Exploring the effect of H2O2 eustress on individual cancer cells using hopping probe scanning ion conductance microscopy (HPICM)

In a recent study published in the multidisciplinary academic journal Science Bulletin, a semi-monthly high-caliber peer-reviewed research outlet covering a broad range of natural sciences and high-tech fields, researchers from the Nano Life Science Institute (WPI-NanoLSI) at Kanazawa University utilized hopping probe scanning ion conductance microscopy (HPICM) and highly sensitive platinum-functionalized nanoelectrodes to conduct an in-depth investigation of the dynamic response of individual living colorectal cancer Caco-2 cells to changes in intracellular and extracellular hydrogen peroxide (H₂O₂) gradients, specifically focusing on eustress, at the single-cell level and in real-time. Their findings hold promise for innovative therapies against cancer and H₂O₂-related inflammatory diseases.

Reactive Oxygen Species (ROS) production plays a significant role in various diseases, including atherosclerosis, chronic obstructive pulmonary disease, and cancer. Despite promising preclinical antioxidant therapies, clinical trials have yielded unsatisfactory results. Hydrogen peroxide (H₂O₂), a stable ROS derivative, acts as a crucial participant in physiological signaling by serving as a eustressor. The concentration of H₂O₂ in the tumor microenvironment is closely linked to the occurrence and progression of colorectal cancer. A deeper understanding of how H₂O₂ functions and its specific efficacy in individual cancer cells may pave the way for more effective ROS-related treatments.

The authors utilized hopping probe scanning ion conductivity microscopy (HPICM) alongside Pt-functionalized nanoelectrodes to quantitatively assess the dynamic response in cell morphology, cell mechanical properties, and extracellular to intracellular eustress H₂O₂ gradients of individual colorectal cancer Caco-2 cells under H₂O₂ eustress. The investigation revealed that exposure to 0.1 or 1 mmol/L H₂O₂ eustress increased the extracellular to intracellular H₂O₂ gradient from 0.3 to 1.91 or 3.04, respectively. Additionally, the study found that F-actin-dependent cell stiffness increased under eustress of 0.1 mmol H₂O₂ but decreased under eustress of 1 mmol H₂O₂. Furthermore, eustress-induced cell stiffness was positively regulated by AKT activation and negatively influenced the expression of the H₂O₂-scavenging enzyme GPX2, ultimately maintaining relatively stable cellular H₂O₂ levels.

This study suggests that the eustress induced by low levels of H₂O₂ may contribute to the failure of some H₂O₂ targeted therapies. The results uncover a novel interplay between cellular physical properties and biochemical signaling in cancer cells’ antioxidant defense, shedding light on the utilization of H₂O₂ eustress for survival at the single-cell level. This understanding is critical for comprehending cancer development and other H₂O₂-related inflammatory diseases. Inhibiting GPX under H₂O₂ eustress resulted in cytotoxicity, suggesting a potential enhancement for colon cancer treatment. These findings hold promise for the development of innovative therapies targeting cancer and H₂O₂-related inflammatory diseases.

Funder
The work was supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan, JSPS Grants-in-Aid for Scientific Research (21H01770, 22K04890).

Glossary

Hopping Probe Scanning Ion Conductance Microscopy (HPICM)

The principle of scanning ion conductance microscopy (SICM) relies on monitoring the ion current that flows through a nanopipette containing electrolyte. It can map the topography of a sample by adjusting the nanopipette height to maintain a constant ion current as it is scanned over the sample surface. The proximity to the sample surface has a measurable effect on the ion current flow and, hence, feedback-controlled nanopipette withdrawal before the nanopipette makes contact with the sample, making it useful for non-contact imaging of living biological specimens.

In this study, SICM has been used in hopping probe mode, named Hopping Probe Scanning Ion Conductance Microscopy (HPICM), where the nanopipette constantly approaches and retracts from the sample, further reducing the potential for sample damage, particularly where the sample surface is not flat. The authors demonstrated that their HPICM can detect the dynamic changes in both cellular mechanical properties and topographical morphology of individual cancer cells in real-time.

About the World Premier International Research Center Initiative (WPI)

The WPI program was launched in 2007 by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

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Nano Life Science Institute (WPI-NanoLSI)

Kanazawa University

Understanding nanoscale mechanisms of life phenomena by exploring “uncharted nano-realms”

Cells are the basic units of almost all life forms. We are developing nanoprobe technologies that allow direct imaging, analysis, and manipulation of the behavior and dynamics of important macromolecules in living organisms, such as proteins and nucleic acids, at the surface and interior of cells. We aim at acquiring a fundamental understanding of the various life phenomena at the nanoscale.

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