Photoreactivity of bleomycin and its implications

The bleomycin family of glycopeptide anti-tumour antibiotics has recently been shown to be markedly photosensitive. This photosensitivity has been observed not only for the free antibiotics but also for complexes with metal ions and with DNA. More importantly, the pattern of DNA cleavage by bleomycin, and some of its metal complexes, is significantly changed by irradiation with light in 300-350 nm or UV regions. Bleomycin is a strong, reversible inhibitor of the enzyme, dopamine beta-hydroxylase (EC 1.14.17.1) in the dark. Photoexposure converts this to a strong irreversible inhibition. In this review the above aspects are discussed along with the chemical nature of the origins of the photoreactivity of bleomycin and analogues. The implications of the photoactivity of this useful drug are pointed out.