CIGB-300 is a first-in-class synthetic
peptide-based
drug of 25
amino acids currently undergoing clinical trials in
cancer patients. It contains an amidated
disulfide cyclic undecapeptide fused to the TAT
cell-penetrating peptide through a
beta-alanine spacer.
CIGB-300 inhibits the CK2-mediated phosphorylation leading to apoptosis of
tumor cells in vitro, and in vivo in
cancer patients. Despite the clinical development of
CIGB-300, the characterization of
peptide-related impurities present in the active
pharmaceutical ingredient has not been reported earlier. In the decision tree of ICHQ3A(R2) guidelines, the daily doses intake, the abundance, and the identity of the
peptide-related species are pivotal nodes that define actions to be taken (reporting, identification, and qualification). For this, purity was first assessed by reverse-phase chromatography (>97%) and low-abundance impurities (≤0.27%) were collected and identified by mass spectrometry. Most of the impurities were generated during
peptide synthesis, the spontaneous air oxidation of the reduced
peptide, and the lyophilization step. The most abundant impurity, with no
biological activity, was the full-length
peptide containing Met17 transformed into a
sulfoxide residue. Interestingly, parallel and antiparallel dimers of
CIGB-300 linked by 2 intermolecular
disulfide bonds exhibited a higher antiproliferative activity than the
CIGB-300 monomer. Likewise, very low abundance trimers and tetramers of
CIGB-300 linked by
disulfide bonds (≤0.01%) were also detected. Here we describe for the first time the presence of active dimeric species whose feasibility as novel
CIGB-300 derived entities merits further investigation.