Abstract P3-05-11: The evolution of the estrogen receptor (ER) complex conformation governs estrogen-induced apoptosis in antihormone-resistant breast cancer cells

Over the past decade new insights have been gained into the acquired resistance to tamoxifen and the Aromatase Inhibitors (AIs) with the discovery of the new biology of estrogen-induced apoptosis. However, it has also been learned that estrogens can be classified into planar class I and angular class II estrogens. Using model systems of long-term estrogen-deprived breast cancer cells in vitro (MCF-7:5C), it was previously shown that class I estrogens cause immediate apoptosis over a 3-4 day period. Paradoxically, class II estrogens actually block apoptosis caused by planar class I estrogens. To gain insight into this paradox we have successfully crystallized an angular class II triphenylethylene (TPE) estrogen bound to the ligand binding domain (LBD) of the ER and derived a new conformation for the TPE:ER complex (code 3Q97 in the PDB). Surprisingly, Helix 12 seals the LBD with the class II estrogen, but not the same conformation is observed with the planar class I estrogen 17β-estradiol (E2). There would seem to be no reason why the 3Q97 complex would not cause immediate apoptosis. To address this issue we have used Western blot analysis for protein and qRT-PCR for mRNA levels for the ER. ER parameters were monitored for up to 72 hours and results compared and contrasted between E2, the Class II estrogens, 4-hydroxytamoxifen (4OHT) and endoxifen (Endox). ER protein and mRNA levels with 4OHT or Endox accumulated and remained high throughout the study period. In contrast, the planar estrogen E2 produced a rapid decline in the protein and mRNA levels for the ER complex. The angular class II estrogens initially produced an accumulation of the ER protein complex, which decreased with time. Using a chromatin immunoprecipitation (ChIP) technique we demonstrated that the class II estrogens recruit only half of the ER to the estrogen-responsive genes promoters (TFF1 And BREB1) and less than half co-activator binding compared to E2. The TPEs were only partial agonists compared to planar estrogen. These results explain why the Class II estrogens induce delayed apoptosis. We conclude that, for the first time, we have observed the binding of a ligand to a receptor that changes conformation against time and evolves from an antagonist to an agonist conformation to trigger apoptosis. These observations have current relevance to the decryption of the protective effects of estrogen alone therapy against breast cancer incidence in the Women's Health Initiative (WHI) trial. This work was supported by the Susan G. Komen for the Cure Foundation award SAC100009.

Citation Format: Maximov PY, Sengupta S, Fernandes DJ, Fan P, Curpan RF, Rajan SS, Greene GL, Jordan VC. The evolution of the estrogen receptor (ER) complex conformation governs estrogen-induced apoptosis in antihormone-resistant breast cancer cells. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-05-11.

A non-randomized controlled stepped wedge trial to evaluate the effectiveness of a multi-level mammography intervention in improving appointment adherence in underserved women

BACKGROUND

Considerable racial and socio-economic disparities exist in breast cancer. In spite of the existence of numerous evidence-based interventions (EBIs) aimed at reducing breast cancer screening barriers among the underserved, there is a lack of uptake or sub-optimal uptake of EBIs in community and clinical settings. This study evaluates a theoretically based, systematically designed implementation strategy to support adoption and implementation of a patient navigation-based intervention, called Peace of Mind Program (PMP), aimed at improving breast cancer screening among underserved women.

METHODS/DESIGN

The PMP will be offered to federally qualified health centers and charity clinics in the Greater Houston area using a non-randomized stepped wedge design. Due to practical constraints of implementing and adopting in the real-world, randomization of start times and blinding will not be used. Any potential confounding or bias will be controlled in the analysis. Outcomes such as appointment adherence, patient referral to diagnostics, time to diagnostic referral, patient referral to treatment, time to treatment referral, and budget impact of the intervention will be assessed. Assessment of constructs from the consolidated framework for implementation research (CFIR) will be assessed during implementation and at the end of the study (sustainment) from each participating clinic. Data will be analyzed using descriptive statistics (chi-square tests) and generalized estimating equations (GEE).

DISCUSSION

While parallel group randomized controlled trials (RCT) are considered the gold standard for evaluating EBI efficacy, withholding an effective EBI in practice can be both unethical and/or impractical. The stepped wedge design addresses this issue by enabling all clinics to eventually receive the EBI during the study and allowing each clinic to serve as its own control, while maintaining strong internal validity. We expect that the PMP will prove to be a feasible and successful strategy for reducing appointment no-shows in underserved women.

TRIAL REGISTRATION

CLINICAL TRIALS REGISTRATION NUMBER

NCT02296177.

The prognostic significance of tumour-stroma ratio in oestrogen receptor-positive breast cancer

Background:

A high percentage of stroma predicts poor survival in triple-negative breast cancers but is diminished in studies of unselected cases. We determined the prognostic significance of tumour–stroma ratio (TSR) in oestrogen receptor (ER)-positive male and female breast carcinomas.

Methods:

TSR was measured in haematoxylin and eosin-stained tissue sections (118 female and 62 male). Relationship of TSR (cutoff 49%) to overall survival (OS) and relapse-free survival (RFS) was analysed.

Results:

Tumours with ⩾49% stroma were associated with better survival in female (OS P=0.008, HR=0.2–0.7; RFS P=0.006, HR=0.1–0.6) and male breast cancer (OS P=0.005, HR=0.05–0.6; RFS P=0.01, HR=0.87–5.6), confirmed in multivariate analysis.

Conclusions:

High stromal content was related to better survival in ER-positive breast cancers across both genders, contrasting data in triple-negative breast cancer and highlighting the importance of considering ER status when interpreting the prognostic value of TSR.

Physicochemical characterization of an aspin (rBm-33) from a filarial parasite Brugia malayi against the important human aspartic proteases

The aspartic protease inhibitory efficiency of rBm-33, an aspin from a filarial parasite Brugia malayi was investigated. rBm-33 was found to be thermostable up to 90°C and it forms a stable 'enzyme-product' complex with human pepsin. Aspartic protease inhibitory activity was investigated using UV spectroscopy and isothermal titration calorimetry. Our results suggest that rBm-33 inhibits the activity of important human aspartic proteases that were examined with binding constants (Kb) values between 10.23 × 10(3) and 6.52 × 10(3) M(-1). The binding reactions were enthalpy driven with ΔHb values between -50.99 and -46.07 kJ mol(-1). From kinetic studies, pepsin inhibition by rBm-33 was found to be linear competitive with an inhibition constant (Ki) of 2.5 (±0.8) nM. Because of the inhibitory efficacy of Bm-33 against important human aspartic proteases which play a vital role in immune-regulation along with other functions, Bm-33 can be projected as a drug target for the filariasis.

N-[4-(7-Methoxy-2-oxo-2H-chromen-8-yl)-2-methylbutan-2-yl]propionamide

In the crystal structure of the title osthol derivative, C₁₈H₂₃NO₄, mol­ecules are linked by N—H⋯O hydrogen bonds into an infinite chain running parallel to the c axis. The CH₃CH₂– atoms of the propionamide group are disordered over two sets of sites with refined occupancies of 0.689 (12) and 0.311 (12).

A neo-clerodane diterpene from Teucrium tomentosum. Corrigendum

Corrigendum to Acta Cryst. (2004), E60, o117–o119.

The chemical name of the title compound in the paper by Devi, Malathi, Rajan, Aravind, Krishnakumari & Ravikumar [Acta Cryst. (2004), E60, o117–o119] is corrected and the structural diagram is updated.

Molecular basis of chromium insulin interactions

The physiological role of chromium (III) in diabetes mellitus has been an area of inconclusive research for many years. It is of great interest to explore the interactions made by chromium (III) to get a better insight into their role in glucose metabolism. To understand the molecular basis of chromium action we have carried out spectroscopic and crystallographic investigations on the binding of Cr(III)-Salen with insulin, as Cr(III)-Salen is reported to result in the enhancement of insulin activity. The Cr(III)-insulin complex formation has been characterised at two pHs, viz., 3.5 and 9.0 using UV-Vis and fluorescence studies. The crystallographic analysis of Cr(III)-Salen soaked cubic insulin crystals, using anomalous difference Fourier method, revealed B21 Glu to be the binding site for chromium (III).

Semi-synthetic modification of nimbolide to 6-homodesacetylnimbin and 6-desacetylnimbin and their cytotoxic studies

A new C-seco tetranortriterpenoid named as 6-homodesacetylnimbin 2, has been synthesised for the first time through semi-synthetic modification of nimbolide 1, a potent molecule with anticancer activity. Attempts were made to transesterify the -COOMe moiety in nimbolide using titanium (IV) isopropoxide and ethanol so as to obtain a molecule with -COOEt moiety. However, a novel product was envisaged during the course of the reaction, which was identified as 6-homodesacetylnimbin, a higher homologue of 6-desacetylnimbin 3 through spectroscopic and crystallographic methods. Also, 6-desacetylnimbin has been synthesised through acid hydrolysis of nimbolide. The compounds were screened for their cytotoxic properties through brine shrimp lethality bioassay method using Artemia salina.

The study of helical distortions due to environmental changes: choice of parameters

Parameters like interhelical angles, helical parameters, levels of distortions, etc., have been analysed to test their sensitivity to environmental changes using a method developed in this laboratory. This analysis was done on protein structures solved under different environmental conditions like temperature and pH, and ligand binding. The study reveals that the helical parameters are not sensitive enough to study the effect of environmental changes on protein helices. On the other hand the helical distortions as well as changes in the interhelical angles are more sensitive to these changes. The study also provides with additional information like the origin of distortions in a helix when a ligand binds to a protein, bending in helical axis, identification and extent of domain movements, etc.

Nimbolide and isonimbolide

Nimbolide 1, a potent molecule of biological significance, was isolated. Attempts were made to cleave the ether linkage in nimbolide using boron trifluoride etherate in the presence of tetrabutyl ammonium bromide so as to generate a ring-opened structure akin to azadirachtins, which are known to possess excellent antifeedant properties. However, a novel rearranged product was envisaged during the course of the reaction, which was determined as isonimbolide 2-a structural isomer of nimbolide through spectroscopic methods.

Effect of DNA structural flexibility on promoter strength--molecular dynamics studies of E. coli promoter sequences

To study possible correlations between promoter activity and the structural flexibility of the DNA helix, we have carried out unrestrained molecular dynamics simulations of the -10 consensus region sequence and five variants forming the -10 region of various Escherichia coli promoter sequences. Analyses of the trajectories obtained from the simulations show that the consensus sequence has a pattern of two structurally flexible nucleotide steps sandwiched between two stiff steps. In the other sequences, this pattern varies in consonance with the change in the sequence. The variations in the patterns show correlation with the promoter strength.

Structure of d(TGCGCG).d(CGCGCA) in two crystal forms: effect of sequence and crystal packing in Z-DNA

The sequence d(TGCGCG).d(CGCGCA) crystallized in two crystal forms, orthorhombic and hexagonal, in the presence of cobalt hexammine chloride, a known inducer of the left-handed Z-form of DNA. The crystal structures have been solved and refined at 1.71 A resolution in space group P2(1)2(1)2(1) and 2.0 A resolution in space group P6(5). The orthorhombic structure contains one Z-DNA hexamer duplex, while the hexagonal structure contains two hexamer duplexes in the structure. Of the latter, one is situated on a crystallographic sixfold screw axis, leading to disorder. This paper reports the effects of sequence and crystal packing on the structure of Z-type DNA. The structures lend additional support to the authors' earlier conclusion that a stretch of four C.G base pairs is sufficient to nucleate and define the regular model of the left-handed helix based on the structure of d(CGCGCG)2.

The isomeric compounds nimbolide and isonimbolide

Nimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15beta,17alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,13,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], C27H30O7, was isolated from the leaves of Azadirachta indica, and its isomer, isonimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,16,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], was prepared from a novel rearrangement reaction of nimbolide, using boron trifluoride etherate and tetrabutylammonium bromide. The reaction conditions are probably responsible for the ether cleavage, double-bond rearrangement and reformation of the ether linkage. As a result, there are conformational changes in two cyclopentane rings and the side-chain -CH2COOMe group. In isonimbolide, an R(4)(4)(24) hydrogen-bond motif is observed.

Cobalt hexammine induced tautomeric shift in Z-DNA: the structure of d(CGCGCA)*d(TGCGCG) in two crystal forms

We report here the crystal structure of the DNA hexamer duplex d(CGCGCA)*d(TGCGCG) at 1.71 A resolution. The crystals, in orthorhombic space group, were grown in the presence of cobalt hexammine, a known inducer of the left-handed Z form of DNA. The interaction of this ion with the DNA helix results in a change of the adenine base from the common amino tautomeric form to the imino tautomer. Consequently the A:T base pair is disrupted from the normal Watson-Crick base pairing to a 'wobble' like base pairing. This change is accommodated easily within the helix, and the helical parameters are those expected for Z-DNA. When the cobalt hexammine concentration is decreased slightly in the crystallization conditions, the duplex crystallizes in a different, hexagonal space group, with two hexamer duplexes in the asymmetric unit. One of these is situated on a crystallographic 6-fold screw axis, leading to disorder. The tautomeric shift is not observed in this space group. We show that the change in inter-helix interactions that lead to the two different space groups probably arise from the small decrease in ion concentration, and consequently disordered positions for the ion.

Antifeedant neo-clerodanes from Teucrium tomentosum Heyne. (Labiatae)

From the acetone extract of Teucrium tomentosum, a new antifeedant neo-clerodane diterpenoid teuctosin (1) was isolated along with teuflin (2), teucrin-H(2) (3), 6beta-hydroxyteuscordin (4), 6beta-acetylteuscordin (5) and montanin-D (6). The structure of the new compound was elucidated comprehensively using 1D and 2D NMR methods and confirmed by X-ray crystallography. All the compounds showed effective antifeedancy against Plutella xylostella and Spodoptera litura at 10 mug/cm(2) of leaf area.

A new clerodane diterpene with antifeedant activity from Teucrium tomentosum

A new diterpene, viz. 3beta-acetoxy-4alpha,18:15,16-diepoxy-6beta,12-dihydroxyneocleroda-13(16),14-dien-19,20-olide, C(22)H(28)O(8), exhibiting antifeedant activity against Spodoptera litura was isolated from the aerial parts of Teucrium tomentosum and its structure is reported. One of the two fused rings has a distorted-chair conformation and the other has a chair conformation. The molecules in the crystal are stabilized via O--H...O and C--H...O hydrogen bonds.

Samaderin B and C from Samadera indica

Samaderin B, or (1R,2S,5R,5aR,7aS,11S,11aS,11bR,14S)-1,7,7a,11,11a,11b-hexahydro-1,11-dihydroxy-8,11a,14-trimethyl-2H-5a,2,5-(methanoxymetheno)naphth[1,2-d]oxepine-4,6,10(5H)-trione, C(19)H(22)O(7), and samaderin C, or (1R,2S,5R,5aR,7aS,10S,11S,11aS,11bR,14S)-7,7a,10,11,11a,11b-hexahydro-1,10,11-trihydroxy-8,11a,14-trimethyl-2H-5a,2,5-(methanoxymetheno)naphth[1,2-d]oxepine-4,6(1H,5H)-dione, C(19)H(24)O(7), were isolated from the seed kernels of Samadera indica and were shown to exhibit antifeedant activity against Spodoptera litura third-instar larvae. The replacement of the carbonyl group in samaderin B by a hydroxy group in samaderin C causes conformational changes at the substitution site, but the overall conformation is not affected; however, the compounds pack differently in the crystal lattice.

8-(2-bromo-3-methoxy-3-methylbutyl)-7-methoxycoumarin

The title compound, C(16)H(19)BrO(4), is a derivative of osthol, isolated from the seeds of Imperatoria Osthruthium. The structure was solved in space group P-1, with two molecules in the asymmetric unit, and was refined to a final R factor of 0.064. The two molecules in the asymmetric unit differ in the orientation of their brominated substituent group. The benzopyran ring displays aromatic character. The packing of the molecules in the lattice is mainly due to C-H...O hydrogen bonds.

Azadirachtol, a tetranortriterpenoid from neem kernels

The title compound, dimethyl (-)-(2aR,3R,4R,4aS,5R,7aS,8R,10S,10aR)-3,8,10-trihydroxy-4-[(2R,6R)-2-hydroxy-11-methyl-5,7,10-trioxatetracyclo[6.3.1.0(2,6)0(9,11)]dodec-3-en-9-yl]-4-methylperhydroisobenzofurano[5,4,3a-cd]isobenzofuran-5,10a-diacetate, C(28)H(36)O(13), which exhibits higher antifeedant activity than azadirachtin-A, a known potent antifeedant, was isolated from neem kernels. The asymmetric unit of the structure contains two independent molecules, which differ in the conformations of their functional groups and also in the conformations of some of the rings. The relative orientation between the decalin and furanyl moieties is similar to that observed in the majority of azadirachtin structures, but is different from that in azadirachtin-A. The two symmetry-independent molecules are linked into dimeric units by intermolecular O-H.O hydrogen bonds.

2',3'-Dehydrosalannol

The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)-8-(3-furyl)-2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c-dodecahydro-3-hydroxy-2a,5a,6a,7-tetramethyl-5-(3-methylbut-2-enoyloxy)-2H,3H-cyclopenta[4',5']furo[2',3':6,5]benzo[cd]isobenzofuran-6-acetate, C(32)H(42)O(8), was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been found to possess antifeedant activity against Spodptera litura. The conformations of the functional groups are similar to those of 3-desacetylsalannin, which was isolated from neem kernels. The molecules are linked into chains by intermolecular O-H.O hydrogen bonds.

Structure of d(TGCGCA)2 at 293 K: comparison of the effects of sequence and temperature

The crystal structure of a hexameric DNA fragment with the sequence d(TGCGCA)(2) has been solved and refined at 293 K at a resolution of 1.64 A. The molecule adopts a left-handed Z-type helical conformation which is common in alternating pyrimidine-purine sequences. The presence of A.T base pairs at the two terminals does not perturb the structure to any great degree. However, several sequence-specific microstructural changes are noticeable. The structure of the identical sequence determined at 120 K involving somewhat different crystallization conditions has been reported previously [Harper et al. (1998), Acta Cryst. D54, 1273-1284]. A comparison of the present structure with that at low temperature and with that of d(CGCGCG)(2) shows that the effect of the change in sequence is greater than the combined effect of changes in temperature and environment.

Insect antifeedant activity of tetranortriterpenoids from the Rutales. A perusal of structural relations

Structure-related insect antifeedant relationship of 56 limonoids (both natural and modified) from the plants belonging to the order Rutales was attempted considering substitution patterns, oxidation states, and hydrophobicity, as well as distant geometry derived through conformational analysis on molecular modeling. Orientation of the furan and hydroxylation at specific carbon sites have been shown to influence the antifeedancy against the fall armyworm, Spodoptera litura.

Photooxidation of cedrelone, a tetranortriterpenoid from Toona ciliata

Cedrelone, a tetranortriterpenoid on photolysis by UV light yields a true photooxidation product 3 [14 beta,15beta,22beta,23beta-diepoxy-6-hydroxy-1,5, 20(22)-meliatriene-2,7,21-trione] whose structure is well established by NMR studies and confirmed by X-ray crystallography, along with product 4 [14 beta,15beta-epoxy-6,23-dihydroxy-1,5,20(22)-meliatriene-2,7, 21-trione]. Addition of rose bengal increases the rate of photooxidation whereas DABCO decreases rate of photolysis proving the involvement of singlet oxygen in the photooxygenation. Both the photoproducts exhibited antifeedant activity.

Presence of an N-terminal polyhistidine tag facilitates stable expression of an otherwise unstable N-terminal domain of mouse tissue inhibitor of metalloproteinase-1 in Escherichia coli

The active N-terminal domain of the mouse tissue inhibitor of metalloproteinases-1 is a 14.1-kDa polypeptide with three disulfide bonds. When expressed using a T7 system in Escherichia coli, this truncated protein, in contrast to the WT protein, was found only in trace amounts in the cell. However, when the coding sequence was placed downstream of a 60-bp sequence that encoded an in-frame histidine-rich "tag," the fusion product (NF.TIMP*His) was expressed in considerably increased abundance. WT.TIMP-1 was expressed in abundance with or without the tag. The mRNAs encoding the various forms of TIMP were present in similar amounts in all four cases. NF.TIMP*His, renatured and purified on a nickel affinity column, was found to be about 10-fold less effective than native human TIMP-2 at inhibiting cleavage of collagen type I by human fibroblast collagenase. A thrombin cleavage site in the tag was susceptible to cleavage by low levels of a contaminating proteinase.

Analysis of the conformational stability of the active domain of recombinant mouse TIMP-1 by intrinsic fluorescence

Intrinsic fluorescence was used to examine the stability of an active, N-terminal domain of mouse tissue inhibitor of metalloproteinase (TIMP-1) fused with an N-terminal polyhistidine tag. Emission and quenching studies suggested that the single tryptophan is on the protein surface partially exposed to solvent. The TIMP-1 recombinant unfolded reversibly in the presence of guanidinium chloride with the transition midpoint at 2.35M; extrapolation gave a stabilization free energy of 5.1 kcal mol-1 at 25 degrees C. Analysis of the temperature dependence of the fluorescence intensity gave a melting transition with midpoint at 51 degrees C and an enthalpy and heat capacity change on unfolding of 32 kcal mol-1 and 0.45 kcal K-1 mol-1, respectively, values comparable to other single domain proteins. Comparison with literature data indicated that the stability of mouse recombinant TIMP-1 more closely resembled that of human metalloproteinase inhibitor TIMP-2 than TIMP-1 despite closer homology to the human TIMP-1 protein.

A novel multi-segment surface coil for neuro-functional magnetic resonance imaging

The construction of two novel mult-segment (MS) resonators are described. The signal-to-noise ratio (SNR) and B1 homogeneity of the coils are compared with that of a surface coil and a standard quadrature head coil. The images obtained with the MS designs revealed a surface coil-like fall-off in signal with depth. The SNR offered by MS coils was found to be better than the head coil at depths less than approximately 6 cm. Bilateral motor cortex activation on normal subjects performing finger tapping tasks is demonstrated.

Constrained reconstruction applied to 2-D chemical shift imaging

The method of constrained reconstruction, previously applied to magnetic resonance imaging (MRI), is extended to magnetic resonance spectroscopy. This method assumes a model for the MR signal. The model parameters are estimated directly from the phase encoded data. This process obviates the need for the fast Fourier transform (FFT) (which often exhibits limited resolution and ringing artifact). The technique is tested on simulated data, phantom data, and data acquired from human liver in vivo. In each case, constrained reconstruction offers spatial resolution superior to that obtained with the FFT.

Phosphorus nuclear magnetic resonance spectroscopy: in vivo magnesium measurements in the skeletal muscle of normal subjects

31P nuclear magnetic resonance spectroscopy was used to study the skeletal muscle of 33 normal males and 32 females. Free intracellular magnesium levels and the ratios of the phosphorus metabolites were determined. Males had significantly lower free magnesium levels (499.8 microM +/- 26.3 microM vs. 530.7 microM +/- 36.0 microM, P = 0.001, d.f. = 63, analysis of variance). The free magnesium level (rs = -0.5431, P = 0.001) and the phosphocreatin/Inorganic phosphate ratio in males (rs = -0.4102, P = 0.018), and the phosphocreatine/Inorganic phosphate ratio in females (rn = -0.4759, P = 0.009) fell with the increasing Minnesota Heart Health Program Questionnaire score.

Molecular and crystal structure of azadirachtin-H

Azadirachtin-H, isolated from the seed kernels of Azadirachta indica (neem), crystallizes in space group I4, Z = 8, with disordered ethyl acetate solvent filling channels along the fourfold rotation axes. The crystal structure determination showed that the previously reported molecular structure deduced from NMR studies was correct except for the stereochemistry at C(11). Azadirachtin-H, which belongs to a group of C-seco-tetranortriterpenoids (C-seco-limonoids) of great interest for their insect antifeedant and ecdysis-inhibiting activity, has some unusual features: the absence of a carbomethoxy group at C(11); the presence of a cyclic hemiacetal function at C(11); the α-orientation of the hydroxyl group on C(11), opposite to that in all other known azadirachtins with a hydroxyl group on C(11), except azadirachtin-I. There is no intramolecular hydrogen bonding. In this crystal the rotation of the two major moieties of the azadirachtin-H molecule about the single connecting C(8)—C(14) bond is quite different from that in azadirachtin-A, whose crystal structure has recently been determined.

Flow-sensitive magnetic resonance imaging in the evaluation of cerebrospinal fluid leaks

Cerebrospinal fluid (CSF) leaks involving the skull base are associated with considerable morbidity and mortality, and often present a diagnostic challenge. Current diagnostic methods are invasive and cumbersome and involve substantial radiation exposure of the patient. The authors identified seven patients with clinically suspected CSF leaks and evaluated them with a flow-sensitive magnetic resonance imaging (MRI) sequence in addition to more conventional studies. In cases with active CSF leakage, flow characteristics were documented with slow-flow and diffusion-weighted MRI. Unlike current approaches, MRI offers the advantages of rapidity, non-invasiveness, and absence of ionizing radiation. Preliminary results suggest that flow-sensitive MRI may have a role in the evaluation of CSF leaks involving the skull base and temporal bone.