CpG oligodeoxyribonucleotide 7909 enhances radiosensitivity via downregulating Oct-4 expression in radioresistant lung cancer cells

Cancer cell line microarray as a novel screening method for identification of radioresistance biomarkers in head and neck squamous cell carcinoma

Background

Currently, no clinically useful biomarkers for radioresistance are available in head and neck squamous cell carcinoma (HNSCC). This study assesses the usefulness of Cell Line Microarray (CMA) method to enhance immunohistochemical screening of potential immunohistochemical biomarkers for radioresistance in HNSCC cell lines.

Methods

Twenty-nine HNSCC cell lines were cultured, cell pellets formalin-fixed, paraffin-embedded, and arrayed. Radioresistance features of the cell lines were combined to immunohistochemical stains for p53, NDFIP1, EGFR, stem cell marker Oct4, and PP2A inhibitor CIP2A.

Results

Expression of p53, EGFR or CIP2A did not indicate intrinsic radioresistance in vitro. Stem cell marker Oct4 nuclear positivity and NDFIP1 nuclear positivity was correlated with increased intrinsic radioresistance.

Conclusion

The usefulness of CMA in analysis of HNSCC cell lines and discovery of biomarkers is demonstrated. CMA is very well adapted to both testing of antibodies in a large panel of cell lines as well as correlating staining results with other cell line characteristics. In addition, CMA-based antibody screening proved an efficient and relatively simple method to identify potential radioresistance biomarkers in HNSCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08618-6.

Therapeutic Targeting of Signaling Pathways Related to Cancer Stemness

The theory of cancer stem cells (CSCs) proposes that the different cells within a tumor, as well as metastasis deriving from it, are originated from a single subpopulation of cells with self-renewal and differentiation capacities. These cancer stem cells are supposed to be critical for tumor expansion and metastasis, tumor relapse and resistance to conventional therapies, such as chemo- and radiotherapy. The acquisition of these abilities has been attributed to the activation of alternative pathways, for instance, WNT, NOTCH, SHH, PI3K, Hippo, or NF-κB pathways, that regulate detoxification mechanisms; increase the metabolic rate; induce resistance to apoptotic, autophagic, and senescence pathways; promote the overexpression of drug transporter proteins; and activate specific stem cell transcription factors. The elimination of CSCs is an important goal in cancer therapeutic approaches because it could decrease relapses and metastatic dissemination, which are main causes of mortality in oncology patients. In this work, we discuss the role of these signaling pathways in CSCs along with their therapeutic potential.

Targeting Toll-Like Receptors for Cancer Therapy

The immune system encompasses a broad array of defense mechanisms against foreign threats, including invading pathogens and transformed neoplastic cells. Toll-like receptors (TLRs) are critically involved in innate immunity, serving as pattern recognition receptors whose stimulation leads to additional innate and adaptive immune responses. Malignant cells exploit the natural immunomodulatory functions of TLRs, expressed mainly by infiltrating immune cells but also aberrantly by tumor cells, to foster their survival, invasion, and evasion of anti-tumor immune responses. An extensive body of research has demonstrated context-specific roles for TLR activation in different malignancies, promoting disease progression in certain instances while limiting cancer growth in others. Despite these conflicting roles, TLR agonists have established therapeutic benefits as anti-cancer agents that activate immune cells in the tumor microenvironment and facilitate the expression of cytokines that allow for infiltration of anti-tumor lymphocytes and the suppression of oncogenic signaling pathways. This review focuses on the clinical application of TLR agonists for cancer treatment. We also highlight agents that are undergoing development in clinical trials, including investigations of TLR agonists in combination with other immunotherapies.

Toll-like receptor 9 activation by CpG oligodeoxynucleotide 7909 enhances the radiosensitivity of A549 lung cancer cells via the p53 signaling pathway

Unmethylated cytosine-phosphorothioate-guanine (CpG)-containing oligodeoxynucleotides (ODNs) are synthetic DNA sequences that mimic bacterial DNA, and are known to serve as ligands for Toll-like receptor 9 (TLR9). The interaction between a CpG ODNs with TLR9 activates the complex downstream cascade that contributes to exerting its function. In the present study, the results of clonogenic assays demonstrated that the activation of TLR9 by CpG ODNs significantly increased the radiosensitivity of A549 lung cancer cells, with a sensitivity enhancement ratio (SER) of 1.28. When the expression of TLR9 was effectively silenced, CpG ODNs used alone were identified to produce SERs as low as 1.01. Flow cytometry demonstrated that the interaction between TLR9 and CpG ODN 7909 alone did not significantly affect the rate of apoptosis, but may significantly enhance the radiation-induced apoptosis of A549 cells. Western blot analysis revealed that TLR9 activation by CpG ODN 7909 increased the levels of mitogen-activated protein kinase 14, cellular tumor antigen p53, B-cell lymphoma 2 associated X protein and genome polyprotein, and decreased Bcl-2 expression levels, whereas these effects were not observed in CpG ODN 7909-treated cells in which TLR9 was knocked down. These results suggest that CpG ODN 7909 may enhance radiosensitivity through TLR9 activation, and partially via the p53 pathway in A549 lung cancer cells.

Stimulating Innate Immunity to Enhance Radiation Therapy-Induced Tumor Control

Novel ligands that target Toll-like receptors and other innate recognition pathways represent a potent strategy for modulating innate immunity to generate antitumor immunity. Although many of the current clinically successful immunotherapies target adaptive T-cell responses, both preclinical and clinical studies suggest that adjuvants have the potential to enhance the scope and efficacy of cancer immunotherapy. Radiation may be a particularly good partner to combine with innate immune therapies, because it is a highly efficient means to kill cancer cells but may fail to send the appropriate inflammatory signals needed to act as an efficient endogenous vaccine. This may explain why although radiation therapy is a highly used cancer treatment, true abscopal effects-regression of disease outside the field without additional systemic therapy-are extremely rare. This review focuses on efforts to combine innate immune stimuli as adjuvants with radiation, creating a distinct and complementary approach from T cell-targeted therapies to enhance antitumor immunity.

High-dose irradiation in combination with toll-like receptor 9 agonist CpG oligodeoxynucleotide 7909 downregulates PD-L1 expression via the NF-κB signaling pathway in non-small cell lung cancer cells

Objectives

Irradiation resistance appears as local recurrence and distant metastasis in advanced stages of non-small cell lung cancer (NSCLC). High-dose irradiation combined with immunotherapy improved overall survival and local control of NSCLC. This study explored the underlying molecular mechanism by which the effect of high-dose irradiation plus toll-like receptor 9 (TLR9) agonist CpG oligodeoxynucleotide (CpG ODN) 7909 on NSCLC.

Materials and methods

NSCLC H460 cells were exposed to constant high-dose irradiation (6.37 Gy) in irradiation (IR) group and the irradiation plus CpG group. Gene expression was assessed using quantitative reverse transcriptase-polymerase chain reaction and Western blot. Knockdown of nuclear factor kappa B (NF-κB) p65 expression was conducted using p65 siRNA.

Results

Expression of programmed death-ligand 1 (PD-L1) mRNA was significantly decreased in IR combined with CpG ODN 7909 group compared with the control or IR-alone groups (P<0.05). TLR9 expression was also obviously increased in the combination group compared with the control (P<0.05). Moreover, expression of NF-κB p65 was apparently reduced in the combination group compared with the control (P<0.05). However, expression of PD-L1 was significantly decreased after knockdown of p65 in IR group (P<0.05), but increased in the combination group (P<0.05) and slightly increased in CpG ODN-alone group (P<0.05), which was opposite to that without p65 knockdown group.

Conclusion

This study demonstrated that radiotherapy combined with CpG ODN 7909 was able to downregulate PD-L1 expression through inhibition via the NF-κB signaling pathway.