Olaparib maintenance versus placebo in platinum-sensitive non-small cell lung cancer: the Phase 2 randomized PIPSeN trial

BACKGROUND

Platinum-sensitivity is a phenotypic biomarker of Poly (ADP-ribose) polymerase inhibitors (PARPi) sensitivity in histotypes where PARPi are approved. Approximately one-third of non-small cell lung cancers (NSCLC) are platinum-sensitive. The double-blind, randomized phase II PIPSeN (NCT02679963) study evaluated olaparib, a PARPi, as maintenance therapy for patients with platinum-sensitive advanced NSCLC.

METHODS

Chemonaïve patients with ECOG performance status of 0-1, platinum-sensitive, EGFR- and ALK-wild-type, stage IIIB-IV NSCLC were randomized (R) to receive either olaparib (O) maintenance or a placebo (P). The primary objective was progression-free survival (PFS) from R. Secondary objectives included overall survival (OS) and safety. With an anticipated hazard ratio of 0.65, 144 patients were required to be randomized, and approximately 500 patients enrolled.

RESULTS

The trial was prematurely terminated because anti-PD(L)1 therapy was approved during the trial recruitment. A total of 182 patients were enrolled, with 60 patients randomized: 33 and 27 in the O and P arms, respectively. Patient and tumor characteristics were well-balanced between arms, except for alcohol intake (33% vs 11% in the O and P arms, respectively, p = 0.043). The median PFS was 2.9 and 2.0 months in the O and P arms, respectively (logrank p = 0.99). The median OS was 9.4 and 9.5 months in the O and P arms, respectively (p = 0.28). Grade ≥3 toxicities occurred in 15 and 8 patients in O and P arms, with no new safety concerns.

CONCLUSION

PIPSeN was terminated early after enrollment of only 50% of the pre-planned population, thus being statistically underpowered. Olaparib maintenance did neither improve median PFS nor OS in this patient population.

Seroprevalence and immunological memory against SARS-CoV-2 in lung cancer patients: the SOLID study

Background

At present, we did not find any articles that studied seroprevalence and its persistence several months later in lung cancer patients in the setting of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Most patients with coronavirus disease 2019 (COVID-19) go on to develop antibodies (Abs) against viral proteins. However, it is not known how long these Abs last nor whether cancer treatments could affect the duration of immune response.

Methods

This prospective, longitudinal, multicenter serological study in the setting of SARS-CoV-2 infection was carried out in 50 Spanish hospitals. Eligibility criterion was the diagnosis of any lung cancer. The determination of anti-SARS-CoV-2 IgG Abs was performed by qualitative immuno-enzymatic assay using enzyme-linked immunosorbent assay (ELISA) kit from NovaLisa whose Abs target the recombinant antigen N of the nucleocapsid of SARS-CoV-2. The first Ab determination was performed between April 21 and June 3, 2020. The second Ab determination was performed in all previously seropositive patients, between September 10 and November 20, 2020. Study objectives were to prospectively determine seroprevalence in unselected lung cancer patients during the first wave of the pandemic; the persistence of immunity; protection or lack thereof against reinfection; and the influence of treatments on maintenance or loss of immunity.

Results

Of 1,500 patients, 128 were seropositive, overall prevalence of 8.5% seropositivity [95% confidence interval (CI): 7.2–10.1%]. Seventy-five percent were in active cancer treatment. Forty-seven point seven percent of IgG positive participants had experienced a symptomatic illness suspected of being infected with SARS-CoV-2 (95% CI: 38.8–56.6%). A second determination was performed on average 4.5 months later [interquartile range (IQR), 4.0–5.0 months] and obtained for 104 of the initially seropositive patients (81%), it could not be obtained in 24 patients, the majority due to death caused by disease progression (73%). In the second determination, IgG was not detected in 30.8% of patients. The severity of the infection, the need for hospitalization (P=0.032) and the presence of symptoms at diagnosis (P=0.02) were associated with persistence of immunity in the second determination. No variables or treatments received were associated with Abs loss.

Conclusions

Immunity against SARS-CoV-2 does not appear to be compromised by treatment and persists beyond 4 months. Neither do mortality rates appear to be particularly high in this unselected population.

Trial Registration

ClinicalTrials.gov identifier: NCT04407143.

Seroprevalence and immunological memory against SARS-CoV-2 in lung cancer patients (p): SOLID study

8531

Background: Coronavirus disease 2019 (COVID-19) is diagnosed by detecting the virus by reverse transcription polymerase chain reaction (RT-PCR). The majority of p go on to develop antibodies (Ab) against viral proteins. However, it is not known how long these antibodies last nor whether cancer treatments could affect the duration of immune response. The prognosis and greater or lesser vulnerability of the oncological population are also unknown. Methods: This prospective, longitudinal, multicenter serological study in the setting of SARS-CoV-2 was carried out in 50 Spanish hospitals. Eligibility criteria was a diagnosis of any thoracic cancer. The first determinations were performed between April 21, 2020 and June 3, 2020, either for p in follow up or in active treatment. Between September 10, 2020, and November 20, 2020, the second antibody (Ab) determination was performed in all previously seropositive p. Clinical and treatment data were collected, as was their clinical situation at study end. Study objectives were to prospectively determine seroprevalence in unselected lung cancer p during the first wave of the pandemic; the natural history of these p; the persistence of immunity more than 4 months after first determination; protection or lack thereof against reinfection after this period, and the nature of such protection; and the influence of treatments on maintenance or loss of immunity. Results: Of 1,500 p studied, 128 were seropositive, representing an overall prevalence of 8.5% seropositivity [95% confidence interval [CI], 7.2%, 10.1%]. Seventy-five percent were in active cancer treatment. COVID-19 infection was suspected in 47.7% [95% CI, 38.8%, 56.6%]. A second determination was performed on average 4.5 months later [IQR: 4; 5] and obtained for 104 of the initially seropositive p (81%). A second determination could not be obtained in 24 p, the majority due to death caused by disease progression (73%). In the second determination, IgG was not detected in 30.8% (32/104) of p. The severity of the infection, the need for hospitalization (p: 0.032) and the presence of symptoms at diagnosis (p: 0.02), including fever (p: 0.005) and nasal congestion (p: 0.005), were associated with persistence of immunity in the second determination. No variables or treatments received were associated with Ab loss. At time of last follow-up among those p for whom a second determination was performed, 89% (93 p) had completely recovered from the virus, with no lasting after effects. Only 1 of the 128 (0.78%) seropositive p had died from COVID-19. Conclusions: The prevalence of infection in lung cancer p is similar to that of the general population. Immunity against SARS-CoV-2 does not appear to be compromised by treatment, persisting beyond 4 months. Neither do mortality rates appear to be particularly high in this unselected population.

Molecular profiling by NGS upon progression disease in advanced stage NSCLC patients

e21196

Background: Non-small cells lung cancer (NSCLC) patients treated with Tyrosine Kinase Inhibitors (TKI) at first-line ultimately develop disease progression after 10 to 14 months. Mechanisms underlying TKI-resistance are not complete understood. Tumor re-biopsy is often unfeasible for NSCLC patients and liquid biopsy is a suitable alternative in identify mechanism by which tumors progress. Methods: 113 plasma samples were collected from advanced stage EGFR positive NSCLC patients upon disease progression according to RECIST V1.1. cfDNA NGS profiling was carried out using the Oncomine™ Pan-Cancer Cell-Free Assay and sequenced on an Ion GeneStudio S5 Plus System. Variant calling and annotation were performed with Torrent Suite and Ion Reporter (v5.16) software, respectively. In addition, we developed a bioinformatic pipeline, using RStudio for variant filtering. Results: Overall, 344 somatic variants were detected with an average number of variants per patient of 2.32 and a median Mutant Allele Frequency (MAF) of 0.83%. Most mutated genes were EGFR (63.72%), TP53 (60.18%), APC (16.81%), MAP2K1 (11.50%), PIK3CA (10.62%), FGFR3 (7.08%), KRAS (7.08%) and BRAF (6.19%). As expected, SNPs were the most frequent mutation type (72.67%), following by INDELs (24.41%) and CNVs (2.91%). We found high co-occurrence between MYC-GNA11, MYC-CCND2, HRAS-AR and EGFR-TP53 genes using Jaccard’s score (0.5, 0.5, 0.5 and 0.46, respectively). Within EGFR-mutated patients, 40% had T790M resistance mutation. Finally, we found KRAS mutations and missense PIK3CA mutations were mutually exclusive. Conclusions: Molecular profiling of liquid biopsies collected upon disease progression using NGS help to identify molecular mechanisms underlying treatment failure.

Analysis of circulating tumour DNA to identify patients with epidermal growth factor receptor-positive non-small cell lung cancer who might benefit from sequential tyrosine kinase inhibitor treatment

BACKGROUND

Survival data support the use of first-line osimertinib as the standard of care for epidermal growth factor receptor (EGFR)-positive non-small cell lung cancer (NSCLC). However, it remains unclear whether upfront osimertinib is superior to sequential first- or second-generation tyrosine kinase inhibitors (TKIs) followed by osimertinib for all patients. It is impossible to predict which patients are at high risk of progression, and this constitutes a major limitation of the sequential TKI approach.

PATIENTS AND METHODS

A total of 830 plasma samples from 228 patients with stage IV, EGFR-positive NSCLC who were treated with first-line TKIs were analysed by digital polymerase chain reaction (dPCR).

RESULTS

The circulating tumour DNA (ctDNA) levels helped to identify patients with significantly improved survival rate, regardless of the treatment. Patients treated with first- or second-generation TKIs (N = 189) with EGFR mutations in plasma at a mutant allele frequency (MAF) <7% before treatment initiation (low-risk patients) or who were ctDNA negative after 3 or 6 months of treatment and with an MAF <7% at diagnosis (high responders) had two-thirds lower risk of death than patients in the opposite situation (adjusted hazard ratio [HR] = 0.38; 95% confidence interval [CI]: 0.23-0.64 and HR = 0.22; 95% CI: 0.12-0.42, respectively). The median overall survival (OS) for low-risk patients and high responders treated with first- or second-generation TKIs was 34.2 months and not reached, respectively, regardless of second-line treatment. There were no significant difference in OS between low-risk or high-responder patients treated upfront with osimertinib (N = 39) and those treated under a sequential approach with osimertinib (N = 60). Median OS was not reached in both cases.

CONCLUSIONS

Pre-treatment ctDNA levels identify low-risk patients, who may benefit from sequential TKI treatment. Information regarding EGFR mutation clearance can help to improve patient selection.

Osimertinib in advanced EGFR-T790M mutation-positive non-small cell lung cancer patients treated within the Special Use Medication Program in Spain: OSIREX-Spanish Lung Cancer Group

BACKGROUND

AURA study reported 61% objective response rate and progression-free survival of 9.6 months with osimertinib in patients with EGFR/T790M+ non-small cell lung cancer. Due to lack of real-world data, we proposed this study to describe the experience with osimertinib in Spain.

METHODS

Post-authorization, non-interventional Special Use Medication Program, multicenter, retrospective study in advanced EGFR/T790M+ non-small cell lung cancer. One hundred-fifty five patients were enrolled (August 2016-December 2018) from 30 sites.

PRIMARY OBJECTIVE

progression-free survival. Secondary objectives: toxicity profile, objective response rate, and use of health service resources.

RESULTS

70% women, median age 66. 63.9% were non-smokers and 99% had adenocarcinoma. Most patients had received at least one prior treatment (97%), 91.7% had received previous EGFR-tyrosine kinase inhibitors and 2.8% osimertinib as first-line treatment. At data cutoff, median follow-up was 11.8 months. One hundred-fifty five patients were evaluable for response, 1.3% complete response, 40.6% partial response, 31% stable disease and 11.6% disease progression. Objective response rate was 42%. Median progression-free survival was 9.4 months. Of the 155 patients who received treatment, 76 (49%) did not reported any adverse event, 51% presented some adverse event, most of which were grade 1 or 2. The resource cost study indicates early use is warranted.

CONCLUSION

This study to assess the real-world clinical impact of osimertinib showed high drug activity in pretreated advanced EGFR/T790M+ non-small cell lung cancer, with manageable adverse events.

TRIAL REGISTRATION

Clinical trial registration number: NCT03790397 .

SEOM clinical guidelines for the treatment of malignant pleural mesothelioma (2020)

Mesothelioma is a rare and aggressive tumour with dismal prognosis arising in the pleura and associated with asbestos exposure. Its incidence is on the rise worldwide. In selected patients with early-stage MPM, a maximal surgical cytoreduction in combination with additional antitumour treatment may be considered in selected patients assessed by a multidisciplinary tumor board. In patients with unresectable or advanced MPM, chemotherapy with platinum plus pemetrexed is the standard of care. Currently, no standard salvage therapy has been approved yet, but second-line chemotherapy with vinorelbine or gemcitabine is commonly used. Novel therapeutic approaches based on dual immunotherapy or chemotherapy plus immunotherapy demonstrated promising survival benefit and will probably be incorporated in the future.

Phase II clinical trial with metronomic oral vinorelbine and tri-weekly cisplatin as induction therapy, subsequently concomitant with radiotherapy (RT) in patients with locally advanced, unresectable, non-small cell lung cancer (NSCLC). Analysis of survival and value of ctDNA for patient selection

BACKGROUND

Little progress has been achieved in non-small cell lung cancer (NSCLC) patients with unresectable stage III disease and new drug schemes are warranted.

MATERIAL AND METHODS

In this open-label, single-arm, phase II trial 65 treatment-naïve stage III NSCLC deemed surgically unresectable by a multidisciplinary team were treated with 2 cycles of induction cisplatin at 80 mg/m² every 21 days plus metronomic oral vinorelbine at 50 mg/day every Monday, Wednesday and Friday. During the concomitant treatment with thoracic radiotherapy cisplatin was administered in the same manner but oral vinorelbine was reduced to 30 mg/day. The objective was to administer a total radiotherapy dose of 66 Gy in 33 daily fractions of 2 Gy. The primary endpoint was progression-free survival (PFS). Correlation between circulating tumor DNA (ctDNA) levels and survival was also evaluated.

RESULTS

Fifty-five (78.5 %) patients completed treatment. Overall response rate, by RECIST criteria, was 66.2 %. Four (6.2 %) patients had complete response, 39 (60.0 %) partial response and 12 (18.5 %) stable disease. Seven patients (10.8 %) had progressive disease during the induction period. Median follow-up was 29.1 months (m), median PFS was 11.5 m (95 %CI: 9.6-15.4). PFS at 12 m in the intention-to-treat (ITT) population was 47.8 % (95 %CI: 35.1-59.4 %) and median OS was 35.6 m (95 %CI: 24.4-46.8). Grade ≥3 treatment-related adverse events occurred in 14 (21.5 %) patients during induction and in 13 (24.5 %) patients during concomitant treatment with esophagitis occurring in 3% and pneumonitis in 1.5 % of the patients. Patients with undetectable ctDNA after 3 m follow-up had median PFS and OS of 18.1 m (95 %CI: 8.8-NR) and not reached (NR) (95 %CI: 11.3-NR), respectively, compared with 8.0 m (95 %CI: 2.7-NR) and 24.7 m (95 %CI: 5.7-NR) for patients who remained ctDNA positive at that time point.

CONCLUSIONS

Metronomic oral vinorelbine and cisplatin obtains similar efficacy results with significantly lower toxicity than the same chemotherapy at standard doses. ctDNA can identify populations with particularly good prognosis.

Patient preference for oral chemotherapy in the treatment of metastatic breast and lung cancer

OBJECTIVES

Although new therapies against metastatic cancer have been developed in recent decades, chemotherapy is still an important treatment option. Prolonged treatment and side-effects are often discouraging for patients, and in many cases, therapy is only palliative, not curative. This study explores patient preference for oral or intravenous (IV) chemotherapy in the treatment of metastatic breast or lung cancer.

METHODS

It is a descriptive, open label, multicentre, nation-wide study, in which a 16-item questionnaire consisting of single-choice questions scored on a 5-point Likert scale was administered to patients in a single visit, and another 11-item questionnaire was self-administered by the patient's oncologist.

RESULTS

A total of 131 breast and lung cancer specialists at 64 hospitals enrolled 412 patients (lung cancer = 161; breast cancer = 251). To be eligible, patients must have already received IV therapy and at least 2 cycles of oral chemotherapy. Most (77%) patients expressed preference for oral therapy. Most considered their daily life was less disrupted with tablets (70.4%), had no trouble swallowing them (86.9%), and were not concerned about forgetting to take them (56.8%). Half (56.3%) were worried about problems related to drug infusion with IV therapy, 61.7% were concerned about nurses failing to find a suitable vein, and 63.1% were dissatisfied with hospital waiting times. A uniform response was obtained from both samples of patients.

CONCLUSION

Convenience, ease of administration, fewer side effects and better quality of life tilt the balance towards oral drug administration.

Preliminary immunogenicity, safety, and efficacy of JNJ-64041757 (JNJ-757) in non-small cell lung cancer (NSCLC): Results from two phase 1 studies

9093

Background: The immunogenicity, safety, and efficacy of JNJ-757, a live attenuated, double-deleted Listeria monocytogenes-based immunotherapy expressing human mesothelin (MSLN), were evaluated in patients (pts) with advanced NSCLC (adenocarcinoma) as monotherapy (phase 1) and in combination with nivolumab (phase 1b/2). Methods: Adult pts with Stage IIIB/IV NSCLC who had received prior systemic therapy (including 1 platinum-based chemotherapy, prior PD-1/PD-L1 therapy allowed) were included. Dose-limiting toxicities, adverse events (AEs), tumor response, T cell response, and JNJ-757 bacterial shedding profile were evaluated in pts treated with JNJ-757 (108 or 109 colony forming units [CFU]) alone or JNJ-757 (109 CFU)+nivolumab 240 mg combination therapy until progression. Results: In the monotherapy trial, 18 pts (median age 63.5 years; women 61%) were treated with JNJ-757 108 or 109 CFU with a median duration of 1.4 months (range 0-29). Most common AEs were pyrexia (72%) and chills (61%), which were usually mild and resolved within 48 hours, suggesting transient activation of an innate immune response to JNJ-757. Treatment-related grade ≥3 AEs were infrequent (4 [22%]). Induction of peripheral proinflammatory cytokines and lymphocyte activation was observed post-treatment with transient MSLN-specific T cell responses in 10/13 evaluable pts, consistent with the mechanism of action of JNJ-757. With monotherapy, 4/18 response-evaluable pts had stable disease (SD) ≥16 weeks, including 1 pt with a 53% reduction in target lesions. In the combination therapy study, 12 pts were enrolled (median age 63.5 years; women 33%). The most common AEs were pyrexia (67%) and chills (58%); 6 pts had grade ≥3 AEs including 2 cases of treatment-related fatal pneumonitis. Best overall response for the combination was SD in 4/9 evaluable pts. JNJ-757 in combination with nivolumab suggested increased risk of pneumonitis. Conclusions: As monotherapy, JNJ-757 was tolerable with mild infusion-related fever and chills supporting the initiation of the combination therapy study. However, the risk-benefit profile of JNJ-757+nivolumab, did not support proceeding to phase 2. Clinical trial information: NCT02592967, NCT03371381.

Structural and functional studies of the metalloregulator Fur identify a promoter-binding mechanism and its role in Francisella tularensis virulence

Francisella tularensis is a Gram-negative bacterium causing tularaemia. Classified as possible bioterrorism agent, it may be transmitted to humans via animal infection or inhalation leading to severe pneumonia. Its virulence is related to iron homeostasis involving siderophore biosynthesis directly controlled at the transcription level by the ferric uptake regulator Fur, as presented here together with the first crystal structure of the tetrameric F. tularensis Fur in the presence of its physiological cofactor, Fe²⁺. Through structural, biophysical, biochemical and modelling studies, we show that promoter sequences of F. tularensis containing Fur boxes enable this tetrameric protein to bind them by splitting it into two dimers. Furthermore, the critical role of F. tularensis Fur in virulence and pathogenesis is demonstrated with a fur-deleted mutant showing an attenuated virulence in macrophage-like cells and mice. Together, our study suggests that Fur is an attractive target of new antibiotics that attenuate the virulence of F. tularensis.

Pérard et al. report the structure of Francisella tularensis Fur (FtFur) with its physiological cofactor Fe²⁺, and show that FtFur is important for virulence. This study identifies a promoter-driven tetramer splitting mechanism that may provide insight into future antibiotics development.

Mobilization of selenite by Ralstonia metallidurans CH34

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.

A simplifed functional version of the Escherichia coli sulfite reductase

Escherichia coli sulfite reductase (SiR) is a large and soluble enzyme with an alpha(8)beta(4) quaternary structure. Protein alpha (or sulfite reductase flavoprotein) contains both FAD and FMN, whereas protein beta (or sulfite reductase hemoprotein (SiR-HP)) contains an iron-sulfur cluster coupled to a siroheme. The enzyme is set up to arrange the redox cofactors in a FAD-FMN-Fe(4)S(4)-Heme sequence to make an electron pathway between NADPH and sulfite. Whereas alpha spontaneously polymerizes, we have been able to produce SiR-FP60, a monomeric but fully active truncated version of it, lacking the N-terminal part (Zeghouf, M., Fontecave, M., Macherel, D., and Covès, J. (1998) Biochemistry 37, 6114-6123). Here we report the cloning, overproduction, and characterization of the beta subunit. Pure recombinant SiR-HP behaves as a monomer in solution and is identical to the native protein in all its characteristics. Moreover, we demonstrate that the combination of SiR-FP60 and SiR-HP produces a functional 1:1 complex with tight interactions retaining about 20% of the activity of the native SiR. In addition, fully active SiR can be reconstituted by incubation of the octameric sulfite reductase flavoprotein with recombinant SiR-HP. Titration experiments and spectroscopic properties strongly suggest that the holoenzyme should be described as an alpha(8)beta(8) with equal amounts of alpha and beta subunits and that the alpha(8)beta(4) structure is probably not correct.

The flavoprotein component of the Escherichia coli sulfite reductase can act as a cytochrome P450c17 reductase

The flavoprotein component (SiR-FP) of the E. coli sulfite reductase was found to support 17 alpha-hydroxylation of pregnenolone in the presence of cytochrome P450c17. Half maximum activity is obtained for a 1:1 ratio of SiR-FP, expressed as monomer concentration, to P450c17. When compared to bovine NADPH-cytochrome P450 reductase, SiR-FP is about 12-15 times less efficient. P450c17 was demonstrated to interact specifically with the FMN-binding domain of the protein and the N-terminal part of SiR-FP is suspected to play a role in electron transfer. A cluster of negatively charged residues was found in SiR-FP by amino acid sequence comparison with rat cytochrome P450 reductase. These results argue in favour of the flavodoxin origin of the FMN-binding domain of SiR-FP.

Flavin mononucleotide-binding domain of the flavoprotein component of the sulfite reductase from Escherichia coli

The flavoprotein component (SiR-FP) of the sulfite reductase from Escherichia coli is an octamer containing one FAD and one FMN as cofactors per polypeptide chain. We have constructed an expression vector containing the DNA fragment encoding for the FMN-binding domain of SiR-FP. The overexpressed protein (SiR-FP23) was purified as a partially flavin-depleted polymer. It could incorporate FMN exclusively upon flavin reconstitution to reach a maximum flavin content of 1.2 per polypeptide chain. Moreover, the protein could stabilize a neutral air-stable semiquinone radical over a wide range of pHs. During photoreduction, the flavin radical accumulated first, followed by the fully reduced state. The redox potentials, determined at room temperature [E'1 (FMNH./FMN) = -130 +/- 10 mV and E'2 (FMNH2/FMNH.) = -335 +/- 10 mV], were very close to those previously reported for Salmonella typhimurium SiR-FP [Ostrowski, J., Barber, M. J., Rueger, D. C., Miller, B. E., Siegel, L. M., & Kredich, N. M. (1989) J. Biol. Chem. 264, 15796-15808]. Both the radical and fully reduced forms of SiR-FP23 were able to transfer their electrons to cytochrome c quantitatively. Altogether, the results presented herein demonstrate that the N-terminal end of E. coli SiR-FP forms the FMN-binding domain. It folds independently, thus retaining the chemical properties of the bound FMN, and provides a good model of the FAD-depleted form of native SiR-FP. Moreover, the FMN prosthetic group in SiR-FP23 and native SiR-FP is compared to that of cytochrome P450 reductase and bacterial cytochrome P450, which also contain one FAD and one FMN per polypeptide chain.

Ferric reductases in Escherichia coli: the contribution of the haemoglobin-like protein

The haemoglobin-like protein (HMP) of E. coli previously isolated as a dihydropteridine reductase was shown to be also a ferric citrate reductase. We demonstrate that, in fact, HMP is a flavin reductase and that its ferric reductase activity is a result of its ability to reduce free flavins. However, when compared to the two main ferric/flavin reductases of E. coli, i.e., the NAD(P)H: flavin oxidoreductase and the sulfite reductase, one can conclude that the contribution of HMP to iron reduction is negligible.

Sulfite reductase of Escherichia coli is a ferrisiderophore reductase

A soluble ferrisiderophore reductase activity of Escherichia coli was purified to homogeneity and identified as the sulfite reductase. The pure enzyme catalyzes the reduction of ferric citrate, ferriaerobactin, ferrioxamin, ferricrocin, ferrichrome and ferrifusarinin by NADPH. Free flavins, riboflavin, FMN, FAD were absolutely required, suggesting that this activity resides in the flavin reductase activity of sulfite reductase.

Reduction and mobilization of iron by a NAD(P)H:flavin oxidoreductase from Escherichia coli

Iron is an essential element in all living cells. Solubilization, uptake and transport of iron by microorganisms is controlled by highly efficient and specific Fe(3+)-chelating agents named siderophores. However, mechanisms of mobilization of iron from ferrisiderophores are still enigmatic. Here, we demonstrate that Escherichia coli contains a powerful enzymatic system for the reduction of ferrisiderophores. Siderophores have a much lower affinity for ferrous iron, which then can be liberated. This system has been previously purified and characterized as a NAD(P)H:flavin oxidoreductase [Fontecave, M., Eliasson, R. and Reichard, P. (1987) J. Biol. Chem. 262, 12,325-12,331)]. It catalyzes the reduction of free flavins, FMN, FAD or riboflavin by NADH or NADPH. Reduced flavins, in turn, transfer their electrons to physiological ferric complexes: ferrisiderophores, ferric citrate and ferritins. The reaction is inhibited by molecular oxygen and greatly stimulated by Fe(2+)-acceptors such as ferrozine or the iron-free form of ribonucleotide reductase subunit R2. We suggest that the reduction and the mobilization of iron from ferrisiderophores in the cell might be regulated by the presence of physiological ferrous traps such as apoproteins.

Inactivation of ribonucleotide reductase by nitric oxide

Ribonucleotide reductase has been demonstrated to be inhibited by NO synthase product(s). The experiments reported here show that nitric oxide generated from sodium nitroprusside, S-nitrosoglutathione and the sydnonimine SIN-1 inhibits ribonucleotide reductase activity present in cytosolic extracts of TA3 mammary tumor cells. Stable derivatives of these nitric oxide donors were either inactive or much less inhibitory. EPR experiments show that the tyrosyl radical of the small subunit of E. Coli or mammalian ribonucleotide reductase is efficiently scavenged by these NO donors.

NAD(P)H oxidation by hydrogen peroxide in Escherichia coli

A protein fraction from Escherichia Coli soluble extracts contain a NAD(P)H:hydrogen peroxide oxidoreductase activity. This activity is compared to and found to be distinct from well-known E. Coli enzymes involved in the protection from peroxides: hydroperoxidase I (HPI) and its o-dianisidine peroxidase component and the alkyl hydroperoxide reductase.