Discovery could lead to new  treatments for cancer and tumors, but probably not to any new diagnostic assays for clinical laboratories

Researchers at the University of Texas Southwestern (UTSW) Medical Center have reported discovery of “acid walls” that appear to protect various types of cancer tumors from attack by the body’s immune system cells. Though the discovery is not directly related to a biomarker for a clinical laboratory diagnostic test, the basic research will help scientists develop ways to address the tumor’s acid wall strategy for defeating the immune system.

The UT scientists made their discovery using an internally developed imaging technique that employs nanoparticle probes to detect levels of acidity in cells. The research, they suggest, “could pave the way for new cancer treatment approaches that alter the acidic environment around tumors,” according to a UTSW press release.

Study leader Jinming Gao, PhD, Professor in the Harold C. Simmons Comprehensive Cancer Center and in the Departments of Biomedical Engineering, Cell Biology, Otolaryngology-Head and Neck Surgery, and Pharmacology at UT Southwestern, leads the Gao Lab which developed the nanoparticle technology.

The researchers published their study, titled “Severely Polarized Extracellular Acidity around Tumour Cells,” in the journal Nature Biomedical Engineering.

Developing Acid Walls

As explained in the press release, scientists have long known that cancer cells are slightly more acidic than most healthy tissue. Gao and his team designed a nanoparticle known as pegsitacianine—a pH-sensitive fluorescent nanoprobe for image-guided cancer surgery—that disassembles and lights up when exposed to the acidic conditions in tumors.

However, “it was unclear why these nanoparticles fluoresced since a tumor’s acidity was thought to be too mild to trigger their activation,” the press release note.

To learn more, they used nanoparticle probes to illuminate a variety of individual cancer cells sampled from humans and mice, including lung, breast, melanoma, and glioblastoma, as well as tumor tissue. They discovered that the cancer cells secreted lactic acid—a waste product of digested glucose—at higher levels than previously known. The cells “pumped” the acid away from their malignant neighbors to form a protective “acid wall” around the tumor, the researchers noted in Nature Biomedical Engineering.

“Samples from human tumors showed that this acid wall was practically devoid of CD8+ T cells within the tumors, an immune cell type known to fight cancer,” the press release states. “When the researchers grew cancer cells and CD8+ T cells together in petri dishes that had been acidified to a 5.3 pH, the cancer cells were spared while the CD8+ T cells perished within three hours, suggesting that this severe acidity might thwart immune cell attack without harming the cancer cells.”

Gao’s team previously discovered that sodium lactate, the “conjugate base of lactic acid” as they describe it, increases the longevity of T cells and thus enhances their cancer-fighting capabilities. The researchers described the two molecules—lactate and lactic acid—as “Dr. Jekyll and Mr. Hyde,” and suggested that future therapies could seek to convert lactic acid to lactate.

“Gao noted that this discovery will lead to several new lines of research, such as studies to better understand how cancer cells polarize their acid excretion, how those cells can withstand the acidity level that kills CD8+ T cells, and how to inhibit acid excretion to allow T cells to better kill cancer cells,” the press release states.

Commercializing the Technology

Pegsitacianine was designed to aid cancer surgeons by illuminating the edges of solid metastatic tumors in real time during surgery, a 2023 UTSW Medical Center press release explains. About 24 hours prior to surgery, nanoprobes are delivered via IV. Then, the surgeon uses a near-infrared camera to visualize the cells.

UTSW has licensed pegsitacianine to OncoNano Medicine, a Dallas-area biotech startup launched to commercialize technologies from Gao Lab. Gao and his colleague Baran Sumer, MD, Professor and Chief of the Division of Head and Neck Oncology in UT Southwestern Medical Center’s Department of Otolaryngology and co-author on the study, both sit on OncoNano’s advisory board.

In January 2023, OncoNano announced that pegsitacianine had received Breakthrough Therapy Designation for Real-Time Surgical Imaging from the US Food and Drug Administration (FDA), which will fast-track the technology for development and regulatory review.

In a Phase II clinical trial published in the Annals of Surgical Oncology, the researchers tested the technology as part of cytoreductive surgery in patients with peritoneal metastases. However, a November 2023 UTSW press release noted that the technology is “tumor-agnostic and could potentially be used in other forms of cancer.” It is currently ready for Phase 3 trials, according to the OncoNano website.

More research and studies are needed to better understand this dynamic of cancer cells. Collectively, this research into cancer by different scientific teams is adding new insights into the way tumors originate and spread. At this time, these insights are not expected to lead to any new diagnostics tests that pathologists and clinical laboratories could use to detect cancer.

—Stephen Beale

Related Information:

UTSW Discovers Protective ‘Acid Wall’ Formed by Cancer Cells

Scientists Discover How Cancer Creates ‘Acid Wall’ Against Immune System

Severely Polarized Extracellular Acidity around Tumour Cells

Fluorescent Nanoprobe Produces ‘Breakthrough’ for Peritoneal Metastases

Pegsitacianine Informs Surgery in Peritoneal Carcinomatosis