6.72.05 (P=0.002); 5637R siCtrl vs. exhibited elevated migratory and invasive abilities, enhanced CSC-like characteristics and radio-resistance. Furthermore, knockdown of STAT3 expression or inhibition of STAT3 activation markedly decreased the self-renewal ability Ciprofloxacin HCl and tumorigenicity of radiation-resistant BCa cells. Kaplan-Meier analysis revealed that decreased STAT3 mRNA levels Ciprofloxacin HCl were associated with increased overall survival times in patients with BCa. Taken together, these data indicated that STAT3 may be an effective therapeutic target for inhibiting the progression, metastasis and recurrence of BCa in patients receiving radiotherapy. strong class=”kwd-title” Keywords: signal transduction and transcription activator 3, radiosensitivity, cancer stem cell, bladder cancer Introduction Bladder cancer (BCa) is a heterogeneous disease that commonly presents as a malignant tumor; there are two main subtypes, non-muscle invasive (NMIBC) and muscle invasive (MIBC) BCa (1). Although 70% of patients are diagnosed with NMIBC, the disease can quickly progress to invade the muscle layer (2). The current treatment for NMIBC consists of transurethral resection of the bladder tumor in conjunction with intravesical chemotherapy or immunotherapy (3). MIBC accounts for ~30% of all BCa cases at initial presentation, and is associated with Ciprofloxacin HCl a higher death rate due to distant metastasis (1). Even after receiving aggressive radical cystectomy (RC), the 5-year mortality rate of patients with MIBC remains at 50C70%, with a high recurrence rate and poor overall prognosis (3). For decades, RC has been the primary treatment method for MIBC; however, improved survival rates cannot be achieved through surgery alone (4). In the past 20 years, as MIBC treatments have aimed to preserve the bladder and improve quality of life, radiation therapy (RT), chemotherapy for radiation sensitization, and immunotherapy have continuously improved (5). This has increased the 5-year overall survival (OS) rate to 40C50%, resulting in improved patient quality of life (6). For patients that are medically unsuitable for RC, or those who prefer non-surgical alternatives, RT and concurrent chemotherapy are currently the most effective treatments. For suitable surgical candidates, bladder conservation can maintain function and result in similar oncologic outcomes to RC (7). However, the resistance of cancer cells to radiation often limits the effectiveness of RT. Furthermore, patients may still experience local tumor recurrence, and acquiring radio-resistance (RR) after initial radiotherapy may exacerbate local tumor recurrence and metastasis (8,9). At present, the mechanisms by which cancer cells acquire RR remain unclear. In the present study, obstacles in the treatment of BCa were considered to be attributed to the radiation tolerance of cancer stem cells (CSCs) present in the tumor (10,11). CSCs may be seen as a reservoir of cancer cells due to their self-renewal and plasticity properties, and the ability to reconstruct heterogeneous tumor cell populations (12). Although there are a lack of supporting clinical data, experimental data and preliminary clinical trials suggest that CSC-targeted treatment has the potential to improve radiotherapeutic efficacy (13,14). Signal transduction and transcription activator 3 (STAT3) is a transcription factor with a number of important biological functions. Increasing evidence suggests that STAT3 is an important regulator of normal and cancer stem cells (15). It is involved in epithelial-to-mesenchymal transition (EMT)-associated pathways, which are hypothesized to be the primary mechanisms for CSC generation (16), and has the ability to promote cancer progression by regulating the activity of CSCs (17). Moreover, our previous studies revealed that high levels of STAT3 phosphorylation are closely associated with the acquired radiation resistance (ARR) of urinary system tumors Ciprofloxacin HCl (18,19). The present study aimed to elucidate the role of STAT3 in RR and its association with the CSC phenotype in BCa cells. The data suggested that the aberrant activation of STAT3 enhanced the migration, invasion and stem-like properties of BCa cells in response to long-term ionizing radiation (IR) exposure. Materials and methods Cell culture and treatment Human BCa cell lines (5637 and T24) were purchased from The Cell Bank Ciprofloxacin HCl of Type Culture Collection of the Chinese Academy of Sciences and cultured in high glucose Dulbecco’s modified Eagle’s medium (DMEM; Invitrogen; Thermo Fisher Scientific, Inc.) containing 10% fetal bovine serum (FBS; Invitrogen; Thermo Fisher Scientific, Inc.), 100 U/ml penicillin and 100 U/ml streptomycin (Sigma-Aldrich; Merck KGaA). The cells were maintained at 37C in a humidified Rabbit polyclonal to FOXRED2 atmosphere with 5% CO2. Cells were irradiated at room temperature in ambient air using a 137Cs source (-ray; Nordion, Inc.) at a dose rate of 0.79 Gy/min. Resistant cells were generated by mimicking clinical radiotherapy treatment as previously described (19). Subsequently, cells.