Arsenic trioxide treatment decreases the oxygen consumption rate of tumor cells and radiosensitizes solid tumors

Inhibition of ERRα Prevents Mitochondrial Pyruvate Uptake Exposing NADPH-Generating Pathways as Targetable Vulnerabilities in Breast Cancer

Most cancer cells exhibit metabolic flexibility, enabling them to withstand fluctuations in intratumoral concentrations of glucose (and other nutrients) and changes in oxygen availability. While these adaptive responses make it difficult to achieve clinically useful anti-tumor responses when targeting a single metabolic pathway, they can also serve as targetable metabolic vulnerabilities that can be therapeutically exploited. Previously, we demonstrated that inhibition of estrogen-related receptor alpha (ERRα) significantly disrupts mitochondrial metabolism and that this results in substantial antitumor activity in animal models of breast cancer. Here we show that ERRα inhibition interferes with pyruvate entry into mitochondria by inhibiting the expression of mitochondrial pyruvate carrier 1 (MPC1). This results in a dramatic increase in the reliance of cells on glutamine oxidation and the pentose phosphate pathway to maintain nicotinamide adenine dinucleotide phosphate (NADPH) homeostasis. In this manner, ERRα inhibition increases the efficacy of glutaminase and glucose-6-phosphate dehydrogenase inhibitors, a finding that has clinical significance.

Piperlongumine increases sensitivity of colorectal cancer cells to radiation: Involvement of ROS production via dual inhibition of glutathione and thioredoxin systems

Piperlongumine (PL), naturally synthesized in long pepper, is known to selectively kill tumor cells via perturbation of reactive oxygen species (ROS) homeostasis. ROS are the primary effector molecules of radiation, and increase of ROS production by pharmacological modulation is known to enhance radioresponse. We therefore investigated the radiosensitizing effect of PL in colorectal cancer cells (CT26 and DLD-1) and CT26 tumor-bearing mice. Firstly, we found that PL induced excessive production of ROS due to depletion of glutathione and inhibition of thioredoxin reductase. Secondly, PL enhanced both the intrinsic and hypoxic radiosensitivity of tumor cells, linked to ROS-mediated increase of DNA damage, G2/M cell cycle arrest, and inhibition of cellular respiration. Finally, the radiosensitizing effect of PL was verified in vivo. PL improved the tumor response to both single and fractionated radiation, resulting in a significant increase of survival rate of tumor-bearing mice, while it was ineffective on its own. In line with in vitro findings, enhanced radioresponse is associated with inhibition of antioxidant systems. In conclusion, our results suggest that PL could be a potential radiosensitizer in colorectal cancer.

A candidate for lung cancer treatment: arsenic trioxide

Arsenic trioxide (ATO), a highly effective drug in treating acute promyelocytic leukemia with low toxicity, demonstrates a significant effect on lung cancer. The anti-cancer mechanisms of ATO include inhibition of cancer stem-like cells, induction of apoptosis, anti-angiogenesis, sensitization of chemotherapy and radiotherapy, anti-cancer effects of hypoxia, and immunoregulation properties. In addition, some studies have reported that different lung cancers respond differently to ATO. It was concluded on numerous studies that the rational combination of administration and encapsulation of ATO have promising potentials in increasing drug efficacy and decreasing adverse drug effects. We reviewed the efficacy of ATO in the treatment of lung cancer in recent years to provide some views for further study.

γ-Tocotrienol inhibits oxidative phosphorylation and triggers apoptosis by inhibiting mitochondrial complex I subunit NDUFB8 and complex II subunit SDHB

Tocotrienols (T3s) are a subgroup of vitamin E and they have been widely tested to inhibit cell growth in various tumor types. Previous studies have shown that T3s inhibit cancer cell growth by targeting multiple signaling transduction and cellular processes. However, the role of T3s in the regulation of cellular bioenergetic processes remains unclear. In this study, we found that γ-T3 interacts with mitochondrial electron transfer chain NDUFB8 (a subunit of complex I) and SDHB (a subunit of complex II) and inhibits oxidative phosphorylation (OXPHOS), and triggers the production of reactive oxygen species (ROS). In addition, we observed that γ-T3 upregulates the glycolytic capacity in cells, but it did not compensate for cellular ATP generation and decreased the ATP levels in cells. Furthermore, we performed western blots and RT-PCR to measure the mRNA and protein levels of mitochondrial electron transfer chain (ETC) proteins and complex V (ATP synthase), where the results indicated that γ-T3 specifically inhibited the levels of NDUFB8 and SDHB, whereas it had little effect on UQCRC2 (a subunit of complex III), COX4I1 (a subunit of complex IV), and ATP5F1A (a subunit of complex V). The inhibition of NDUFB8 and SDHB by γ-T3 led to the overproduction of ROS and the depletion of ATP, which may be responsible for inducing apoptosis in cancer cells. Our results suggest that mitochondrial respiration may be an effective target for anticancer treatments based on γ-T3.

Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

Radiotherapy is a mainstay treatment for many types of cancer and kills cancer cells via generation of reactive oxygen species (ROS). Incorporating radiation with pharmacological ROS inducers, therefore, has been widely investigated as an approach to enhance aerobic radiosensitization. However, this strategy was overlooked in hypoxic counterpart, one of the most important causes of radiotherapy failure, due to the notion that hypoxic cells are immune to ROS insults because of the shortage of ROS substrate oxygen. Paradoxically, evidence reveals that ROS are produced more in hypoxic than normoxic cells and serve as signaling molecules that render cells adaptive to hypoxia. As a result, hypoxic tumor cells heavily rely on antioxidant systems to sustain the ROS homeostasis. Thereby, they become sensitive to insults that impair the ROS detoxification network, which has been verified in diverse models with or without radiation. Of note, hypoxic radioresistance has been overviewed in different contexts. To the best of our knowledge, this review is the first to systemically summarize the interplay among radiation, hypoxia, and ROS, and to discuss whether perturbation of ROS homeostasis could provide a new avenue to tackle hypoxic radioresistance.

Targeting tumour hypoxia: shifting focus from oxygen supply to demand

Tumour hypoxia is a well-recognised barrier to anti-cancer therapy and represents one of the best validated targets in oncology. Previous attempts to tackle hypoxia have focussed primarily on increasing tumour oxygen supply; however, clinical studies using this approach have yielded only modest clinical benefit, with often significant toxicity and practical limitations. Therefore, there are currently no anti-hypoxia treatments in widespread clinical use. As an emerging alternative strategy, we discuss the relevance of inhibiting tumour oxygen metabolism to alleviate hypoxia and highlight recently initiated clinical trials using this approach.

A Multimodal Molecular Imaging Study Evaluates Pharmacological Alteration of the Tumor Microenvironment to Improve Radiation Response

: Hypoxic zones in solid tumors contribute to radioresistance, and pharmacologic agents that increase tumor oxygenation prior to radiation, including antiangiogenic drugs, can enhance treatment response to radiotherapy. Although such strategies have been applied, imaging assessments of tumor oxygenation to identify an optimum time window for radiotherapy have not been fully explored. In this study, we investigated the effects of α-sulfoquinovosylacyl-1,3-propanediol (SQAP or CG-0321; a synthetic derivative of an antiangiogenic agent) on the tumor microenvironment in terms of oxygen partial pressure (pO₂), oxyhemoglobin saturation (sO₂), blood perfusion, and microvessel density using electron paramagnetic resonance imaging, photoacoustic imaging, dynamic contrast-enhanced MRI with Gd-DTPA injection, and T2*-weighted imaging with ultrasmall superparamagnetic iron oxide (USPIO) contrast. SCCVII and A549 tumors were grown by injecting tumor cells into the hind legs of mice. Five days of daily radiation (2 Gy) combined with intravenous injection of SQAP (2 mg/kg) 30 minutes prior to irradiation significantly delayed growth of tumor xenografts. Three days of daily treatment improved tumor oxygenation and decreased tumor microvascular density on T2*-weighted images with USPIO, suggesting vascular normalization. Acute effects of SQAP on tumor oxygenation were examined by pO₂, sO₂, and Gd-DTPA contrast-enhanced imaging. SQAP treatment improved perfusion and tumor pO₂ (ΔpO₂: 3.1 ± 1.0 mmHg) and was accompanied by decreased sO₂ (20%-30% decrease) in SCCVII implants 20-30 minutes after SQAP administration. These results provide evidence that SQAP transiently enhanced tumor oxygenation by facilitating oxygen dissociation from oxyhemoglobin and improving tumor perfusion. Therefore, SQAP-mediated sensitization to radiation in vivo can be attributed to increased tumor oxygenation. SIGNIFICANCE: A multimodal molecular imaging study evaluates pharmacological alteration of the tumor microenvironment to improve radiation response.

Antidiabetic Biguanides Radiosensitize Hypoxic Colorectal Cancer Cells Through a Decrease in Oxygen Consumption

Background and Purpose: The anti-diabetic biguanide drugs metformin and phenformin exhibit antitumor activity in various models. However, their radiomodulatory effect under hypoxic conditions, particularly for phenformin, is largely unknown. This study therefore examines whether metformin and phenformin as mitochondrial complex I blockades could overcome hypoxic radioresistance through inhibition of oxygen consumption.

Materials and Methods: A panel of colorectal cancer cells (HCT116, DLD-1, HT29, SW480, and CT26) was exposed to metformin or phenformin for 16 h at indicated concentrations. Afterward, cell viability was measured by MTT and colony formation assays. Apoptosis and reactive oxygen species (ROS) were detected by flow cytometry. Phosphorylation of AMP-activated protein kinase (AMPK) was examined by western blot. Mitochondria complexes activity and oxygen consumption rate (OCR) were measured by seahorse analyzer. The radiosensitivity of tumor cells was assessed by colony formation assay under aerobic and hypoxic conditions. The in vitro findings were further validated in colorectal CT26 tumor model.

Results: Metformin and phenformin inhibited mitochondrial complex I activity and subsequently reduced OCR in a dose-dependent manner starting at 3 mM and 30 μM, respectively. As a result, the hypoxic radioresistance of tumor cells was counteracted by metformin and phenformin with an enhancement ratio about 2 at 9 mM and 100 μM, respectively. Regarding intrinsic radioresistance, both of them did not exhibit any effect although there was an increase of phosphorylation of AMPK and ROS production. In tumor-bearing mice, metformin or phenformin alone did not show any anti-tumor effect. While in combination with radiation, both of them substantially delayed tumor growth and enhanced radioresponse, respectively, by 1.3 and 1.5-fold.

Conclusion: Our results demonstrate that metformin and phenformin overcome hypoxic radioresistance through inhibition of mitochondrial respiration, and provide a rationale to explore metformin and phenformin as hypoxic radiosensitizers.

Targeting antioxidant enzymes as a radiosensitizing strategy

Radiotherapy represents a major anti-cancer modality and effectively kills cancer cells through generation of reactive oxygen species (ROS). However, cancer cells are commonly characterized by increased activity of ROS-scavenging enzymes in adaptation to intrinsic oxidative stress, leading to radioresistance. Abrogation of this defense network by pharmacological ROS insults therefore is shown to improve radioresponse in preclinical models; some of them are then tested in clinical trials. In this review, we address (1) the importance of ROS in radioresponse, (2) the main systems regulating redox homeostasis with a special focus on their prognostic effect and predictive role in radiotherapy, and (3) the potential radiosensitizers acting through inhibition of antioxidant enzymes.

Oxidative Phosphorylation as an Emerging Target in Cancer Therapy

Cancer cells have upregulated glycolysis compared with normal cells, which has led many to the assumption that oxidative phosphorylation (OXPHOS) is downregulated in all cancers. However, recent studies have shown that OXPHOS can be also upregulated in certain cancers, including leukemias, lymphomas, pancreatic ductal adenocarcinoma, high OXPHOS subtype melanoma, and endometrial carcinoma, and that this can occur even in the face of active glycolysis. OXPHOS inhibitors could therefore be used to target cancer subtypes in which OXPHOS is upregulated and to alleviate therapeutically adverse tumor hypoxia. Several drugs including metformin, atovaquone, and arsenic trioxide are used clinically for non-oncologic indications, but emerging data demonstrate their potential use as OXPHOS inhibitors. We highlight novel applications of OXPHOS inhibitors with a suitable therapeutic index to target cancer cell metabolism. Clin Cancer Res; 24(11); 2482-90. ©2018 AACR.

MR-CBCT image-guided system for radiotherapy of orthotopic rat prostate tumors

Multi-modality image-guided radiotherapy is the standard of care in contemporary cancer management; however, it is not common in preclinical settings due to both hardware and software limitations. Soft tissue lesions, such as orthotopic prostate tumors, are difficult to identify using cone beam computed tomography (CBCT) imaging alone. In this study, we characterized a research magnetic resonance (MR) scanner for preclinical studies and created a protocol for combined MR-CBCT image-guided small animal radiotherapy. Two in-house dual-modality, MR and CBCT compatible, phantoms were designed and manufactured using 3D printing technology. The phantoms were used for quality assurance tests and to facilitate end-to-end testing for combined preclinical MR and CBCT based treatment planning. MR and CBCT images of the phantoms were acquired utilizing a Varian 4.7 T scanner and XRad-225Cx irradiator, respectively. The geometry distortion was assessed by comparing MR images to phantom blueprints and CBCT. The corrected MR scans were co-registered with CBCT and subsequently used for treatment planning. The fidelity of 3D printed phantoms compared to the blueprint design yielded favorable agreement as verified with the CBCT measurements. The geometric distortion, which varied between -5% and 11% throughout the scanning volume, was substantially reduced to within 0.4% after correction. The distortion free MR images were co-registered with the corresponding CBCT images and imported into a commercial treatment planning software SmART Plan. The planning target volume (PTV) was on average 19% smaller when contoured on the corrected MR-CBCT images relative to raw images without distortion correction. An MR-CBCT based preclinical workflow was successfully designed and implemented for small animal radiotherapy. Combined MR-CBCT image-guided radiotherapy for preclinical research potentially delivers enhanced relevance to human radiotherapy for various disease sites. This novel protocol is wide-ranging and not limited to the orthotopic prostate tumor study presented in the study.

Auranofin radiosensitizes tumor cells through targeting thioredoxin reductase and resulting overproduction of reactive oxygen species

Auranofin (AF) is an anti-arthritic drug considered for combined chemotherapy due to its ability to impair the redox homeostasis in tumor cells. In this study, we asked whether AF may in addition radiosensitize tumor cells by targeting thioredoxin reductase (TrxR), a critical enzyme in the antioxidant defense system operating through the reductive protein thioredoxin. Our principal findings in murine 4T1 and EMT6 tumor cells are that AF at 3-10 μM is a potent radiosensitizer in vitro, and that at least two mechanisms are involved in TrxR-mediated radiosensitization. The first one is linked to an oxidative stress, as scavenging of reactive oxygen species (ROS) by N-acetyl cysteine counteracted radiosensitization. We also observed a decrease in mitochondrial oxygen consumption with spared oxygen acting as a radiosensitizer under hypoxic conditions. Overall, radiosensitization was accompanied by ROS overproduction, mitochondrial dysfunction, DNA damage and apoptosis, a common mechanism underlying both cytotoxic and antitumor effects of AF. In tumor-bearing mice, a simultaneous disruption of the thioredoxin and glutathione systems by the combination of AF and buthionine sulfoximine was shown to significantly improve tumor radioresponse. In conclusion, our findings illuminate TrxR in cancer cells as an exploitable radiobiological target and warrant further validation of AF in combination with radiotherapy.

17 O MRS assesses the effect of mild hypothermia on oxygen consumption rate in tumors

Although oxygen consumption is a key factor in metabolic phenotyping, its assessment in tumors remains critical, as current technologies generally display poor specificity. The objectives of this study were to explore the feasibility of direct ¹⁷ O nuclear magnetic resonance (NMR) spectroscopy to assess oxygen metabolism in tumors and its modulations. To investigate the impact of hypometabolism induction in the murine fibrosarcoma FSAII tumor model, we monitored the oxygen consumption of normothermic (37°C) and hypothermic (32°C) tumor-bearing mice. Hypothermic animals showed an increase in tumor pO₂ (measured by electron paramagnetic resonance oximetry) contrary to normothermic animals. This was related to a decrease in oxygen consumption rate (assessed using ¹⁷ O magnetic resonance spectroscopy (MRS) after the inhalation of ¹⁷ O₂ -enriched gas). This study highlights the ability of direct ¹⁷ O MRS to measure oxygen metabolism in tumors and modulations of tumor oxygen consumption rate.

Carbogen-induced increases in tumor oxygenation depend on the vascular status of the tumor: A multiparametric MRI study in two rat glioblastoma models

The alleviation of hypoxia in glioblastoma with carbogen to improve treatment has met with limited success. Our hypothesis is that the eventual benefits of carbogen depend on the capacity for vasodilation. We examined, with MRI, changes in fractional cerebral blood volume, blood oxygen saturation, and blood oxygenation level dependent signals in response to carbogen. The analyses were performed in two xenograft models of glioma (U87 and U251) recognized to have different vascular patterns. Carbogen increased fractional cerebral blood volume, blood oxygen saturation, and blood oxygenation level dependent signals in contralateral tissues. In the tumor core and peritumoral regions, changes were dependent on the capacity to vasodilate rather than on resting fractional cerebral blood volume. In the highly vascularised U87 tumor, carbogen induced a greater increase in fractional cerebral blood volume and blood oxygen saturation in comparison to the less vascularized U251 tumor. The blood oxygenation level dependent signal revealed a delayed response in U251 tumors relative to the contralateral tissue. Additionally, we highlight the considerable heterogeneity of fractional cerebral blood volume, blood oxygen saturation, and blood oxygenation level dependent within U251 tumor in which multiple compartments co-exist (tumor core, rim and peritumoral regions). Finally, our study underlines the complexity of the flow/metabolism interactions in different models of glioblastoma. These irregularities should be taken into account in order to palliate intratumoral hypoxia in clinical trials.

Assessing Tumor Oxygenation for Predicting Outcome in Radiation Oncology: A Review of Studies Correlating Tumor Hypoxic Status and Outcome in the Preclinical and Clinical Settings

Tumor hypoxia is recognized as a limiting factor for the efficacy of radiotherapy, because it enhances tumor radioresistance. It is strongly suggested that assessing tumor oxygenation could help to predict the outcome of cancer patients undergoing radiation therapy. Strategies have also been developed to alleviate tumor hypoxia in order to radiosensitize tumors. In addition, oxygen mapping is critically needed for intensity modulated radiation therapy (IMRT), in which the most hypoxic regions require higher radiation doses and the most oxygenated regions require lower radiation doses. However, the assessment of tumor oxygenation is not yet included in day-to-day clinical practice. This is due to the lack of a method for the quantitative and non-invasive mapping of tumor oxygenation. To fully integrate tumor hypoxia parameters into effective improvements of the individually tailored radiation therapy protocols in cancer patients, methods allowing non-invasively repeated, safe, and robust mapping of changes in tissue oxygenation are required. In this review, non-invasive methods dedicated to assessing tumor oxygenation with the ultimate goal of predicting outcome in radiation oncology are presented, including positron emission tomography used with nitroimidazole tracers, magnetic resonance methods using endogenous contrasts (R₁ and R2*-based methods), and electron paramagnetic resonance oximetry; the goal is to highlight results of studies establishing correlations between tumor hypoxic status and patients’ outcome in the preclinical and clinical settings.

MATE2 Expression Is Associated with Cancer Cell Response to Metformin

BACKGROUND

There is great interest in repurposing the commonly prescribed anti-diabetic drug metformin for cancer therapy. Intracellular uptake and retention of metformin is affected by the expression of organic cation transporters (OCT) 1-3 and by multidrug and toxic compound extrusion (MATE) 1-2. Inside cells, metformin inhibits mitochondrial function, which leads to reduced oxygen consumption and inhibition of proliferation. Reduced oxygen consumption can lead to improved tumor oxygenation and radiation response.

PURPOSE

Here we sought to determine if there is an association between the effects of metformin on inhibiting oxygen consumption, proliferation and expression of OCTs and MATEs in a panel of 19 cancer cell lines.

RESULTS

There was relatively large variability in the anti-proliferative response of different cell lines to metformin, with a subset of cell lines being very resistant. In contrast, all cell lines demonstrated sensitivity to the inhibition of oxygen consumption by metformin, with relatively small variation. The expression of OCT1 correlated with expression of both OCT2 and OCT3. OCT1 and OCT2 were relatively uniformly expressed, whereas expression of OCT3, MATE1 and MATE2 showed substantial variation across lines. There were statistically significant associations between resistance to inhibition of proliferation and MATE2 expression, as well as between sensitivity to inhibition of oxygen consumption and OCT3 expression. One cell line (LNCaP) with high OCT3 and low MATE2 expression in concert, had substantially higher intracellular metformin concentration than other cell lines, and was exquisitely sensitive to both anti-proliferative and anti-respiratory effects. In all other cell lines, the concentration of metformin required to inhibit oxygen consumption acutely in vitro was substantially higher than that achieved in the plasma of diabetic patients. However, administering anti-diabetic doses of metformin to tumor-bearing mice resulted in intratumoral accumulation of metformin and reduced hypoxic tumor fractions.

CONCLUSIONS

All cancer cells are susceptible to inhibition of oxygen consumption by metformin, which results in reduced hypoxic tumor fractions beneficial for the response to radiotherapy. High MATE2 expression may result in resistance to the anti-proliferative effect of metformin and should be considered as a negative predictive biomarker in clinical trials.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Effects of Arsenic Trioxide on Minor Progressive High-Grade Osteosarcoma of the Extremities Metastatic to the Lung: Results of 39 Patients Treated in a Single Institution

Patients who mildly progressed after first-line chemotherapy were administered arsenic trioxide (ATO) 5–10 mg intravenously daily. Thirty-nine patients were finally enrolled in the study, of whom 19 patients received first-line chemotherapy with ATO infusion while 20 patients did not. Progression-free survival at 4 months was 89.2 and 62.7% (p = 0.043) for the ATO group and the control group, respectively, while the 2-year overall survival was 61 and 16.4% (p = 0.032).

Morphine Attenuated the Cytotoxicity Induced by Arsenic Trioxide in H9c2 Cardiomyocytes

Arsenic trioxide (ATO) is an efficient drug for the treatment of the patients with acute promyelocytic leukemia (APL). Inhibition of proliferation as well as apoptosis, attenuation of migration, and induction of differentiation in tumor cells are the main mechanisms through which ATO acts against APL. Despite advantages of ATO in treatment of some malignancies, certain harmful side effects, such as cardiotoxicity, have been reported. It has been well documented that morphine has antioxidant, anti-apoptotic, and cytoprotective properties and is able to attenuate cytotoxicity. Therefore, in this study, we aimed to investigate the protective effects of morphine against ATO toxicity in H9c2 myocytes using multi-parametric assay including thiazolyl blue tetrazolium bromide (MTT) assay, reactive oxygen species (ROS) generation, caspase 3 activity, nuclear factor kappa B (NF-κB) phosphorylation assay, and expression of apoptotic markers. Our results showed that morphine (1 μM) attenuated cytotoxicity induced by ATO in H9c2 cells. Results of this study suggest that morphine may have protective properties in management of cardiac toxicity in patients who receive ATO as an anti-cancer treatment.

Molecular Pathways: A Novel Approach to Targeting Hypoxia and Improving Radiotherapy Efficacy via Reduction in Oxygen Demand

Tumor hypoxia presents a unique therapeutic challenge in the treatment of solid malignancies. Its presence has been established to be a poor prognostic factor in multiple cancer types, and past hypoxia-directed approaches have yielded generally disappointing results. Previous approaches have centered on either increasing oxygen delivery or administering agents that preferentially radiosensitize or kill hypoxic cells. However, a novel and potentially more effective method may be to increase therapeutic benefit by decreasing tumor oxygen consumption via agents such as metformin or nelfinavir in a patient population that is enriched for tumor hypoxia. This promising approach is currently being investigated in clinical trials and the subject of this article.

A Fast Hydrogen Sulfide-Releasing Donor Increases the Tumor Response to Radiotherapy

Hydrogen sulfide (H2S) is the last gaseous transmitter identified in mammals, and previous studies have reported disparate conclusions regarding the implication of H2S in cancer progression. In the present study, we hypothesized that sodium hydrosulfide (NaHS), a fast H2S-releasing donor, might interfere with the mitochondrial respiratory chain of tumor cells, increase tumor oxygenation, and potentiate the response to irradiation. Using electron paramagnetic resonance (EPR) oximetry, we found a rapid increase in tumor pO2 after NaHS administration (0.1 mmol/kg) in two human tumor models (breast MDA-MB-231 and cervix SiHa), an effect that was due to a decreased oxygen consumption and an increased tumor perfusion. Tumors irradiated 15 minutes after a single NaHS administration were more sensitive to irradiation compared with those that received irradiation alone (increase in growth delay by 50%). This radiosensitization was due to the oxygen effect, as the increased growth delay was abolished when temporarily clamped tumors were irradiated. In contrast, daily NaHS injection (0.1 mmol/kg/day for 14 days) did not provide any effect on tumor growth in vivo. To understand these paradoxical data, we analyzed the impact of external factors on the cellular response to NaHS. We found that extracellular pH had a dramatic effect on the cell response to NaHS, as the proliferation rate (measured in vitro by BrdU incorporation) was increased at pH = 7.4, but decreased at pH = 6.5. Overall, our study highlights the complex role of environmental components in the response of cancer cells to H2S and suggests a new approach for the use of H2S donors in combination with radiotherapy.

Reprogramming of tumor metabolism by targeting mitochondria improves tumor response to irradiation

BACKGROUND

The Warburg phenotype identified decades ago describes tumor cells with increased glycolysis and decreased mitochondrial respiration even in the presence of oxygen. This particular metabolism also termed 'aerobic glycolysis' reflects an adaptation of tumor cells to proliferation in a heterogeneous tumor microenvironment. Although metabolic alterations in cancer cells are common features, their impact on the response to radiotherapy is not yet fully elucidated. This study investigated the impact of cellular oxygen consumption inhibition on the tumor response to radiotherapy.

MATERIAL AND METHODS

Warburg-phenotype tumor cells with impaired mitochondrial respiration (MD) were produced and compared in respect to their metabolism to the genetically matched parental cells (WT). After characterization of their metabolism we compared the response of MD cells to irradiation in vivo and in vitro to the genetically matched parental cells (WT).

RESULTS

We first confirmed that MD cells were exclusively glycolytic while WT cells exhibited mitochondrial respiration. We then used these cells for assessing the response of WT and MD tumors to a single dose of radiation and showed that the in vivo tumor growth delay of the MD group was increased, indicating an increased radiosensitivity compared to WT while the in vitro ability of both cell lines to repair radiation-induced DNA damage was similar.

CONCLUSION

Taken together, these results indicate that in addition to intrinsic radiosensitivity parameters the tumor response to radiation will also depend on their metabolic rate of oxygen consumption.

A selenium-containing ruthenium complex as a cancer radiosensitizer, rational design and the important role of ROS-mediated signalling

We have described the rational design of selenium-containing ruthenium complexes and their use as cancer radiosensitizers through regulating ROS-mediated pathways.

Inhibition of transforming growth factor beta/SMAD signal by MiR-155 is involved in arsenic trioxide-induced anti-angiogenesis in prostate cancer

Prostate cancer is the most common cause of cancer-related deaths in men. Current practices for treatment of prostate cancer are less than satisfactory because of metastasis and recurrence, which are primarily attributed to angiogenesis. Hence, anti-angiogenesis treatment is becoming a promising new approach for prostate cancer therapy. In addition to treating acute promyelocytic leukemia, arsenic trioxide (As₂O₃) suppresses other solid tumors, including prostate cancer. However, the effects of As₂O₃ on angiogenesis in prostate cancer cells, and the underlying molecular mechanisms remain unclear. In the present study, As₂O₃ attenuated angiogenic ability through microRNA-155 (miR-155)-mediated inhibition of transforming growth factor beta (TGF-β)/SMAD signal pathway in human prostate cancer PC-3 and LNCaP cells in vitro and in vivo. Briefly, As₂O₃ inhibited the activations/expressions of both TGFβ-induced and endogenous SMAD2/3. Furthermore, As₂O₃ improved the expression of miR-155 via DNA-demethylation. MiR-155, which targeted the SMAD2-3′UTR, decreased the expression and function of SMAD2. Knockdown of miR-155 abolished the As₂O₃-induced inhibitions of the TGF-β/SMAD2 signaling, the vascular endothelial growth factor secretion and angiogenesis. Through understanding a novel mechanism whereby As₂O₃ inhibits angiogenic potential of prostate cancer cells, our study would help in the development of As₂O₃ as a potential chemopreventive agent when used alone or in combination with other current anticancer drugs.

Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research

The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

Inhibition of TGF-β/SMAD3/NF-κB signaling by microRNA-491 is involved in arsenic trioxide-induced anti-angiogenesis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related mortality worldwide. Current standard practices for treatment of HCC are less than satisfactory because of metastasis and recurrence, which are primarily attributed to the angiogenesis. So, the anti-angiogenesis treatment has become the new approach for HCC therapy. In addition to treating leukemia, arsenic trioxide (As2O3) also suppresses other solid tumors, including HCC. However, the roles of As2O3 in the angiogenesis potential of HCC cells remain unclear. In our present study, As2O3 attenuated the angiogenic ability by the microRNA-491 (miR-491)-mediated inhibition of TGF-β/SMAD3/NF-κB signal pathway in MHCC97H and MHCC97L cells. Briefly, in these cells, As2O3 improved the expression of miR-491 via DNA-demethylation; miR-491, which targeted the SMAD3-3'-UTR, decreased the expression/function of SMAD3, leading to the inactivation of NF-κB/IL-6/STAT-3 signaling; knockdown of miR-491 abolished the As2O3-induced inhibitions of the TGF-β/SMAD3/NF-κB pathway, the VEGF secretion, and the angiogenesis. By understanding a novel mechanism whereby As2O3 inhibits the angiogenic potential in HCC cells, our study would help in the design of future strategies of developing As2O3 as a potential chemopreventive agent when used alone or in combination with other current anticancer drugs.

Reporter cell activity within hydrogel constructs quantified from oxygen-independent bioluminescence

By providing a three-dimensional (3D) support to cells, hydrogels offer a more relevant in vivo tissue-like environment as compared to two-dimensional cell cultures. Hydrogels can be applied as screening platforms to investigate in 3D the role of biochemical and biophysical cues on cell behaviour using bioluminescent reporter cells. Gradients in oxygen concentration that result from the interplay between molecular transport and cell metabolism can however cause substantial variability in the observed bioluminescent reporter cell activity. To assess the influence of these oxygen gradients on the emitted bioluminescence for various hydrogel geometries, a combined experimental and modelling approach was implemented. We show that the applied model is able to predict oxygen gradient independent bioluminescent intensities which correlate better to the experimentally determined viable cell numbers, as compared to the experimentally measured bioluminescent intensities. By analysis of the bioluminescence reaction dynamics we obtained a quantitative description of cellular oxygen metabolism within the hydrogel, which was validated by direct measurements of oxygen concentration within the hydrogel. Bioluminescence peak intensities can therefore be used as a quantitative measurement of reporter cell activity within a hydrogel, but an unambiguous interpretation of these intensities requires a compensation for the influence of cell-induced oxygen gradients on the luciferase activity.

Autophagy interplays with apoptosis and cell cycle regulation in the growth inhibiting effect of Trisenox in HEP-2, a laryngeal squamous cancer

Laryngeal squamous cell carcinoma (LSCC) is the most common among several types of head and neck cancers. Current treatments have a poor effect on early and advanced cases, and further investigations for novel agents against LSCCs are desirable. In this study, we elucidate the cytotoxic enhancing effect of arsenic trioxide (As2O3) combined with L-buthionine sulfoximine (BSO) in LSCC. The effect of BSO with As2O3 or Cisplatin (CDDP) on cell viability was examined using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The reactive oxygen species (ROS) levels, cell cycle, and apoptosis were measured by flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), propidium iodide (PI) and annexin V/PI. The acidic vacuolar organelles were visualized by fluorescence microscope and quantified using flow cytometry. Neither CDDP nor As2O3 when used alone reduced the cell viability. BSO was found to enhance only As2O3 sensitivity, leading to G2/M arrest and autophagy with no correlation of ROS induction. This result suggests that modulation of glutathione enhances autophagy, which interplays with apoptosis. In this study, we obtained initial preclinical evidence for the potential efficacy of these drugs in a combined therapy protocol.

Regulation of O2 consumption by the PI3K and mTOR pathways contributes to tumor hypoxia

BACKGROUND

Inhibitors of the phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) pathway are currently in clinical trials. In addition to antiproliferative and proapoptotic effects, these agents also diminish tumor hypoxia. Since hypoxia is a major cause of resistance to radiotherapy, we sought to understand how it is regulated by PI3K/mTOR inhibition.

METHODS

Whole cell, mitochondrial, coupled and uncoupled oxygen consumption were measured in cancer cells after inhibition of PI3K (Class I) and mTOR by pharmacological means or by RNAi. Mitochondrial composition was assessed by immunoblotting. Hypoxia was measured in spheroids, in tumor xenografts and predicted with mathematical modeling.

RESULTS

Inhibition of PI3K and mTOR reduced oxygen consumption by cancer cell lines is predominantly due to reduction of mitochondrial respiration coupled to ATP production. Hypoxia in tumor spheroids was reduced, but returned after removal of the drug. Murine tumors had increased oxygenation even in the absence of average perfusion changes or tumor necrosis.

CONCLUSIONS

Targeting the PI3K/mTOR pathway substantially reduces mitochondrial oxygen consumption thereby reducing tumor hypoxia. These alterations in tumor hypoxia should be considered in the design of clinical trials using PI3K/mTOR inhibitors, particularly in conjunction with radiotherapy.

Arsenic trioxide attenuates the invasion potential of human liver cancer cells through the demethylation-activated microRNA-491

Hepatocellular carcinoma (HCC) represents the third leading cause of cancer-related mortality worldwide. Current standard practices for treatment of HCC are less than satisfactory because of metastasis and recurrence. In addition to treating acute promyelocytic leukemia (APL), arsenic trioxide (As2O3) also suppresses other solid tumors, such as HCC. However, the effects of As2O3 on the migration/invasion potential of liver cancer cells and the molecular mechanisms underlying in remain unclear. Here we found that As2O3 attenuated the migration/invasion potential of HCC cell lines by blocking matrix metalloproteinases (MMPs) activities and inducing a mesenchymal to epithelial transition (MET). Indeed, As2O3 elevated the expression of microRNA-491 (miR-491) via demethylation. On one hand, as a target miRNA of MMP9, miR-491 decreased the MMP9 expression. On the other hand, miR-491 blocked the activation of nuclear factor κB (NF-κB), which transcriptionally inactivated MMP2 and induced a MET (as determined by the increased expression of E-cadherin and decreased expressions of snail, slug, and vimentin). Knockdown of miR-491 abolished the As2O3-induced MMPs inactivation, MET, and the migration/invasion potential of HCC cell lines. By understanding a novel mechanism how As2O3 inhibits the migration/invasion potential of liver cancer cells, our study may help to identify potential therapeutic targets for liver cancer.

Cellular characterization of ultrasound-stimulated microbubble radiation enhancement in a prostate cancer xenograft model

Tumor radiation resistance poses a major obstacle in achieving an optimal outcome in radiation therapy. In the current study, we characterize a novel therapeutic approach that combines ultrasound-driven microbubbles with radiation to increase treatment responses in a prostate cancer xenograft model in mice. Tumor response to ultrasound-driven microbubbles and radiation was assessed 24 hours after treatment, which consisted of radiation treatments alone (2 Gy or 8 Gy) or ultrasound-stimulated microbubbles only, or a combination of radiation and ultrasound-stimulated microbubbles. Immunohistochemical analysis using in situ end labeling (ISEL) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) revealed increased cell death within tumors exposed to combined treatments compared with untreated tumors or tumors exposed to radiation alone. Several biomarkers were investigated to evaluate cell proliferation (Ki67), blood leakage (factor VIII), angiogenesis (cluster of differentiation molecule CD31), ceramide-formation, angiogenesis signaling [vascular endothelial growth factor (VEGF)], oxygen limitation (prolyl hydroxylase PHD2) and DNA damage/repair (γH2AX). Results demonstrated reduced vascularity due to vascular disruption by ultrasound-stimulated microbubbles, increased ceramide production and increased DNA damage of tumor cells, despite decreased tumor oxygenation with significantly less proliferating cells in the combined treatments. This combined approach could be a feasible option as a novel enhancing approach in radiation therapy.

Reprogramming metabolism with metformin improves tumor oxygenation and radiotherapy response

PURPOSE

Tumor hypoxia is a negative prognostic factor in multiple cancers, due in part to its role in causing resistance to radiotherapy. Hypoxia arises in tumor regions distal to blood vessels as oxygen is consumed by more proximal tumor cells. Reducing the rate of oxygen consumption is therefore a potential strategy to reduce tumor hypoxia. We hypothesized that the anti-diabetic drug metformin, which reduces oxygen consumption through inhibition of mitochondrial complex I, would improve radiation response by increasing tumor oxygenation.

EXPERIMENTAL DESIGN

Tumor hypoxia was measured in xenografts before and after metformin treatment using 2-nitroimidazole hypoxia markers quantified by immunohistochemistry (IHC), flow cytometry, and positron emission tomography (PET) imaging. Radiation response was determined by tumor growth delay and clonogenic survival in xenografts with and without administration of metformin. The impact of metformin use on outcome was assessed in 504 patients with localized prostate cancer treated with curative-intent, image-guided radiotherapy (IGRT) from 1996 to 2012. Three-year biochemical relapse-free rates were assessed using the Kaplan-Meier method.

RESULTS

Metformin treatment significantly improved tumor oxygenation in two xenograft models as measured by IHC, flow cytometry, and PET imaging. Metformin also led to improved radiotherapy responses when mice were administered metformin immediately before irradiation. Clinically, metformin use was associated with an independent and significant decrease in early biochemical relapse rates (P = 0.0106).

CONCLUSION

Our data demonstrate that metformin can improve tumor oxygenation and response to radiotherapy. Our study suggests that metformin may represent an effective and inexpensive means to improve radiotherapy outcome with an optimal therapeutic ratio.

Oxidative stress and replication-independent DNA breakage induced by arsenic in Saccharomyces cerevisiae

Arsenic is a well-established human carcinogen of poorly understood mechanism of genotoxicity. It is generally accepted that arsenic acts indirectly by generating oxidative DNA damage that can be converted to replication-dependent DNA double-strand breaks (DSBs), as well as by interfering with DNA repair pathways and DNA methylation. Here we show that in budding yeast arsenic also causes replication and transcription-independent DSBs in all phases of the cell cycle, suggesting a direct genotoxic mode of arsenic action. This is accompanied by DNA damage checkpoint activation resulting in cell cycle delays in S and G2/M phases in wild type cells. In G1 phase, arsenic activates DNA damage response only in the absence of the Yku70-Yku80 complex which normally binds to DNA ends and inhibits resection of DSBs. This strongly indicates that DSBs are produced by arsenic in G1 but DNA ends are protected by Yku70-Yku80 and thus invisible for the checkpoint response. Arsenic-induced DSBs are processed by homologous recombination (HR), as shown by Rfa1 and Rad52 nuclear foci formation and requirement of HR proteins for cell survival during arsenic exposure. We show further that arsenic greatly sensitizes yeast to phleomycin as simultaneous treatment results in profound accumulation of DSBs. Importantly, we observed a similar response in fission yeast Schizosaccharomyces pombe, suggesting that the mechanisms of As(III) genotoxicity may be conserved in other organisms.

EPR oxygen images predict tumor control by a 50% tumor control radiation dose

Clinical trials to ameliorate hypoxia as a strategy to relieve the radiation resistance it causes have prompted a need to assay the precise extent and location of hypoxia in tumors. Electron paramagnetic resonance oxygen imaging (EPR O2 imaging) provides a noninvasive means to address this need. To obtain a preclinical proof-of-principle that EPR O2 images could predict radiation control, we treated mouse tumors at or near doses required to achieve 50% control (TCD50). Mice with FSa fibrosarcoma or MCa4 carcinoma were subjected to EPR O2 imaging and immediately radiated to a TCD50 or TCD50 ± 10 Gy. Statistical analysis was permitted by collection of approximately 1,300 tumor pO2 image voxels, including the fraction of tumor voxels with pO2 less than 10 mm Hg (HF10). Tumors were followed for 90 days (FSa) or 120 days (MCa4) to determine local control or failure. HF10 obtained from EPR images showed statistically significant differences between tumors that were controlled by the TCD50 and those that were not controlled for both FSa and MCa4. Kaplan-Meier analysis of both types of tumors showed that approximately 90% of mildly hypoxic tumors were controlled (HF10%< 10%), and only 37% (FSA) and 23% (MCa4) tumors controlled if hypoxic. EPR pO2 image voxel distributions in these approximately 0.5 mL tumors provide a prediction of radiation curability independent of radiation dose. These data confirm the significance of EPR pO2 hypoxic fractions. The 90% control of low HF10 tumors argue that 0.5 mL subvolumes of tumors may be more sensitive to radiation and may need less radiation for high tumor control rates. Cancer Res; 73(17); 5328-35. ©2013 AACR.

Arsenic trioxide induces cardiac fibroblast apoptosis in vitro and in vivo by up-regulating TGF-β1 expression

Arsenic trioxide (As2O3; ATO) is clinically effective in treating acute promyelocytic leukemia (APL); however, it frequently causes cardiotoxic effects. This study was designed to investigate whether ATO could induce apoptosis of cardiac fibroblasts (CFs) that play very important roles in maintaining the structure integrity and function of the heart. Cardiac fibroblasts from guinea pigs administered with ATO (1mg/kgbw) were used to test the pro-apoptotic role of ATO in vivo. The current study demonstrated that ATO induced morphological characteristics of apoptosis and Caspase-3 activation in CFs of guinea pigs along with a significant up-regulation in TGF-β1 protein expression, Bax/Bcl-2 ratio and ERK1/2 phosphorylation. In vitro MTT assay showed that ATO remarkably reduced the viability of cultured cardiac fibroblasts (NRCFs) from neonatal rat in a concentration- and time-dependent manner. Consistent with the notions in vivo, ATO significantly induced the apoptosis in NRCFs, dramatically up-regulated TGF-β1 protein level and Bax/Bcl-2 ratio in a time-dependent fashion and activated Caspase-3 and ERK1/2. Finally, pretreatment with LY364947, an inhibitor of TGF-β signaling could apparently reverse these changes. We therefore conclude that TGF-β is functionally linked to ERK1/2 and that TGF-β signaling is responsible for ATO-induced CFs apoptosis, which provides a novel mechanism of ATO related cardiac toxicology.

Comparison of optical and power Doppler ultrasound imaging for non-invasive evaluation of arsenic trioxide as a vascular disrupting agent in tumors

Small animal imaging provides diverse methods for evaluating tumor growth and acute response to therapy. This study compared the utility of non-invasive optical and ultrasound imaging to monitor growth of three diverse human tumor xenografts (brain U87-luc-mCherry, mammary MCF7-luc-mCherry, and prostate PC3-luc) growing in nude mice. Bioluminescence imaging (BLI), fluorescence imaging (FLI), and Power Doppler ultrasound (PD US) were then applied to examine acute vascular disruption following administration of arsenic trioxide (ATO).

During initial tumor growth, strong correlations were found between manual caliper measured tumor volume and FLI intensity, BLI intensity following luciferin injection, and traditional B-mode US. Administration of ATO to established U87 tumors caused significant vascular shutdown within 2 hrs at all doses in the range 5 to 10 mg/kg in a dose dependant manner, as revealed by depressed bioluminescent light emission. At lower doses substantial recovery was seen within 4 hrs. At 8 mg/kg there was >85% reduction in tumor vascular perfusion, which remained depressed after 6 hrs, but showed some recovery after 24 hrs. Similar response was observed in MCF7 and PC3 tumors. Dynamic BLI and PD US each showed similar duration and percent reductions in tumor blood flow, but FLI showed no significant changes during the first 24 hrs.

The results provide further evidence for comparable utility of optical and ultrasound imaging for monitoring tumor growth, More specifically, they confirm the utility of BLI and ultrasound imaging as facile assays of the vascular disruption in solid tumors based on ATO as a model agent.

Hepatocytes determine the hypoxic microenvironment and radiosensitivity of colorectal cancer cells through production of nitric oxide that targets mitochondrial respiration

PURPOSE

To determine whether host hepatocytes may reverse hypoxic radioresistance through nitric oxide (NO)-induced oxygen sparing, in a model relevant to colorectal cancer (CRC) liver metastases.

METHODS AND MATERIALS

Hepatocytes and a panel of CRC cells were incubated in a tissue-mimetic coculture system with diffusion-limited oxygenation, and oxygen levels were monitored by an oxygen-sensing fluorescence probe. To activate endogenous NO production, cocultures were exposed to a cytokine mixture, and the expression of inducible nitric oxide synthase was analyzed by reverse transcription-polymerase chain reaction, Western blotting, and NO/nitrite production. The mitochondrial targets of NO were examined by enzymatic activity. To assess hypoxic radioresponse, cocultures were irradiated and reseeded for colonies.

RESULTS

Resting hepatocytes consumed 10-40 times more oxygen than mouse CT26 and human DLD-1, HT29, HCT116, and SW480 CRC cells, and thus seemed to be the major effectors of hypoxic conditioning. As a result, hepatocytes caused uniform radioprotection of tumor cells at a 1:1 ratio. Conversely, NO-producing hepatocytes radiosensitized all CRC cell lines more than 1.5-fold, similar to the effect of selective mitochondrial inhibitors. The radiosensitizing effect was associated with a respiratory self-arrest of hepatocytes at the level of aconitase and complex II, which resulted in profound reoxygenation of tumor cells through oxygen sparing. Nitric oxide-producing hepatocytes were at least 10 times more active than NO-producing macrophages to reverse hypoxia-induced radioresistance.

CONCLUSIONS

Hepatocytes were the major determinants of the hypoxic microenvironment and radioresponse of CRC cells in our model of metabolic hypoxia. We provide evidence that reoxygenation and radiosensitization of hypoxic CRC cells can be achieved through oxygen sparing induced by endogenous NO production in host hepatocytes.

Effect of glucosamine and chitooligomer on the toxicity of arsenite against Escherichia coli

Escherichia coli was selected as the sample to study the toxicity of arsenite in the presence of saccharides. The effect of glucosamine, N-acetylglucosamine, glucose, lactose, sucrose, glucosamine and cyclodextrin on the toxicity of arsenite against E. coli was investigated by microcalorimetry. The glucosamine and the tested chitooligomer decreased the toxicity of arsenite on cells of E. coli, and the effect of glucosamine was stronger than that of the chitooligomer. These results suggest that the glucosamine and chitooligomer may be employed as the assistant antidote for arsenite.

Arsenic trioxide inhibits cell growth and induces apoptosis through inactivation of notch signaling pathway in breast cancer

Arsenic trioxide has been reported to inhibit cell growth and induce apoptotic cell death in many human cancer cells including breast cancer. However, the precise molecular mechanisms underlying the anti-tumor activity of arsenic trioxide are still largely unknown. In the present study, we assessed the effects of arsenic trioxide on cell viability and apoptosis in breast cancer cells. For mechanistic studies, we used multiple cellular and molecular approaches such as MTT assay, apoptosis ELISA assay, gene transfection, RT-PCR, Western blotting, and invasion assays. For the first time, we found a significant reduction in cell viability in arsenic trioxide-treated cells in a dose-dependent manner, which was consistent with induction of apoptosis and also associated with down-regulation of Notch-1 and its target genes. Taken together, our findings provide evidence showing that the down-regulation of Notch-1 by arsenic trioxide could be an effective approach, to cause down-regulation of Bcl-2, and NF-κB, resulting in the inhibition of cell growth and invasion as well as induction of apoptosis. These results suggest that the anti-tumor activity of arsenic trioxide is in part mediated through a novel mechanism involving inactivation of Notch-1 and its target genes. We also suggest that arsenic trioxide could be further developed as a potential therapeutic agent for the treatment of breast cancer.

Electron paramagnetic resonance highlights that the oxygen effect contributes to the radiosensitizing effect of paclitaxel

BACKGROUND

Paclitaxel (PTX) is a potent anti-cancer chemotherapeutic agent and is widely used in the treatments of solid tumors, particularly of the breast and ovaries. An effective and safe micellar formulation of PTX was used to administer higher doses of PTX than Taxol® (the current commercialized drug). We hypothesize that PTX-loaded micelles (M-PTX) may enhance tumor radiosensitivity by increasing the tumor oxygenation (pO(2)). Our goals were (i) to evaluate the contribution of the "oxygen effect" to the radiosensitizing effect of PTX; (ii) to demonstrate the therapeutic relevance of the combination of M-PTX and irradiation and (iii) to investigate the underlying mechanisms of the observed oxygen effect.

METHODOLOGY AND PRINCIPAL FINDINGS

We used (PEG-p-(CL-co-TMC)) polymeric micelles to solubilize PTX. pO(2) was measured on TLT tumor-bearing mice treated with M-PTX (80 mg/kg) using electron paramagnetic resonance (EPR) oximetry. The regrowth delay following 10 Gy irradiation 24 h after M-PTX treatment was measured. The tumor perfusion was assessed by the patent blue staining. The oxygen consumption rate and the apoptosis were evaluated by EPR oximetry and the TUNEL assay, respectively. EPR oximetry experiments showed that M-PTX dramatically increases the pO(2) 24 h post treatment. Regrowth delay assays demonstrated a synergy between M-PTX and irradiation. M-PTX increased the tumor blood flow while cells treated with M-PTX consumed less oxygen and presented more apoptosis.

CONCLUSIONS

M-PTX improved the tumor oxygenation which leads to synergy between this treatment and irradiation. This increased pO(2) can be explained both by an increased blood flow and an inhibition of O(2) consumption.