Tumor-Targeted Delivery of IL-2 by Fusing with a pH Low Insertion Peptide for Antitumor Immunotherapy.

As a pleiotropic cytokine, interleukin-2 (IL-2) can effectively regulate lymphocyte proliferation, survival, and active antitumor immune responses in tumor microenvironments. Although the ability of IL-2 to boost immune responses was reported in cancer patients, its short circulating half-life and high toxicity hinder its broad and continual clinical application. Herein, we developed a novel tumor target agent by fusing pH low insertion peptides (pHLIP) with IL-2, forming the fusion protein pHLIP-IL2. Based on the low pH insertion property of pHLIP, the pHLIP-IL2 fusion protein could be selectively delivered to the acidic tumor microenvironments and then promote the proliferation of killer immune cells to elicit tumor regression. We found that pHLIP-IL2 fusion proteins can be significantly enriched in tumor tissues and can effectively reduce tumor size in diverse tumor models, including breast cancer and melanoma, without apparent adverse effects. These data suggest that the pHLIP-IL2 fusion protein may be a promising solution for the continual and extensive application of IL-2, and pHLIP-IL2 is a potential and valuable therapeutic drug for cancer patients with antitumor immunotherapy.