Targeting Tax Interacting Protein 1 Results in Cytotoxic and Radiosensitizing Effects in Cancer

Abstract

Abstract INTRODUCTION Poor survival of patients afflicted with glioblastoma continues to fuel the search for new molecular targets to improve therapy. Previously we have shown that Tax interacting protein 1 (TIP1), a protein known to be involved in cancer progression, is overexpressed and radiation-inducible in gliolblastoma. In this study, we investigated the effect of anti-TIP1 antibodies on glioblastoma in vitro and in vivo. METHODS We analyzed the expression profile of TIP1 in glioblastoma via the cancer genome atlas. Radiation induction of TIP1 was confirmed in tumor-bearing mice with near infrared imaging after exposure to ionizing radiation (XRT). We assessed the effect of TIP1 antibodies on cell proliferation and compared these to genetic knockout of TIP1 mediated by CRISPR/Cas9. We assessed the affinity of TIP1 antibodies with surface plasmon resonance.The mTOR pathway was analyzed by western blot following antibody treatment, and cell death was assessed with Annexin-V/PI by flow cytometry. Tumor growth delay was assessed in Vivo by measuring tumor volumes over time in mice bearing heterotopic tumors treated with/without TIP antibody and XRT. RESULTS We found that antibody binding to the functional domain of TIP1 results in endocytosis of the antibody-protein complex and subsequent cytotoxicity. We also show that these antibodies bound with high affinity to cancer cells and synergized with ionizing radiation to enhance net cytotoxicity in vitro and delay tumor growth in Vivo. These effects were also associated with downregulation of mTOR-AKT signaling. CONCLUSION TIP1 is a new therapeutic target for cancer treatment that may be combined with ionizing radiation therapy to enhance treatment efficacy. The mechanism of TIP1-mediated cytotoxicty involves endocytosis of protein-antibody complexes with associated reduction in pro-survival signaling pathways.