CARRIER DESIGN - CYTOTOXICITY AND IMMUNOGENICITY OF SYNTHETIC BRANCHED POLYPEPTIDES WITH POLY(L-LYSINE) BACKBONE

Several synthetic branched polypeptides have been evaluated for in vitro toxicity and for immunogenicity. Preliminary investigations were carried out on the effect of these compounds on haematologic and serum parameters of mice in vivo. The polymers contain poly[Lys] backbone and short side chains composed of about three DL-Ala residues and one other amino acid residue (X) either at the end of the branches {poly[Lys-(X(i)-DL-Ala(m))], XAK} or at position next to the backbone {poly[Lys-(DL-Ala(m)-X(i))], AXK}. Cytotoxicity was analyzed in three systems using rat liver, mouse spleen and HeLa cells. Our data clearly suggest that there is a strong correlation between charge and cell killing activity of branched polypeptides. Thus polypeptides of amphoteric character are basically non-toxic, while compounds with predominantly cationic groups were found to be toxic or highly toxic. Immunogenicity and antigenicity of polypeptides were studied in three mouse strains (BALB/c, CBA, C57/B1). In contrast to the most immunogenic, cationic polypeptide X = D-Leu (D-UK), the glutamic acid containing analogues (EAK, D-EAK) induced IgG type immune responses only in BALB/c mice. The difference in the potency of EAK compared to D-EAK to elicit IgG type antibodies suggests that the introduction of chain terminating D-amino acids can enhance antigenicity. These results demonstrate the value of branched polypeptides in studying chemical structure-biological function correlations required for drug delivery and/or for constructing synthetic vaccine.