The targeting of tumor cells by peptides for drug delivery is a promising strategy for cancer therapy. Interleukin-2 (IL-2), which mediates anti-tumor cellular immune responses, has been approved as a therapy for cancer. However, the serious side effects and short half-life of recombinant IL-2 (rIL-2) has limited its use clinically. Somatostatin receptors (SSTRs), which are expressed in a large number of human tumors, are the targets for in vivo tumor targeting. In this study, we have constructed and expressed a novel chimeric recombinant protein containing octreotide analogs and IL-2 in order to target the SSTR binding with tumor cells. The fusion protein somatostatin receptor targeted interleukin-2 (SIL), which was purified from bacterial inclusion bodies and refolded with high purity, was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse-phase high-performance liquid chromatography. Tryptophan emission fluorescence was used to measure the structural changes in SIL after renaturation. Cell proliferation experiments showed that this chimeric protein retained the biological activities of hIL-2. Furthermore, the tumor binding capacity of SIL acting through SSTRs was shown through co-immunoprecipitation. Competition binding with octreotide of tumor cells also confirmed that SIL binds to tumor cells through the target peptide octreotide. Moreover, the performance of SIL in stimulating the proliferation of lymphocyte cell lines after binding to tumor cells showed that the immunocytokine, SIL, retained its bioactivity at the tumor site. These results suggest that SIL is a recombinant fusion protein that may be used for tumor-targeted drug delivery.

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