Abstract 1791: Targeting radiation-inducible cell surface GRP78 using GIRLRG peptide as a novel imaging and therapeutic strategy for tumors

Abstract

Abstract Traditional radiation therapy is often associated with significant toxicity to normal cells that could limit the success of cancer therapy. The greater understanding in the molecular differences between cancer cells and normal cells has lead to targeted therapies in cancer treatment. We have discovered novel radiation-inducible antigens in cancer using phage-display peptide libraries. One such inducible-antigen is Glucose regulated protein 78kDa (GRP78) that was shown to bind the hexapeptide GIRLRG. GRP78 is known to regulate cellular stresses, including hypoglycemia, hypoxia and the ER stress response. It is over-expressed in different cancer subtypes and has been correlated to their poor prognosis. In this study, we evaluated the cell surface induction of GRP78 post irradiation (IR) on lung cancer (A549 and LLC), glioma (D54 and GL261) and endothelial (HUVEC and 3B11) cell lines using flow cytometry. Significantly higher surface expression of GRP78 was observed in all cell lines. We determined the specificity of GIRLRG to bind tumors in vivo using nano SPECT technology. GIRLRG was conjugated to a 40KDa PEG (for longer circulation time) and radiolabelled with 111Indium (111In) using diethylene triamine pentaacetic acid (DTPA) as the chelator. The A549 tumor bearing nude mice were irradiated (3Gy x 3 times) or sham irradiated prior to tail vein injections of 111In labeled GIRLRG. The mice were imaged 48h and 96h post injection using nano CT-SPECT imager. The SPECT images revealed that GIRLRG specifically bound to the irradiated A549 tumors while little or no binding was seen in the sham irradiated tumors. The post-SPECT imaging bio-distrubution also revealed maximum uptake in irradiated tumors. We further evaluated tumor binding of GIRLRG in Glioma (D54), esophageal cancer (OE33), cervical cancer (HT3), and pancreatic cancer (BxPC3). The nano-SPECT imaging showed that GIRLRG specifically bound to all the irradiated tumors tested. Phosphor images of the tumor sections showed that GIRLRG specifically bound to the tumors and not to normal tissues. In conclusion, GIRLRG peptide has high affinity to GRP78 in vitro and in vivo. Radiolabeled GIRLRG is a novel tool for imaging tumors and may be developed further as a therapeutic agent to deliver cancer specific drugs or therapeutic radioisotopes. Citation Format: Vaishali Kapoor, David Dadey, Kim Nguyen, Hua Li, Buck Rogers, Dinesh Thotala, Dennis Hallahan. Targeting radiation-inducible cell surface GRP78 using GIRLRG peptide as a novel imaging and therapeutic strategy for tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1791. doi:10.1158/1538-7445.AM2015-1791