Broad sialic acid usage amongst species D human adenovirus

Human adenoviruses (HAdV) are widespread pathogens causing usually mild infections. The Species D (HAdV-D) cause gastrointestinal tract infections and epidemic keratoconjunctivitis (EKC). Despite being significant pathogens, knowledge around HAdV-D mechanism of cell infection is lacking. Sialic acid (SA) usage has been proposed as a cell infection mechanism for EKC causing HAdV-D. Here we highlight an important role for SA engagement by many HAdV-D. We provide apo state crystal structures of 7 previously undetermined HAdV-D fiber-knob proteins, and structures of HAdV-D25, D29, D30 and D53 fiber-knob proteins in complex with SA. Biologically, we demonstrate that removal of cell surface SA reduced infectivity of HAdV-C5 vectors pseudotyped with HAdV-D fiber-knob proteins, whilst engagement of the classical HAdV receptor CAR was variable. Our data indicates variable usage of SA and CAR across HAdV-D. Better defining these interactions will enable improved development of antivirals and engineering of the viruses into refined therapeutic vectors.

Multi-modal efficacy of a chimeric vesiculovirus expressing the Morreton glycoprotein in sarcoma

Vesiculoviruses are attractive oncolytic virus platforms due to their rapid replication, appreciable transgene capacity, broad tropism, limited preexisting immunity, and tumor selectivity through type I interferon response defects in malignant cells. We developed a synthetic chimeric virus (VMG) expressing the glycoprotein (G) from Morreton virus (MorV) and utilizing the remaining structural genes from vesicular stomatitis virus (VSV). VMG exhibited in vitro efficacy by inducing oncolysis in a broad range of sarcoma subtypes across multiple species. Notably, all cell lines tested showed the ability of VMG to yield productive infection with rapid replication kinetics and induction of apoptosis. Furthermore, pilot safety evaluations of VMG in immunocompetent, non-tumor-bearing mice showed an absence of toxicity with intranasal doses as high as 1e10 50% tissue culture infectious dose (TCID50)/kg. Locoregional administration of VMG in vivo resulted in tumor reduction in an immunodeficient Ewing sarcoma xenograft at doses as low as 2e5 TCID50. In a murine syngeneic fibrosarcoma model, while no tumor inhibition was achieved with VMG, there was a robust induction of CD8+ T cells within the tumor. The studies described herein establish the promising potential for VMG to be used as a novel oncolytic virotherapy platform with anticancer effects in sarcoma.

Characterization of Morreton virus as an oncolytic virotherapy platform for liver cancers

BACKGROUND

Morreton virus (MORV) is an oncolytic Vesiculovirus , genetically distinct from vesicular stomatitis virus (VSV).

AIM

To report that MORV induced potent cytopathic effects (CPEs) in cholangiocarcinoma (CCA) and hepatocellular carcinoma (HCC) in vitro models.

APPROACH AND RESULTS

In preliminary safety analyses, high intranasal doses (up to 10 10 50% tissue culture infectious dose [TCID 50 ]) of MORV were not associated with significant adverse effects in immune competent, non-tumor-bearing mice. MORV was shown to be efficacious in a Hep3B hepatocellular cancer xenograft model but not in a CCA xenograft HuCCT1 model. In an immune competent, syngeneic murine CCA model, single intratumoral treatments with MORV (1 × 10 7 TCID 50 ) triggered a robust antitumor immune response leading to substantial tumor regression and disease control at a dose 10-fold lower than VSV (1 × 10 8 TCID 50 ). MORV led to increased CD8 + cytotoxic T cells without compensatory increases in tumor-associated macrophages and granulocytic or monocytic myeloid-derived suppressor cells.

CONCLUSIONS

Our findings indicate that wild-type MORV is safe and can induce potent tumor regression via immune-mediated and immune-independent mechanisms in HCC and CCA animal models without dose limiting adverse events. These data warrant further development and clinical translation of MORV as an oncolytic virotherapy platform.

Development of a low-seroprevalence, αvβ6 integrin-selective virotherapy based on human adenovirus type 10

Oncolytic virotherapies (OV) hold immense clinical potential. OV based on human adenoviruses (HAdV) derived from HAdV with naturally low rates of pre-existing immunity will be beneficial for future clinical translation. We generated a low-seroprevalence HAdV-D10 serotype vector incorporating an αvβ6 integrin-selective peptide, A20, to target αvβ6-positive tumor cell types. HAdV-D10 has limited natural tropism. Structural and biological studies of HAdV-D10 knob protein highlighted low-affinity engagement with native adenoviral receptors CAR and sialic acid. HAdV-D10 fails to engage blood coagulation factor X, potentially eliminating "off-target" hepatic sequestration in vivo. We engineered an A20 peptide that selectively binds αvβ6 integrin into the DG loop of HAdV-D10 fiber knob. Assays in αvβ6+ cancer cell lines demonstrated significantly increased transduction mediated by αvβ6-targeted variants compared with controls, confirmed microscopically. HAdV-D10.A20 resisted neutralization by neutralizing HAdV-C5 sera. Systemic delivery of HAdV-D10.A20 resulted in significantly increased GFP expression in BT20 tumors. Replication-competent HAdV-D10.A20 demonstrated αvβ6 integrin-selective cell killing in vitro and in vivo. HAdV-D10 possesses characteristics of a promising virotherapy, combining low seroprevalence, weak receptor interactions, and reduced off-target uptake. Incorporation of an αvβ6 integrin-selective peptide resulted in HAdV-D10.A20, with significant potential for clinical translation.

Synergistic combination of cytotoxic chemotherapy and cyclin-dependent kinase 4/6 inhibitors in biliary tract cancers

BACKGROUND AND AIMS

Biliary tract cancers (BTCs) are uncommon, but highly lethal, gastrointestinal malignancies. Gemcitabine/cisplatin is a standard-of-care systemic therapy, but has a modest impact on survival and harbors toxicities, including myelosuppression, nephropathy, neuropathy, and ototoxicity. Whereas BTCs are characterized by aberrations activating the cyclinD1/cyclin-dependent kinase (CDK)4/6/CDK inhibitor 2a/retinoblastoma pathway, clinical use of CDK4/6 inhibitors as monotherapy is limited by lack of validated biomarkers, diffident preclinical efficacy, and development of acquired drug resistance. Emerging studies have explored therapeutic strategies to enhance the antitumor efficacy of CDK4/6 inhibitors by the combination with chemotherapy regimens, but their mechanism of action remains elusive.

APPROACH AND RESULTS

Here, we report in vitro and in vivo synergy in BTC models, showing enhanced efficacy, reduced toxicity, and better survival with a combination comprising gemcitabine/cisplatin and CDK4/6 inhibitors. Furthermore, we demonstrated that abemaciclib monotherapy had only modest efficacy attributable to autophagy-induced resistance. Notably, triplet therapy was able to potentiate efficacy through elimination of the autophagic flux. Correspondingly, abemaciclib potentiated ribonucleotide reductase catalytic subunit M1 reduction, resulting in sensitization to gemcitabine.

CONCLUSIONS

As such, these data provide robust preclinical mechanistic evidence of synergy between gemcitabine/cisplatin and CDK4/6 inhibitors and delineate a path forward for translation of these findings to preliminary clinical studies in advanced BTC patients.

ChAdOx1 interacts with CAR and PF4 with implications for thrombosis with thrombocytopenia syndrome

Vaccines derived from chimpanzee adenovirus Y25 (ChAdOx1), human adenovirus type 26 (HAdV-D26), and human adenovirus type 5 (HAdV-C5) are critical in combatting the severe acute respiratory coronavirus 2 (SARS-CoV-2) pandemic. As part of the largest vaccination campaign in history, ultrarare side effects not seen in phase 3 trials, including thrombosis with thrombocytopenia syndrome (TTS), a rare condition resembling heparin-induced thrombocytopenia (HIT), have been observed. This study demonstrates that all three adenoviruses deployed as vaccination vectors versus SARS-CoV-2 bind to platelet factor 4 (PF4), a protein implicated in the pathogenesis of HIT. We have determined the structure of the ChAdOx1 viral vector and used it in state-of-the-art computational simulations to demonstrate an electrostatic interaction mechanism with PF4, which was confirmed experimentally by surface plasmon resonance. These data confirm that PF4 is capable of forming stable complexes with clinically relevant adenoviruses, an important step in unraveling the mechanisms underlying TTS.

To clot or not to clot? Ad is the question-Insights on mechanisms related to vaccine-induced thrombotic thrombocytopenia

Vaccine-induced immune thrombotic thrombocytopenia (VITT) has caused global concern. VITT is characterized by thrombosis and thrombocytopenia following COVID-19 vaccinations with the AstraZeneca ChAdOx1 nCov-19 and the Janssen Ad26.COV2.S vaccines. Patients present with thrombosis, severe thrombocytopenia developing 5-24 days following first dose of vaccine, with elevated D-dimer, and PF4 antibodies, signifying platelet activation. As of June 1, 2021, more than 1.93 billion COVID-19 vaccine doses had been administered worldwide. Currently, 467 VITT cases (0.000024%) have been reported across the UK, Europe, Canada, and Australia. Guidance on diagnosis and management of VITT has been reported but the pathogenic mechanism is yet to be fully elucidated. Here, we propose and discuss potential mechanisms in relation to adenovirus induction of VITT. We provide insights and clues into areas warranting investigation into the mechanistic basis of VITT, highlighting the unanswered questions. Further research is required to help solidify a pathogenic model for this condition.

In Vitro and In Vivo Evaluation of Human Adenovirus Type 49 as a Vector for Therapeutic Applications

The human adenovirus phylogenetic tree is split across seven species (A-G). Species D adenoviruses offer potential advantages for gene therapy applications, with low rates of pre-existing immunity detected across screened populations. However, many aspects of the basic virology of species D-such as their cellular tropism, receptor usage, and in vivo biodistribution profile-remain unknown. Here, we have characterized human adenovirus type 49 (HAdV-D49)-a relatively understudied species D member. We report that HAdV-D49 does not appear to use a single pathway to gain cell entry, but appears able to interact with various surface molecules for entry. As such, HAdV-D49 can transduce a broad range of cell types in vitro, with variable engagement of blood coagulation FX. Interestingly, when comparing in vivo biodistribution to adenovirus type 5, HAdV-D49 vectors show reduced liver targeting, whilst maintaining transduction of lung and spleen. Overall, this presents HAdV-D49 as a robust viral vector platform for ex vivo manipulation of human cells, and for in vivo applications where the therapeutic goal is to target the lung or gain access to immune cells in the spleen, whilst avoiding liver interactions, such as intravascular vaccine applications.

The Fiber Knob Protein of Human Adenovirus Type 49 Mediates Highly Efficient and Promiscuous Infection of Cancer Cell Lines Using a Novel Cell Entry Mechanism

The human adenovirus (HAdV) phylogenetic tree is diverse, divided across seven species and comprising over 100 individual types. Species D HAdV are rarely isolated with low rates of preexisting immunity, making them appealing for therapeutic applications. Several species D vectors have been developed as vaccines against infectious diseases, where they induce robust immunity in preclinical models and early phase clinical trials. However, many aspects of the basic virology of species D HAdV, including their basic receptor usage and means of cell entry, remain understudied. Here, we investigated HAdV-D49, which previously has been studied for vaccine and vascular gene transfer applications. We generated a pseudotyped HAdV-C5 presenting the HAdV-D49 fiber knob protein (HAdV-C5/D49K). This pseudotyped vector was efficient at infecting cells devoid of all known HAdV receptors, indicating HAdV-D49 uses an unidentified cellular receptor. Conversely, a pseudotyped vector presenting the fiber knob protein of the closely related HAdV-D30 (HAdV-C5/D30K), differing in four amino acids from HAdV-D49, failed to demonstrate the same tropism. These four amino acid changes resulted in a change in isoelectric point of the knob protein, with HAdV-D49K possessing a basic apical region compared to a more acidic region in HAdV-D30K. Structurally and biologically we demonstrate that HAdV-D49 knob protein is unable to engage CD46, while potential interaction with coxsackievirus and adenovirus receptor (CAR) is extremely limited by extension of the DG loop. HAdV-C5/49K efficiently transduced cancer cell lines of pancreatic, breast, lung, esophageal, and ovarian origin, indicating it may have potential for oncolytic virotherapy applications, especially for difficult to transduce tumor types.IMPORTANCE Adenoviruses are powerful tools experimentally and clinically. To maximize efficacy, the development of serotypes with low preexisting levels of immunity in the population is desirable. Consequently, attention has focused on those derived from species D, which have proven robust vaccine platforms. This widespread usage is despite limited knowledge in their basic biology and cellular tropism. We investigated the tropism of HAdV-D49, demonstrating that it uses a novel cell entry mechanism that bypasses all known HAdV receptors. We demonstrate, biologically, that a pseudotyped HAdV-C5/D49K vector efficiently transduces a wide range of cell lines, including those presenting no known adenovirus receptor. Structural investigation suggests that this broad tropism is the result of a highly basic electrostatic surface potential, since a homologous pseudotyped vector with a more acidic surface potential, HAdV-C5/D30K, does not display a similar pantropism. Therefore, HAdV-C5/D49K may form a powerful vector for therapeutic applications capable of infecting difficult to transduce cells.

Identification of folate receptor α (FRα) binding oligopeptides and their evaluation for targeted virotherapy applications

Oncolytic virotherapies (OV) based on human adenoviral (HAdV) vectors hold significant promise for the treatment of advanced ovarian cancers where local, intraperitoneal delivery to tumour metastases is feasible, bypassing many complexities associated with intravascular delivery. The efficacy of HAdV-C5-based OV is hampered by a lack of tumour selectivity, where the primary receptor, hCAR, is commonly downregulated during malignant transformation. Conversely, folate receptor alpha (FRα) is highly expressed on ovarian cancer cells, providing a compelling target for tumour selective delivery of virotherapies. Here, we identify high-affinity FRα-binding oligopeptides for genetic incorporation into HAdV-C5 vectors. Biopanning identified a 12-mer linear peptide, DWSSWVYRDPQT, and two 7-mer cysteine-constrained peptides, CIGNSNTLC and CTVRTSAEC that bound FRα in the context of the phage particle. Synthesised lead peptide, CTVRTSAEC, bound specifically to FRα and could be competitively inhibited with folic acid. To assess the capacity of the elucidated FRα-binding oligopeptides to target OV to FRα, we genetically incorporated the peptides into the HAdV-C5 fiber-knob HI loop including in vectors genetically ablated for hCAR interactions. Unfortunately, the recombinant vectors failed to efficiently target transduction via FRα due to defective intracellular trafficking following entry via FRα, indicating that whilst the peptides identified may have potential for applications for targeted drug delivery, they require additional refinement for targeted virotherapy applications.

Oncolytic Virus with Attributes of Vesicular Stomatitis Virus and Measles Virus in Hepatobiliary and Pancreatic Cancers

Recombinant vesicular stomatitis virus (VSV)-fusion and hemagglutinin (FH) was developed by substituting the promiscuous VSV-G glycoprotein (G) gene in the backbone of VSV with genes encoding for the measles virus envelope proteins F and H. Hybrid VSV-FH exhibited a multifaceted mechanism of cancer-cell killing and improved neurotolerability over parental VSV in preclinical studies. In this study, we evaluated VSV-FH in vitro and in vivo in models of hepatobiliary and pancreatic cancers. Our results indicate that high intrahepatic doses of VSV-FH did not result in any significant toxicity and were well tolerated by transgenic mice expressing the measles virus receptor CD46. Furthermore, a single intratumoral treatment with VSV-FH yielded improved survival and complete tumor regressions in a proportion of mice in the Hep3B hepatocellular carcinoma model but not in mice xenografted with BxPC-3 pancreatic cancer cells. Our preliminary findings indicate that VSV-FH can induce potent oncolysis in hepatocellular and pancreatic cancer cell lines with concordant results in vivo in hepatocellular cancer and discordant in pancreatic cancer without the VSV-mediated toxic effects previously observed in laboratory animals. Further study of VSV-FH as an oncolytic virotherapy is warranted in hepatocellular carcinoma and pancreatic cancer to understand broader applicability and mechanisms of sensitivity and resistance.

Human adenovirus type 26 uses sialic acid-bearing glycans as a primary cell entry receptor

Adenoviruses are clinically important agents. They cause respiratory distress, gastroenteritis, and epidemic keratoconjunctivitis. As non-enveloped, double-stranded DNA viruses, they are easily manipulated, making them popular vectors for therapeutic applications, including vaccines. Species D adenovirus type 26 (HAdV-D26) is both a cause of EKC and other diseases and a promising vaccine vector. HAdV-D26-derived vaccines are under investigation as protective platforms against HIV, Zika, and respiratory syncytial virus infections and are in phase 3 clinical trials for Ebola. We recently demonstrated that HAdV-D26 does not use CD46 or Desmoglein-2 as entry receptors, while the putative interaction with coxsackie and adenovirus receptor is low affinity and unlikely to represent the primary cell receptor. Here, we establish sialic acid as a primary entry receptor used by HAdV-D26. We demonstrate that removal of cell surface sialic acid inhibits HAdV-D26 infection, and provide a high-resolution crystal structure of HAdV-D26 fiber-knob in complex with sialic acid.

Diversity within the adenovirus fiber knob hypervariable loops influences primary receptor interactions

Adenovirus based vectors are of increasing importance for wide ranging therapeutic applications. As vaccines, vectors derived from human adenovirus species D serotypes 26 and 48 (HAdV-D26/48) are demonstrating promising efficacy as protective platforms against infectious diseases. Significant clinical progress has been made, yet definitive studies underpinning mechanisms of entry, infection, and receptor usage are currently lacking. Here, we perform structural and biological analysis of the receptor binding fiber-knob protein of HAdV-D26/48, reporting crystal structures, and modelling putative interactions with two previously suggested attachment receptors, CD46 and Coxsackie and Adenovirus Receptor (CAR). We provide evidence of a low affinity interaction with CAR, with modelling suggesting affinity is attenuated through extended, semi-flexible loop structures, providing steric hindrance. Conversely, in silico and in vitro experiments are unable to provide evidence of interaction between HAdV-D26/48 fiber-knob with CD46, or with Desmoglein 2. Our findings provide insight into the cell-virus interactions of HAdV-D26/48, with important implications for the design and engineering of optimised Ad-based therapeutics.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Ad5NULL-A20: A Tropism-Modified, αvβ6 Integrin-Selective Oncolytic Adenovirus for Epithelial Ovarian Cancer Therapies

Purpose: Virotherapies are maturing in the clinical setting. Adenoviruses (Ad) are excellent vectors for the manipulability and tolerance of transgenes. Poor tumor selectivity, off-target sequestration, and immune inactivation hamper clinical efficacy. We sought to completely redesign Ad5 into a refined, tumor-selective virotherapy targeted to αvβ6 integrin, which is expressed in a range of aggressively transformed epithelial cancers but nondetectable in healthy tissues.Experimental Design: Ad5_NULL-A20 harbors mutations in each major capsid protein to preclude uptake via all native pathways. Tumor-tropism via αvβ6 targeting was achieved by genetic insertion of A20 peptide (NAVPNLRGDLQVLAQKVART) within the fiber knob protein. The vector's selectivity in vitro and in vivo was assessed.Results: The tropism-ablating triple mutation completely blocked all native cell entry pathways of Ad5_NULL-A20 via coxsackie and adenovirus receptor (CAR), αvβ3/5 integrins, and coagulation factor 10 (FX). Ad5_NULL-A20 efficiently and selectively transduced αvβ6⁺ cell lines and primary clinical ascites-derived EOC ex vivo, including in the presence of preexisting anti-Ad5 immunity. In vivo biodistribution of Ad5_NULL-A20 following systemic delivery in non-tumor-bearing mice was significantly reduced in all off-target organs, including a remarkable 10⁷-fold reduced genome accumulation in the liver compared with Ad5. Tumor uptake, transgene expression, and efficacy were confirmed in a peritoneal SKOV3 xenograft model of human EOC, where oncolytic Ad5_NULL-A20-treated animals demonstrated significantly improved survival compared with those treated with oncolytic Ad5.Conclusions: Oncolytic Ad5_NULL-A20 virotherapies represent an excellent vector for local and systemic targeting of αvβ6-overexpressing cancers and exciting platforms for tumor-selective overexpression of therapeutic anticancer modalities, including immune checkpoint inhibitors. Clin Cancer Res; 24(17); 4215-24. ©2018 AACR.

Doctors, capitation payments and the first Labour Government

The Health Funding Authority (HFA) proposes to change the way general practitioners (GPs) are paid for patient visits. Most doctors charge patients a fee for each visit, minus a subsidy from the general medical services benefit where applicable for those holding community services cards. Seeking to set strict limits on costs, the HFA proposes a block or 'capitation' payment for all practices based on the number and age of patients. Almost 60 years ago the first Labour government proposed just such a payment for the general practitioner service outlined in the Social Security Act 1938. Led by the local branch of the British Medical Association, doctors eventually persuaded the government to offer instead a statutory fee-for-service. They could charge their patients over and above this fee. This article shows how and why the Labour Government compromised in this way so that doctors' payment did not come wholly from the state, and that they remained independent professionals.

Identification of n-acetylmethamphetamine in a sample of illicitly synthesized methamphetamine

Analysis of illicit methamphetamine samples revealed the presence of a hitherto unreported impurity. This was identified as N-acetylmethamphetamine by synthesis and GC-MS. This impurity is believed to arise by transesterification of methamphetamine during reflux with propyl acetate. Other circumstantial evidence and intelligence data indicate that propyl acetate was used to increase yields of methamphetamine hydrochloride by azeotropic removal of water remaining after salt formation with aqueous hydrochloric acid.

Metal Complexes of 1,3-Bis(Pyridin-2-yl)pyrazole: Spectral, Magnetic and Structural Studies

Bis(ligand)iron(II) and nickel(II) complexes of the asymmetric tridentate ligand 1,3-bis(pyridin-2-yl) pyrazole , L, have been prepared. The iron(II) complex, [FeL2] [PF6]2, is high-spin in the solid state over the temperature range 304-102 K, with a magnetic moment of 5.27 BM at room temperature. The crystal structure of bis (1,3-bis(pyridin-2-yl) pyrazole )iron(II) bis (hexafluorophosphate ) has been determined by single-crystal X-ray diffractometry. The compound crystallized as yellow prisms, with the structure being disordered in the tetragonal space group P421c with Z = 2. Crystal data a = b = 8.785(1) Ǻ, c = 19.804(6) Ǻ. The iron(II) centre is in an N6 environment, where the six donor nitrogen atoms are provided by the two tridentate heterocyclic ligands. The complex cation has an approximately octahedral structure exhibiting tetragonal compression. The observed Fe-N(pyridine) and Fe-N( pyrazole ) distances are 2.308(4) and 2.019(7) Ǻ respectively, with the Fe-N(pyridine) distance being the longest observed to date.

The Crystal Structure of Bis(2,2′:6′,2″-terpyridine)nickel(II) Perchlorate Hydrate

The crystal structure of bis (2,2′:6′,2″-terpyridine)nickel(II) bis (perchlorate) hydrate has been determined by single-crystal X-ray diffractometry . The compound is monoclinic, space group P21, with two molecules in a unit cell of dimensions a 8.827(4), b 8.910(2), c 20.148(9) Ǻ, β 98.71(2)°. The structure was refined by least-squares to a residual of 0.065 for 2184 observed reflections. The compound is found to be isomorphic with the iron(II) analogue previously reported: the cation has approximate D2d symmetry, with the main distortion from octahedral symmetry being an axial compression. Both the solid state reflectance and solution spectra have been measured and some significant differences are noted.

X-ray and scanning electron microscopic analysis of the structural composition of tear ferns

Dried tears from keratoconjunctivitis sicca eyes fail to exhibit the fern-like crystallization patterns observed with tears from eyes with normal tear function. To test our hypothesis that the extent of ferning depends on the ratio of salts to protein and mucin in the tear sample, dried tears from six normal subjects were subjected to scanning electron microscopy (SEM) and X-ray analyses. X-ray diffraction identified sodium chloride and potassium chloride as the major components of tear fern crystals. X-ray fluorescence detected the elements potassium, chlorine, calcium, and sulfur in the dried tear samples, with sulfur indicating the presence of protein and/or mucin. As well as confirming the presence of cubic fern nuclei, SEM revealed two kinds of material, having crystalline and globular appearances, that are hypothesized to be composed of salts and protein/mucin, respectively. Globular material appeared to block extension of crystal fern arms or to coat crystalline material, but did not crystallize. These findings suggest that tear fern crystals are composed of sodium and potassium chloride, with proteinaceous material controlling crystallization indirectly by coating crystal faces and blocking fern extension. This structural composition is consistent with the hypothesis that the ratio of salt to macromolecular species is an important determinant of tear ferning.

The Crystal and Molecular Structures of Bis(diethyldithiocarbamato)platinum(II) and Bis[di(2-hydroxyethyl)dithiocarbamato]platinum(II)

The structures of [Pt(S2CN(C2H5)2)2] (1) and [Pt(S2CN(C2H4OH)2)2] (2) have been determined by single-crystal X-ray diffractometry. Compound (1) crystallizes in the tetragonal space group P42/n, a 16.4692(10),c 6.2160(6) � (Z = 4); R was 0.029 for 1012 observed reflections. Compound (2) is monoclinic, space group Pc, a 6-0663(11), b 1.1784(15), c 12.5740(21) � ,β92.569(8)� (Z = 2); R was 0.019 for 1573 observed reflections. The presence of electron-withdrawing groups in the ligands of (2) appears to have little effect on the Pt-S distances but causes an increase in the C-N bond length, with the C-N bond lengths being significantly different at the 2 σ level.

Refined atomic structures of N9 subtype influenza virus neuraminidase and escape mutants

The crystal structure of the N9 subtype neuraminidase of influenza virus was refined by simulated annealing and conventional techniques to an R-factor of 0.172 for data in the resolution range 6.0 to 2.2 A. The r.m.s. deviation from ideal values of bond lengths is 0.014 A. The structure is similar to that of N2 subtype neuraminidase both in secondary structure elements and in their connections. The three-dimensional structures of several escape mutants of neuraminidase, selected with antineuraminidase monoclonal antibodies, are also reported. In every case, structural changes associated with the point mutation are confined to the mutation site or to residues that are spatially immediately adjacent to it. The failure of antisera to cross-react between N2 and N9 subtypes may be correlated with the absence of conserved, contiguous surface structures of area 700 A2 or more.

Palladium(II) Complexes of Tridentate Ligands. The Crystal Structure of Chloro[2,6-di(2-imidazolin-2-yl)pyridine]palladium(II) Chloride

Mono(ligand) palladium(II) complexes of 2,6-di-(thiazol-2-yl)pyridine (1a), 2,6-di(4-methylthia-zol-2-yl)pyridine (1b), 2,6-di(thiazol-4-yl)pyridine (2a), 2,6-di(imidazolin-2-yl]pyridine (3) and 2,6-di(benzimidazol-2-yl)pyridine (4a) of the general formula [ PdLCl ] Cl have been prepared. Stoichiometries have been confirmed by C, H, N and Pd analyses; the presence of solvate molecules has been confirmed by thermogravimetry . The crystal structure of [ PdLCl ]Cl.H2O, L = (3), has been determined by single-crystal X-ray diffractometry. The compound crystallizes in an orthorhombic space group, Pna21, a 7.427(2), b 21.932(3), c 8.935(1)Ǻ. The geometry of the complex cation is approximately square planar. The imidazolinyl rings closely approach planarity which is imposed by the delocalization of π-density in the NCN moiety. A hydrogen-bonding scheme involving the imino hydrogens of the ligand, chloride ions and the water molecule is present. The structure was refined by least-squares methods to a residual of 0.018 for 1273 reflections.

Iron(II) and Nickel(II) Complexes of 2,6-Di(thiazol-2-yl)pyridine and Related Ligands

2,6-Di(thiazol-2-yl]pyridine (1a), 2,6-di(4-methylthiazol-2-yl)pyridine (1b) and 2,6-di(2-imid-azolin-2-yl)pyridine (3) have been prepared by the reaction of pyridine-2,6-dicarbothioamide with bromoacetaldehyde diethyl acetal, bromoacetone and ethylenediamine, severally. Bis ( ligand ) iron(II) and nickel(II) complexes of all ligands have been prepared. The bis ( ligand ) iron(II) complexes of (1a) and (3) are low-spin whereas that of (1b) is high-spin at room temperature and undergoes a thermally induced spin transition. The field strengths of the ligands , determined from the spectra of their nickel(II) complexes, correlate well with the observed magnetic behaviour of their iron(II) complexes. The field strengths of (1a) and (1b) are found to be marginally less than those of the isomeric ligands 2,6-di(thiazol-4-yl)pyridine (2a) and 2,6-di(2-methylthiazol-4-yl)pyridine (2b).

Changes in collagen stability and folding in lethal perinatal osteogenesis imperfecta. The effect of alpha 1 (I)-chain glycine-to-arginine substitutions

The effect of glycine-to-arginine mutations in the alpha 1 (I)-chain on collagen triple-helix structure in lethal perinatal osteogenesis imperfecta was studied by determination of the helix denaturation temperature and by computerized molecular modelling. Arginine substitutions at glycine residues 391 and 667 resulted in similar small decreases in helix stability. Molecular modelling suggested that the glycine-to-arginine-391 mutant resulted in only a relatively small localized disruption to the helix structure. Thus the glycine-to-arginine substitutions may lead to only a small structural abnormality of the collagen helix, and it is most likely that the over-modification of lysine, poor secretion, increased degradation and other functional sequelae result from a kinetic defect in collagen helix formation resulting from the mutation.

Three-dimensional structures of influenza virus neuraminidase-antibody complexes

X-ray diffraction analysis of crystals of a monoclonal Fab fragment NC41 bound to a viral antigen, influenza virus neuraminidase, shows an epitope involving five surface loops of the antigen. In addition it reveals an unusual pairing pattern between the domains of light and heavy chains in the variable module of the antibody. We interpret this result to imply that association with antigen can induce changes in the quaternary structure of the Fab, through a sliding of domains at the variable light/variable heavy chains (VL-VH) interface. In addition, Fab binding has altered the conformation of some of the surface loops of the antigen. The structure of the NC10 Fab-neuraminidase complex has now also been solved. It binds an epitope that overlaps the NC41 epitope. In this structure, there is no electron density for the C-module of the Fab fragment, implying it is disordered in the crystal lattice. The implications of these, and other antibody-antigen structures, for immune recognition are discussed.

Structural, Magnetic and Spectral Properties of Iron(II) and Nickel(II) Complexes of N1-(Pyridin-2-yl)-3,5-dimethylpyrazole

Iron(II) and nickel(II) complexes of N1-(pyridin-2-yl)-3,5-dimethylpyrazole (L) are described. Salts of [FeL3]2+ undergo a reversible temperature-induced singlet (1A1) ↔ quintet (5T2) transition, both in the solid state and in solution. The singlet- quintet change in acetone solution is characterized by ΔH = 25 � 2 kJ mol-1 and ΔS = 95 � 5 J K-1 mol-1. Mossbauer spectral data for solid [FeL3] [BF4]2 confirm a change in ground state for the metal atom with change in temperature and indicate two low-spin species at low temperatures and two high-spin species at elevated temperatures. The average M-N bond length changes accompanying the spin change have been estimated as 0.19 � from data obtained by determination of the structures of [FeL3][ClO4]2 at 135 K and 294 K and of [NiL3][BF4]2 at 294 K by single-crystal X-ray diffractometry. The crystals were all refined as disordered structures in space group P3c1 with Z = 2. Crystal data: [FeL3] [ClO4]2 at 294 K, a = b 10.489(2), 17.521(5) � ;[FeL3][ClO4]2 at 135 K, a = b 10.355(3), c 17.464(5) � ; [NiL3] [BF4]2 at 294 K, a = b 10.404(3), c 17.618(8) � .

Antigenic structure and variation in an influenza virus N9 neuraminidase

We previously determined, by X-ray crystallography, the three-dimensional structure of a complex between influenza virus N9 neuraminidase (NA) and the Fab fragments of monoclonal antibody NC-41 [P. M. Colman, W. G. Laver, J. N. Varghese, A. T. Baker, P. A. Tulloch, G. M. Air, and R. G. Webster, Nature (London) 326:358-363, 1987]. This antibody binds to an epitope on the upper surface of the NA which is made up of four polypeptide loops over an area of approximately 600 A2 (60 nm2). We now describe properties of NC-41 and other monoclonal antibodies to N9 NA and the properties of variants selected with these antibodies (escape mutants). All except one of the escape mutants had single amino acid sequence changes which affected the binding of NC-41 and which therefore are located within the NC-41 epitope. The other one had a change outside the epitope which did not affect the binding of any of the other antibodies. All the antibodies which selected variants inhibited enzyme activity with fetuin (molecular weight, 50,000) as the substrate, but only five, including NC-41, also inhibited enzyme activity with the small substrate N-acetylneuramin-lactose (molecular weight, 600). These five probably inhibited enzyme activity by distorting the catalytic site of the NA. Isolated, intact N9 NA molecules form rosettes in the absence of detergent, and these possess high levels of hemagglutinin activity (W.G. Laver, P.M. Colman, R.G. Webster, V.S. Hinshaw, and G.M. Air, Virology 137:314-323, 1984). The enzyme activity of N9 NA was inhibited efficiently by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, whereas hemagglutinin activity was unaffected. The NAs of several variants with sequence changes in the NC-41 epitope lost hemagglutinin activity without any loss of enzyme activity, suggesting that the two activities are associated with separate sites on the N9 NA head.

Three-dimensional structure of a complex of antibody with influenza virus neuraminidase

The structure of a complex between influenza virus neuraminidase and an antibody displays features inconsistent with the inflexible 'lock and key' model of antigen-antibody binding. The structure of the antigen changes on binding, and that of the antibody may also change; the interaction therefore has some of the character of a handshake.

Three-dimensional structure of neuraminidase of subtype N9 from an avian influenza virus

Neuraminidases from different subtypes of influenza virus are characterized by the absence of serological cross-reactivity and an amino acid sequence homology of approximately 50%. The three-dimensional structure of the neuraminidase antigen of subtype N9 from an avian influenza virus (A/tern/Australia/G70c/75) has been determined by X-ray crystallography and shown to be folded similarly to neuraminidase of subtype N2 isolated from a human influenza virus. This result demonstrates that absence of immunological cross-reactivity is no measure of dissimilarity of polypeptide chain folding. Small differences in the way in which the subunits are organized around the molecular fourfold axis are observed. Insertions and deletions with respect to subtype N2 neuraminidase occur in four regions, only one of which is located within the major antigenic determinants around the enzyme active site.

Metal-Complexes of Thiocholinate, -SCH2CH2Nme3+. I. Preparation and Crystal-Structure of Pentakis(Thiocholinato)Dilead(II) Hexafluorophosphate

Aqueous solutions containing lead(II) and deprotonated thiocholine contain water-soluble homoleptic lead thiolates , which crystallize as yellow needles of [Pb2(SCH2CH2NMe3)5] (PF6)4 in the presence of PF6-, but crystallize [ Pb (SCH2CH2NMe3)2](ClO4)2 with 1 : 2 stoichiometry in the presence of ClO4-. Crystalline [Pb2(SCH2CH2NMe3)5](PF6)4 contains almost linear chains composed of end-linked {(SR)2Pb(μ-SR) Pb (SR)2} coordination units, within which the primary Pb -S coordination (mean 2.73 Ǻ, sample e.s.d . 0.10 Ǻ) is orthogonal trigonal (S- Pb -S, mean 88.9°, sample e.s.d .3.7°) at each lead atom. Within the {Pb2(SR)5} unit there is one double bridge with two rimary bonds, and one double bridge involving one secondary Pb --S connection (mean 3.23 Ǻ, sample e.s.d . 0.12 Ǻ). Three double-bridges involving secondary Pb --S coordination link the ends of the dimetallic units, and consequently bis - and tris -double thiolate bridges alternate along the chain. Overall coordination at each lead atom is pseudo-octahedral, with one non-bonding electron pair and two cis secondary Pb --S bonds. The cationic tails of the ligands radiate from the chains into a matrix of PF6- ions, and the chains are approximately hexagonally close-packed with a separation of 14.4 Ǻ. Along the b axis there are homogeneous stacks of the ammonium functions, the anions, and the Pb, S chains, with a pseudo-symmetric repeat of b/3 in each stack, allowing disorder due to stacking faults. This disorder has been adequately modelled in the refinement, which also incorporated back-Fourier-transform techniques to avoid inaccuracies due to spherically disordered PF6- ions. Crystal data: Cc, 25.535(8), b 43.13(1), c 15.123(5)Ǻ, β 100.36(9)°, Z 12 (× Pb2S5C25H65N5P4F24), 3585 observed data, R 0.066.

Iron(II) and Nickel(II) Complexes of 2,6-Di(Thiazol-4-Yl)Pyridine and Related Ligands: Magnetic, Spectral and Structural Studies

2,6-Di(thiazol-4-yl)pyridine (1a), 2,6-di(2-methylthiazol-4-yl)pyridine (1b) and 2,6-di(2-phenylthiazol-4-yl)pyridine (1c) have been prepared by Hantzsch syntheses from 2,6-di(ω- bromoacetyl )pyridine and the appropriate thioamide. Bis ( ligand ) iron(II) and nickel(II) complexes of (1a) and (1b) have been prepared but no metal complexes of (1c) were isolated. The bis ( ligand ) iron(II) complexes of (1a) are low-spin whereas those of (1b) undergo thermally induced spin-transitions, both in the solid state and solution. The field strengths of the ligands , determined from the spectra of their nickel(II) complexes, correlate well with the observed magnetic behaviour of their iron(II) complexes. The structure of [FeL2][ClO4]2.H2O, L = (1a), was determined by single-crystal X-ray diffractometry . The complex cation has the meridional configuration with the ligand functioning as an approximately planar tridentate. The structural parameters relating to the Fe-N6 coordination sphere are remarkably similar to those found for bis (2,2′:6′, 2′- terpyridine )iron(II) bis ( perchlorate ) monohydrate.

Iron(II) and Nickel(II) Complexes of 4,4′-Bithiazole: Spectral, Magnetic and Structural Studies

Iron(II) and nickel(II) complexes of 4,4′-bithiazole (L) have been prepared. Salts of [FeL3]2+ undergo thermally induced spin-state transitions, in the solid state and in solution. The structures of both [FeL3] [ClO4]2 and [NiL3] [ClO4]2 have been determined by single-crystal X-ray diffractometry . The compounds are isomorphous : monoclinic with space group C2/c, with four molecules in a unit cell of dimensions (Fe, Ni): a 17.250(3), 17.379(3); b 9.8168(9), 9.685(1); c 16.867(3), 17.135(3) Ǻ; β 105.943(7), 104.860(7)°. The structures were refined by least-squares methods to residuals of 0.033 (Fe) and 0.033 (Ni) for 1917 (Fe) and 2017 (Ni) observed reflections. The cations have a distorted octahedral structure with the average Ni-N bond length being 0.11 Ǻ longer than the average Fe-N bond length.

Crystal Structure of Bis(2,2':6',2"-terpyridine)iron(II) Bis(perchlorate) Hydrate

The crystal structure of bis (2,2′:6′,2″-terpyridine)iron(II) bis ( perchlorate ) hydrate has been determined by single-crystal X-ray diffractometry . The compound is monoclinic, space group P21, with two molecules in a unit cell of dimensions a 8.830(3), b 8.914(1), c 20.037(6)Ǻ, β 100.82(1)°. The structure was refined by least squares to a residual of 0.048 for 2007 observed reflections. The cation is found to have approximate D2d symmetry, with the principal distortion from octahedral symmetry being an axial compression. The lattice water molecule and anions are oriented towards the interligand pockets of the cation. There is hydrogen bonding between the water molecule and one anion.

Five-coordination in complexes of 2-(3,5-Dimethylpyrazol-1-yl)quinoline, a sterically hindered diimine system

The bidentate diimine-type ligand 2-(3,5-dimethylpyrazol-1-yl)quinoline forms mono complexes with the bivalent chlorides of iron, cobalt, nickel and copper. These complexes are magnetically dilute, but electronic spectral data indicate that, except for the cobalt complex which is tetrahedral, the metal atoms are five-coordinate and hence a chloro-bridged structure is proposed. The cobalt(II) complex readily adds a water molecule, and structure determination by X-ray diffraction shows that the complex aquadichloro[2-(3,5-dimethylpyrazol-1-yl)quinoline]cobalt(II) is monomeric and five-coordinate, the coordination environment approximating trigonal bipyramidal.

The crystal structure of Bis[2-(pyridin-2-ylamino)-4-(pyridin-2-yl)thiazole]iron(II) Bis(tetrafluoroborate) trihydrate

The crystal structure of an iron(II) complex of 2-(pyridin-2-ylamino)-4-(pyridin-2-yl)tliazoe (paptH) has been determined by single-crystal X-ray diffractometry. [Fe(paptH)2] [BF4]2.3H2O is monoclinic, space group P21/c, with Z = 4 in a cell of dimensions a 8.968(6), b 9.038(4), c 41.15(2)�, β 94.81(2)�. The disordered structure was refined to a residual R 0.0826 for 2549 observed reflections. The ligands and anions are orientationally disordered, and the waters of crystallization are positionally disordered. Comprehensive constrained refinement, with 220 parameters for 139 atom positions, produced reliable geometry. The complex cation has a distorted octahedral structure of meridional configuration with both paptH ligands functioning as tridentates.

Nickel(II) and iron(II) complexes of 4-(Pyridin-2-yl)thiazole: Spectral, magnetic and structural studies

Iron(II) and nickel(II) complexes of 4-(pyridin-2-yl)thiazole (L) have been prepared. The electronic spectrum of [NiL3] [ClO2,]2 is similar to that of the corresponding complex of 2,2'-bipyridine (bpy) but indicates that the thiazole provides the weaker field, the actual value of Dq(Ni2+) being within the range which suggests the likely appearance of a spin transition in iron(III). The iron(II) complexes [FeL3] X2 (X = ClO4, BF4) are, however, low-spin both in the solid state and in solution. The structure of [NiL3] [ClO4]2.3H2O has been determined, and this reveals a close similarity in the coordination environment to that in [Ni(bpy),] SO4.7.5H2O. The compound is monoclinic, space group P21/c, with four molecules in a unit cell of dimensions a 9.404(4), b 29.169(8), c 17.900(8)ź, β 137.76(1)�. The disordered structure was refined to a residual R 0.087 for 2307 observed reflections. The pseudo-symmetric ligands are orientationally disordered and one anion was also disordered. Restrained refinement with 194 parameters for 85 atomic positions produced a reliable geometry. The ligands function as bidentates, giving the cation a distorted octahedral structure.

The singlet-quintet transition in Tris[2-(pyridin-2-yl)benzothiazole]iron(II) Bis(tetraphenylborate)

The tris[2-(pyridin-2-yl)benzothiazole]iron(II) ion has been isolated as the tetraphenylborate salt which is stable in the atmosphere for short periods. The deep red complex displays a temperature-dependent magnetic moment and thermochroism which are associated with a thermally induced singlet (1A1) ↔ quintet (5T2) spin transition. An empirical treatment of the transition, which is continuous, yields ∆H and ∆S values of 22.7 kJ mol-1 and 91 JK-1 mol-1 over the range 275-364 K. Spectral data for the corresponding nickel(11) complex confirm the intermediate nature of the field strength of the benzothiazole and indicate that it is a weaker ligand than the corresponding thiazole derivative.

Iron complexes of pyridylimidazole derivatives

Complexes of iron(II) with 2-(2-pyridyl)benzimidazole (pbi) and 2-(6- methyl-2-pyridyl)benzimidazole (mpbi) have been characterized. [Fe(pbi)3] [BF4]2 undergoes a temperature-induced spin transition the course of which is determined by the extent of hydration. [Fe(mpbi)3] [ClO4]2 is high-spin and the differences in the properties of the two complexes are correlated with electronic spectral data. [Fe(pbi)2(CN)2] is low-spin. Iron(III) complexes of deprotonated pbi and 2-(2- pyridyl)imidazole (pyim), [Fe(pbi-H)3] and [Fe(pyim-H)3], result when the cationic iron(II) complexes are treated with base. Magnetic and Mossbauer effect data show that these complexes, which display strong π → t2 charge-transfer absorption, are low-spin.