L-DOPA Dioxygenase Activity on 6-Substituted Dopamine Analogues.

Dioxygenase enzymes are essential protein catalysts for the breakdown of catecholic rings, structural components of plant woody tissue. This powerful chemistry is used in nature to make antibiotics and other bioactive materials or degrade plant material, but we have a limited understanding of the breadth and depth of substrate space for these potent catalysts. Here we report steady-state and pre-steady-state kinetic analysis of dopamine derivatives substituted at the 6-position as substrates of L-DOPA dioxygenase, and an analysis of that activity as a function of the electron-withdrawing nature of the substituent. Steady-state and pre-steady-state kinetic data demonstrate the dopamines are impaired in binding and catalysis with respect to the cosubstrate molecular oxygen, which likely afforded spectroscopic observation of an early reaction intermediate, the semiquinone of dopamine. The reaction pathway of dopamine in the pre-steady state is consistent with a nonproductive mode of binding of oxygen at the active site. Despite these limitations, L-DOPA dioxygenase is capable of binding all of the dopamine derivatives and catalyzing multiple turnovers of ring cleavage for dopamine, 6-bromodopamine, 6-carboxydopamine, and 6-cyanodopamine. 6-Nitrodopamine was a single-turnover substrate. The variety of substrates accepted by the enzyme is consistent with an interplay of factors, including the capacity of the active site to bind large, negatively charged groups at the 6-position and the overall oxidizability of each catecholamine, and is indicative of the utility of extradiol cleavage in semisynthetic and bioremediation applications.

A New Way of Belonging: Active-Site Investigation of L-DOPA Dioxygenase, a VOC Family Enzyme from Lincomycin Biosynthesis.

Extradiol dioxygenase chemistry is essential for catechol breakdown. The largest natural reservoir of catechols, or 1,2-dihydroxybenzenes, is the plant woody-tissue polymer lignin. Vicinal-oxygen-chelate (VOC) dioxygenases make up the largest group of characterized extradiol dioxygenases, and while most are found as part of catabolic pathways degrading a variety of natural and human-made aromatic rings, L-DOPA (l-3,4-dihydroxyphenylalanine) dioxygenase is a VOC enzyme that participates in the biosynthesis of a natural product. All VOC superfamily members shared conserved elements of catalysis, yet despite decades of investigation of VOC enzymes, the relationships between VOC domain architecture and enzymatic function remain complex and poorly understood. Herein, we present evidence that L-DOPA dioxygenase is the representative member of a new topological class of VOC extradiol dioxygenases. Guided by its evolutionary similarity to glyoxylase enzymes, we performed a careful investigation of the Streptomyces lincolnensis L-DOPA dioxygenase (LmbB1) active site through mutagenesis, kinetic, and pH studies. Our results demonstrate that the L-DOPA dioxygenase reaction depends upon an active-site tyrosine and histidine and is remarkably resilient to mutation, even at the iron-ligating residues. Evaluation of the cleavage reaction as a function of pH supports the role of a histidine in acid-base catalysis. The active-site architecture is functionally consistent with the existing knowledge of VOC extradiol dioxygenase catalysis.

Gefitinib and Methotrexate to Treat Ectopic Pregnancies with a Pre-Treatment Serum hCG 1000-10,000 IU/L: Phase II Open Label, Single Arm Multi-Centre Trial.

BACKGROUND: Ectopic pregnancies are a leading cause of maternal mortality. Most are treated surgically. We evaluated the efficacy and safety of combining oral gefitinib (epidermal growth factor receptor inhibitor) with methotrexate to treat larger ectopic pregnancies. METHODS: We performed a phase II, single arm, open label study across four hospitals in Edinburgh and Melbourne. We recruited women with a stable tubal ectopic pregnancy and a pre-treatment serum hCG between 1000 and 10,000 IU/L. We administered intramuscular methotrexate (50 mg/m2) once, and oral gefitinib (250 mg) for seven days. The primary outcome was the percentage successfully treated without needing surgery. To show the treatment is at least 70% effective, 28 participants were required, and 24 or more successfully treated without surgery. Secondary outcomes were safety, tolerability, and time to resolution. This study is registered (ACTRN12611001056987). FINDINGS: 30 participants with stable tubal ectopic pregnancies were recruited but two withdrew, leaving 28 participants. The median (± range) pre-treatment serum hCG was 2039 (1031-8575) IU/L and nine had pre-treatment hCGs levels >3000 IU/L. The treatment successfully resolved 86% (24/28) cases with a median (±range) time to resolution of 32 (18-67) days. The treatment caused transient rash and diarrhoea, but no serious adverse events. INTERPRETATION: Combination gefitinib and methotrexate is at least 70% effective in resolving ectopic pregnancies with a pre-treatment serum hCG 1000-10,000 IU/L. This may be a new way to treat most stable ectopic pregnancies, but needs to be validated via a randomised clinical trial.

Ultrasound-guided hysteroscopy to remove a levonorgestrel intrauterine system in early pregnancy.

BACKGROUND: Correctly placed levonorgestrel-releasing intrauterine systems (LNG-IUSs) are rarely associated with intrauterine pregnancy when pregnancy occurs. LNG-IUS retrieval, termination of pregnancy and conservative management if retracted strings prevent ready removal are the usual clinical options given to women. The conservative course raises concerns about teratogenesis related to high local progestin exposure for the developing fetus. STUDY DESIGN: This case report describes combined saline hysteroscopy and ultrasound to retrieve an LNG-IUS at less than 9 weeks of gestational age. A systematic review of the literature was performed to identify similar case reports by contacting the manufacturer and searching Pubmed from 1900 through November 2011 using the terms ((levonorgestrel AND intrauterine) OR mirena) AND (pregnan* OR fetal OR fetus OR teratogen*) NOT (menorrhagia OR hyperplas* OR ectopic OR malig* OR cancer). RESULTS: We identified 37 cases of LNG-IUS pregnancy exposures in the absence of spontaneous expulsion or myometrial or intraperitoneal placement of LNG-IUS. Given the presence of two congenital anomalies reported in the group, the anomaly rate is 5.4%, 95% confidence interval 0% to 11.5%. CONCLUSIONS: Intrauterine LNG-IUS exposure is associated with a low frequency of congenital anomalies. Combining hysteroscopy with ultrasound facilitates surgically precise LNG-IUS removal despite retracted strings.