An optimized integrin α6-targeted peptide capable of delivering toxins for melanoma treatment.

BACKGROUND: Peptide-based therapeutics for melanoma have received increasing attention in medical research. However, the local delivery of such therapeutics poses unique challenges. Cell-penetrating peptides (CPPs) with the ability to selectively enter cancer cells, with sufficient stability and increased endosomal escape mechanisms, can provide a new and improved delivery strategy for therapeutic agents for treating cancer. METHODS: We developed a new combination strategy for the synthesis of penetrating peptides functionalized with targeting of integrin α6. The linear peptide S5 was multimerized with 4 copies in linear sequential order spaced by GSG between each copy to yield the 4S5 peptide. The multimerized 4S5 peptide coupled with an intracellular delivery peptide (N) and endosomal escape peptide (G) was separated by a GGS spacer. This optimized peptide was called 4S5NG. The 4S5NG, EGFP or PE24 peptide-protein conjugates were purified via a C-terminal His-tag. The uptake efficacy, intracellular distribution and integrin α6-targeting ability of these 4S5NG peptides were systematically characterized via IncuCyte, flow cytometry and in vivo imaging using 4S5NG-Cy5 or 4S5NG-EGFP. Moreover, 4S5NG-incorporated Pseudomonas aeruginosa (PE24) exotoxin A generated therapeutic peptides. The antitumor efficacy and underlying mechanism were studied in cell lines and a mouse model. In addition, the effect of 4S5NG-PE24 on antitumor immunity of a healthy immune system was investigated via a mouse model. RESULTS: Images of living cells and mice indicated that 4S5NG accumulated at tumor sites in vitro and in vivo and was much more effective than the S5 and 4S5 peptides. 4S5NG-PE24 induced cell pyroptosis in integrin α6-expressing melanoma through the caspase 3/gasdermin E (GSDME) signaling pathway in the absence of histological alterations in other organs. 4S5NG-PE24 also promoted the response rate of programmed cell death protein-1 (PD-1) checkpoint blockade to increase antitumor efficacy. CONCLUSIONS: Collectively, these results highlight the potential use of 4S5NG to deliver the toxin PE24 to selectively eliminate integrin α6(+) cells in melanoma, which may represent a novel treatment approach for melanoma patients.