Evaluation of quiescent cells in in vitro EMT6/Ro tumor models

Very little is known about the physiological biophysical, or radiosensitivity of Q cells (non-proliferating or quiescent). It is conceivable that cells become quiescent because of the local mileau, such as oxygen or nutrient deprivation, or excessive catabolities. Using in vitro tumor models, the authors attempted to study the amount of Q cells under different microenvironments and to see whether such microenvironments changes can be manifested as changes in size, buoyant density, or radiosensitivity of the cells. EMT6/Ro exponential and fed plateau monolayers, and multicellular spheroids grown in Bellco flasks were used. Hypoxia was induced using hypoxic chambers. Two-step acridine orange staining and dual parameter flow cytometric analysis were used to quantify Q cells. Percoll buoyant density gradients and centrifugal elutriation were used to isolate subpopulations of Q cells. Preliminary results suggest: 1) Plateau cells were smaller and heavier than exponential cells and contained Q cells that could be isolated by centrifugal elutriation; 2) Acute radiobiologic hypoxic cells were bigger and lighter than either exponential or plateau cells, with some Q cells; 3) Spheroids grown in Bellco flasks contained few hypoxic or Q cells. Experimentals examining the radiosensitivity of isolated quiescent populations from monolayers and spheroids grown in different glucose concentrations are presently being conducted