ABSTRACT
The NGR peptide is one of the well-known peptides for targeting tumor cells. It has the ability to target aminopeptidase N (CD13) on tumor cells or the tumor vascular endothelium. In this study, the NGR peptide was used for targeting A subunit of the Shiga toxin to cancer cells. The cytotoxic effect of the A-NGR fusion protein was assessed on HT1080, U937, HT29 cancer cells and MRC-5 normal cells. For this purpose, cells were treated with different concentrations of A-NGR (0.5-40 µg/ml). The evaluation of cell viability was achieved by MTT assay. Apoptosis was determined by annexin-V/PI double staining flow cytometry. Alterations in the mRNA expression of apoptosis - related genes were assessed by real time RT- PCR. The results showed that A-NGR fusion protein effectively inhibited the growth of HT1080 and U937 cancer cells in comparison to negative control (PBS) but for CD13-negative HT-29 cancer cells, only at high concentrations of fusion protein was inhibited growth recorded. On the other hand, A-NGR had little cytotoxic effect on MRC-5 normal cells. The flow cytometry results showed that A-NGR induces apoptosis. Furthermore, the results of real time RT-PCR revealed that A-NGR significantly increases the mRNA expression of caspase 3 and caspase 9. Conclusively, A-NGR fusion protein has the ability of targeting CD13-positive cancer cells, the cytotoxic effect on CD13-positive cancer cells as well as has low cytotoxic effect on normal cells.
ABSTRACT
PURPOSE: Interleukin-24 (IL-24) is a unique cytokine in the IL-10 family that reveals tumor-suppressive activity against a broad range of cancers. Alternative splicing of human IL-24 generates several isoforms with different pro-apoptotic activities. In the current study, we aimed to investigate the cytotoxic properties of a recombinant smallest isoform of IL-24 (sIL-24) and the underlying molecular mechanisms in PC-3, A549, U937, and Raji cancer cells as well as normal cell line MRC-5. METHODS: Following treatment of the cells with recombinant sIL-24 peptide and full-length IL-24 protein, cytotoxicity was determined by MTT assay. Apoptosis induction was evaluated using annexin-V/PI double staining flow cytometry and Hoechst 33342 staining. The expression of Bax, Bcl-2, cytochrome c, and caspase-3 was analyzed by Western blotting. RESULTS: MTT assay exhibited that sIL-24 dose and time dependently inhibited the proliferation of IL-24 receptor-positive PC-3, U937, and Raji cells more effectively than full-length IL-24. In contrast, sIL-24 had little cytotoxic effect on A549 cells lacking the IL-24 receptor, or on MRC-5 normal cells. Flow cytometric analysis and morphological observation revealed an efficient apoptosis induction in the receptor-positive cells. Furthermore, Western blot assay demonstrated that cell death induced by sIL-24 was associated with upregulation of the Bax/Bcl-2 ratio, cytochrome c release, and the expression of cleaved caspase-3, suggesting that sIL-24 induced apoptosis mainly through the mitochondrial pathway. Notably, among the tested cells, induction of apoptosis was more significant in PC-3 cells. CONCLUSION: Our results suggest that the sIL-24 peptide is a promising candidate for potential treatment of human cancers.
