Extracellular matrix (ECM) and cytoskeletal modulation of cellular radiosensitivity

Modulation of radiosensitivity by components of the extracellular matrix (ECM) and cytoskeletal elements has not been adequately studied. Although differences in the radiosensitivities of cells grown as monolayers, as spheroids, or grown in vitro in animal models are known, explanations have in the past neglected possible influences by the ECM and cytoskeleton. Using collagen gel cultures, it is shown that the fibrillar component of the ECM (which is responsible for cell anchorage) induces shifts in radiosensitivity. The effect is critically dependent on the affinity of the cell type towards collagen. The shifts in radiosensitivity induced by ECM alteration are manifested as changed D(q) values. By applying four specific cytoskeletal poisons which either stabilize or destabilize specific cytoskeletal elements, the involvement of microfilaments and microtubuli was qualitatively appraised. Cytochalasin B, which destabilizes microfilaments (by preventing polymerization), caused a significant rise in radioresistance. This rise was due to increased D₀. Although the cellular morphological change accompanying cytochalasin B treatment was essentially similar to that obtained with trypsin, the respective shifts in radioresponses were qualitatively different and opposite, suggesting differences in mechanism of action.