Synthesis, proton-affinity and anti-cancer properties of the prodigiosin-group natural products

The prodigiosin-group natural products are a family of tripyrrole red-pigments that are produced by microorganisms such as Streptomyces and Serratia and contain a common 4-methoxy-2,2'-bipyrrole ring system. They were first isolated in 1929 and studied as antibiotic and cytotoxic agents in the 1960s, but were not developed clinically due to their high systemic toxicity. However, during the past decade some prodigiosins have shown potentially useful immunosuppressive activity when administered at doses that are not toxic. They have also been found to exhibit selective cytotoxicity against melanoma and liver cancer cells. These results have fueled various studies on the biological mechanisms of the prodigiosins and it has now been established that they inhibit phosphorylation and activation of JAK-3, a cytoplasmic tyrosine kinase associated with the cell surface receptor component called common gamma-chain. They also uncouple lysosomal vacuolar-type ATPases through promotion of H(+)/Cl(-) symport and facilitate oxidative double-strand DNA cleavage in the presence of copper. A simple and elegant synthesis of the prodigiosins has also been developed, which has allowed a number of the natural prodigiosins and synthetic analogues to be prepared. These studies have served to renew interest in the prodigiosin-group natural products. In this review the recent advances on the synthesis, proton-affinity and biological activities of the prodigiosins are discussed. With regard to their anti-cancer properties, particular attention is given to their ability to facilitate oxidative DNA damage, which provides a rationale for the cytotoxic properties of the prodigiosin-group natural products.