Effect of Radiation and Ibuprofen on Normoxic Renal Carcinoma Cells Overexpressing Hypoxia-Inducible Factors by Loss of von Hippel–Lindau Tumor Suppressor Gene Function

microRNAs and Prostate Cancer

microRNAs are noncoding RNAs that are important for embryonic stem cell development and epithelial to mesenchymal transition (EMT). Tumor cells hijack EMT and stemness to grow and metastasize to distant organs including bone. In the tumor microenvironment, tumor cells interact with the stromal fibroblasts at the primary and metastatic sites and this interaction leads to tumor growth, EMT, and bone metastasis. Tumor-stromal interactions are a dynamic process that involves both cell-cell communications and extracellular vesicles and soluble factors. Growing body of evidence suggests that microRNAs are part of the payload that comprises the extracellular vesicles. microRNAs induce reactive stroma and thus convert normal stroma into tumor-associated stroma to promote aggressive tumorigenicity in vitro and in vivo. Landmark published studies demonstrate that expression of specific microRNAs of DLK1-DIO3 stem cell cluster correlates with patient survival in metastatic prostate cancer. Thus, microRNAs mediate tumor growth, EMT, and metastasis through cell intrinsic mechanisms and extracellular communications and could be novel biomarkers and therapeutic targets in bone metastatic prostate cancer.

The expression level of the transcription factor Aryl hydrocarbon receptor nuclear translocator (ARNT) determines cellular survival after radiation treatment

Background

Tumour hypoxia promotes radioresistance and is associated with poor prognosis. The transcription factor Aryl hydrocarbon receptor nuclear translocator (ARNT), also designated as Hypoxia-inducible factor (HIF)-1β, is part of the HIF pathway which mediates cellular adaptations to oxygen deprivation and facilitates tumour progression.

The subunits HIF-1α and ARNT are key players within this pathway. HIF-1α is regulated in an oxygen-dependent manner whereas ARNT is considered to be constitutively expressed. However, there is mounting evidence that certain tumour cells are capable to elevate ARNT in hypoxia which suggests a survival benefit.

Therefore the objective of this study was to elucidate effects of an altered ARNT expression level on the cellular response to radiation.

Methods

Different human cell lines (Hep3B, MCF-7, 786-Owt, 786-Ovhl, RCC4wt and RCC4vhl) originating from various tumour entities (Hepatocellular carcinoma, breast cancer and renal cell carcinoma respectively) were X-irradiated using a conventional linear accelerator. Knockdown of ARNT expression was achieved by transient siRNA transfection. Complementary experiments were performed by forced ARNT overexpression using appropriate plasmids. Presence/absence of ARNT protein was confirmed by Western blot analysis. Clonogenic survival assays were performed in order to determine cellular survival post irradiation. Statistical comparison of two groups was achieved by the unpaired t-test.

Results

The results of this study indicate that ARNT depletion renders tumour cells susceptible to radiation whereas overexpression of this transcription factor confers radioresistance.

Conclusions

These findings provide evidence to consider ARNT as a drug target and as a predictive marker in clinical applications concerning the response to radiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-015-0539-9) contains supplementary material, which is available to authorized users.

miR-154* and miR-379 in the DLK1-DIO3 microRNA mega-cluster regulate epithelial to mesenchymal transition and bone metastasis of prostate cancer

PURPOSE

MicroRNAs in the delta-like 1 homolog-deiodinase, iodothyronine 3 (DLK1-DIO3) cluster have been shown to be critical for embryonic development and epithelial to mesenchymal transition (EMT). DLK1-DIO3 cluster miRNAs are elevated in the serum of patients with metastatic cancer. However, the biologic functions of these miRNAs in the EMT and metastasis of cancer cells are poorly understood. We previously demonstrated the oncogenic and metastatic role of miR-409-3p/5p, a member of this cluster, in prostate cancer. In this study, we defined the role of miR-154* and miR-379, two key members of this cluster, in prostate cancer progression and bone metastasis in both cell line models and clinical specimens.

EXPERIMENTAL DESIGN

Genetic manipulation of miR-154* and miR-379 was performed to determine their role in tumor growth, EMT, and bone metastasis in mouse models. We determined the expression of miR-154* in prostate cancer clinical samples and bone metastasis samples using in situ hybridization and quantum dot labeling.

RESULTS

Elevated expression of miR-154* and miR-379 was observed in bone metastatic prostate cancer cell lines and tissues, and miR-379 expression correlated with progression-free survival of patients with prostate cancer. Intracardiac inoculation (to mimic systemic dissemination) of miR-154* inhibitor-treated bone metastatic ARCaPM prostate cancer cells in mice led to decreased bone metastasis and increased survival.

CONCLUSION

miR-154* and miR-379 play important roles in prostate cancer biology by facilitating tumor growth, EMT, and bone metastasis. This finding has particular translational importance because miRNAs in the DLK1-DIO3 cluster can be attractive biomarkers and possible therapeutic targets to treat bone metastatic prostate cancer.

Effect of Ku70 expression on radiosensitivity in renal carcinoma 786-O cells

Background

Radiotherapy plays an important role in cancer therapy. However, the radioresistance of some human cancers, particularly renal carcinoma, often results in radiotherapy failure. The Ku protein is essential for the repair of a majority of DNA double-strand breaks in mammalian cells, but effect of Ku70 expression on radiosensitivity in renal carcinoma is unclear. Here, we investigate the impact of Ku70 on radiosensitivity in renal carcinoma cells through regulating the expression of Ku70.

Methods

The stable overexpression of Ku70 or suppression of Ku70 in renal carcinoma cell line (786-O) was generated by retrovirus-mediated Ku70 cDNA or shRNA targeting Ku70. Ku70 expression was determined by RT-PCR and Western blot analysis, the apoptosis of the stable cells was assayed with flow cytometry and TUNEL assay and the effect of radiation on the livability of stable cells was assessed by MTT assay.

Results

Up-regulation of Ku70 expression of 786-O cells could inhibit cell apoptosis and reduce susceptibility to radiation. On the contrary, 786-O cells with suppression of Ku70 expression could induce cell apoptosis and significantly enhance the sensitivity to radiation.

Conclusions

These findings indicated that Ku70 might play an important role in radioresistance of renal carcinoma, and inhibition of Ku70 can increase the radiosensitivity of 786-O cells by enhancing apoptosis, suggesting down-regulation of Ku70 expression combined with radiotherapy will be a potential strategy for renal cell carcinoma therapy.

Zoledronic acid sensitizes renal cell carcinoma cells to radiation by downregulating STAT1

Zoledronic acid (ZOL), a third-generation bisphosphonate that strongly inhibits osteoclast activity, is widely used for the treatment of bone metastasis from a variety of malignancies, including renal cell carcinoma (RCC). We previously reported that zoledronic acid (ZOL) clinically potentiates antitumor effects of radiotherapy (RT) on bone metastases from RCC. To date, however, it remains unknown whether ZOL radiosensitizes RCC and if it does, how. Here, we demonstrated that ZOL directly radiosensitizes RCC cells independent of osteoclast activity by potentiating the caspase-3-mediated apoptosis pathway. The radiosensitization by ZOL was observed in 786-O, A-498, and ACHN cells but not in Caki-1 cells. As its underlying molecular mechanism, we found that the signal transducer and activator of transcription 1 (STAT1) plays a key role. The three RCC cell lines, in which ZOL exerted a radiosensitizing effect, expressed STAT1 abundantly but Caki-1 cells did not. ZOL downregulated endogenous STAT1 expression in 786-O, A-498, and ACHN cells by a post-transcriptional modification. We confirmed that knockdown of endogenous STAT1 by siRNA sensitized 786-O cells to RT equivalently to ZOL, and that introduction of exogenous STAT1 rendered Caki-1 cells more RT-resistant. This is the first study to clarify the molecular mechanism by which ZOL directly radiosensitizes tumor cells. Because tumor cells commonly overexpress STAT1 and ZOL reportedly radiosensitizes various types of tumor cells, ZOL warrants further clinical and translational studies as a potent radiosensitizer against RT-resistant tumors overexpressing STAT1.

Gene expression profile of coronary artery cells treated with nonsteroidal anti-inflammatory drugs reveals off-target effects

Nonsteroidal anti-inflammatory drugs (NSAIDs) have come under scrutiny because of the gastrointestinal, renal, and cardiovascular toxicity associated with prolonged use of these drugs. The purpose of this study was to identify molecular targets for NSAIDs related to cellular toxicity with a view to optimize drug efficacy in the clinic. Coronary artery smooth muscle cells and endothelial cells were treated with low (clinically achievable) and high (typically used in preclinical studies) concentrations of celecoxib, NS398, and ibuprofen for 24 hours. NSAIDs-induced gene expression changes were evaluated by microarray analysis and validated by real-time reverse-transcription polymerase chain reaction and western blotting. The functional significance of differentially expressed genes was evaluated by Ingenuity Pathway Analysis. At high concentrations, NSAIDs altered the expression of genes regulating cell proliferation and cell death. NSAIDs also altered genes associated with cardiovascular functions including inflammation, thrombosis, fibrinolysis, coronary artery disease, and hypertension. The gene expression was most impacted by ibuprofen, celecoxib, and NS398, in that order. This study revealed that NSAIDs altered expression of an array of genes associated with cardiovascular events and emphasizes the potential for fingerprinting drugs in preclinical studies to assess the potential drug toxicity and to optimize the drug efficacy in clinical settings.

Stabilisation and knockdown of HIF--two distinct ways comparably important in radiotherapy

BACKGROUND

Radiotherapy is one of the most widely used treatments for cancer. The benefit of radiation is known to be negatively affected by tumor hypoxia and the expression of hypoxia-inducible factors (HIF), respectively. HIF-1α/ β and HIF-2α/ β are transcriptional activators of oxygen-regulated genes. The aim of the study was to examine cell type-specific effects of HIF-1α and -2α knockdown or oxygen-independent HIF-stabilisation on radiosensitivity.

METHODS

Herein, we treated four different wildtype and HIF-1α- or HIF-2α-deficient human cancer cell lines, cultured under normoxic or hypoxic conditions, with ionising radiation in doses from 2 to 6 Gy and examined clonogenic survival. Furthermore, the cells were partly preincubated with a HIF-stabiliser (di-tert-butyroyl-oxymethyl-2,4-pyridine-dicarboxylate, (t)Bu-2,4-PDC).

RESULTS

The results show that both hypoxia exposure and treatment with (t)Bu-2,4-PDC increased the radioresistance of human cancer cells. The HIF-mediated decrease of radioresponsiveness induced by the chemical stabiliser emerged to be as strong as the one caused by hypoxia. Clonogenic survival assays furthermore revealed that HIF-1 expression enhanced resistance to radiation, whereas knocking-down HIF-1 increased the sensitivity to radiation under normoxic as well as under hypoxic conditions.

CONCLUSION

These data extend previous observations of HIF-1α and broaden the view by showing HIF-2α inverse correlation between HIF expression and prognosis for the outcome of radiotherapy.

Clinical significance of HIF-2α immunostaining area in radioresistant cervical cancer

OBJECTIVE

Hypoxia has been established as a key factor influencing the pathophysiology of malignant growth. Hypoxia-induced changes in gene expression are coordinated primarily by hypoxia inducible factor-1 alpha (HIF-1α) and HIF-2α. The purpose of this study was to determine whether or not HIF-2α expression is associated with survival and response to radiation in patients with cervical cancer.

METHODS

After reviewing the medical records of 119 patients treated in our institution by primary therapy for stage IIB-IVA cervical cancer, we performed a case-control study. Cases (n=12) were selected from patients with local recurrence or radiation failure after primary radiation therapy with or without concurrent chemoradiation. For each case, we selected two controls from patients who had no evidence of local recurrence. Using pre-treatment paraffin-embedded tissues, we evaluated the expression of HIF-2α by immunohistochemistry. Staining was scored based on intensity (intensity score [IS], 0-3) and proportion (proportion score [PS], 0-100). The results were analyzed by the Student t-test, Mann-Whitney U test, Fisher's exact test, and Cox proportional hazards regression model.

RESULTS

Cytoplasmic expression of HIF-2α, representing the degree of hypoxia, had a relationship with poor response to radiotherapy. The hazard ratio of recurrence was 1.71 for the HIF-2α IS (p=0.110) and 1.04 for the HIF-2α PS (p<0.001), indicating that the HIF-2α staining area correlates weakly with the risk for recurrence.

CONCLUSION

The HIF-2α expression area may have an important role in radioresistance in patients with locally advanced cervical cancer. We conclude that a wider area of hypoxia predicts an increased probability of radioresistance.

A new hypoxia inducible factor-2 inhibitory pyrrolinone alkaloid from roots and stems of Piper sarmentosum

A new trimethoxycinnamoyl-2-pyrrolinone alkaloid, langkamide (1), along with the known compounds piplartine (2) and 3,4,5-trimethoxycinnamic acid (3) were isolated from the roots and stems of the shrub Piper sarmentosum ROXB. The structures were established by spectroscopic analyses and comparison of their spectral data with values reported in the literature. The compounds were tested for their ability to modulate hypoxia inducible factor-2 (HIF-2) transcription activity and all three showed HIF-2 inhibitory activity with EC₅₀ values of 14.0, 4.8, and 60.6 μM, respectively, for compounds 1, 2, and 3.

PX-478, an inhibitor of hypoxia-inducible factor-1alpha, enhances radiosensitivity of prostate carcinoma cells

Overexpression of hypoxia-inducible factor-1alpha (HIF-1alpha) in human tumors is associated with poor prognosis and poor outcome to radiation therapy. Inhibition of HIF-1alpha is considered as a promising approach in cancer therapy. The purpose of this study was to test the efficacy of a novel HIF-1alpha inhibitor PX-478 as a radiosensitizer under normoxic and hypoxic conditions in vitro. PC3 and DU 145 prostate carcinoma cells were treated with PX-478 for 20 hr, and HIF-1alpha protein level and clonogenic cell survival were determined under normoxia and hypoxia. Effects of PX-478 on cell cycle distribution and phosphorylation of H2AX histone were evaluated. PX-478 decreased HIF-1alpha protein in PC3 and DU 145 cells. PX-478 produced cytotoxicity in both cell lines with enhanced toxicity under hypoxia for DU-145. PX-478 (20 mumol/L) enhanced the radiosensitivity of PC3 cells irradiated under normoxic and hypoxic condition with enhancement factor (EF) 1.4 and 1.56, respectively. The drug was less effective in inhibiting HIF-1alpha and enhancing radiosensitivity of DU 145 cells compared to PC3 cells with EF 1.13 (normoxia) and 1.25 (hypoxia) at 50 mumol/L concentration. PX-478 induced S/G2M arrest in PC3 but not in DU 145 cells. Treatment of PC3 and DU 145 cells with the drug resulted in phosphorylation of H2AX histone and prolongation of gammaH2AX expression in the irradiated cells. PX-478 is now undergoing Phase I clinical trials as an oral agent. Although the precise mechanism of enhancement of radiosensitivity remains to be identified, this study suggests a potential role for PX-478 as a clinical radiation enhancer.

Effects of lentivirus-mediated HIF-1alpha knockdown on hypoxia-related cisplatin resistance and their dependence on p53 status in fibrosarcoma cells

Therapy targeting hypoxia-inducible factor-1 (HIF-1) to reverse the hypoxia-related drug resistance has received much interest. Despite a close interaction between HIF-1 and p53 and that p53 mutation is seen in >50% of tumors, whether HIF-1 silencing by targeted therapy depends on tumor p53 status remains unknown. Two isogenic fibrosarcoma cells HT1080 (wild-type p53) and HT1080-6TG (mutant p53) were transduced with HIF-1alpha-specific RNAi lentiviral vectors and selected with blasticidin. Real-time PCR and western blot analysis of HIF-1alpha mRNA and protein respectively validated the silencing effects. Cells were first preconditioned under hypoxia (0.5% O(2)) for 4 h and then co-treated with cisplatin for another 24 h. MTT was used for assessment of chemosensitivity to cisplatin. Moreover, annexin V and propidium iodide staining was detected on flow cytometry for analysis of cisplatin-induced apoptosis. Furthermore, changes of some Bcl-2 family members were detected on western blotting. Exposure to hypoxia significantly increased resistance to cisplatin than exposure to normoxia. HIF-1alpha knockdown could reverse hypoxia-related resistance to cisplatin and apoptotic resistance only in HT1080 cells, but had little effect on HT1080-6TG cells. With HIF-1alpha knockdown, Bid expression was higher in HT1080 than in HT1080-6TG under hypoxia. In summary, HIF-1 targeted therapy to reverse hypoxia-related cisplatin resistance depends on normal p53 status. Changes of Bid expression levels under hypoxia might contribute in part to the differential response to HIF-1alpha silencing in cells with different p53 status.

Hypoxia-inducible factor-2alpha: effect on radiation sensitivity and differential regulation by an mTOR inhibitor

OBJECTIVE

To determine the role of hypoxia-inducible factor-2alpha (HIF2alpha) on the sensitivity of renal cell carcinoma (RCC) cell lines to ionizing radiation and to determine if the mTOR antagonist, rapamycin, could decrease HIF2alpha protein levels.

MATERIALS AND METHODS

Cell lines expressing stable short-hairpin RNAs (shRNAs) encoding HIF2alpha shRNAs or an empty vector were transfected with a hypoxia responsive element (HRE)-driven firefly luciferase reporter gene. Two separate paired cell lines were assayed for their response to increasing doses of ionizing radiation. Proliferation and cell cycle kinetics were compared for cell lines expressing HIF2alpha shRNAs and empty vectors. The effect of an mTOR antagonist, rapamycin on HIF1alpha and HIF2alpha proteins levels was also assessed.

RESULTS

We confirmed that the 786-O RCC lines with stably integrated shRNAs against HIF2alpha had decreased activation of a plasmid with a HRE-driven firefly luciferase reporter gene. Lines from two separate cell clones with decreased HIF2alpha levels showed a significant increase in radiation sensitivity and an increase in G2 cell cycle arrest. Rapamycin, while effective in decreasing HIF1alpha protein levels, did not affect HIF2alpha levels in either of the RCC cell lines.

CONCLUSIONS

These results show that decreasing levels of HIF2alpha leads to an increased sensitivity to ionizing radiation. This finding may explain in part, the known resistance of RCC to radiation therapy. Although mTOR antagonists are approved for the treatment of RCC, these agents do not decrease HIF2alpha levels and therefore might not be effective in enhancing the radio-sensitivity of these tumours.

Radiation sensitivity of human carcinoma cells transfected with small interfering RNA targeted against cyclooxygenase-2

PURPOSE

Cyclooxygenase-2 (COX-2) is considered a potential target for cancer therapy, because COX-2 levels are elevated in the majority of human tumors compared with the normal tissues. COX-2 inhibitors inhibit tumor growth and enhance radiation response in vitro as well as in vivo. However, the precise role of COX-2 in radiation response is not clear. The purpose of the present study was to investigate the in vitro radiosensitivity of tumor cells as a function of COX-2 expression.

EXPERIMENTAL DESIGN AND RESULTS

PC3 and HeLa cells express COX-2 protein constitutively. We silenced the COX-2 gene in these cells using small interfering RNA (siRNA). Transfection of PC3 cells with 100 nmol/L siRNA targeted against COX-2 resulted in reduction of COX-2 protein by 75% and inhibition of arachidonic acid-induced prostaglandin E2 synthesis by approximately 50% compared with the vehicle control. In HeLa cells, 100 nmol/L COX-2 siRNA inhibited COX-2 protein expression by 80%. Cell cycle analysis showed that transfection with COX-2 siRNA did not alter the cell cycle distribution. Radiosensitivity was determined by clonogenic cell survival assay. There was no significant difference in the radiosensitivity of cells in which COX-2 was silenced compared with the cells transfected vehicle or with negative control siRNAs (enhancement ratio = 1.1).

CONCLUSIONS

These data indicate that the in vitro radiosensitivity of tumor cells is minimally dependent on the cellular COX-2 status. Given that a number of potential mechanisms are attributed to COX-2 inhibitors for radiosensitization, specific intervention of COX-2 by RNA interference could help elucidate the precise role of COX-2 in cancer therapy and to optimize strategies for COX-2 inhibition.

Enzyme-linked immunosorbent assay for pharmacological studies targeting hypoxia-inducible factor 1alpha

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of a wide range of genes related to oxygen delivery and metabolic adaptation under hypoxic (low-oxygen) conditions. HIF-1 is, in fact, a heterodimer of two subunits, HIF-1alpha and HIF-1beta. The only analytical methods available for measuring HIF-1alpha levels in tumors are immunohistochemistry and Western blotting. Immunohistochemistry has the advantage of allowing the identification and direct examination of HIF-1alpha-expressing cells, but has the intrinsic limitation, as for Western blotting, of being nonquantitative. We developed and validated an enzyme-linked immunosorbent assay (ELISA) approach to measure HIF-1alpha levels in cultured tumor cell lines in vitro. HIF-1alpha was expressed in thirteen tumor cell lines grown under hypoxic conditions; however, the levels differed strongly between cell lines. These data point to intrinsic differences between cell lines for the induction of HIF-1alpha under hypoxic conditions. The ELISA developed in the present study is thus an interesting alternative to other analytical methods used to measure HIF-1alpha protein levels and should be useful in preclinical pharmacological studies targeting HIF-1alpha.