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Radiotherapy with bladder preservation is highly acceptable among patients bearing bladder cancer (BCa), but the occurrence of secondary tolerance (ARR) during treatment is one of the important reasons for the failure of clinical radiotherapy. COX-2 has been frequently reported to be highly expressed and associated with radio-resistance in various cancers. In this study, the feasibility of Taraxasterol (Tara) as a radiosensitizer was investigated, and the target effect of Tara on COX-2 and its underlying mechanism were explored. The toxicity of Tara toward BCa cells was detected with the MTT method and cells in response to IR or Tara + IR were compared by clone formation assay. Next, a small RNA interference system (siRNA) was employed to decrease endogenous COX-2 expression in BCa cells, and the stem cell-like features and motion abilities of BCa cells under different treatments were investigated using microsphere formation and transwell chamber assay, respectively. Meanwhile, the expression of a series of inflammation-related molecules and stem cell characteristic molecules was determined by qRT-PCR, western blot and ELISA method. In vivo studies, BCa cells were subcutaneously injected into the right flank of each male mouse. Those mice were then grouped and exposed to different treatment: Tara, IR, IR + Tara and untreated control. The volumes of each tumor were measured every two days and target proteins were detected with immunohistochemical (IHC) staining. The results show that COX-2 decline, due to COX-2 knocking-down or Tara treatment, could greatly enhance BCa cells' radiosensitivity and significantly decrease their migration, invasion and microsphere formation abilities, companied with the reduce of JAK2, phos-STAT3, MMP2 and MMP9 expression. However, Tara could not further reduce the expression of an above molecule of cells in COX-2-deficient BCa cells. Correspondingly, Tara treatment could not further enhance those siCOX-2 BCa cells response to IR. Our data support that Tara can improve the radiosensitivity of BCa cells by targeting COX-2/PGE2. The mechanism may involve regulating STAT3 phosphorylation, DNA damage response protein activation, and expression of MMP2/MMP9. [ABSTRACT FROM AUTHOR]

As a part of breast-conserving therapy (BCT), postoperative radiotherapy is one of the main means to improve the clinical efficacy of breast cancer (BCa). However, ionizing radiation (IR) may induce BCa cells to develop radioresistance, which causes tumor recurrence and metastasis after treatment. Recently, DOC-2/DAB2 interactive protein (DAB2IP) has been reported often down-regulated in a variety of cancers and is related to tumor tolerance to radiotherapy. In this study, BCa cell lines were introduced to study how DAB2IP deficient influenced BCa cell radiosensitivity in vitro and in vivo and discuss the possible mechanism. Small RNA interference system (siRNA) was employed to decrease DAB2IP expression in two BCa cell lines, MDA-MB-231 and 4T1. Cells in response to IR or antineoplastics were detected by clone formation assay or MTT method, respectively. For in vivo studies, siDAB2IP or siControl cells were subcutaneously injected into the right flank of each female mouse. Sphere formation assay, soft agar colony anchoring assay and in vivo tumorigenesis assay were implemented to examine the stem cell-like features of BCa cells. Tube formation assay as well as immunofluorescence assay (IFA) were respectively applied to determine the angiogenesis of tumor cells in vitro and in vivo. The expression of a series of angiogenesis-related molecules was analyzed by qRT-PCR, western blot and IFA. It was observed that the downregulation of DAB2IP could significantly improve the clone formation ability of BCa cells, reduce their sensitivity to radiation and chemotherapy drugs, enhance their migration and invasion abilities and increase their stemness characteristics. It was also noted that either DAB2IP-knocking down or treated with the conditioned medium from DAB2IP-deficient BCa cells could promote the tube-forming ability of the endothelial cell. Similarly, in vivo studies showed that tumors developed from siDAB2IP BCa cells had higher tumor microvascular density (MVD) and more severe oxygen deficiency than that in DAB2IP- sufficient tumors. Meanwhile, Knock-down of DAB2IP inhibited vascular maturation and promoted the formation of vasculogenic mimicry (VM) in BCa tissues. Down-regulation of STAT3 could enhance siDAB2IP cells sensitivity to IR, accompanied by the decrease of VEGF expression. Our data support that loss of DAB2IP confers radio-resistance of BCa could be due to increased hypoxia, inhibited vascular maturation and promoted VM formation. STAT3 inhibition could be a potential way to overcome such DAB2IP-deficient induced tolerance in BCT. [ABSTRACT FROM AUTHOR]

Purpose:To evaluate the effect of fractionated irradiation (FI) on tumor cells’ sensitivity to ionizing radiation (IR) and antineoplastic drugs, and examine the potential of early growth response-1 (EGR-1) inhibition to sensitize tumor cells to IR. Materials and methods:PC3 and HepG2 cells were subjected 10 times to γ-rays at 2 Gy. The surviving cells were named PC3/R and HepG2/R, respectively. The cells’ sensitivity to irradiation and chemotherapeutic drugs, including cisplatin (PT), doxorubicin (DOX), mitomycin C (MMC) and 5-fluorouracil (5-FU), were identified by colony formation assay and MMT method, respectively. Quantitative real-time polymerase chain reaction (RT-qPCR) analysis was utilized to compare the difference of gene expression between radioresistant cells and parental cells. The small interfering RNA system was implemented to inhibit endogenous EGR-1 expression in radiation-resistant cells. Western blot was employed to identify the possible mechanism by which EGR-1 regulates cells’ radiosensitivity. Results:FI induced cross-resistant to IR and MMC in tumor cells. Along with the reduction of ovarian cancer-2/disabled homolog 2 (DOC-2/DAB2) interactive protein (DAB2IP) expression, EGR-1 gene was upregulated in FI-treated cells. On the other hand, downregulation of EGR-1 gene expression sensitized radioresistant cells to IR accompanied by DAB2IP overexpression and STAT3 inactivation. In addition, NF-κB inhibitor, BAY11-7082 enhanced resistant cells’ radiosensitivity and chemosensitivity. Conclusions:Conventionally FI has a higher risk of forming acquired radioresistance (ARR) in vitro. EGR-1 gene-targeted drug design could be an effective strategy to overcome DAB2IP-dysregulation-induced ARR in tumor patients. [ABSTRACT FROM AUTHOR]

Bladder cancer (BCa) is the most common cancer of the human urinary system, and is associated with poor patient prognosis and a high recurrence rate. Cancer stem cells (CSCs) are the primary cause of tumor recurrence and metastasis, possessing self-renewal properties and resistance to radiation therapy. Our previous studies indicated that phosphorylated signal transduction and transcription activator 3 (STAT3) may be a potential biomarker to predict radiation tolerance and tumor recurrence in patients with BCa, following conventional radiotherapy. The aim of the present study was to investigate the underlying mechanism of STAT3 in the radio-resistance of BCa cells. It was found that fractionated irradiation promoted the activation of two STAT3-associated CSCs signaling pathways in BCa cells, namely suppressor of variegation 3–9 homolog 1/GATA binding protein 3/STAT3 and Janus kinase 2/STAT3. Surviving cells 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 and tumorigenicity of radiation-resistant BCa cells. Kaplan-Meier analysis revealed that decreased STAT3 mRNA levels 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. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of Ixabepilone on quiescent or hypoxic cells response to ionizing radiation., Methods: NCI-H460 and A549, two human NSCLC cell lines, were employed in this experiment. Quiescent cells (QC) or hypoxic cells (HC) were induced as mentioned previously and untreated cells as control. A colony forming assay was applied to compare cellular radio-sensitivity with or without Ixabepilone. Flow cytometry and Western blot analysis were used to detect cell cycle distribution and apoptosis., Results: Along with an increased population of G1 cell (NCI-H46 P=0.001 3; A549 P=0.006), both HC and QC were exhibited radio-resistance compared to untreated cells (survival fraction: NCI-H460 P=0.003; A549 P=0.000 1). Moreover, it was found that Ixabepilone, which induced apoptosis in both IR-treated or untreated NSCLC cells, significantly enhanced cells death under hypoxia (decrease of survival fraction: NCI-H460 P=0.000 2; A549 P<0.01)., Conclusion: The existence of quiescent or hypoxic cells in solid tumors poses a critical therapeutic problem since they were resistant to IR. Ixabepilone, which induces apoptosis in NSCLC, showed great radio-sensitization effect on hypoxic cells. Following work will focus on whether Ixabepilone could increase hypoxic tumor cells radio-sensitivity in vivo, which could provide useful data for the application of Ixabepilone in clinical practice.