Antitumor activity of opiorphin, sialorphin and their conjugates with a peptide klaklakklaklak.

This is the study on the effect of opiorphin, sialorphin and their analogs on antitumor activity. We demonstrated that conjugation of opiorphin and sialorphin with a proapoptotic, antimicrobial peptide klak (klaklakklaklak) led to compounds (opio-klak and sialo-klak) that were cytotoxic against cancer cells (LN18, PC3, A549, HCT116 and B10-F16) in the MTT test. The conjugated analogs were designed to increase the effectiveness of the peptide. The opio-klak derivative was the most effective in the in vitro assays and led to a decrease in viability of cancer cells over time as compared with that of untreated controls. In contrast, treatment with either the untargeted klak peptide or opiorphin as a negative control led to a negligible loss in viability. Antitumor effect of the opio-klak was also observed in vivo in murine melanoma tumor-bearing mice. Cessation of peptide administration resulted in tumor regrowth. Our results are seemingly valuable for the development of opiorphin analogs with potential clinical applications. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.