Role of the primary structure in the antitumor mechanism of
CIGB-552.
Biostability of peptides in blood and serum is an important issue for
development of peptides as clinically drugs. In vitro degradation
of peptides in serum and plasma is considered the primary methodology
for studying the degradation pattern of peptides
(Werle, 2006). For that reason, our group
examined the in vitro metabolic stability of CIGB-552 in serum
during 120 minutes. A typical serine-proteases degradation pattern was
suggested for this peptide sequence
(Vallespi et al., 2014). The main
metabolites of CIGB-552 showed no great differences regarding
hydrophobicity, hydrophilicity, and isoelectric point. However, the
analysis of the cytotoxic effect, cell-penetrating capacity, antitumor
mechanism and interaction with its intracellular target, COMMD1,
demonstrated a loss of antitumor capacity for the metabolites compared
to CIGB-552 (Figure 4). These findings suggest the importance of
C-terminal amino acidic residues (Lys18, Phe19 and Trp20) in the
antitumor activity of CIGB-552 (Astrada et
al., 2016). The role of these residues in the peptide-membrane
interaction was analyzed by molecular dynamic simulation
(Astrada et al., 2016). CIGB-552 and the
17 amino acid metabolite (named as 5) have a conserved structural motif.
Two tryptophan residues and a tyrosine create a hydrophobic cluster that
brings together the C-terminal carboxylate moieties and one arginine
residue, forming a stable salt bridge interaction that leads to a looped
conformation. Indeed, tryptophan–tryptophan and arginine–C-terminal
carboxylate distances in both systems display very stable interactions.
Altogether, these results demonstrate that the primary structure of
CIGB-552 is considered the minimum active sequence needed to produce a
potent antitumor effect in cell and animal models. In this sense, the
protection of CIGB-552 from proteolitic degradation is one of the most
important challenges that face this peptide in its development as an
anticancer drug. The use of different encapsulation systems such as
liposomes, multilayer emulsions or nanoparticle vehicles could be an
alternative to deal with this issue.