Copper(II)-based metal affinity chromatography for the isolation of the anticancer agent bleomycin from Streptomyces verticillus culture

Abstract

The glycopeptide-based bleomycins are structurally complex natural products produced by Streptomyces verticillus used in combination therapy against testicular and other cancers. Bleomycin has a high affinity towards a range of transition metal ions with the 1:1 Fe(II) complex relevant to its mechanism of action in vivo and the 1:1 Cu(II) complex relevant to its production from culture. The affinity between Cu(II) and bleomycin was the underlying principle for using Cu(II)-based metal affinity chromatography in this work to selectively capture bleomycin from crude S. verticillus culture. A solution of standard bleomycin was retained at a binding capacity of 300nmolmL−1 on a 1-mL bed volume of Cu(II)-loaded iminodiacetate (IDA) resin at pH 9 via the formation of the heteroleptic immobilized complex [Cu(IDA)(bleomycin)]. Bleomycin was eluted from the resin at pH 5 as the metal-free ligand under conditions where pKa (IDA)<pH<pKa β-hydroxyhistidine amide (bleomycin). Bleomycin was captured on a Cu(II)-loaded IDA resin at pH 9 in 50% yield from bleomycin-containing S. verticillus culture that was pre-processed using XAD-2 resin to remove endogenously bound Cu(II). The approximate 25-fold purification of bleomycin from complex culture supernatant under aqueous conditions in a single step demonstrates the potential of Cu(II)-based metal affinity chromatography as a green chemistry platform for streamlined access to this high-value therapeutic agent.