Cancer burden in adolescents and young adults in Europe.

BACKGROUND: Cancer epidemiology is unique in adolescents and young adults (AYAs; aged 15-39 years). The European Society for Medical Oncology/European Society for Paediatric Oncology (ESMO/SIOPE) AYA Working Group aims to describe the burden of cancers in AYAs in Europe and across European Union (EU) countries. PATIENTS AND METHODS: We used data available on the Global Cancer Observatory. We retrieved crude and age-standardised (World Standard Population) incidence and mortality rates. We reported about AYA cancer burden in Europe and between 28 EU member states. We described incidence and mortality for all cancers and for the 13 cancers most relevant to the AYA population. RESULTS: Incidence and mortality varied widely between countries with the highest mortality observed in Eastern EU countries. Cancers of the female breast, thyroid and male testis were the most common cancers across countries followed by melanoma of skin and cancers of the cervix. Variations in cancer incidence rates across different populations may reflect different distribution of risk factors, variations in the implementation or uptake of screening as well as overdiagnosis. AYA cancer mortality disparities may be due to variation in early-stage diagnoses, different public education and awareness of cancer symptoms, different degrees of access or availability of treatment. CONCLUSIONS: Our results highlight the future health care needs and requirements for AYA-specialised services to ensure a homogeneous treatment across different countries as well as the urgency for preventive initiatives that can mitigate the increasing burden.

Impact of COVID-19 on social media as perceived by the oncology community: results from a survey in collaboration with the European Society for Medical Oncology (ESMO) and the OncoAlert Network.

BACKGROUND: The COVID-19 pandemic has impacted all aspects of modern-day oncology, including how stakeholders communicate through social media. We surveyed oncology stakeholders in order to assess their attitudes pertaining to social media and how it has been affected during the pandemic. MATERIALS AND METHODS: A 40-item survey was distributed to stakeholders from 8 July to 22 July 2020 and was promoted through the European Society for Medical Oncology (ESMO) and the OncoAlert Network. RESULTS: One thousand and seventy-six physicians and stakeholders took part in the survey. In total, 57.3% of respondents were medical oncologists, 50.6% aged <40 years, 50.8% of female gender and mostly practicing in Europe (51.5%). More than 90% of respondents considered social media a useful tool for distributing scientific information and for education. Most used social media to stay up to date on cancer care in general (62.5%) and cancer care during COVID-19 (61%) given the constant flow of information. Respondents also used social media to interact with other oncologists (78.8%) and with patients (34.4%). Overall, 61.1% of respondents were satisfied with the role that social media was playing during the COVID-19 pandemic. On the other hand, 41.1% of respondents reported trouble in discriminating between credible and less credible information and 30% stated social networks were a source of stress. For this reason, one-third of respondents reduced its use during the COVID-19 pandemic. Regarding meeting attendance, a total of 59.1% of responding physicians preferred in-person meetings to virtual ones, and 51.8% agreed that virtual meetings and social distancing could hamper effective collaboration. CONCLUSION: Social media has a useful role in supporting cancer care and professional engagement in oncology. Although one-third of respondents reported reduced use of social media due to stress during the COVID-19 pandemic, the majority found social media useful to keep up to date and were satisfied with the role social media was playing during the pandemic.

Adolescents and young adults (AYA) with cancer: a position paper from the AYA Working Group of the European Society for Medical Oncology (ESMO) and the European Society for Paediatric Oncology (SIOPE).

It is well recognised that adolescents and young adults (AYA) with cancer have inequitable access to oncology services that provide expert cancer care and consider their unique needs. Subsequently, survival gains in this patient population have improved only modestly compared with older adults and children with cancer. In 2015, the European Society for Medical Oncology (ESMO) and the European Society for Paediatric Oncology (SIOPE) established the joint Cancer in AYA Working Group in order to increase awareness among adult and paediatric oncology communities, enhance knowledge on specific issues in AYA and ultimately improve the standard of care for AYA with cancer across Europe. This manuscript reflects the position of this working group regarding current AYA cancer care, the challenges to be addressed and possible solutions. Key challenges include the lack of specific biological understanding of AYA cancers, the lack of access to specialised centres with age-appropriate multidisciplinary care and the lack of available clinical trials with novel therapeutics. Key recommendations include diversifying interprofessional cooperation in AYA care and specific measures to improve trial accrual, including centralising care where that is the best means to achieve trial accrual. This defines a common vision that can lead to improved outcomes for AYA with cancer in Europe.

Potential for a novel manganese porphyrin compound as adjuvant canine lymphoma therapy.

PURPOSE: Manganese porphyrins are redox-active drugs and superoxide dismutase mimics, which have been shown to chemosensitize lymphoma, a cancer which frequently occurs in dogs. This study aimed to identify critical information regarding the pharmacokinetics and toxicity of Mn(III) meso-tetrakis (N-n-butoxyetylpyridium-2-yl) porphyrin, (MnTnBuOE-2-PyP5+, MnBuOE) in dogs as a prelude to a clinical trial in canine lymphoma patients. METHODS: A single-dose pharmacokinetic (PK) study in normal dogs was performed to determine the plasma half-life (t 1/2) of MnBuOE. A dose reduction study was performed to establish the maximum tolerated dose (MTD) of MnBuOE. The safety and PK of a multi-dosing protocol was assessed. RESULTS: Peak plasma drug concentration occurred 30 min post-injection. The t 1/2 was defined as 7 h. MnBuOE induced an anaphylactic reaction and prolonged tachycardia. The MTD was defined as 0.25 mg/kg. The dogs were given MTD 3×/week for 2-3 weeks. The highest recorded tissue drug levels were in the lymph nodes (4-6 µM), followed by kidney and liver (2.5, 2.0 uM, respectively). CONCLUSIONS: We obtained critical information regarding the PK and toxicity of MnBuOE in dogs. The acute drug reaction and tachycardia post-injection have not been described in other species and may be specific to canines. The high tissue drug levels in lymph nodes have not been previously reported. MnBuOE accumulation in lymph nodes has important implications for the utility of adjuvant MnBuOE to treat lymphoma. With MnBuOE lymph node accumulation, reduction in the dose and/or administration frequency could be possible, leading to reduced toxicity.

Cystine addiction of triple-negative breast cancer associated with EMT augmented death signaling.

This corrects the article DOI: 10.1038/onc.2016.394.

Cystine addiction of triple-negative breast cancer associated with EMT augmented death signaling.

Despite the advances in the diagnosis and treatment of breast cancer, breast cancers still cause significant mortality. For some patients, especially those with triple-negative breast cancer, current treatments continue to be limited and ineffective. Therefore, there remains an unmet need for a novel therapeutic approach. One potential strategy is to target the altered metabolic state that is rewired by oncogenic transformation. Specifically, this rewiring may render certain outside nutrients indispensable. To identify such a nutrient, we performed a nutrigenetic screen by removing individual amino acids to identify possible addictions across a panel of breast cancer cells. This screen revealed that cystine deprivation triggered rapid programmed necrosis, but not apoptosis, in the basal-type breast cancer cells mostly seen in TNBC tumors. In contrast, luminal-type breast cancer cells are cystine-independent and exhibit little death during cystine deprivation. The cystine addiction phenotype is associated with a higher level of cystine-deprivation signatures noted in the basal type breast cancer cells and tumors. We found that the cystine-addicted breast cancer cells and tumors have strong activation of TNFα and MEKK4-p38-Noxa pathways that render them susceptible to cystine deprivation-induced necrosis. Consistent with this model, silencing of TNFα and MEKK4 dramatically reduces cystine-deprived death. In addition, the cystine addiction phenotype can be abrogated in the cystine-addictive cells by miR-200c, which converts the mesenchymal-like cells to adopt epithelial features. Conversely, the introduction of inducers of epithelial-mesenchymal transition (EMT) in cystine-independent breast cancer cells conferred the cystine-addiction phenotype by modulating the signaling components of cystine addiction. Together, our data reveal that cystine-addiction is associated with EMT in breast cancer during tumor progression. These findings provide the genetic and mechanistic basis to explain how cystine deprivation triggers necrosis by activating pre-existing oncogenic pathways in cystine-addicted TNBC with prominent mesenchymal features.

Controversial issues in early-stage breast cancer: a global collaborative survey, supported by the European Society for Medical Oncology (ESMO).

BACKGROUND: To explore the current clinical management of early-stage breast cancer (BC) patients, identify areas of controversy, and interrogate how treating physicians implement latest advances. METHODS: We conducted a 27-item survey, disseminated in two stages: paper distribution at selected BC sessions at the ESMO 2012 Congress, and dedicated mailings to ESMO members. Descriptive statistical analysis and logistic regression analysis were applied to explore potential associations between the demographic characteristics of the participants and replies. RESULTS: A total of 512 physicians from 79 countries participated in the study, accounting for 465 (91%) fully completed questionnaires. The majority of the participants were ESMO members (66%), medical oncologists (86.5%), and working in multidisciplinary teams (91.6%). Heterogeneous results were captured, such as the following: 40.9% of the participants consider no genetic test useful for making adjuvant treatment decisions; 15.3% consider PET-CT a useful imaging modality for staging; 68.8% consider that postmenopausal patients with hormone receptor positive disease should always be offered an aromatase inhibitor as part of their adjuvant therapy; 78.7% prefer to administer trastuzumab concurrently with the taxane component of chemotherapy; and 27% would consider bevacizumab in the neoadjuvant setting. The logistic regression analysis did not identify any strong predictor of the probability of giving a reply fully compatible with evidence in the literature. CONCLUSION: This survey captures clinical practice and whether the latest research advances are implemented in the treatment of early-stage BC by an extended number of physicians. Significant individual differences were found. Areas of controversy were detected, and they deserve further exploration in order to generate 'tailored' educational tools, with the final goal being the standardization of the treatment of early-stage BC patients.

Chemoprevention for breast cancer.

Despite the progress that has been made in breast cancer diagnosis and treatment, this disease is still a major health problem, being the most frequently diagnosed cancer and the first leading cause of cancer death among women both in developed and economically developing countries. In some developed countries incidence rate start to decrease from the end of last millennium and this can be explained, at least in part, by the decrease in hormone replacement therapy use by post-menopausal women. Chemoprevention has the potential to be an approach of utmost importance to reduce cancer burden at least among high-risk populations. Tamoxifen and raloxifene are both indicated for the prevention of breast cancer in women at high risk for the development of the disease, although raloxifene may have a more favorable adverse-effect profile, causing fewer uterine cancers and thromboembolic events. Aromatase inhibitors will most probably become an additional prevention treatment option in the near future, in view of the promising results observed in adjuvant trials and the interesting results of the very recently published first chemoprevention trial using an aromatase inhibitor.(2) Despite impressive results in most clinical trials performed to date, chemoprevention is still not widely used. Urgently needed are better molecular risk models to accurately identify high-risk subjects, new agents with a better risk/benefit ratio and validated biomarkers.

Lapatinib ditosylate: expanding therapeutic options for receptor tyrosine-protein kinase erbB-2-positive breast cancer.

Receptor tyrosine-protein kinase erbB-2 (HER2)-positive breast cancer is a specific entity with an aggressive behavior. Trastuzumab, a monoclonal antibody targeting erbB-2 (HER2) deeply transformed the outcome in patients. Nevertheless, resistance to trastuzumab is still a major concern. Lapatinib ditosylate is an orally available, small molecule targeting the tyrosine activity of the HER2 receptor. Lapatinib as a single agent and in combination therapy showed interesting activity in trastuzumab-resistant advanced tumors. In addition, lapatinib use seemed suitable in recurrent locally advanced inflammatory breast cancer and brain metastases. More recently, the Neo-ALTTO (NeoAdjuvant Lapatinib and/or Trastuzumab Treatment Optimisation) trial showed that lapatinib in combination with trastuzumab and paclitaxel significantly improved the pathological complete response in a neoadjuvant setting. Several clinical trials are still ongoing and data that may change current clinical practice are awaited with much interest.

Supraspinal inactivation of mitochondrial superoxide dismutase is a source of peroxynitrite in the development of morphine antinociceptive tolerance.

Effective treatment of chronic pain with morphine is limited by decreases in the drug's analgesic action with chronic administration (antinociceptive tolerance). Because opioids are mainstays of pain management, restoring their efficacy has great clinical importance. We have recently reported that formation of peroxynitrite (ONOO(-), PN) in the dorsal horn of the spinal cord plays a critical role in the development of morphine antinociceptive tolerance and have further documented that nitration and enzymatic inactivation of mitochondrial superoxide dismutase (MnSOD) at that site provides a source for this nitroxidative species. We now report for the first time that antinociceptive tolerance in mice is also associated with the inactivation of MnSOD at supraspinal sites. Inactivation of MnSOD led to nitroxidative stress as evidenced by increased levels of products of oxidative DNA damage and activation of the nuclear factor poly (ADP-ribose) polymerase in whole brain homogenates. Co-administration of morphine with potent Mn porphyrin-based peroxynitrite scavengers, Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP5+) and Mn(III) 5,10,15,20-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (MnTnHex-2-PyP5+) (1) restored the enzymatic activity of MnSOD, (2) attenuated PN-derived nitroxidative stress, and (3) blocked the development of morphine-induced antinociceptive tolerance. The more lipophilic analogue, MnTnHex-2-PyP5+ was able to cross the blood-brain barrier at higher levels than its lipophylic counterpart MnTE-2-PyP5+ and was about 30-fold more efficacious. Collectively, these data suggest that PN-mediated enzymatic inactivation of supraspinal MnSOD provides a source of nitroxidative stress, which in turn contributes to central sensitization associated with the development of morphine antinociceptive tolerance. These results support our general contention that PN-targeted therapeutics may have potential as adjuncts to opiates in pain management.

Optimizing melphalan pharmacokinetics in regional melanoma therapy: does correcting for ideal body weight alter regional response or toxicity?

BACKGROUND: This study aims to determine what effect correcting melphalan dosing for ideal body weight (IBW) has on toxicity and response in isolated limb infusion (ILI) in patients with advanced extremity melanoma. METHODS: This was an open observational study examining whether correcting the melphalan dose for IBW will influence response and toxicity in patients undergoing ILI for advanced extremity melanoma in 41 patients undergoing 42 procedures (13 without correction for IBW; and 29 with correction for IBW). Melphalan pharmacokinetics, limb toxicity, serologic toxicity, and response at 3 months were compared. RESULTS: The corrected group had a lower estimated limb volume (V (esti)) to melphalan volume at steady state (V (ss)) (P < .0001) ratio as well as lower incidence of grade > or =3 regional toxicity, serologic toxicity, and compartment syndrome (P = .0249, P = .027, P = .02). There was a positive correlation of V (esti)/V (ss) to toxicity (P = .0127, r = .382). No significant difference in response (P = .3609) between the groups was found, although there was a trend of association between V (esti)/V (ss) and response (P = .051, r = .3383). CONCLUSIONS: Correcting for IBW in ILI lowers toxicity without significantly altering response rates.

Role of fructose in the adaptation of plants to cold-induced oxidative stress.

This work presents findings, which indicate important role of fructose, fructose 6-phosphate (F6P), and fructose 1,6-bisphosphate (FBP) in preservation of homeostasis in plants under low temperature. Cold combined with light is known to incite increased generation of superoxide in chloroplasts leading to photoinhibition, but also an increased level of soluble sugars. In the present study, oxidative stress in pea leaves provoked by cold/light regime was asserted by the observed decrease of the level of oxidized form of PSI pigment P700 (P700+). Alongside, the increased antioxidative status and the accumulation of fructose were observed. The antioxidative properties of fructose and its phosphorylated forms were evaluated to appraise their potential protective role in plants exposed to chilling stress. Fructose, and particularly F6P and FBP exhibited high capacities for scavenging superoxide and showed to be involved in antioxidative protection in pea leaves. These results combined with previously established links implicate that the increase in level of fructose sugars through various pathways intercalated into physiological mechanisms of homeostasis represents important non-enzymatic antioxidative defense in plants under cold-related stress.

Treatment with imatinib improves drug delivery and efficacy in NSCLC xenografts.

Imatinib, an inhibitor of PDGF-Rbeta and other tyrosine kinase receptors, has been shown to decrease microvessel density and interstitial fluid pressure in solid tumours, thereby improving subsequent delivery of small molecules. The purpose of this study was to test whether pretreatment with imatinib increases the efficacy of traditional chemotherapy in mice bearing non-small cell lung carcinoma xenografts, and to investigate the effects of imatinib on liposomal drug delivery. Efficacy treatment groups included (n=9-10): saline control, imatinib alone (oral gavage, 100 mg kg(-1) x 7 days), docetaxel alone (10 mg kg(-1) i.p. 2 x /week until killing), and imatinib plus docetaxel (started on day 7 of imatinib). Tumours were monitored until they reached four times the initial treatment volume (4 x V) or 28 days. A separate experiment compared tumour doxorubicin concentrations (using high performance liquid chromatography) 24 h after treatment with liposomal doxorubicin alone (6 mg kg(-1) i.v., n=9) or imatinib plus liposomal doxorubicin (n=16). Imatinib plus docetaxel resulted in significantly improved antitumour efficacy (0/10 animals reached 4 x V by 28 days) when compared to docetaxel alone (3/9 reached 4 x V, P=0.014) or imatinib alone (9/10 reached 4 x V, P=0.025). Pretreatment with imatinib also significantly increased tumour concentrations of liposomal doxorubicin. Overall, these preclinical studies emphasise the potential of imatinib as an adjunct to small molecule or liposomal chemotherapy.

Phase I/II trial of intravenous Doxil and whole abdomen hyperthermia in patients with refractory ovarian cancer.

OBJECTIVE: A phase I/II study of Doxil combined with whole abdomen hyperthermia was conducted in patients with refractory ovarian cancer. Liposomal doxorubicin combined with hyperthermia has been shown to increase both liposomal delivery and drug extravasation into tumour xenografts resulting in enhanced cytotoxic effects. PATIENTS AND METHODS: Thirty patients with either recurrent or persistent epithelial ovarian cancer were enrolled. All patients had either measurable or assessable disease. Patients received intravenous (IV) Doxil at a dose of 40 mg m-2 as a 1-h infusion followed by whole abdomen hyperthermia. The phase I portion of the study was performed to determine the maximal tolerated dose (MTD) of hyperthermia. Quality of life (QoL) was performed at baseline, prior to each cycle and every 3 months. Plasma pharmacokinetic studies were performed with the first cycle. RESULTS: Ten patients participated in the phase I portion of the study which demonstrated that the MTD of hyperthermia was 60 min after either average vaginal and rectal temperatures of 40 degrees C had been achieved or after 30 min of power application, whichever was shorter. All 30 patients were either paclitaxel and/or platinum resistant initially or developed resistant disease. The median number of prior chemotherapeutic regimens was three (range 2-8) and six patients had been previously treated with Doxil. There were three partial responses for a response rate of 10% (95% CI: [2%, 27%]) and eight patients (27%; 95% CI: [12%, 46%]) had disease stabilization. The median time to progression or death was 3.4 months (95% CI: [2.6, 5.2]) and the median survival was 10.8 months (95% CI: [8.8, 17.4]). Twelve patients (40%) experienced palmar-plantar erythrodysesthesia (PPE), but only four (13%) experienced grade 3-4 PPE toxicity. Doxil systemic exposure was higher in those with grade 3-4 PPE compared to those with no PPE. None of the patients had grade 3-4 thermal toxicity due to hyperthermia. QoL was not decreased in patients responding to therapy. CONCLUSIONS: Therapy with intravenous Doxil and whole abdomen hyperthermia for patients with platinum/paclitaxel resistant ovarian cancer is feasible and does not negatively impact quality of life.

Synthesis, ligand pK(a), and Fe(III) complexation constants for a series of bipodal dihydroxamic acids.

The synthesis of four bipodal dihydroxamic acids containing an apical C atom and amide linkages is described, where Ia,b represent "normal" and "retro" hydroxamate isomers: (R)CH[C(=O)NH(CH(2))(2)NHC(=O)(CH(2))(n)()R'](2) (Ia, R = CH(3), R' = N(OH)(C=O)CH(3), n = 2; Ib, R = CH(3), R' = (C=O)N(OH)CH(3), n = 2; Ic, R = CH(3), R' = (C=O)N(OH)CH(3), n = 3; Id, R = C(4)H(9), R' = (C=O)N(OH)CH(3), n = 2.). The pK(a1) and pK(a2) values in aqueous solution are reported, and some degree of cooperativity is noted. Complexation equilibria with Fe(aq)(3+) are described, and values for stepwise and overall equilibrium constants are reported. log beta(230) values for Ia-d are 59.22, 59.45, 58.91, and 58.46, slightly lower than for rhodotorulic acid, although the pFe values for the synthetic siderophores are comparable to that for rhodotorulic acid.

Aqueous solution speciation of Fe(III) complexes with dihydroxamate siderophores alcaligin and rhodotorulic acid and synthetic analogues using electrospray ionization mass spectrometry.

Aqueous solutions of Fe3+ complexes of cyclic (alcaligin) and linear (rhodotorulic acid) dihydroxamate siderophores and synthetic linear eight-carbon-chain and two-carbon-chain dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln; n = 2 and 8) were investigated by electrospray ionization mass spectrometry (ESI-MS). Information was obtained relevant to the structure and the speciation of various Fe(III)-dihydroxamate complexes present in aqueous solution by (1) comparing different ionization techniques (ESI and FAB), (2) altering the experimental parameters (Fe3+/ligand ratio, pH, cone voltage), (3) using high-stability hexacoordinated Fe(III) siderophore complex mixtures (ferrioxamine B/ferrioxamine E) as a calibrant to quantify intrinsically neutral (H+ clustered or protonated) and intrinsically charged complexes, and (4) using mixed-metal complexes containing Fe3+, Ga3+, and Al3+. These results illustrate that for all dihydroxamic acid ligands investigated multiple tris- and bis-chelated mono- and di-Fe(III) species are present in relative concentrations that depend on the pH and Fe/L ratio.

Manganese(III) biliverdin IX dimethyl ester: a powerful catalytic scavenger of superoxide employing the Mn(III)/Mn(IV) redox couple.

A manganese(III) complex of biliverdin IX dimethyl ester, (MnIIIBVDME)2, was prepared and characterized by elemental analysis, UV/vis spectroscopy, cyclic voltammetry, chronocoulometry, electrospray mass spectrometry, freezing-point depression, magnetic susceptibility, and catalytic dismuting of superoxide anion (O2.-). In a dimeric conformation each trivalent manganese is bound to four pyrrolic nitrogens of one biliverdin dimethyl ester molecule and to the enolic oxygen of another molecule. This type of coordination stabilizes the +4 metal oxidation state, whereby the +3/+4 redox cycling of the manganese in aqueous medium was found to be at E1/2 = +0.45 V vs NHE. This potential allows the Mn(III)/Mn(IV) couple to efficiently catalyze the dismutation of O2.- with the catalytic rate constant of kcat = 5.0 x 10(7) M-1 s-1 (concentration calculated per manganese) obtained by cytochrome c assay at pH 7.8 and 25 degrees C. The fifth coordination site of the manganese is occupied by an enolic oxygen, which precludes binding of NO., thus enhancing the specificity of the metal center toward O2.-. For the same reason the (MnIIIBVDME)2 is resistant to attack by H2O2. The compound also proved to be an efficient SOD mimic in vivo, facilitating the aerobic growth of SOD-deficient Escherichia coli.

Characterization of cell envelope-associated proteinases of thermophilic lactobacilli.

The proteolytic activities of two natural isolates of thermophilic lactobacilli, Lactobacillus acidophilus BGRA43 and Lact. delbrueckii BGPF1, and Lact. acidophilus CH2 (Chr. Hansen's strain) and Lact. acidophilus V74 (Visby's strain), were compared. Results revealed that optimal pH for all four proteinases is 6.5, whereas temperature optimum varied among proteinases. Determination of caseinolytic activity done under optimal conditions for each strain revealed that the CH2 and V74 proteinases completely hydrolysed both alphaS1-casein and beta-casein, showing very low activity towards kappa-casein. The BGPF1 proteinase completely hydrolysed only beta-casein. The BGRA43 proteinase completely hydrolysed all three casein fractions. The proteolytic activities of whole cells were inhibited by serine proteinase inhibitors, suggesting that all four strains produce serine proteinases. DNA-DNA hybridization and PCR analysis showed that BGPF1 contains the prtB-like proteinase gene. Characterized thermophilic strains BGPF1 and BGRA43 were successfully used as starter cultures for production of yoghurt and acidophilus milk, respectively.

Nitrosylation of manganese(II) tetrakis(N-ethylpyridinium-2-yl)porphyrin: a simple and sensitive spectrophotometric assay for nitric oxide.

Reaction between NO(*) and manganese tetrakis(N-ethylpyridinium-2-yl)porphyrin (Mn(III)TE-2-PyP(5+)) was investigated at 25 degrees C. At high excess of NO(*) (1.5 mM) the reaction with the oxidized, air-stable form Mn(III)TE-2-PyP(5+) (5 microM), proceeds very slowly (t(1/2) congruent with 60 min). The presence of excess ascorbate (1 mM) produces the reduced form, Mn(II)TE-2-PyP(4+), which reacts with NO(*) stoichiometrically and in the time of mixing (k congruent with 1 x 10(6) M(-1) s(-1)). The high rate of formation and the stability of the product, Mn(II)TE-2-PyP(NO)(4+) (¿Mn(NO)¿(6)), make the reaction outcompete the reaction of NO(*) with O(2). Our in vitro measurements show a linear absorbance response upon addition of NO to a PBS, pH 7.4, solution containing an excess of ascorbate over Mn(III)TE-2-PyP(5+). Thus, the observed interactions can be the basis of a convenient and sensitive spectrophotometric assay for NO(*). Also, it may have important implications for the in vivo behavior of Mn(III)TE-2-PyP(5+) which is currently exploited as a possible therapeutic agent for various oxygen-radical related disorders.

Lucigenin: redox potential in aqueous media and redox cycling with O-(2) production.

The use of lucigenin luminescence as a measure of ¿O-(2) has been questioned because lucigenin has been shown to be capable of mediating the production of O-(2). This being the case, lucigenin can signal the presence of O-(2) even in systems not producing it in the absence of lucigenin. The reduction potential of lucigenin should be in accord with its ability to mediate O-(2) production; but it has not heretofore been measured in aqueous media. The problems facing such measurement are the insolubility of the divalently reduced form, which deposits on the electrode, and the slow conformational transition that follows the second electron transfer and which interferes with reversibility. We have now used rapid scan cyclic voltammetry to determine that the reduction potential for lucigenin is -0.14 +/- 0.02 V versus the normal hydrogen electrode. This value applies to both the first and the second electron transfers to lucigenin and it is in accord with the facile mediation of O-(2) production by this compound.