The Homologous Recombination Repair Pathway is Associated with Resistance to Radiotherapy in Nasopharyngeal Carcinoma

Loss of PDE4D7 expression promotes androgen independence, neuroendocrine differentiation and alterations in DNA repair: implications for therapeutic strategies

BACKGROUND

Androgen signalling remains the seminal therapeutic approach for the management of advanced prostate cancer. However, most tumours eventually shift towards an aggressive phenotype, characterised by androgen independence and treatment resistance. The cyclic adenosine monophosphate (cAMP) pathway plays a crucial role in regulating various cellular processes, with the phosphodiesterase PDE4D7 being a vital modulator of cAMP signalling in prostate cancer cells.

METHODS

Using shRNA-mediated PDE4D7 knockdown in LNCaP cells and downstream analysis via RNA sequencing and phenotypic assays, we replicate clinical observations that diminished PDE4D7 expression promotes an aggressive prostate cancer phenotype.

RESULTS

Our study provides evidence that loss of PDE4D7 expression represents a pivotal switch driving the transition from an androgen-sensitive state to hormone unresponsiveness and neuroendocrine differentiation. In addition, we demonstrate that PDE4D7 loss affects DNA repair pathways, conferring resistance to poly ADP ribose polymerase (PARP) inhibitors.

CONCLUSION

Reinstating PDE4D7 expression sensitises prostate cancer cells to anti-androgens, DNA damage response inhibitors, and cytotoxic therapies. These findings provide significant insight into the regulatory role of PDE4D7 in the development of lethal prostate cancer and the potential of its modulation as a novel therapeutic strategy.

The kinesin light chain-2, a target of mRNA stabilizing protein HuR, inhibits p53 protein phosphorylation to promote radioresistance in NSCLC

BACKGROUND

Radioresistance hinders radiotherapy for the treatment of lung cancer. Kinesin light chain-2 (KLC2) has been found to be upregulated in lung cancer and also to be associated with poor prognosis. This study aimed to investigate the effect of KLC2 on radiosensitivity in lung cancer.

METHODS

The radioresistant role of KLC2 was determined by colony formation, neutral comet assay, and γH2AX immunofluorescent staining assay. We further verified the function of KLC2 in a xenograft tumor model. The downstream of KLC2 was identified through gene set enrichment analysis and validated by western blot. Finally, we analyzed clinical data from the TCGA database to reveal the upstream transcription factor of KLC2, which was validated by RNA binding protein immunoprecipitation assay.

RESULTS

Here, we found that downregulation of KLC2 could significantly reduce colony formation, increase γH2AX level, and double-stranded DNA breaks in vitro. Meanwhile, overexpressed KLC2 significantly increased the proportion of the S phase in lung cancer cells. KLC2 knockdown could activate P53 pathway, and ultimately promoting radiosensitivity. The mRNA of KLC2 was observed to bind with Hu-antigen R (HuR). The mRNA and protein expression of KLC2 in lung cancer cells was significantly reduced when combined with siRNA-HuR. Interestingly, KLC2 overexpression significantly increased the expression of HuR in lung cancer cells.

CONCLUSION

Taken together, these results indicated that HuR-KLC2 forms a positive feedback loop, which decreases the phosphorylation of p53 and thereby weaken the radiosensitivity of lung cancer cells. Our findings highlight the potential prognosis and therapeutic target value of KLC2 in lung cancer patients treated with radiotherapy.

DNA‑PKcs phosphorylation specific inhibitor, NU7441, enhances the radiosensitivity of clinically relevant radioresistant oral squamous cell carcinoma cells

Radioresistant cancer cells lead to poor prognosis after radiotherapy. However, the mechanisms underlying cancer cell radioresistance have not been fully elucidated. Thus, the DNA damage response of clinically relevant radioresistant oral squamous cell carcinoma HSC2-R cells, established by long-term exposure of parental HSC2 cells to fractionated radiation, was investigated. The DNA double-strand break (DSB) repair protein-specific inhibitor, NU7441, which targets DNA-dependent protein kinase catalytic subunit (DNA-PKcs) phosphorylation, and IBR2, which targets Rad51, were administered to HSC2 and HSC2-R cells. NU7441 administration eliminated colony formation in both cell lines under 6 Gy X-ray irradiation, whereas IBR2 did not affect colony formation. NU7441 and IBR2 significantly enhanced 6 Gy X-ray irradiation-induced apoptosis in HSC2-R cells. In HSC2-R cells, cell cycle arrest released earlier than in HSC2 cells, and phosphorylated-H2A histone family member X (γH2AX) expression rapidly decreased. Following NU7441 administration, γH2AX expression and the cell percentages of the G2/M phase were not decreased at 48 h after treatment in HSC2-R cells. DNA-PKcs has been demonstrated to regulate non-homologous end-joining (NHEJ) and homologous recombination (HR) repair, and the later phase of DSB repair is dominated by HR. Therefore, the results of the present study indicated that the DSB repair mechanism in HSC2-R cells strongly depends on NHEJ and loss of HR repair function. The present study revealed a potential mechanism underlying the acquired radioresistance and therapeutic targets in radioresistant cancer cells.

Profiling of Tumor Cell-Delivered Exosome by Surface Enhanced Raman Spectroscopy-Based Biosensor for Evaluation of Nasopharyngeal Cancer Radioresistance

Although the advancement of radiotherapy significantly improves the survival of nasopharyngeal cancer (NPC), radioresistance associated with recurrence and poor outcomes still remains a daunting challenge in the clinical scenario. Currently, effective biomarkers and convenient detection methods for predicting radioresistance have not been well established. Here, the surface-enhanced Raman spectroscopy combined with proteomics is used to firstly profile the characteristic spectral patterns of exosomes secreted from self-established NPC radioresistance cells, and reveals specific variations of proteins expression during radioresistance formation, including collagen alpha-2 (I) chain (COL1A2) that is associated with a favorable prognosis in NPC and is negatively associated with DNA repair scores and DNA repair-related genes via bioinformatic analysis. Furthermore, deep learning model-based diagnostic model is generated to accurately identify the exosomes from radioresistance group. This work demonstrates the promising potential of exosomes as a novel biomarker for predicting the radioresistance and develops a rapid and sensitive liquid biopsy method that will provide a personalized and precise strategy for clinical NPC treatment.

DNA Damage Response Mechanisms in Head and Neck Cancer: Significant Implications for Therapy and Survival

Head and neck cancer (HNC) is a term collectively used to describe a heterogeneous group of tumors that arise in the oral cavity, larynx, nasopharynx, oropharynx, and hypopharynx, and represents the sixth most common type of malignancy worldwide. Despite advances in multimodality treatment, the disease has a recurrence rate of around 50%, and the prognosis of metastatic patients remains poor. HNCs are characterized by a high degree of genomic instability, which involves a vicious circle of accumulating DNA damage, defective DNA damage repair (DDR), and replication stress. Nonetheless, the damage that is induced on tumor cells by chemo and radiotherapy relies on defective DDR processes for a successful response to treatment, and may play an important role in the development of novel and more effective therapies. This review summarizes the current knowledge on the genes and proteins that appear to be deregulated in DDR pathways, their implication in HNC pathogenesis, and the rationale behind targeting these genes and pathways for the development of new therapies. We give particular emphasis on the therapeutic targets that have shown promising results at the pre-clinical stage and on those that have so far been associated with a therapeutic advantage in the clinical setting.

DNA Damage Response in Cancer Therapy and Resistance: Challenges and Opportunities

Resistance to chemo- and radiotherapy is a common event among cancer patients and a reason why new cancer therapies and therapeutic strategies need to be in continuous investigation and development. DNA damage response (DDR) comprises several pathways that eliminate DNA damage to maintain genomic stability and integrity, but different types of cancers are associated with DDR machinery defects. Many improvements have been made in recent years, providing several drugs and therapeutic strategies for cancer patients, including those targeting the DDR pathways. Currently, poly (ADP-ribose) polymerase inhibitors (PARP inhibitors) are the DDR inhibitors (DDRi) approved for several cancers, including breast, ovarian, pancreatic, and prostate cancer. However, PARPi resistance is a growing issue in clinical settings that increases disease relapse and aggravate patients' prognosis. Additionally, resistance to other DDRi is also being found and investigated. The resistance mechanisms to DDRi include reversion mutations, epigenetic modification, stabilization of the replication fork, and increased drug efflux. This review highlights the DDR pathways in cancer therapy, its role in the resistance to conventional treatments, and its exploitation for anticancer treatment. Biomarkers of treatment response, combination strategies with other anticancer agents, resistance mechanisms, and liabilities of treatment with DDR inhibitors are also discussed.

Silibinin Radiosensitizes EGF Receptor-knockdown Prostate Cancer Cells by Attenuating DNA Repair Pathways

Emergence of radioresistance in prostate cancer (PCa) cells is a major obstacle in cancer therapy and contributes to the relapse of the disease. EGF receptor (EGFR) signaling plays an important role in the development of radioresistance. Herein, we have assessed the modulatory effects of silibinin on radiation-induced resistance via DNA repair pathways in EGFR-knockdown DU145 cells. shRNA-based silencing of EGFR was done in radioresistant human PCa DU145 cells and effects of ionizing radiation (IR) and silibinin were assessed using clonogenic and trypan blue assays. Furthermore, radiosensitizing effects of silibinin on PCa in context with EGFR were analyzed using flow cytometry, comet assay, and immunoblotting. Silibinin decreased the colony formation ability with an increased death of DU145 cells exposed to IR (5 Gray), with a concomitant decrease in Rad51 protein expression. Silibinin (25 μM) augmented the IR-induced cytotoxic effect in EGFR-knockdown PCa cells, along with induction of G2/M phase cell cycle arrest. Further, we studied homologous recombination (HR) and non-homologous end joining (NHEJ) pathways in silibinin-induced DNA double-strand breaks in EGFR-knockdown DU145 cells. Silibinin down-regulated the expression of Rad51 and DNA-dependent protein kinase proteins without any considerable effect on Ku70 and Ku80 in IR-exposed EGFR-knockdown PCa cells. The pro-survival signaling proteins, phospho-extracellular signal-regulated kinases (ERK)1/2, phospho-Akt and phospho-STAT3 were decreased by silibinin in EGFR-deficient PCa cells. These findings suggest a novel mechanism of silibinin-induced radiosensitization of PCa cells by targeting DNA repair pathways, HR and NHEJ, and suppressing the pro-survival signaling pathways, ERK1/2, Akt and STAT3, in EGFR-knockdown PCa cells.

Treatment of Recurrent Nasopharyngeal Carcinoma: A Sequential Challenge

Simple Summary

Recurrent nasopharyngeal carcinoma is one of the major causes of death among NPC patients. However, there are no international guidelines for the treatment of patients with recurrent NPC now. In this article, we summarize past publications on clinical research and mechanistic studies related to recurrent NPC, combined with the experience and lessons learned by our institutional multidisciplinary team in the treatment of recurrent NPC. We propose an objective protocol for the treatment of recurrent NPC.

Abstract

Recurrent nasopharyngeal carcinoma (NPC), which occurs in 10–20% of patients with primary NPC after the initial treatment modality of intensity-modulated radiation therapy (IMRT), is one of the major causes of death among NPC patients. Patients with recurrent disease without distant metastases still have a chance to be saved, but re-treatment often carries more serious toxicities or higher risks. For this group of patients, both otolaryngologists and oncologists are committed to developing more appropriate treatment regimens that can prolong patient survival and improve survival therapy. Currently, there are no international guidelines for the treatment of patients with recurrent NPC. In this article, we summarize past publications on clinical research and mechanistic studies related to recurrent NPC, combined with the experience and lessons learned by our institutional multidisciplinary team in the treatment of recurrent NPC. We propose an objective protocol for the treatment of recurrent NPC.

Biological Adaptations of Tumor Cells to Radiation Therapy

Radiation therapy has been used worldwide for many decades as a therapeutic regimen for the treatment of different types of cancer. Just over 50% of cancer patients are treated with radiotherapy alone or with other types of antitumor therapy. Radiation can induce different types of cell damage: directly, it can induce DNA single- and double-strand breaks; indirectly, it can induce the formation of free radicals, which can interact with different components of cells, including the genome, promoting structural alterations. During treatment, radiosensitive tumor cells decrease their rate of cell proliferation through cell cycle arrest stimulated by DNA damage. Then, DNA repair mechanisms are turned on to alleviate the damage, but cell death mechanisms are activated if damage persists and cannot be repaired. Interestingly, some cells can evade apoptosis because genome damage triggers the cellular overactivation of some DNA repair pathways. Additionally, some surviving cells exposed to radiation may have alterations in the expression of tumor suppressor genes and oncogenes, enhancing different hallmarks of cancer, such as migration, invasion, and metastasis. The activation of these genetic pathways and other epigenetic and structural cellular changes in the irradiated cells and extracellular factors, such as the tumor microenvironment, is crucial in developing tumor radioresistance. The tumor microenvironment is largely responsible for the poor efficacy of antitumor therapy, tumor relapse, and poor prognosis observed in some patients. In this review, we describe strategies that tumor cells use to respond to radiation stress, adapt, and proliferate after radiotherapy, promoting the appearance of tumor radioresistance. Also, we discuss the clinical impact of radioresistance in patient outcomes. Knowledge of such cellular strategies could help the development of new clinical interventions, increasing the radiosensitization of tumor cells, improving the effectiveness of these therapies, and increasing the survival of patients.

Silencing UCHL3 enhances radio-sensitivity of non-small cell lung cancer cells by inhibiting DNA repair

UCHL3 belongs to the UCH family and is involved in multiple biological processes. However, the biological functions and underlying mechanisms of action of UCHL3 in radio-sensitivity of non-small cell lung cancer (NSCLC) remain unknown. Here, we reported that the expression of UCHL3 was significantly up-regulated in NSCLC tissues and cell lines, and associated with poor prognosis of NSCLC patients. The expression of UCHL3 of NSCLC cells was increased after exposure to ionizing radiation (IR). Moreover, we found that knockdown of UCHL3 enhanced the radio-sensitivity of NSCLC cells both in vitro and in vivo. Furthermore, γH2AX foci staining and Western blot analysis showed that knockdown of UCHL3 increased IR-induced DNA damage. Knockdown of UCHL3 in NSCLC cells decreased homologous recombination (HR) repair efficiency and RAD51 foci formation. Collectively, our study revealed that knockdown of UCHL3 enhanced the radio-sensitivity of NSCLC cells and increased IR-induced DNA damage via impairing HR repair.

Rab1A promotes cancer metastasis and radioresistance through activating GSK-3β/Wnt/β-catenin signaling in nasopharyngeal carcinoma

Many articles have reported that Rab1A was overexpressed in a variety of human cancers and involved in tumor progression and metastasis. However, the biological function and molecular mechanism of Rab1A in nasopharyngeal carcinoma (NPC) remained unknown until now. Here we found that Rab1A overexpression is a common event and was positively associated with distant metastasis and poor prognosis of NPC patients. Functionally, Rab1A depletion inhibited the migration and EMT phenotype of NPC cells, whereas Rab1A overexpression led to the opposite effect. Furthermore, we reveal an important role for Rab1A protein in the induction of radioresistance via regulating homologous recombination (HR) signaling pathway. Mechanistically, Rab1A activated Wnt/β-catenin signaling by inhibiting the activity of GSK-3β via phosphorylation at Ser9. Then Wnt/β-catenin signaling induced NPC cells radioresistance and metastasis through nuclear translocation of β-catenin and transcription upregulation of HR pathway-related and EMT-related genes expression. In general, this study shows that Rab1A may serve as a potential biomarker for predicting prognosis in NPC patients. Targeting Rab1A and Wnt/β-catenin signaling may hold promise to overcome NPC radioresistance.