Inhibition of β1 Integrins Increases Radiosensitivity in Therapy-Naïve and –Resistant Pancreatic Cancer Cell Lines

Introduction: Despite some therapeutic progress, pancreatic ductal adenocarcinoma (PDAC) remains hard to treat. Disruption of cell adhesion to extracellular matrix (ECM) in this tumor entity with an ECM-rich microenvironment and an overexpression of integrin cell adhesion molecules, including β1 integrins, seems promising. As the efficacy of β1 integrin targeting and its underlying mechanisms remain elusive, this study aims to decipher the potential of β1 integrin inhibition in therapy-naïve and -radioresistant PDAC cells.
Methods: We investigated the effect of the β1 integrin inhibitory antibody AIIB2 on cell survival after irradiation, chemotherapy or their combination in six therapy-naïve and one therapy-resistant pancreatic cancer cell lines using 3D, matrix-based colony formation assays. In addition to TCGA transcriptome data sets (Oncomine, OncoLnc, COSMIC), siRNA-mediated knockdown and stable overexpression of Itgb1, protein expression and phosphorylation (Western blot, immunofluorescence staining) were employed. A broad-spectrum kinase activity profiling of phosphotyrosine kinases (PTKs) and serine/threonine kinases (STKs) by PAMgene technology was conducted to characterize therapy-naïve and -resistant PDAC cells.
Results: TCGA mRNA data analysis showed a strong correlation of high β1 integrin expression with shorter survival of PDAC patients. AIIB2, similar to knockdown, significantly enhanced the radiosensitivity of all tested cell lines differing in β1 integrin expression levels. We observed a cell line-dependent reduction of the SF6 by 2- to more than 7-fold. Likewise, sensitization to radiochemotherapy as well as sensitization of the radioresistant cell line down to the level of the therapy-naïve cell line is accomplished by AIIB2. Kinase activity profiles demonstrated a higher degree of deactivation in PTKs than STKs after AIIB2 in therapy-naïve cells; a finding similarly found in resistant cells. However, comparison of naïve and -resistant cell populations showed different kinases to be altered specifically. Validation experiments are on-going.
Conclusion: Our results reveal, like in other tumor types, β1 integrins as potential targets in per se therapy-sensitive and -resistant PDAC cells. We demonstrate that different molecular mechanisms and signaling proteins associated with β1 integrins elicit therapy-resistance, thus, providing multiple options for therapeutic multi-targeting intervention.