Increased radioresistance of an in vitro transformed human small cell lung cancer cell line

After 4-6 months in continuous culture the human small cell lung cancer (SCLC) cell line, U-1906, changed its radiobiological characteristics spontaneously. The cell line became more radioresistant indicating an increased repair capacity. This change was accompanied by a more adherent growth pattern, a higher clonogeneity, a decrease in the cytokeratin (tissue polypeptide antigen) content and increased glucagon and neuron-specific enolase (NSE) production. Other parameters such as the estramustine-binding protein (EMBP) and the proliferation associated antigen Ki-67 were unaltered. This spontaneous transformation in vitro of U-1906 may reflect a clinically important in vivo phenomenon of SCLC, which frequently develops resistance both to radio- and chemotherapy.