Antigens that are over-expressed in cancer in response to radiation are being used as novel targets. We showed tax interacting protein 1 (TIP-1) to be radiation-inducible that translocated to the surface of the cancer cell following irradiation. TIP-1, which consists of a single PDZ domain plays an important role in cell signaling, cancer development, and progression. TIP-1’s involvement in various survival pathways makes it an attractive target for anticancer therapeutics. We used antibodies specific to this PDZ domain to determine its role in cancer cell survival. We monitored proliferation in lung cancer (A549 and H460) and glioblastoma (D54 and U251) cells after 24, 48, 72 and 96h treatment with the anti-PDZ antibody. We observed a time-dependent proliferation arrest with anti-PDZ antibody treatment which was associated with increased apoptosis. The anti-PDZ antibody when combined with radiation (3Gy) led to reduced proliferation and colony formation. Anti-PDZ antibody had no effect on the proliferation of normal lung (MRC-5) and endothelial (HUVEC) cells. Cells treated with anti-PDZ antibody showed decreased levels of the phosphorylated forms of AKT, mTOR, and a downstream substrate of mTOR, 4EBP1. Anti-PDZ antibody treatment also led to an overall reduction in basal levels of AKT, mTOR, and 4EBP1. Further, we evaluated the effect of the anti-PDZ antibody on tumor growth in heterotopic mouse models of lung cancer (A549) and glioma (U251). We observed significant growth delay in mice treated with anti-PDZ antibody treatment when compared to mice treated with the isotype control. The combination of the anti-PDZ antibody with radiation showed an additive effect. Immunoblot analysis of tumor tissues also showed downregulation of phosphorylated and total levels of AKT, mTOR and 4EBP1 in the tumors treated with anti-PDZ antibody. Overall, our results suggest that TIP-1 is a promising therapeutic target for treatment of lung cancer and glioblastoma. Antibodies specific to the PDZ domain of TIP-1 enhance the efficacy of radiotherapy. The anti-PDZ antibodies need to be optimized further before translating it into the clinic.

Citation Format: Vaishali Kapoor, David Dadey, Kelly Hoye, Andrea Collins, Dinesh Thotala, Dennis Hallahan. Antibody targeting PDZ domain of TIP-1 induces proliferation arrest through AKT/mTOR signaling inhibition in lung cancer and glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4599. doi:10.1158/1538-7445.AM2017-4599