Increasing the potential of cell-penetrating peptides for cancer therapy using a new pentagonal scaffold

Cancer treatment is one of the major fields of interest for the scientific community. Investment in cancer research is costly but essential to provide patients with more effective and safe treatments. In this project, we describe the synthesis and characterization of new thiazole derivatives coupled to CPP2, a cell-penetrating peptide (CPP) reported for colon cancer cells. Using a human adenocarcinoma-derived cell line (Caco-2), these new CPPs were evaluated for antiproliferative (³H-thymidine incorporation) and cytotoxic effect (extracellular lactate dehydrogenase activity). One of these derivatives, the BTZCA thiazole compound and its peptide-conjugated (BTZCA-CPP2) also showed the ability to decrease tumour cell viability and proliferation, with potential cytotoxic effect against human breast cancer MCF-7 cells. Then, cytotoxicity studies were developed against J774, L929 and THP1 cell lines and this new family showed no significant cytotoxicity, when compared to their counterparts alone (BTZCA and CPP2). The use of smaller CPP conjugated with this family of derivatives can be also considered in future for the development of new drugs to cancer therapy.

CPP2-p16MIS treatment-induced colon carcinoma cell death in vitro and prolonged lifespan of tumor-bearing mice

Background

Cell-penetrating peptides (CPPs) are a research hotspot due to their noninvasive delivery ability. Among the identified CPPs, the TAT and R8 peptides have been preferentially applied to transduction into different cells. However, this process is nonselective among various cells. Recent research suggested that CPP2 could selectively penetrate human colorectal cancer (CRC) cells.

Methods

Using in vitro experiments, the mean fluorescence intensity of fluorescein isothiocyanate–labeled CPPs (CPPs-FITC) incubated with different cell lines was compared to corroborate the colon tumor targeting ability of CPP2. The targeting ability of CPP2 was determined in the same way in tumor-bearing mice. We synthesized antitumor peptides by fusing CPP2 to the minimal inhibitory sequence of p16 (p16MIS), which had the ability to restore the function of lost p16, the expression of which was absent in tumor cell lines of various origins. The antitumor effect of the combined peptide was tested in both CRC cell lines and tumor-bearing mice.

Results

In each CRC cell line, the mean fluorescence intensity of CPP2-FITC was higher than that of the TAT-FITC (p < 0.001) and R8-FITC (p < 0.001) groups. CPP2-p16MIS, the targeting carrier, showed a higher antitumor response in the in vitro cell research. CPP2-p16MIS showed a prolonged mean lifespan of tumor-bearing mice, further characterizing its role in specific tumor-targeting ability in vivo. Survival analysis showed that the mice treated with CPP2-p16MIS had significantly longer survival than the mice treated with phosphate-buffered saline (p < 0.05) or those treated with control peptides, including the CPP2 (p < 0.05) and p16MIS (p < 0.05) groups.

Conclusion

CPP2 could more selectively penetrate CRC cells than TAT or R8 as well as effectively deliver the p16MIS to the tumor.