TGM2 Novel Biomarker Of Radiation Response After Neo-Adjuvant TMZ In Glioblastoma

Abstract

It is becoming increasingly evident that treatment drives rapid changes in the molecular state of tumor cells to provide a pro-survival phenotype to cells. Transglutaminase-2 (TGM2) is a membrane protein which has previously been implicated in driving radiation resistance in multiple cancers. We hypothesized that Transglutaminase-2 (TGM2) level is a predictor of response to radiation in Glioblastoma (GBM). We have investigated how exposure to neo-adjuvant Temozolomide (TMZ) in glioma stem cells (GSCs) with different levels of TGM2 would affect the response to subsequent radiation in these GSCs Primary Glioma Stem cells lines (TGM2-high: 1123, 83; TGM2-low: 528, OPK49) were used to explore the role of TGM2 expression in radiation response and modulation of expression by TMZ. We utilized pre-clinical in vivo models to assess whether a novel regime which included neo-adjuvant TMZ prior to chemoradiation was superior to upfront concurrent chemoradiation regimes. We provide evidence that TGM2 drives radioresistance in GBM through restriction of p53 mediated repression of expression RAD51, a DNA damage repair gene. We demonstrate that exposure of GBM to the standard TMZ drives rapid downregulation of TGM2 in vitro and that this phenomenon is recapitulated in vivo. Interestingly, we confirm previous reports that radiation (RT) is able to drive reciprocal changes in TGM2 and promotes reactivation of TGM2 in TGM2-high tumors but not TGM2-low tumors. Given these observations, we hypothesized that exposure to neo-adjuvant TMZ in TGM2-low tumors would increase the efficacy of subsequent RT in these tumors. Comparison of the effect of standard treatment consisting of 3 weeks of concurrent TMZ and RT (Stupp) to a novel regime (neo-Stupp) consisting of 1 week of neo-adjuvant TMZ followed by two weeks of TMZ and hypofractionated RT revealed a superior survival benefit of this novel regime in in TGM2-low tumors but not in TGM2-high tumors. Utilization of the TGM2 inhibitor GK921 in combination with neo-Stupp prevented rapid relapse previously observed in TGM2-high tumors. We propose that neo-Stupp treatment regimen is superior to standard chemoradiation regimes in a subset of tumors identified by low TGM2 expression