Therapy-naive and radioresistant 3-dimensional pancreatic cancer cell cultures are effectively radiosensitized by β1 integrin targeting

Abstract

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is a cancer with unmet needs. The role of highly conformal radiation therapy is still under debate for PDAC. Owing to its desmoplastic nature, integrin-mediated interactions between PDAC cells and extracellular matrix (ECM) profoundly contribute to PDAC therapy resistance. In this study, we investigated the radiochemosensitizing potential of beta 1 integrin targeting in therapy-naive and radioresistant PDAC cell cultures grown in 3-dimensional (3D) ECM.Methods and Materials: In a panel of 3D, ECM-based PDAC cell cultures, beta 1 integrin was inhibited by antibodies or siRNA-mediated knockdown. Together with x-ray irradiation and specific chemotherapies, we determined 3D colony formation capacity in therapy-naive and radioresistant PDAC cultures. We used kinome profiling, Western blotting, and immunofluorescence stainings to characterize these cell lines. Various siRNA screens were conducted to identify novel therapeutic targets.Results: We found a significant radiosensitizing potential of beta 1 integrin inhibition both in therapy-naive and radioresistant PDAC cell cultures. Kinome profiling upon beta 1 integrin targeting identified a generally declined tyrosine and serine/threonine kinase activity, which presented less prominent in radioresistant than in therapy-naive PDAC cells. siRNA screens employing the top 34 deregulated kinases in combination with beta 1 integrin inhibition revealed less efficacy and less radiosensitization in radioresistant relative to therapy-naive PDAC cell cultures. Triple inhibition of beta 1 integrin, protein kinase D1, and rearranged during transfection turned out to be most effective in reducing 3D colony formation of radioresistant PDAC cells.Conclusions: Our study clearly shows that beta 1 integrins are robust targets for overcoming radioresistance in PDAC. This seems to apply equally to therapy-sensitive and radioresistant cells. Concerning tumor heterogeneity, this dual therapy-sensitizing potential might be exploitable for a significant improvement of patient survival. (C) 2021 Elsevier Inc. All rights reserved.