Low toxicity and high antitumour activity of daunomycin by conjugation to an immunopotential amphoteric branched polypeptide.

The acid labile derivative of Daunomycin cis-aconityl Daunomycin (cAD), was coupled to an amphoteric polypeptide, poly[Lys-(Glui-DL-Alam)] (EAK), which was selected for conjugation on the basis of its pharmacological and immunological properties. The systemic toxicity of covalently attached Daunomycin was studied by monitoring body weight, life-span, bone marrow and haematological parameters of BDF1 mice. More than 3-fold the lethal dose of free Daunomycin could be applied without serious toxic effect when the drug was attached to EAK. The dose- and time-dependent modulatory effect of free drug and [cAD]-EAK conjugate on the humoral and cellular immune response to sheep red blood cell antigens in mice was studied. The conjugation of Daunomycin to EAK carrier polypeptide compensated for the immunosuppression induced by free Daunomycin. [cAD]-EAK conjugate at Daunomycin doses of 2-10 mg/kg was very effective against L1210 leukaemia producing 66-100% long-term survivors (> 60 days), while Daunomycin in itself increased the mean survival only by 52%, with no long-term survivors. The mixture of free Daunomycin and EAK polypeptide had similar toxicity and antitumour activity as free Daunomycin, indicating the important role of covalent attachment in increased therapeutic efficacy.