Correlation between actin content and laser phase shift of adhesive normal and malignant prostate epithelial cells

Aiming to establish the noninvasive discrimination of cancer cells from normal cells in adherent culture, we examined in this study the reason why the laser phase shift, which is the product of refractive index and height of malignant cancer cells, was markedly smaller than that of normal cells. Both of the phase shift measured by phase-shifting laser microscopy (PLM) and the relative actin content of cells of the adhesive human prostatic carcinoma epithelial cell line (PC-3) were markedly lower than those of adhesive human prostate epithelial cells (PRECs), while there was almost no difference in morphology observed under a conventional inverted microscope, between them. The decrease in relative actin content by the addition of cytochalasin D resulted in the decrease in phase shift in both cell lines, and these cell lines showed a marked positive correlation between phase shift and relative actin content (r = 0.84). The height and refractive index of adhesive cells were determined using PLM and the height of PC-3 cells were apparently lower than those of PRECs, while there was no difference in refractive indices between PC-3 cells and PRECs. Consequently, the smaller height of PC-3 cells caused by lower actin content than of PRECs might be the reason for the lower phase shift of PC-3 cells.