November 04, 2025

Release Subtitle: Researchers use a mouse cancer model to show that tumors expressing Archaerhodopsin 3 shrink after exposure to green light

Release Summary Text: Archaerhodopsin 3 (AR3) is a microbial proton pump that increases alkalinity inside a cell when exposed to green light. Scientists from Okayama University successfully inserted AR3 genes into two mouse cancer cell lines. Upon exposure to green laser light, these modified cells died due to increased alkalinity, both in vitro and in mouse tumor model. This mechanism points the way to highly specific and minimally toxic anti-cancer therapies.

Full text of release: One of the hallmarks of cancer cells is their ability to evade apoptosis, or programmed cell death, through changes in protein expression. Inducing apoptosis in cancer cells has become a major focus of novel cancer therapies, as these approaches may be less toxic to healthy tissue than conventional chemotherapy or radiation. Many chemical agents are currently being tested for their ability to trigger apoptosis, and researchers are increasingly exploring light-activated molecules that can be precisely targeted to tumor sites using lasers, sparing surrounding healthy tissue.

Cancer cells have mitochondria that supply energy for rapid growth and division, but an overly alkaline environment is thought to disrupt mitochondrial function, leading to apoptosis.

A microbial protein called Archaerhodopsin-3 (AR3) may hold the key to alkalinity-induced apoptosis. When exposed to green light, AR3 pumps hydrogen ions out of the cell, increasing alkalinity, disrupting cellular functions, and eventually inducing apoptosis. The ability of AR3 to induce apoptosis in cancer-specific cell lines was described in a recent paper by Professor Yuki Sudo, Dr. Keiichi Kojima, Dr. Shin Nakao, and their team from the Graduate School of Medicine, Dentistry and Pharmaceutical Sciences at Okayama University, Japan. Their findings were published online in the Journal of the American Chemical Society on November 4, 2025.

“In our previous study, we established a novel optogenetic method to induce apoptotic cell death via intracellular pH alkalinization using AR3,” said Prof. Sudo. He added, “In this study, we applied our AR3-based optogenetic strategy to murine cancer cell lines and demonstrated its high efficacy in inducing apoptosis and antitumor effects both in vitro and in vivo.”

The authors first used genetically modified viruses to insert AR3 genes into a mouse colorectal cancer cell line (MC38) and a melanoma cell line (B16F10). Cells without AR3 expression survived normally when exposed to green light. In contrast, AR3-expressing cells showed high rates of cell death—over 40% in MC38 and over 60% in B16F10—along with clear signs of mitochondrial disruption as the cause of apoptosis. No apoptosis occurred without green light, confirming that AR3 activity was specifically light-induced.

Encouraged by these findings, the team used these cell lines to induce the formation of tumors in healthy mice. When these tumors were exposed to green laser light 6 days later, AR3-expressing tumors showed significant cell death and reduced multiplication of cells at the outer layers of the tumor. More importantly, at 13 days after tumor implantation, AR3-expressing tumors were 65% to 75% smaller than non-AR3 tumors.

“Notably, in tumors derived from MC38 cells, a reduction in tumor volume was observed between days 10 and 13 after cell transplantation. This delayed regression may reflect not only the direct effects of apoptosis induction and inhibition of cell proliferation but also the engagement of antitumor immune responses,” adds Prof. Sudo.

While these findings are highly promising, the study used cancer cells genetically modified before implantation, and further research is needed to determine whether pre-existing tumors can be made to express AR3 effectively. The authors also note that light penetration remains a limitation, as green laser light can induce apoptosis only to a depth of about 1 mm.

“By demonstrating light-triggered apoptosis and significant tumor growth suppression in two distinct cancer models, MC38 and B16F10, we highlight the generalizability and effectiveness of this approach,” said Prof. Sudo, emphasizing the importance of these findings. The authors suggest that AR3-based optogenetic therapy could eventually be combined with other cancer treatments to enhance effectiveness and target a broader range of tumors.

Release URL: EurekAlert!: Light-sensitive microbial protein may herald new cancer therapies

Reference: Title of original paper: Optogenetic Cancer Therapy Using the Light-Driven Outward Proton Pump Rhodopsin Archaerhodopsin‐3 (AR3) Journal: Journal of the American Chemical Society DOI: 10.1021/jacs.5c13053

Contact Person: *Professor Yuki Sudo from Okayama University * Yuki Sudo is a Professor at the Graduate School of Medicine, Dentistry and Pharmaceutical Sciences at Okayama University, Japan. Prof. Sudo completed his PhD from Hokkaido University in 2005 and has over 130 academic publications to his name. His research focuses on the light-sensitive protein rhodopsin, and its potential applications. He has received awards from the Ministry of Education, Culture, Sports, Science and Technology, and the Biophysical Society of Japan. In addition to his research, Prof. Sudo has served on the editorial boards of prominent biophysics journals including Biophysics and Physicobiology and the Journal of Biological Chemistry.

About Dr. Keiichi Kojima from Okayama University Keiichi Kojima is a Lecturer at the Graduate School of Medicine, Dentistry and Pharmaceutical Sciences at Okayama University, Japan. Dr. Kojima completed his PhD from Kyoto University in 2005 and has authored over 50 research papers. His research focuses on biochemistry, specifically opsins. He has received awards for young scientists from Ministry of Education, Culture, Sports, Science and Technology, as well as several Japanese research societies. Dr. Kojima serves on the editorial boards of Scientific Reports and the Biophysical Society Journal.

About Dr. Shin Nakao from Okayama University Shin Nakao is a researcher at Okayama University, Japan, specialising in Pharmacy and Pharmaceutical Sciences. His work primarily focuses on rhodopsin, a light-sensitive protein involved in cellular signalling and optogenetic applications. At the Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Dr. Nakao’s research explores how rhodopsin and related photoreceptive proteins can be harnessed for innovative therapeutic strategies, including light-driven modulation of cellular processes. His expertise lies at the intersection of biopharmaceutical science and photobiology, contributing to advancements in optogenetic tools and light-based biomedical research.