In a study recently published in the journal Biomaterials, researchers from Kanazawa University use a niche type of microscopy to characterize hostile colon cancer cells
Colon cancer is a highly fatal and metastatic (fast-spreading) form of cancer. To formulate better therapies, oncologists must truly understand the nature of metastatic tumors. Current atomic force microscopy (AFM) techniques that are relied upon to visualize nanoscale images of colon tumors often damage the tissues, thereby yielding an inaccurate depiction. A research group spearheaded by Masanobu Oshima and Shinji Watanabe at Kanazawa university has utilized a novel form of microscopy to now bridge this gap.
Colon cancer stems from various genetic mutations found in cells. Some of these mutations result in more aggressive tumors that spread to distant organs. To first understand the physical manifestations of these metastatic mutants, the team employed different types of mouse colon cells: a healthy group, a benign tumor group, and a metastatic tumor group (Fig. 1 top). However, when a standard electron microscope was used to capture these cells, no discernable differences were found between the groups. Thus, high-speed scanning ion conductance microscopy (HS-SICM) was subsequently adopted.
HS-SICM showed that the metastatic tumor cells had peculiar ridges on their periphery (Fig. 1 middle). In fact, these ridges seemed to appear and disappear when viewed in real-time. These cells also showed a considerable roughness on their surface accompanied by fluctuations in surface volume, suggesting that the cells were potentially changing shape. Now, metastatic tumors are generally known to be soft in nature. Therefore, the softness, or elasticity, of these mutant cells was examined next using HS-SICM. As expected, highly metastatic cells showed elastic properties (Fig. 1 bottom). These physical characteristics combined were indicative of cells with migratory and invasive abilities.
Next, the team found a high correlation between the physical properties (volume change, surface roughness and elasticity) and the genetic sequences of cells in the metastatic tumor group (Fig. 2). The physical changes observed in these cells could thereby be attributed to their genetic alterations. Finally, similar observations using HS-SICM were attempted in human colon cancer cells. The cells were first chemically treated to induce malignancy and emulate the metastatic mouse mutant cells. Indeed, these cells proceeded to show increased surface roughness, volume changes, and elasticity after treatment. HS–SICM proved to be a useful tool in human studies too.
“HS-SICM analysis is useful for clarifying the genotype regulated physical properties and their role in malignant progression, in addition to predicting the metastatic potential of cancer cells,” conclude the researchers. A combination of the physical and genetic characteristics of colon cancer cells is imperative in identifying the nature of tumors and determining the subsequent course of treatment.
Figure 1. Top. A graphical representation of colon normal and cancer cells with define genetic mutations (i.e., A, K, T, P, F), showing their invasion deeper into healthy intestinal tissue and subsequent migration into the liver.
Middle. HS-SICM topography images show characteristic micro-ridge structures on the highly metastatic AKTP and AKTPF cell surface, while microvilli are observed on AK, AKF and AKT cells. (arrow heads)
Bottom. HS-SICM shows the difference in elasticity, or softness (red coloration), between the highly metastatic mutant cancer cells and the less invasive mutant as well as normal cells. License type: CC-BY
Figure 2. Correlation of the physical properties detected by HS-SICM and genetic mutation patterns of colon cancer cells. License type: CC-BY
High-speed scanning ion conductance microscopy (HS-SICM): Microscopy techniques like atomic force microscopy (AFM) or scanning electron microscopy (SEM) are traditionally used to provide nanoscale images of biomolecules. However, these techniques come with a set of challenges. AFM often ends up damaging delicate tissues and SEM requires chemical treatment of tissues which impacts their structure.
However, HS-SICM depicts the topography of cells and biomolecules without physically touching the samples. It involves the use of a sharp glass tip connected to a detector. An electrical signal flows between a solution and the glass tip. However, when glass tip approaches the cells or biomolecules close, electrical signal flows change. Such changes in electrical signals are then measured by the detector, which are in turn indicative of the surface topography of cells.
HS-SICM thus allows for real-time structural measurement of cells without making direct contact with them or requiring any additional chemical treatment.
Dong Wang, Linhao Sun, Satoru Okuda, Daisuke Yamamoto, Mizuho Nakayama, Hiroko Oshima, Hideyuki Saito, Yuta Kouyama, Koshi Mimori, Toshio Ando, Shinji Watanabe, Masanobu Oshima.
Nano-scale physical properties characteristic to metastatic intestinal cancer cells identified by high-speed scanning ion conductance microscope.