Method for evaluating protrusion-forming ability of cell spheroids

1. A method for evaluating a protrusion-forming ability of cell spheroids, the method comprising:

step (a) of imaging a cell spheroid labeled with a fluorescent substance using a fluorescence microscope at a resolution capable of identifying individual cells, and acquiring a plane tomographic image of a fluorescence emitted from the fluorescent substance,

step (b) of analyzing the plane tomographic image acquired in step (a) to determine a protrusion part of the cell spheroid, and

step (c) of evaluating a protrusion-forming ability of the cell spheroid based on the protrusion part determined in step (b),

wherein:

in step (a), two or more plane tomographic images of the fluorescence emitted from the fluorescent substance are acquired, the tomographic images having different focal positions,

in step (b), the two or more plane tomographic images acquired in step (a) are superimposed to construct a stereoscopic image of the cell spheroid, and the stereoscopic image is analyzed to determine the protrusion part of the cell spheroid, and

in step (c), the protrusion-forming ability of the cell spheroid is evaluated based on one of (i) a ratio between a total volume of the cell spheroid and a volume of a substantially spherical central part of the cell spheroid, (ii) a ratio between a volume of the protrusion and a volume of a substantially spherical central part of the cell spheroid, and (iii) a ratio between a volume of the protrusion and a total volume of the cell spheroid.

2. The method according to claim 1 , wherein the cell spheroid to be imaged in step (a) is a cell spheroid in which a cytoskeleton is further fluorescently labeled.

3. The method according to claim 1 , wherein:

the cell spheroid to be imaged in step (a) is a cell spheroid in which a nucleic acid is further fluorescently labeled, and

in step (a), a plane tomographic image of the fluorescence emitted from the nucleic acid is also acquired.

4. The method according to claim 3 , further comprising:

step (d) of analyzing the plane tomographic image of the fluorescence emitted from the nucleic acid of the cell spheroid to determine live/dead of respective cells constituting the cell spheroid.

5. The method according to claim 1 , wherein in step (c), the protrusion-forming ability of the cell spheroid is evaluated based on one of a length, a maximum width, and presence/absence of branching of each protrusion formed on the cell spheroid.

6. The method according to claim 1 , wherein in step (c), the protrusion-forming ability of the cell spheroid is evaluated based on one or more selected from the group consisting of a number, a directionality, a maximum length, an average length per protrusion, and an average number of branches per protrusion of protrusions formed on the cell spheroid.

7. The method according to claim 1 , wherein the cell spheroid is embedded in a gel.

8. The method according to claim 7 , wherein:

the cell spheroid a protrusion of which is labeled with the fluorescent substance in step (a) is obtained by applying an external stimulation to the cell spheroid embedded in the gel to form the protrusion, and then labelling the protrusion with the fluorescent substance, and

the protrusion-forming ability is evaluated in a state where the cell spheroid is applied with the external stimulation.

9. The method according to claim 8 , wherein:

the external stimulation is a physiologically active substance, and

the cell spheroid to be imaged in step (a) is a cell spheroid in which a protrusion is formed on the cell spheroid after contacting with the physiologically active substance, and labeled with the fluorescent substance.

10. The method according to claim 9 , wherein the physiologically active substance is an anticancer agent.

11. The method according to claim 8 , wherein:

the external stimulation is one of a non-ionizing radiation and an ionizing radiation, and

the cell spheroid to be imaged in step (a) is a cell spheroid in which the protrusion is formed on the cell spheroid after irradiating at least a part of the cell spheroid embedded in the gel with the one of the non-ionizing radiation and the ionizing radiation, and labeled with the fluorescent substance.