Metalloporphyrin antioxidants ameliorate normal tissue radiation damage in rat brain

Spaceflight increases sarcoplasmic reticulum Ca2+ leak and this cannot be counteracted with BuOE treatment

Spending time in a microgravity environment is known to cause significant skeletal muscle atrophy and weakness via muscle unloading, which can be partly attributed to Ca2+ dysregulation. The sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) pump is responsible for bringing Ca2+ from the cytosol into its storage site, the sarcoplasmic reticulum (SR), at the expense of ATP. We have recently demonstrated that, in the soleus of space-flown mice, the Ca2+ uptake ability of the SERCA pump is severely impaired and this may be attributed to increases in reactive oxygen/nitrogen species (RONS), to which SERCA is highly susceptible. The purpose of this study was therefore to investigate whether treatment with the antioxidant, Manganese(III) meso-tetrakis(N-n-butoxyethylpyridinium-2-yl)porphyrin, MnTnBuOE-2-PyP5+ (BuOE), could attenuate muscle atrophy and SERCA dysfunction. We received soleus muscles from the rodent research 18 mission which had male mice housed on the international space station for 35 days and treated with either saline or BuOE. Spaceflight significantly reduced the soleus:body mass ratio and significantly increased SERCA's ionophore ratio, a measure of SR Ca2+ leak, and 4-HNE content (marker of RONS), none of which could be rescued by BuOE treatment. In conclusion, we find that spaceflight induces significant soleus muscle atrophy and SR Ca2+ leak that cannot be counteracted with BuOE treatment. Future work should investigate alternative therapeutics that are specifically aimed at increasing SERCA activation or reducing Ca2+ leak.

The effects of myricitrin and chebulinic acid on the rat hippocampus exposed to gamma radiation: A stereological, histochemical and biochemical study

AIM

Gamma radiation, a form of ionizing radiation, is used in many different areas, especially in the health field and in the treatment of cancer. However, gamma radiation used for therapeutic purposes also has numerous harmful effects on human health. This study was planned to investigate the impacts of exposure to gamma radiation on the hippocampal area and the preventive effects of myricitrin and chebulinic acid against that damage.

MATERIAL AND METHOD

Thirty-six male Wistar albino rats were randomly divided into six groups. The control group was exposed to no treatment. The chebulinic acid and myricitrin groups were injected with the relevant drug at a dosage of 0.033 mg/kg) (vehicle; normal saline) per day. The gamma groups were placed in a plexiglass test setup with their heads positioned close to the source. The subjects were exposed to radiation with a mixed source containing radioactive Cs-137 and Co-60 isotopes obtained from Ondokuz Mayıs University Physics Department Nuclear Physics Laboratory for 1 h. Gamma radiation was applied 16 mGy for one hour per day for 10 days. The gamma radiation+chebulinic acid and the gamma radiation myricitrin groups also received 0.033 mg/kg per day of these drugs via injection. Immediately after the experimental procedure, all animals were subjected to behavioural tests, and perfused brain tissues were analyzed using stereological methods.

RESULTS

Stereological analysis showed that gamma radiation caused a decrease in the numbers of neurons in the hippocampal area (p < 0.01; One-way ANOVA) and that chebulinic acid and myricitrin reduced this decrease (p < 0.01; One-way ANOVA). Decreases in learning and memory capacity were detected in behavioural tests in rats from the Gamma group.

CONCLUSION

The study findings showed that that the adverse health effects of Gamma radiation can be ameliorated using myricitrin and chebulinic acid. Myricitrin was more effective in terms of cell proliferation and defence against oxidative stress than chebulinic acid, and exhibited a more neuroprotective effect. However, more detailed analyses should be performed before using either antioxidant for therapeutic purposes.

Evidence of Spaceflight-Induced Adverse Effects on Photoreceptors and Retinal Function in the Mouse Eye

The goal of the present study was to characterize acute oxidative damage in ocular structure and retinal function after exposure to spaceflight, and to evaluate the efficacy of an antioxidant in reducing spaceflight-induced changes in the retina. Ten-week-old adult C57BL/6 male mice were flown aboard the ISS on Space-X 24 over 35 days, and returned to Earth alive. The mice received a weekly injection of a superoxide dismutase mimic, MnTnBuOE-2-PyP 5+ (BuOE), before launch and during their stay onboard the ISS. Ground control mice were maintained on Earth under identical environmental conditions. Before the launch, intraocular pressure (IOP) was measured using a handheld tonometer and retinal function was evaluated using electroretinogram (ERG). ERG signals were recorded when the mouse eye was under dark-adapted conditions in response to ultraviolet monochromatic light flashes. Within 20 h after splashdown, IOP and ERG assessments were repeated before euthanasia. There were significant increases in body weight for habitat control groups post-flight compared to pre-flight measurements. However, the body weights were similar among flight groups before launch and after splashdown. The IOP measurements were similar between pre- and post-flight groups with no significant differences between BuOE-treated and saline controls. Immunofluorescence evaluation showed increases in retinal oxidative stress and apoptotic cell death after spaceflight. BuOE treatment significantly decreased the level of the oxidative stress biomarker. ERG data showed that the average amplitudes of the a- and b-wave were significantly decreased (39% and 32% by spaceflight, respectively) compared to that of habitat ground controls. These data indicate that spaceflight conditions induce oxidative stress in the retina, which may lead to photoreceptor cell damage and retinal function impairment.

Risk of symptomatic radiation necrosis in patients treated with stereotactic radiosurgery for brain metastases

INTRODUCTIO

Stereotactic radiosurgery (SRS) is a treatment option in the initial management of patients with brain metastases. While its efficacy has been demonstrated in several prior studies, treatment-related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We thus examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases.

PATIENTS AND METHODS

We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. Diagnosis of symptomatic RN was determined by appearance on serial MRIs, MR spectroscopy, requirement of therapy, and the development of new neurological complaints without evidence of disease progression.

RESULTS

We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to symptomatic RN was 8.3 months. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001), V50% (p<0.0001), V12Gy (p<0.0001), and V10Gy (p=0.0002), compared to the rest of the cohort. Single-fraction treatment (p=0.0025) and diabetes (p=0.019) were also significantly associated with symptomatic RN.

CONCLUSION

SRS is an effective treatment option for patients with brain metastases; however, a subset of patients may develop symptomatic RN. We found that patients with larger tumor size, larger plan V100%, V50%, V12Gy, or V10Gy, who received single-fraction SRS, or who had diabetes were all at higher risk of symptomatic RN.

Radiobiological Studies of Microvascular Damage through In Vitro Models: A Methodological Perspective

Ionizing radiation (IR) is used in radiotherapy as a treatment to destroy cancer. Such treatment also affects other tissues, resulting in the so-called normal tissue complications. Endothelial cells (ECs) composing the microvasculature have essential roles in the microenvironment's homeostasis (ME). Thus, detrimental effects induced by irradiation on ECs can influence both the tumor and healthy tissue. In-vitro models can be advantageous to study these phenomena. In this systematic review, we analyzed in-vitro models of ECs subjected to IR. We highlighted the critical issues involved in the production, irradiation, and analysis of such radiobiological in-vitro models to study microvascular endothelial cells damage. For each step, we analyzed common methodologies and critical points required to obtain a reliable model. We identified the generation of a 3D environment for model production and the inclusion of heterogeneous cell populations for a reliable ME recapitulation. Additionally, we highlighted how essential information on the irradiation scheme, crucial to correlate better observed in vitro effects to the clinical scenario, are often neglected in the analyzed studies, limiting the translation of achieved results.

Risk of symptomatic radiation necrosis in patients treated with stereotactic radiosurgery for brain metastases

INTRODUCTIO

Stereotactic radiosurgery (SRS) is a treatment option in the initial management of patients with brain metastases. While its efficacy has been demonstrated in several prior studies, treatment-related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We thus examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases.

PATIENTS AND METHODS

We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. Diagnosis of symptomatic RN was determined by appearance on serial MRIs, MR spectroscopy, requirement of therapy, and the development of new neurological complaints without evidence of disease progression.

RESULTS

We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to symptomatic RN was 8.3 months. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001), V50% (p<0.0001), V12Gy (p<0.0001), and V10Gy (p=0.0002), compared to the rest of the cohort. Single-fraction treatment (p=0.0025) and diabetes (p=0.019) were also significantly associated with symptomatic RN.

CONCLUSION

SRS is an effective treatment option for patients with brain metastases; however, a subset of patients may develop symptomatic RN. We found that patients with larger tumor size, larger plan V100%, V50%, V12Gy, or V10Gy, who received single-fraction SRS, or who had diabetes were all at higher risk of symptomatic RN.

MnTnBuOE-2-PyP protects normal colorectal fibroblasts from radiation damage and simultaneously enhances radio/chemotherapeutic killing of colorectal cancer cells

Manganese porphyrins have been shown to be potent radioprotectors in a variety of cancer models. However, the mechanism as to how these porphyrins protect normal tissues from radiation damage still remains largely unknown. In the current study, we determine the effects of the manganese porphyrin, MnTnBuOE-2-PyP, on primary colorectal fibroblasts exposed to irradiation. We found that 2 Gy of radiation enhances the fibroblasts' ability to contract a collagen matrix, increases cell size and promotes cellular senesence. Treating fibroblasts with MnTnBuOE-2-PyP significantly inhibited radiation-induced collagen contraction, preserved cell morphology and also inhibited cellular senescence. We further showed that MnTnBuOE-2-PyP enhanced the overall viability of the fibroblasts following exposure to radiation but did not protect colorectal cancer cell viability. Specifically, MnTnBuOE-2-PyP in combination with irradiation, caused a significant decrease in tumor clonogenicity. Since locally advanced rectal cancers are treated with chemoradiation therapy followed by surgery and non-metastatic anal cancers are treated with chemoradiation therapy, we also investigated the effects of MnTnBuOE-2-PyP in combination with radiation, 5-fluorouracil with and without Mitomycin C. We found that MnTnBuOE-2-PyP in combination with Mitomycin C or 5-fluorouracil further enhances those compounds' ability to suppress tumor cell growth. When MnTnBuOE-2-PyP was combined with the two chemotherapeutics and radiation, we observed the greatest reduction in tumor cell growth. Therefore, these studies indicate that MnTnBuOE-2-PyP could be used as a potent radioprotector for normal tissue, while at the same time enhancing radiation and chemotherapy treatment for rectal and anal cancers.

Nonhuman primates as models for the discovery and development of radiation countermeasures

INTRODUCTION

Despite significant scientific advances over the past six decades toward the development of safe and effective radiation countermeasures for humans using animal models, only two pharmaceutical agents have been approved by United States Food and Drug Administration (US FDA) for hematopoietic acute radiation syndrome (H-ARS). Additional research efforts are needed to further develop large animal models for improving the prediction of clinical safety and effectiveness of radiation countermeasures for ARS and delayed effects of acute radiation exposure (DEARE) in humans. Area covered: The authors review the suitability of animal models for the development of radiation countermeasures for ARS following the FDA Animal Rule with a special focus on nonhuman primate (NHP) models of ARS. There are seven centers in the United States currently conducting studies with irradiated NHPs, with the majority of studies being conducted with rhesus monkeys. Expert opinion: The NHP model is considered the gold standard animal model for drug development and approval by the FDA. The lack of suitable substitutes for NHP models for predicting response in humans serves as a bottleneck for the development of radiation countermeasures. Additional large animal models need to be characterized to support the development and FDA-approval of new radiation countermeasures.

A Cell-Penetrant Manganese Superoxide Dismutase (MnSOD) Mimic Is Able To Complement MnSOD and Exerts an Antiinflammatory Effect on Cellular and Animal Models of Inflammatory Bowel Diseases

Inorganic complexes are increasingly used for biological and medicinal applications, and the question of the cell penetration and distribution of metallodrugs is key to understanding their biological activity. Oxidative stress is known to be involved in inflammation and in inflammatory bowel diseases for which antioxidative defenses are weakened. We report here the study of the manganese complex Mn1 mimicking superoxide dismutase (SOD), a protein involved in cell protection against oxidative stress, using an approach in inorganic cellular chemistry combining the investigation of Mn1 intracellular speciation using mass spectrometry and of its quantification and distribution using electron paramagnetic resonance and spatially resolved X-ray fluorescence with evaluation of its biological activity. More precisely, we have looked for and found the MS signature of Mn1 in cell lysates and quantified the overall manganese content. Intestinal epithelial cells activated by bacterial lipopolysaccharide were taken as a cellular model of oxidative stress and inflammation. DNBS-induced colitis in mice was used to investigate Mn1 activity in vivo. Mn1 exerts an intracellular antiinflammatory activity, remains at least partially coordinated, with diffuse distribution over the whole cell, and functionally complements mitochondrial MnSOD.

Analysis of risk and predictors of brain radiation necrosis after radiosurgery

In this study, we examined the factors contributing to brain radiation necrosis and its predictors of patients treated with Cyberknife radiosurgery. A total of 94 patients with primary or metastatic brain tumours having been treated with Cyberknife radiotherapy from Sep. 2006 to Oct. 2011 were collected and retrospectively analyzed. Skull based tracking was used to deliver radiation to 104 target sites. and the prescribed radiation doses ranged from 1200 to 4500 cGy in 1 to 8 fractions with a 60% to 87% isodose line. Radiation necrosis was confirmed by imaging or pathological examination. Associations between cerebral radiation necrosis and factors including diabetes, cardio-cerebrovascular disease, target volume, isodose line, prescribed dosage, number of fractions, combination with whole brain radiation and biologically equivalent dose (BED) were determined by logistic regression. ROC curves were created to measure the predictive accuracy of influence factors and identify the threshold for brain radiation necrosis. Our results showed that radiation necrosis occurred in 12 targets (11.54%). Brain radiation necrosis was associated by BED, combination with whole brain radiotherapy, and fractions (areas under the ROC curves = 0.892±0.0335, 0.650±0.0717, and 0.712±0.0637 respectively). Among these factors, only BED had the capability to predict brain radiation necrosis, and the threshold dose was 7410 cGy. In conclusion, BED is the most effective predictor of brain radiation necrosis, with a dose of 7410 cGy being identified as the threshold.

Pathophysiological Responses in Rat and Mouse Models of Radiation-Induced Brain Injury

The brain is the major dose-limiting organ in patients undergoing radiotherapy for assorted conditions. Radiation-induced brain injury is common and mainly occurs in patients receiving radiotherapy for malignant head and neck tumors, arteriovenous malformations, or lung cancer-derived brain metastases. Nevertheless, the underlying mechanisms of radiation-induced brain injury are largely unknown. Although many treatment strategies are employed for affected individuals, the effects remain suboptimal. Accordingly, animal models are extremely important for elucidating pathogenic radiation-associated mechanisms and for developing more efficacious therapies. So far, models employing various animal species with different radiation dosages and fractions have been introduced to investigate the prevention, mechanisms, early detection, and management of radiation-induced brain injury. However, these models all have limitations, and none are widely accepted. This review summarizes the animal models currently set forth for studies of radiation-induced brain injury, especially rat and mouse, as well as radiation dosages, dose fractionation, and secondary pathophysiological responses.

Leukoencephalopathy After Stereotactic Radiosurgery for Brain Metastases

PURPOSE

Although the use of stereotactic radiosurgery (SRS) in the treatment of multiple brain metastases has increased dramatically during the past decade to avoid the neurocognitive dysfunction induced by whole brain radiation therapy (WBRT), the cumulative neurocognitive effect of numerous SRS sessions remains unknown. Because leukoencephalopathy is a sensitive marker for radiation-induced central nervous system damage, we studied the clinical and dosimetric predictors of SRS-induced leukoencephalopathy.

METHODS AND MATERIALS

Patients treated at our institution with at least 2 sessions of SRS for brain metastases from 2007 to 2013 were reviewed. The pre- and post-SRS magnetic resonance imaging sequences were reviewed and graded for white matter changes associated with radiation leukoencephalopathy using a previously validated scale. Patient characteristics and SRS dosimetric parameters were reviewed for factors that contributed to leukoencephalopathy using Cox proportional hazards modeling.

RESULTS

A total of 103 patients meeting the inclusion criteria were identified. The overall incidence of leukoencephalopathy was 29% at year 1, 38% at year 2, and 53% at year 3. Three factors were associated with radiation-induced leukoencephalopathy: (1) the use of WBRT (P=.019); (2) a higher SRS integral dose to the cranium (P=.036); and (3) the total number of intracranial metastases (P=.003).

CONCLUSIONS

Our results have established that WBRT plus SRS produces leukoencephalopathy at a much higher rate than SRS alone. In addition, for patients who did not undergo WBRT before SRS, the integral dose was associated with the development of leukoencephalopathy. As the survival of patients with central nervous system metastases increases and as the neurotoxicity of chemotherapeutic and targeted agents becomes established, these 3 potential risk factors will be important to consider.

Medical Countermeasures for Radiation Exposure and Related Injuries: Characterization of Medicines, FDA-Approval Status and Inclusion into the Strategic National Stockpile

World events over the past decade have highlighted the threat of nuclear terrorism as well as an urgent need to develop radiation countermeasures for acute radiation exposures and subsequent bodily injuries. An increased probability of radiological or nuclear incidents due to detonation of nuclear weapons by terrorists, sabotage of nuclear facilities, dispersal and exposure to radioactive materials, and accidents provides the basis for such enhanced radiation exposure risks for civilian populations. Although the search for suitable radiation countermeasures for radiation-associated injuries was initiated more than half a century ago, no safe and effective radiation countermeasure for the most severe of these injuries, namely acute radiation syndrome (ARS), has been approved by the United States Food and Drug Administration (FDA). The dearth of FDA-approved radiation countermeasures has prompted intensified research for a new generation of radiation countermeasures. In this communication, the authors have listed and reviewed the status of radiation countermeasures that are currently available for use, or those that might be used for exceptional nuclear/radiological contingencies, plus a limited few medicines that show early promise but still remain experimental in nature and unauthorized for human use by the FDA.

Mechanisms of cardiac radiation injury and potential preventive approaches

In addition to cytostatic treatment and surgery, the most common cancer treatment is gamma radiation. Despite sophisticated radiological techniques however, in addition to irradiation of the tumor, irradiation of the surrounding healthy tissue also takes place, which results in various side-effects, depending on the absorbed dose of radiation. Radiation either damages the cell DNA directly, or indirectly via the formation of oxygen radicals that in addition to the DNA damage, react with all cell organelles and interfere with their molecular mechanisms. The main features of radiation injury besides DNA damage is inflammation and increased expression of pro-inflammatory genes and cytokines. Endothelial damage and dysfunction of capillaries and small blood vessels plays a particularly important role in radiation injury. This review is focused on summarizing the currently available data concerning the mechanisms of radiation injury, as well as the effectiveness of various antioxidants, anti-inflammatory cytokines, and cytoprotective substances that may be utilized in preventing, mitigating, or treating the toxic effects of ionizing radiation on the heart.

Therapeutic potential of peroxynitrite decomposition catalysts: a patent review

INTRODUCTION

Peroxynitrite is a cytotoxic oxidant species implicated in a host of pathologies, including inflammatory and neurodegenerative diseases, cancer, radiation injury and chronic pain. With the recognition of the role of peroxynitrite in disease, numerous experimental and therapeutic tools have arisen to probe peroxyntirite's pathophysiological contribution and attenuate its oxidative damage. Peroxynitrite decomposition catalysts (PNDCs) are redox-active compounds that detoxify peroxynitrite by catalyzing its isomerization or reduction to nitrate or nitrite.

AREAS COVERED

This review discusses recent research articles and patents published 1995 - 2014 on the development and therapeutic use of PNDCs. Iron and manganese metalloporphyrin PNDCs attenuate the toxic effects of peroxynitrite and are currently being developed for clinical applications. Additionally, some Mn porphyrin-based PNDCs have optimized pharmaceutical properties such that they exhibit greater peroxynitrite selectivity. Other classes of PNDC agents, including bis(hydroxyphenyl)dipyrromethenes and metallocorroles, have demonstrated preclinical efficacy, oral availability and reduced toxicity risk.

EXPERT OPINION

Interest in the drug-like properties of peroxynitrite-neutralizing agents has grown with the realization that PNDCs will be powerful tools in the treatment of disease. The design of compounds with enhanced oral availability and peroxynitrite selectivity is a critical step toward the availability of safe, effective and selective redox modulators for the treatment of peroxynitrite-associated pathologies.

Radioprotection of the brain white matter by Mn(III) n-Butoxyethylpyridylporphyrin-based superoxide dismutase mimic MnTnBuOE-2-PyP5+

Cranial irradiation is a standard therapy for primary and metastatic brain tumors. A major drawback of radiotherapy (RT), however, is long-term cognitive loss that affects quality of life. Radiation-induced oxidative stress in normal brain tissue is thought to contribute to cognitive decline. We evaluated the effectiveness of a novel mimic of superoxide dismutase enzyme (SOD), MnTnBuOE-2-PyP(5+)(Mn(III) meso-tetrakis(N-n-butoxyethylpyridinium-2-yl)porphyrin), to provide long-term neuroprotection following 8 Gy of whole brain irradiation. Long-term RT damage can only be assessed by brain imaging and neurocognitive studies. C57BL/6J mice were treated with MnTnBuOE-2-PyP(5+) before and after RT and evaluated three months later. At this time point, drug concentration in the brain was 25 nmol/L. Mice treated with MnTnBuOE-2-PyP(5+)/RT exhibited MRI evidence for myelin preservation in the corpus callosum compared with saline/RT treatment. Corpus callosum histology demonstrated a significant loss of axons in the saline/RT group that was rescued in the MnTnBuOE-2-PyP(5+)/RT group. In addition, the saline/RT groups exhibited deficits in motor proficiency as assessed by the rotorod test and running wheel tests. These deficits were ameliorated in groups treated with MnTnBuOE-2-PyP(5+)/RT. Our data demonstrate that MnTnBuOE-2-PyP(5+) is neuroprotective for oxidative stress damage caused by radiation exposure. In addition, glioblastoma cells were not protected by MnTnBuOE-2-PyP(5+) combination with radiation in vitro. Likewise, the combination of MnTnBuOE-2-PyP(5+) with radiation inhibited tumor growth more than RT alone in flank tumors. In summary, MnTnBuOE-2-PyP(5+) has dual activity as a neuroprotector and a tumor radiosensitizer. Thus, it is an attractive candidate for adjuvant therapy with RT in future studies with patients with brain cancer.

Radiation countermeasure agents: an update (2011-2014)

INTRODUCTION

Despite significant scientific advances over the past 60 years towards the development of a safe, nontoxic and effective radiation countermeasure for the acute radiation syndrome (ARS), no drug has been approved by the US FDA. A radiation countermeasure to protect the population at large from the effects of lethal radiation exposure remains a significant unmet medical need of the US citizenry and, thus, has been recognized as a high priority area by the government.

AREA COVERED

This article reviews relevant publications and patents for recent developments and progress for potential ARS treatments in the area of radiation countermeasures. Emphasis is placed on the advanced development of existing agents since 2011 and new agents identified as radiation countermeasure for ARS during this period.

EXPERT OPINION

A number of promising radiation countermeasures are currently under development, seven of which have received US FDA investigational new drug status for clinical investigation. Four of these agents, CBLB502, Ex-RAD, HemaMax and OrbeShield, are progressing with large animal studies and clinical trials. G-CSF has high potential and well-documented therapeutic effects in countering myelosuppression and may receive full licensing approval by the US FDA in the future.

Effects of metalloporphyrins on reducing inflammation and autoimmunity

SIGNIFICANCE

High levels of reactive oxygen species can facilitate DNA and protein damage beyond the control of endogenous antioxidants, resulting in oxidative stress. Oxidative stress then triggers inflammation, which can lead to pathological conditions. In genetically susceptible individuals, the conglomeration of oxidative stress and inflammation can enhance autoreactive immune cell activation, causing beta-cell destruction in autoimmune type 1 diabetes. As a means of shielding pancreatic islets, manganese porphyrin (MnP) oxidoreductant treatment has been tested in a number of reported studies.

RECENT ADVANCES

MnP affects both innate and adaptive immune cell responses, blocking nuclear factor kappa-B activation, proinflammatory cytokine secretion, and T helper 1 T-cell responses. As a result, MnP treatment protects against type 1 diabetes onset in nonobese diabetic mice and stabilizes islets for cellular transplantation.

CRITICAL ISSUES

MnP displays global immunosuppressive properties, exemplified by decreased cytokine production from all T-helper cell subsets. This quality may impact infection control in the setting of autoimmunity. Nonetheless, because of their cytoprotective and immunomodulatory function, MnPs should be considered as a safer alternative to other clinical immunosuppressive agents (i.e., rapamycin) for transplantation.

FUTURE DIRECTIONS

Although MnP likely affects only redox-sensitive targets, the mechanism behind global T-cell immunosuppression and the outcome on infection clearance will have to be elucidated. Based on the increased primary engraftment seen with MnP use, protection against primary nonfunction in porcine to human xenotransplants would likely be enhanced. Further, a better understanding of MnP oxidoreductase function may allow for its use in other chronic inflammatory conditions.

SOD therapeutics: latest insights into their structure-activity relationships and impact on the cellular redox-based signaling pathways

SIGNIFICANCE

Superoxide dismutase (SOD) enzymes are indispensable and ubiquitous antioxidant defenses maintaining the steady-state levels of O2·(-); no wonder, thus, that their mimics are remarkably efficacious in essentially any animal model of oxidative stress injuries thus far explored.

RECENT ADVANCES

Structure-activity relationship (half-wave reduction potential [E1/2] versus log kcat), originally reported for Mn porphyrins (MnPs), is valid for any other class of SOD mimics, as it is dominated by the superoxide reduction and oxidation potential. The biocompatible E1/2 of ∼+300 mV versus normal hydrogen electrode (NHE) allows powerful SOD mimics as mild oxidants and antioxidants (alike O2·(-)) to readily traffic electrons among reactive species and signaling proteins, serving as fine mediators of redox-based signaling pathways. Based on similar thermodynamics, both SOD enzymes and their mimics undergo similar reactions, however, due to vastly different sterics, with different rate constants.

CRITICAL ISSUES

Although log kcat(O2·(-)) is a good measure of therapeutic potential of SOD mimics, discussions of their in vivo mechanisms of actions remain mostly of speculative character. Most recently, the therapeutic and mechanistic relevance of oxidation of ascorbate and glutathionylation and oxidation of protein thiols by MnP-based SOD mimics and subsequent inactivation of nuclear factor κB has been substantiated in rescuing normal and killing cancer cells. Interaction of MnPs with thiols seems to be, at least in part, involved in up-regulation of endogenous antioxidative defenses, leading to the healing of diseased cells.

FUTURE DIRECTIONS

Mechanistic explorations of single and combined therapeutic strategies, along with studies of bioavailability and translational aspects, will comprise future work in optimizing redox-active drugs.

Superoxide dismutase mimic, MnTE-2-PyP(5+) ameliorates acute and chronic proctitis following focal proton irradiation of the rat rectum

Radiation proctitis, an inflammation and damage to the lower part of colon, is a common adverse event of the radiotherapy of tumors in the abdominal and pelvic region (colon, prostate, cervical). Several Mn(III) porphyrin-based superoxide dismutase mimics have been synthesized and successfully evaluated in preclinical models as radioprotectants. Here we report for the first time the remarkable rectal radioprotection of frequently explored Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin, MnTE-2-PyP(5+). A batch prepared in compliance with good manufacturing practice (GMP), which has good safety/toxicity profile, was used for this study. MnTE-2-PyP(5+) was given subcutaneously at 5 mg/kg, either 1 h before or 1 h after irradiation, with additional drug administered at weekly intervals thereafter. MnTE-2-PyP(5+) ameliorated both acute and chronic radiation proctitis in male Sprague-Dawley rats irradiated with 20-30 Gy protons delivered to 2.5 cm span of rectum using spread-out Bragg peak of a proton treatment beam. Focal irradiation of the rectum produced acute proctitis, which healed, followed by chronic rectal dilation and symptomatic proctitis. MnTE-2-PyP(5+) protected rectal mucosa from radiation-induced crypt loss measured 10 days post-irradiation. Significant effects were observed with both pre- and post-treatment regimens. However, only MnTE-2-PyP(5+) pre-treatment, but not post-treatment, prevented the development of rectal dilation, indicating that proper dosing regimen is critical for radioprotection. The pre-treatment also prevented or delayed the development of chronic proctitis depending on the radiation dose. Further work aimed at developing MnTE-2-PyP(5+) and similar drugs as adjunctive agents for radiotherapy of pelvic tumors is warranted. The present study substantiates the prospects of employing this and similar analogs in preserving normal tissue during cancer radiation as well as any other radiation exposure.

Baicalein attenuates impaired hippocampal neurogenesis and the neurocognitive deficits induced by γ-ray radiation

BACKGROUND AND PURPOSE

Whole-brain irradiation (WBI) therapy produces learning and memory deficits in patients with brain tumours. Although the pathological cascade of cognitive deficits remains unknown, it may involve reduced neurogenesis within the hippocampus. Baicalein is a flavonoid derived from the roots of Huangqin, Scutellaria baicalensis Georgi, and has been shown to have antioxidant effects. Here, we have investigated the protective effects of baicalein on irradiation-induced impairments in hippocampal neurogenesis and cognitive function.

EXPERIMENTAL APPROACH

Radioprotective effects of baicalein were evaluated in C17.2 neural progenitor cells and 6-week-old male C57BL/6 mice during hippocampal neurogenesis. Mice were given a single dose of 5 Gy WBI. Changes in hippocampal neurogenesis, oxidative stress and BDNF-pCREB signalling were evaluated. Morris water maze and passive avoidance test were used to assess learning and memory.

KEY RESULTS

Baicalein protected neural progenitor cells against irradiation-induced necrotic cell death. Pretreatment with baicalein attenuated the irradiation-induced impairment of hippocampal neurogenesis by modulating oxidative stress and elevating BDNF-pCREB signalling. Furthermore, baicalein prevented the spatial learning and memory retention deficits follwing WBI.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that baicalein can be viewed as a potential therapeutic agent that protects against the impaired neurogenesis induced by WBI, and its neurocognitive consequences.

A nonclinical safety assessment of MnTE-2-PyP, a manganese porphyrin

Manganese (III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP or BMX-010; CASRN 219818-60-7) is a manganese porphyrin compound developed as a potential drug substance for use as a radioprotective and for the ex vivo treatment of cells, tissues, and organs intended for transplantation. In preparation for an investigational new drug filing, a full good laboratory practice nonclinical safety assessment was conducted in order to evaluate the safety of MnTE-2-PyP and included the performance of in vitro genotoxicity studies, local tissue tolerance evaluation, safety pharmacology core battery studies, and single- and repeat-dose intravenous (iv) toxicity studies in mice and monkeys. The MnTE-2-PyP was determined not to be genotoxic or hemolytic, did not demonstrate flocculation or elicit adverse pharmacologic effects on respiration, the central nervous system (CNS), and had limited transitory effects on the cardiovascular system only at levels well above the therapeutic target dose. The intended iv clinical solution did not cause venous irritation in rabbits. The no observed adverse effect level (NOAEL) in mice was determined to be 10 mg/kg/day after 18 consecutive days of bolus iv dosing once daily in the morning. The NOAEL in monkeys after 14 days of bolus iv dosing in the morning was determined to be 5 mg/kg/day. At doses relevant to clinical use in humans, neither study revealed any indication of any specific target organ toxicity, including the classic heme porphyrin kidney, liver, CNS, or cardiac toxicities, or manganese toxicity. Mortality seen shortly after dosing in individual animals at higher doses was not accompanied by any organ or clinical pathology indications, suggesting a functional pharmacological-mediated effect. Based on the results of these studies, a conservative safe initial starting clinical dose of 5.0 mg (0.083 mg/kg in a 60 kg adult) was proposed for the initiation of human trials. Because of patent life issues, use of MnTE-2-PyP as a transplantation aid or radioprotective agent is not currently being pursued past the preclinical stages. It serves as a model for the clinical development of this class of drugs.

Design, mechanism of action, bioavailability and therapeutic effects of mn porphyrin-based redox modulators

Based on aqueous redox chemistry and simple in vivo models of oxidative stress, Escherichia coli and Saccharomyces cerevisiae, the cationic Mn(III) N-substituted pyridylporphyrins (MnPs) have been identified as the most potent cellular redox modulators within the porphyrin class of drugs; their efficacy in animal models of diseases that have oxidative stress in common is based on their high ability to catalytically remove superoxide, peroxynitrite, carbonate anion radical, hypochlorite, nitric oxide, lipid peroxyl and alkoxyl radicals, thus suppressing the primary oxidative event. While doing so MnPs could couple with cellular reductants and redox-active proteins. Reactive species are widely accepted as regulators of cellular transcriptional activity: minute, nanomolar levels are essential for normal cell function, while submicromolar or micromolar levels impose oxidative stress, which is evidenced in increased inflammatory and immune responses. By removing reactive species, MnPs affect redox-based cellular transcriptional activity and consequently secondary oxidative stress, and in turn inflammatory processes. The equal ability to reduce and oxidize superoxide during the dismutation process and recently accumulated results suggest that pro-oxidative actions of MnPs may also contribute to their therapeutic effects. All our data identify the superoxide dismutase-like activity, estimated by log k(cat)O2-*), as a good measure for the therapeutic efficacy of MnPs. Their accumulation in mitochondria and their ability to cross the blood-brain barrier contribute to their remarkable efficacy. We summarize herein the therapeutic effects of MnPs in cancer, central nervous system injuries, diabetes, their radioprotective action and potential for imaging. Few of the most potent modulators of cellular redox-based pathways, MnTE2-PyP5+, MnTDE-2-ImP5+, MnTnHex-2-PyP5+ and MnTnBuOE-2-PyP5+, are under preclinical and clinical development.

Analysis of a metalloporphyrin antioxidant mimetic (MnTE-2-PyP) as a radiomitigator: prostate tumor and immune status

Due to radiation-induced immune depression and development of pathologies such as cancer, there is increasing urgency to identify radiomitigators that are effective when administered after radiation exposure. The main goal of this study was to determine the radiomitigation capacity of MnTE-2-PyP[Mn(III) tetrakis (N-ethylpyridinium-2-yl) porphyrin], a superoxide dismutase (SOD) mimetic, and evaluate leukocyte parameters in spleen and blood. C57BL/6 mice were total-body exposed to 2 Gy γ-rays (Co-60), i.e., well below a lethal dose, followed by subcutaneous implantation of 5 × 10(5) RM-9 prostate tumor cells and initiation of MnTE-2-PyP treatment (day 0); interval between each procedure was 1-2 h. The drug was administered daily (12 times). Tumor progression was monitored and immunological analyses were performed on a subset per group on day 12. Animals treated with MnTE-2-PyP alone had significantly slower tumor growth compared to mice that did not receive the drug (P < 0.05), while radiation alone had no effect. Treatment of tumor-bearing mice with MnTE-2-PyP alone significantly increased spleen mass relative to body mass; the numbers of splenic white blood cells (WBC) and lymphocytes (B and T), as well as circulating WBC, granulocytes, and platelets, were high compared to one of more of the other groups (P < 0.05). The results show that MnTE-2-PyP slowed RM-9 tumor progression and up-regulated immune parameters, but mitigation of the effects of 2 Gy total-body irradiation were minimal.

Diverse functions of cationic Mn(III) N-substituted pyridylporphyrins, recognized as SOD mimics

Oxidative stress, a redox imbalance between the endogenous reactive species and antioxidant systems, is common to numerous pathological conditions such as cancer, central nervous system injuries, radiation injury, diabetes etc. Therefore, compounds able to reduce oxidative stress have been actively sought for over 3 decades. Superoxide is the major species involved in oxidative stress either in its own right or through its progeny, such as ONOO⁻, H₂O₂, •OH, CO₃•⁻, and •NO₂. Hence, the very first compounds developed in the late 1970-ies were the superoxide dismutase (SOD) mimics. Thus far the most potent mimics have been the cationic meso Mn(III) N-substituted pyridylporphyrins and N,N'-disubstituted imidazolylporphyrins (MnPs), some of them with k(cat)(O₂·⁻) similar to the k(cat) of SOD enzymes. Most frequently studied are ortho isomers MnTE-2-PyP⁵⁺, MnTnHex-2-PyP⁵⁺, and MnTDE-2-ImP⁵⁺. The ability to disproportionate O₂·⁻ parallels their ability to remove the other major oxidizing species, peroxynitrite, ONOO⁻. The same structural feature that gives rise to the high k(cat)(O₂·⁻) and k(red)(ONOO⁻), allows MnPs to strongly impact the activation of the redox-sensitive transcription factors, HIF-1α, NF-κB, AP-1, and SP-1, and therefore modify the excessive inflammatory and immune responses. Coupling with cellular reductants and other redox-active endogenous proteins seems to be involved in the actions of Mn porphyrins. While hydrophilic analogues, such as MnTE-2-PyP⁵⁺ and MnTDE-2-ImP⁵⁺ are potent in numerous animal models of diseases, the lipophilic analogues, such as MnTnHex-2-PyP⁵⁺, were developed to cross blood brain barrier and target central nervous system and critical cellular compartments, mitochondria. The modification of its structure, aimed to preserve the SOD-like potency and lipophilicity, and diminish the toxicity, has presently been pursued. The pulmonary radioprotection by MnTnHex-2-PyP⁵⁺ was the first efficacy study performed successfully with non-human primates. The Phase I toxicity clinical trials were done on amyotrophic lateral sclerosis patients with N,N'-diethylimidazolium analogue, MnTDE-2-ImP⁵⁺ (AEOL10150). Its aggressive development as a wide spectrum radioprotector by Aeolus Pharmaceuticals has been supported by USA Federal government. The latest generation of compounds, bearing oxygens in pyridyl substituents is presently under aggressive development for cancer and CNS injuries at Duke University and is supported by Duke Translational Research Institute, The Wallace H. Coulter Translational Partners Grant Program, Preston Robert Tisch Brain Tumor Center at Duke, and National Institute of Allergy and Infectious Diseases. Metal center of cationic MnPs easily accepts and donates electrons as exemplified in the catalysis of O₂·⁻ dismutation. Thus such compounds may be equally good anti- and pro-oxidants; in either case the beneficial therapeutic effects may be observed. Moreover, while the in vivo effects may appear antioxidative, the mechanism of action of MnPs that produced such effects may be pro-oxidative; the most obvious example being the inhibition of NF-κB. The experimental data therefore teach us that we need to distinguish between the mechanism/s of action/s of MnPs and the effects we observe. A number of factors impact the type of action of MnPs leading to favorable therapeutic effects: levels of reactive species and oxygen, levels of endogenous antioxidants (enzymes and low-molecular compounds), levels of MnPs, their site of accumulation, and the mutual encounters of all of those species. The complexity of in vivo redox systems and the complex redox chemistry of MnPs challenge and motivate us to further our understanding of the physiology of the normal and diseased cell with ultimate goal to successfully treat human diseases.

Cellular redox modulator, ortho Mn(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin, MnTnHex-2-PyP(5+) in the treatment of brain tumors

Despite intensive efforts to improve multimodal treatment of brain tumor, survival remains limited. Current therapy consists of a combination of surgery, irradiation and chemotherapy with predisposition to long-term complications. Identifying novel targeted therapies is therefore at the forefront of brain tumor research. This study explores the utility of a manganese porphyrin in a brain tumor model. The compound used is ortho isomer, mangnese(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin, MnTnHex-2-PyP(5+). It is a powerful SOD mimic and peroxynitrite scavenger and a potent modulator of redox-based cellular transcriptional activity, able to suppress excessive immune and inflammatory responses and in turn proliferative pathways. It is further one of the most lipophilic compound among cationic Mn(III) N-alkylpyridylporphyrins, and thus accumulates predominantly in mitochondria relative to cytosol. In mitochondria, MnTnHex-2-PyP(5+) mimics our key antioxidant system, mitochondrial superoxide dismutase, MnSOD, whose overexpression has been widely shown to suppress tumor growth. Importantly, MnTnHex-2-PyP(5+) crosses blood brain barrier in sufficient amounts to demonstrate efficacy in treating CNS injuries. For those reasons we elected to test its effects in inhibiting brain tumor growth. This study is the first report of the antitumor properties of MnTnHex-2-PyP(5+) as a single agent in adult and pediatric glioblastoma multiforme (D-54 MG, D-245 MG, D-256 MG, D-456 MG) and pediatric medulloblastoma (D-341 MED), and is the first case where a redox-able metal complex has been used in glioma therapy. When given subcutaneously to mice bearing subcutaneous and intracranial xenografts, MnTnHex-2-PyP(5+) caused a significant (P ≤ 0.001) growth delay in D 245 MG, D-256 MG, D-341 MED, and D-456 MG tumors. Growth delay for mice bearing subcutaneous xenografts ranged from 3 days in D-54 MG to 34 days in D-341 MED. With mice bearing intracranial xenografts, MnTnHex-2-PyP(5+) increases median survival by 33% in adult glioblastoma multiforme (D-256 MG; p≤ 0.001) and 173% in pediatric medulloblastoma (D-341 MED, <0.001). The beneficial effects of MnTnHex-2-PyP(5+) are presumably achieved either (1) indirectly via elimination of signaling reactive oxygen and nitrogen species (in particular superoxide and peroxynitrite) which in turn would prevent activation of transcription factors; or (2) directly by coupling with cellular reductants and redox-sensitive signaling proteins. The former action is antioxidative while the latter action is presumably pro-oxidative in nature. Our findings suggest that the use of Mn porphyrin-based SOD mimics, and in particular lipophilic analogues such as MnTnHex-2-PyP(5+), is a promising approach for brain tumor therapy.