Combination Therapy in Cancer: Doxorubicin in Combination with an N-terminal Peptide of Endostatin Suppresses Angiogenesis and Stimulates Apoptosis in the Breast Cancer.

The combination of chemotherapy drugs with angiogenesis inhibitors improves response and survival and reduces the cytotoxic side effects and drug resistance in patients compared to chemotherapy alone. Here, we investigated the efficacy of the concomitant administration of doxorubicin and a peptide derived from the N-terminal domain of Endostatin (called ES-SS) in the 4T1 mammary carcinoma tumor model. Tumor-bearing mice were divided into the control and three treatment groups, including ES-SS, doxorubicin, and the combination. Injections were performed daily for two weeks and tumor volumes were measured during the treatment. Immunohistochemical analysis of Ki-67, CD31, CD34, Bcl-2, p53 expression, and TUNEL assay were performed on tumor tissues at the end of treatment. Besides, molecular dynamics and docking simulations were performed. It was demonstrated that tumor growth was inhibited in mice treated with peptide plus doxorubicin more significantly than in each treatment alone (P<0.05). No weight loss or adverse effects were observed. Moreover, combination therapy was more effective in tumor angiogenesis suppression and apoptosis stimulation (P<0.05). Docking simulations by ClusPro server demonstrated that ES-SS binds to integrin α5β1, Transglu-taminase 2, and Matrix metalloproteinase 2 with more negative binding energy and hydrogen bonds compared to the native peptide. Generally, we proposed that ES-SS can augment the therapeutic efficacy of doxorubicin through angiogenesis prevention and apoptosis induction in breast tumor. Owing to the advantages of peptides to recombinant proteins or monoclonal antibodies, further preclinical and clinical evaluations of this combination strategy are worth taking into consideration.