Conjugation of cell-penetrating peptides to anticancer peptides is an effective strategy to enhance tumor treatment. The hybrid peptide, kla-TAT, by attaching the TAT peptide to the C-terminus of the pro-apoptotic peptide kla exhibited strong anticancer activity when co-administration with other peptide, but the systematic mechanism was not clear. In this study, the mechanisms of action of kla-TAT including the uptake pathway, distribution in cytoplasm, apoptosis-inducing ability and micro-morphology were investigated. The results indicated that the hybrid peptide internalized into A549 cells through two transmembrane mechanisms: endocytosis mediated by the clathrin-mediated endocytosis route and the rapid membrane disruption mechanism. Peptides that were endocytosed could interact with the mitochondrial membrane, while peptides internalized by disrupting the cell membrane caused disruption of the mitochondrial membrane. Thus, the hybrid kla-TAT peptide transfers through the cell membrane, inducing apoptosis by destroying the mitochondrial membrane and causethe expression of cyclin-D1 down-regulation. Meanwhile, the changes of the micro-morphology of the cancer cells was detected using atomic force microscope (AFM) and scanning electron microscope (SEM), which provided the visualized evidence for the mechanism of the peptides.
In this study, a peptide–peptide co-administration therapy between hybrid peptide kla-TAT and cationic anticancer peptide HPRP-A1 was designed to increase the anticancer activity of the combination peptides through synergistic effect. kla is a pro-apoptotic peptide which could induce rapid cancer cell apoptosis by disruption the mitochondrial membrane when internalized the cells. To enhance more kla peptides pass through cell membrane, a double improvement strategy was designed by chemically conjugation with cell penetration peptide TAT as well as co-administration with cationic membrane active peptide HPRP-A1, and the double anticancer mechanism of the kla-TAT peptide and HPRP-A1 including membrane disruption and apoptosis induction was verified through in vitro experiments. The CompuSyn synergism/antagonism analysis showed that kla-TAT acted synergistically with HPRP-A1 against a non-small cell lung cancer (NSCLC) A549 cell line. The anticancer activities of the two peptides were dramatically increased by co-administration, under the mechanism of cell membrane disruption, caspase-dependent apoptosis induction, as well as cyclin-D1 down-regulation based G1 phase arrest. We believe that the synergic therapeutic strategy would be a meaningful method for the anticancer peptides used in cancer treatment.
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