Photoisomerization of colchicine. Loss of significant antimitotic activity in human lymphocytes

Colchicine exposed to ultraviolet light is photoisomerized to form the lumicolchicines. Other studies have shown that light‐altered colchicine has reduced biologic activity in plants and lower animals. The effects of colchicine and lumicolchicine on arresting mitosis in metaphase were studied in human lymphocytes in tissue culture. Lumicolchicine was ineffective and not different from controls, even in concentrations of 1 × 10 −6 M. The possible clinical relevance of these data are discussed.