Possible new treatment for triple-negative breast cancer

Triple-negative breast cancer, or TNBC, affects 10-15% of patients with breast cancer in the US. TNBC is called "triple-negative" because the cancer lacks an estrogen receptor, a progesterone receptor, and a HER2 (human epidermal growth factor) receptor. The absence of any of these receptors -- receptors that, when present in other forms of breast cancer, can be effectively targeted during treatment -- makes treating TNBC quite difficult, and patients with TNBC have limited treatment options. TNBC's notorious aggression makes the technical challenge of finding a reliably effective treatment target all the more serious: compared to other breast cancers, TNBC grows faster and resists treatment more stubbornly. All these factors contribute to the fact that TNBC patients suffer from worse prognoses.

But Zachary Schug, Ph.D., and co-authors have demonstrated the efficacy of a double-acting concept: silencing the gene ACSS2 impairs TNBC metabolism while simultaneously boosting the immune system's ability to fight it. ACSS2 regulates acetate, a nutrient that cancer cells -- and TNBC cells in particular -- take advantage of to grow and spread. Schug and his team used two methods to de-activate ACSS2: CRISPR-Cas9 gene editing, and the compound VY-3-135, a potent ACSS2 inhibitor identified by Schug and his colleagues in 2021.

The researchers found that targeting ACSS2 in this preclinical study not only hampered this aggressive cancer's ability to metabolize acetate and grow -- it also triggered the immune system to recognize and attack the cancer. Because cancer cells with inhibited ACSS2 can't process acetate very well, the tumor region becomes bathed in acetate, which alerts the immune system of something amiss.

This process of guiding the immune system to the cancer -- called "immunosensitization" -- has confounded other TNBC researchers. But Schug's approach showed that ACSS2 inhibition immunosensitized against TNBC so well that tumor growth was drastically reduced, even to the point of wiping out the cancer completely in some experiments.

"Basically, we've proved that the immune system can take advantage of acetate that the tumor can't process. It kicks the cancer while it's down," said Schug. "In fact, the immune system does this so well that it remembers how to attack TNBC in the future -- even if that tumor's ACSS2 gene is still active."

Another group's different ACSS2-inhibiting approach is in human clinical trials, and Schug's research shows how ACSS2-inhibiting treatment might be able to improve outcomes for patients diagnosed with the infamous TNBC. By testing ACSS2 inhibitors alongside standard anti-breast-cancer chemotherapy, Schug et al. found that ACSS2 inhibition enhanced the treatment's effectiveness.

"We knew that ACSS2 was a promising target for TNBC. Our research shows us how the immune effects of ACSS2 inhibition could eventually be used in for TNBC patients with limited treatment options," said Schug. "More research is needed, but by combining this approach with other cancer therapies, we expect to see big improvements in treating TNBC."

Co-authors: Katelyn D. Miller, Seamus O'Connor, Katherine A. Pniewski, Toshitha Kannan, Reyes Acosta, Gauri Mirji, Sara Papp, Michael Hulse, Fabrizio Bertolazzi, Yellamelli V. V. Srikanth, Rahul S. Shinde, Daniel T. Claiborne, Andrew Kossenkov, Joseph M. Salvino and Zachary T. Schug of The Wistar Institute; Fabrizio Bertolazzi of the University of Bologna; and Steven Zhao and Kathryn E. Wellen of the University of Pennsylvania.

Work supported by: This work was supported by grants from the National Institutes of Health (NIH) National Cancer Institute (NCI) DP2 CA249950-01, NIH NCI P01 CA114046, NIH R21 CA259240-01, the W.W. Smith Charitable Trust, Susan G. Komen CCR19608782 and the V Foundation for Cancer Research. This research and project is funded, in part, by a contract with the Pennsylvania Breast Cancer Coalition. The PBCC takes no part in and is in no way responsible for any analyses, interpretations or conclusions contained herein. We acknowledge funding from the NIH NCI T32 CA009171 and the American Cancer Society Rena and Victor Damone Postdoctoral Fellowship PF-20-1225-01-CCG. The Wistar Molecular Screening Facility and Genomics Facility are supported by NIH grant P30 CA010815. The Wistar Proteomic and Metabolomic Facility is supported, in part, by NIH grants R50 CA221838 and S10OD023586. The HIC is supported, in part, by NIH P30 AI045008 and P30 CA016520.