Synthesis, conformation, biodistribution, and in vitro cytotoxicity of daunomycin-branched polypeptide conjugates

Daunomycin has been attached to various structurally related synthetic branched polypeptides with a polylysine backbone, using its acid-labile cis-aconityl derivative (cAD). Due to the importance of the side-chain structure in alpha-helix formation and immunological and pharmacological properties of branched polypeptides, we have investigated the conformation, biodistribution, and in vitro cytotoxicity of cAD-carrier conjugates with polypeptides containing amino acid residues of different identity and/or configuration at the side-chain end (XAK type) or at the position next to the polylysine backbone (AXK type), where X = Leu, D-Leu, Pro, Glu, or D-Glu. According to CD studies, polycationic conjugates with hydrophobic Leu in the side chains could assume a highly ordered conformation, while amphoteric conjugates containing Glu proved to be unordered in PBS. The reduction of in vitro cytotoxic activity of cAD by conjugation to carriers and the biodistribution profile of the conjugates were found to be dependent predominantly on the charge properties and on the side-chain sequence of the carrier polypeptide. It was demonstrated that by proper combination of structural elements of the carrier molecule, it is feasible to construct a cAD-branched polypeptide conjugate with significantly prolonged blood survival and with no reduction in in vitro cytotoxicity of the drug.