ESTRO 2024 - Abstract Book

S5398

Radiobiology - Tumour biology

ESTRO 2024

Ashok Kumar 1 , Priyani V. Rajasekara 1 , Sarah E. Biehn 2 , Sasha Beyer 1 , Aline P. Becker 1 , Anca L. Grosu 3 , Steffen Lindert 2 , Heather R. Manring 1 , Saikh J. Haque 1 , Arnab Chakravarti 1 1 The Ohio State University, Department of Radiation Oncology, Columbus, Ohio, USA. 2 The Ohio State University, Department of Chemistry & Biochemistry, Columbus, Ohio, USA. 3 University of Freiburg, Germany, Department of Radiation Oncology, Freiburg, Germany

Purpose/Objective:

Glioblastoma (GBM; WHO grade 4) is the most common malignant glioma of all brain tumors. Current therapeutic regimens of maximal safe surgical resection followed by radiation treatment (RT) and concomitant and adjuvant temozolomide (TMZ) constitute the standard of care for GBM patients with only 5% five-year survival rate. Chemoresistance and radioresistance are the major obstacles in GBM treatment. Treatment resistance is mainly due to highly aggressive and invasive tumor phenotype leading to recurrence and mortality. Hence, it is crucial to identify actionable targets and associated pathways for the development of effective therapeutic agents to help overcome treatment resistance. We have previously identified Transgelin-2 (TAGLN2) to be significantly upregulated in GBM through multiple molecular profiling studies. TAGLN2 induces actin polymerization, thereby playing a critical role in cytoskeletal reorganization leading to cell proliferation, migration/invasion, and therapeutic resistance in GBM and other malignancies. This study aims to explore the mechanisms by which TAGLN2 upregulates oncogenic signaling pathway(s) driving GBM progression and invasion resulting in treatment resistance phenotype. Additionally, we hypothesize that targeting Transgelin-2 may overcome therapeutic resistance mechanisms. To this end, active drug development efforts are underway in our laboratory to inhibit TAGLN2-mediated GBM progression and invasion for circumventing therapeutic resistance mechanisms in GBM.

Material/Methods:

Immunohistochemistry (IHC) performed on pseudopalisading tumor cells for Transgelin-2 expression. RNAi-mediated TAGLN2 knockdown (KD) was employed to assess the functions of TAGLN2 in GBM patient-derived xenograft (PDX) cell lines. Series of in vitro functional assays were performed to assess the role of TAGLN2 in these cell lines. Cell proliferation, invasion ± RT and/or TMZ were assessed by MTS and Trans-well invasion assays. Subsequently, WB analysis of oncogenic signaling pathways was performed following TAGLN2 KD. Co-IP assays and Biacore/SPR analyses were performed to study the binding affinity and kinetics of interaction of PTEN with TAGLN2. Structure based computational screening of small molecule inhibitors (SMIs) that can bind to TAGLN2 protein was performed. In silico (SwissADME) and in vitro validation of these SMIs for their ability to permeate through the blood brain barrier (BBB).

Results:

Histopathological studies of human GBM tumors and Transgelin-2-overexpressing tumors grown in mouse showed elevated expression of TAGLN2 in pseudopalisading cells in the peri-necrotic region of tumors indicating TAGLN2 transcription was upregulated under hypoxic condition. To this end, we and others found a functional hypoxia response element was located in the TAGLN2 promoter. We also found that TAGLN2 was induced in hypoxic microenvironments with GBM PDX cell lines and its overexpression enhanced cellular resistance towards conventional therapy. Conditional (doxycycline-inducible) knock-down (KD) of TAGLN2 reduced cell proliferation, survival and invasive potential of GBM PDX cell lines in vitro. TAGLN2 has been shown to activate the PI3K-AKT