Objective: To study the cell morphology change in dormancy and proliferation stage of colorectal cancer stem cells in order to provide reference to the treatment of colorectal cancer.
Methods: The subpopulation of EpCAM(high)/CD44(+)/CD133(+) was isolated from fresh colorectal cancer tissues. These cells were tested by xenograft assay in NOD/SCID nude mice. Colorectal cancer stem cells underwent three-dimensional culture, and the growth curve of stem cells was drawn by WST-1. The expression of P27 and Ki-67 was examined by flow cytometry to understand the phase of dormancy and proliferation of colorectal cancer stem cells. Then the morphological differences of colorectal cancer stem cells between dormant and proliferation stages were recognized by immunofluorescence staining of actin.
Results: The percentage of EpCAM(high)/CD44(+)/CD133(+) was 1.6%, and the subpopulation was confirmed to be colorectal cancer stem cells by means of the experiment of tumorigenicity in vivo. The growth curve of colorectal cancer stem cells was "S" type. Colorectal cancer stem cells grew slowly in the first three days. The expression of P27 was gradually up-regulated, and the level of Ki-67 was very low. These cells remained quiescence, which was the so-called dormancy. The expression of Ki-67 of colorectal cancer stem cells was at high level since the fourth day, and the P27 level was very low. According to the growth curve, this period belonged to the proliferative stage of colorectal cancer stem cells. On immunofluorescence staining, colorectal cancer stem cells with high level of P27 were round, large, and few pseudopodium, but no obvious death was found. These cells showed characteristics of dormancy. In contrast, the stem cells with high level of Ki-67 had much pseudopodium, showing proliferation and invasion.
Conclusions: Cancer recurrence and metastasis may be associated with the change of growth state of cancer stem cells. Colorectal cancer stem cells in the proliferation stage show greater proliferative and invasive ability as compared to the dormancy stage, which provides a new perspective for the treatment of colorectal cancer, and recurrence and metastasis of other tumors.