV), a minimally infectious virus engineered to carry genes and promote their expression for therapeutic purposes.
The team refined the system to enhance its cancer specificity by adding a promoter protein to drive up expression of the CoChR and bioluminescent enzyme only in cancer cells. The researchers also manufactured the AAV using human cells that encased the gene-packed virus inside a natural nanocarrier resembling extracellular vesicles that circulate in human blood and biological fluids.
"This construction assures stability in the human body because this particle comes from a human cell line," Liu said.
Finally, the researchers developed and attached to the delivery particle a monoclonal antibody designed to seek out receptors on cancer cell surfaces.
"This monoclonal antibody can identify a specific receptor, so it finds cancer cells and delivers our therapeutic genes. We used multiple tools to confirm this effect," she said. "After constructing AAVs with a cancer-specific promoter and a cancer-targeting nanoparticle, we found this therapy is very powerful to treat multiple cancers."
Experiments in mouse models showed the gene therapy strategy significantly reduced the tumor burden compared to untreated animals in two fast-growing, difficult-to-treat cancers: glioblastoma brain cancer and triple negative breast cancer. In addition to shrinking the tumors, the treatment extended survival of mice with glioblastomas.
Animal imaging studies also confirmed the effects of the gene therapy were limited to cancer tissue and were undetectable in normal tissue. Results further suggested that attaching the monoclonal antibody had the added benefit of inducing an immune response against cancer cells in the tumor microenvironment.
The team is studying additional potential therapeutic effects of the mLumiOpto in glioblastoma, triple negative breast cancer and other cancers. Ohio State has submitted a provisional patent application for the technologies.
This research was supported by the U.S. Department of Defense and the National Institutes of Health.
Kai Chen of Liu's lab and Patrick Ernst of Zhou's lab were co-first authors of the study. Additional co-authors were Anusua Sarkar, Seulhee Kim, Yingnan Si, Tanvi Varadkar and Matthew Ringel, all of Ohio State.
