Discovery of 5-{4-[(7-Ethyl-6-oxo-5,6-dihydro-1,5-naphthyridin-3-yl)methyl]piperazin-1-yl}-N-methylpyridine-2-carboxamide (AZD5305): A PARP1-DNA Trapper with High Selectivity for PARP1 over PARP2 and Other PARPs

Poly-ADP-ribose-polymerase (PARP) inhibitors have achieved regulatory approval in oncology for homologous recombination repair deficient tumors including BRCA mutation. However, some have failed in combination with first-line chemotherapies, usually due to overlapping hematological toxicities. Currently approved PARP inhibitors lack selectivity for PARP1 over PARP2 and some other 16 PARP family members, and we hypothesized that this could contribute to toxicity. Recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for driving efficacy in a BRCA mutant background. Herein, we describe the structure- and property-based design of 25 (AZD5305), a potent and selective PARP1 inhibitor and PARP1-DNA trapper with excellent in vivo efficacy in a BRCA mutant HBCx-17 PDX model. Compound 25 is highly selective for PARP1 over other PARP family members, with good secondary pharmacology and physicochemical properties and excellent pharmacokinetics in preclinical species, with reduced effects on human bone marrow progenitor cells in vitro.

Potent and Selective Inhibitors of the Epidermal Growth Factor Receptor to Overcome C797S-Mediated Resistance

The epidermal growth factor receptor (EGFR) harboring activating mutations is a clinically validated target in non-small-cell lung cancer, and a number of inhibitors of the EGFR tyrosine kinase domain, including osimertinib, have been approved for clinical use. Resistance to these therapies has emerged due to a variety of molecular events including the C797S mutation which renders third-generation C797-targeting covalent EGFR inhibitors considerably less potent against the target due to the loss of the key covalent-bond-forming residue. We describe the medicinal chemistry optimization of a biochemically potent but modestly cell-active, reversible EGFR inhibitor starting point with sub-optimal physicochemical properties. These studies culminated in the identification of compound 12 that showed improved cell potency, oral exposure, and in vivo activity in clinically relevant EGFR-mutant-driven disease models, including an Exon19 deletion/T790M/C797S triple-mutant mouse xenograft model.

Prevalence of Loss of Smell and/or Taste and other Otorhinolaryngology Symptoms in COVID-19 Patients

Background Loss of smell and/or taste have been described in COVID-19 patients. Studies have not been conducted to evaluate the loss of smell and/or taste in the context of Nepal. Objective To investigate the prevalence of Ear, Nose and Throat related symptoms and assess smell and taste disorders in laboratory-confirmed SARS-CoV-2 patients. Method This prospective cross-sectional study evaluated patients from September 2020 to March 2021 with preceding COVID-19 diagnosis from a tertiary centre in Kathmandu. COVID-19 positive patients visiting out-patient department, quarantined or admitted were included. Patients were given questionnaire consisting of demographic data, history of smoking and evaluation of presenting symptoms. Loss of smell and taste were subjectively tested and followed up via telephone for ten weeks to evaluate for recovery time and degree of recovery. Result A total of 226 patients participated in the study, 18-92 years old (mean age, 36.77 ± 15.23 years; 53.5% males, 69% non-smokers). Majority of the patients had Myalgia (n = 128, 56.6%) as their presenting symptoms followed by fever (n = 122, 53.9%), loss of smell (n = 117, 51.7%), cough (n = 107, 47.34) and sore throat (n = 102, 45.1%). Loss of sense of smell and taste was reported in 51.8% and 42% respectively. The association between loss of sense of smell and taste was statistically significant (p < .001). All patients had some degree of recovery with 64.1% recovery of smell and 64.2% recovery of taste within 14 days of onset of symptoms. The mean recovery time for sense of smell and taste was 14.34 ± 9.82 days and 15.03 ± 10.06 days, respectively. Conclusion Olfactory and gustatory dysfunctions are cardinal features of COVID-19. They recover spontaneously along with other symptoms within few weeks. The absence of smell or taste in times of pandemic can be suggestive of potential COVID-19 infection and be used as a screening tool for early diagnosis and reduce transmission of the infection.

Dyschromatosis Universalis Hereditaria

Dyschromatosis universalis hereditaria (DUH) is a rare pigmentary genodermatosis usually inherited in autosomal dominant fashion characterized by multiple pinpoint to pea-sized hypo- and hyper-pigmented macules arranged in reticulate pattern that develops within the first few years of life. An 11 years old boy presented with multiple gradually progressive asymptomatic hypopigmented macules on hyperpigmented background on trunk, extremities and face since 2 years of age. Family history was absent. Punch biopsies revealed increased number of melanocytes in the epidermis with basal cell vacuolar alteration and pigmentary incontinence and perivascular infiltration by lymphocytes and melanophages in the dermis. We herein present a sporadic case of dyschromatosis universalis hereditaria.

CRISPR GUARD protects off-target sites from Cas9 nuclease activity using short guide RNAs

Precise genome editing using CRISPR-Cas9 is a promising therapeutic avenue for genetic diseases, although off-target editing remains a significant safety concern. Guide RNAs shorter than 16 nucleotides in length effectively recruit Cas9 to complementary sites in the genome but do not permit Cas9 nuclease activity. Here we describe CRISPR Guide RNA Assisted Reduction of Damage (CRISPR GUARD) as a method for protecting off-targets sites by co-delivery of short guide RNAs directed against off-target loci by competition with the on-target guide RNA. CRISPR GUARD reduces off-target mutagenesis while retaining on-target editing efficiencies with Cas9 and base editor. However, we discover that short guide RNAs can also support base editing if they contain cytosines within the deaminase activity window. We explore design rules and the universality of this method through in vitro studies and high-throughput screening, revealing CRISPR GUARD as a rapidly implementable strategy to improve the specificity of genome editing for most genomic loci. Finally, we create an online tool for CRISPR GUARD design.

Antibody fragments structurally enable a drug-discovery campaign on the cancer target Mcl-1

Mcl-1 is an important cancer target for drug therapy, through which normal apoptosis may be restored by inhibiting its protective function. An scFv and a Fab have been used to generate an apo Mcl-1 crystal system that is amenable to iterative structure-guided drug design.

Apoptosis is a crucial process by which multicellular organisms control tissue growth, removal and inflammation. Disruption of the normal apoptotic function is often observed in cancer, where cell death is avoided by the overexpression of anti-apoptotic proteins of the Bcl-2 (B-cell lymphoma 2) family, including Mcl-1 (myeloid cell leukaemia 1). This makes Mcl-1 a potential target for drug therapy, through which normal apoptosis may be restored by inhibiting the protective function of Mcl-1. Here, the discovery and biophysical properties of an anti-Mcl-1 antibody fragment are described and the utility of both the scFv and Fab are demonstrated in generating an Mcl-1 crystal system amenable to iterative structure-guided drug design.

Positioning High-Throughput CETSA in Early Drug Discovery through Screening against B-Raf and PARP1

Methods to measure cellular target engagement are increasingly being used in early drug discovery. The Cellular Thermal Shift Assay (CETSA) is one such method. CETSA can investigate target engagement by measuring changes in protein thermal stability upon compound binding within the intracellular environment. It can be performed in high-throughput, microplate-based formats to enable broader application to early drug discovery campaigns, though high-throughput forms of CETSA have only been reported for a limited number of targets. CETSA offers the advantage of investigating the target of interest in its physiological environment and native state, but it is not clear yet how well this technology correlates to more established and conventional cellular and biochemical approaches widely used in drug discovery. We report two novel high-throughput CETSA (CETSA HT) assays for B-Raf and PARP1, demonstrating the application of this technology to additional targets. By performing comparative analyses with other assays, we show that CETSA HT correlates well with other screening technologies and can be applied throughout various stages of hit identification and lead optimization. Our results support the use of CETSA HT as a broadly applicable and valuable methodology to help drive drug discovery campaigns to molecules that engage the intended target in cells.

Quantifying the relationship between inhibition of VEGF receptor 2, drug-induced blood pressure elevation and hypertension

BACKGROUND AND PURPOSE

Several anti-angiogenic cancer drugs that inhibit VEGF receptor (VEGFR) signalling for efficacy are associated with a 15-60% incidence of hypertension. Tyrosine kinase inhibitors (TKIs) that have off-target activity at VEGFR-2 may also cause blood pressure elevation as an undesirable side effect. Therefore, the ability to translate VEGFR-2 off-target potency into blood pressure elevation would be useful in development of novel TKIs. Here, we have sought to quantify the relationship between VEGFR-2 inhibition and blood pressure elevation for a range of kinase inhibitors.

EXPERIMENTAL APPROACH

Porcine aortic endothelial cells overexpressing VEGFR-2 (PAE) were used to determine IC₅₀ for VEGFR-2 phosphorylation. These IC₅₀ values were compared with published reports of exposure attained during clinical use and the corresponding incidence of all-grade hypertension. Unbound average plasma concentration (C_av,u ) was selected to be the most appropriate pharmacokinetic parameter. The pharmacokinetic-pharmacodynamic (PKPD) relationship for blood pressure elevation was investigated for selected kinase inhibitors, using data derived either from clinical papers or from rat telemetry experiments.

KEY RESULTS

All-grade hypertension was predominantly observed when the C_av,u was >0.1-fold of the VEGFR-2 (PAE) IC₅₀ . Furthermore, based on the PKPD analysis, an exposure-dependent blood pressure elevation >1 mmHg was observed only when the C_av,u was >0.1-fold of the VEGFR-2 (PAE) IC₅₀ .

CONCLUSIONS AND IMPLICATIONS

Taken together, these data show that the risk of blood pressure elevation is proportional to the amount of VEGFR-2 inhibition, and a margin of >10-fold between VEGFR-2 IC₅₀ and C_av,u appears to confer a minimal risk of hypertension.

Mapping the sugar dependency for rational generation of a DNA-RNA hybrid-guided Cas9 endonuclease

The CRISPR-Cas9 RNA-guided endonuclease system allows precise and efficient modification of complex genomes and is continuously developed to enhance specificity, alter targeting and add new functional moieties. However, one area yet to be explored is the base chemistry of the associated RNA molecules. Here we show the design and optimisation of hybrid DNA-RNA CRISPR and tracr molecules based on structure-guided approaches. Through careful mapping of the ribose requirements of Cas9, we develop hybrid versions possessing minimal RNA residues, which are sufficient to direct specific nuclease activity in vitro and in vivo with reduced off-target activity. We identify critical regions within these molecules that require ribose nucleotides and show a direct correlation between binding affinity/stability and cellular activity. This is the first demonstration of a non-RNA-guided Cas9 endonuclease and first step towards eliminating the ribose dependency of Cas9 to develop a XNA-programmable endonuclease.

Potent and Selective Inhibitors of MTH1 Probe Its Role in Cancer Cell Survival

Recent literature has claimed that inhibition of the enzyme MTH1 can eradicate cancer. MTH1 is one of the "housekeeping" enzymes that are responsible for hydrolyzing damaged nucleotides in cells and thus prevent them from being incorporated into DNA. We have developed orthogonal and chemically distinct tool compounds to those published in the literature to allow us to test the hypothesis that inhibition of MTH1 has wide applicability in the treatment of cancer. Here we present the work that led to the discovery of three structurally different series of MTH1 inhibitors with excellent potency, selectivity, and proven target engagement in cells. None of these compounds elicited the reported cellular phenotype, and additional siRNA and CRISPR experiments further support these observations. Critically, the difference between the responses of our highly selective inhibitors and published tool compounds suggests that the effect reported for the latter may be due to off-target cytotoxic effects. As a result, we conclude that the role of MTH1 in carcinogenesis and utility of its inhibition is yet to be established.

Transient protein states in designing inhibitors of the MDM2-p53 interaction

Reactivation of p53 by release of the functional protein from its inhibition by MDM2 provides an efficient, nongenotoxic approach to a wide variety of cancers. We present the cocrystal structures of two complexes of MDM2 with inhibitors based on 6-chloroindole scaffolds. Both molecules bound to a distinct conformational state of MDM2 with nM-μM affinities. In contrast to other structurally characterized antagonists, which mimic three amino acids of p53 (Phe19, Trp23, and Leu26), the compounds induced an additional hydrophobic pocket on the MDM2 surface and unveiled a four-point binding mode. The enlarged interaction interface of the inhibitors resulted in extension of small molecules binding toward the "lid" segment of MDM2 (residues 19-23)--a nascent element that interferes with p53 binding. As supported by protein engineering and molecular dynamics studies, employing these unstable elements of MDM2 provides an efficient and yet unexplored alternative in development of MDM2-p53 association inhibitors.

On the mechanism of action of SJ-172550 in inhibiting the interaction of MDM4 and p53

SJ-172550 (1) was previously discovered in a biochemical high throughput screen for inhibitors of the interaction of MDMX and p53 and characterized as a reversible inhibitor (J. Biol. Chem. 2010; 285∶10786). Further study of the biochemical mode of action of 1 has shown that it acts through a complicated mechanism in which the compound forms a covalent but reversible complex with MDMX and locks MDMX into a conformation that is unable to bind p53. The relative stability of this complex is influenced by many factors including the reducing potential of the media, the presence of aggregates, and other factors that influence the conformational stability of the protein. This complex mechanism of action hinders the further development of compound 1 as a selective MDMX inhibitor.

Use of double-balloon catheter in the management of epistaxis: a boon for the periphery

BACKGROUND

Epistaxis is one of the most commonly encountered emergencies in ENT practise. It has been reported that almost 60% of general population experience epistaxis of small or large quantity in his /her lifetime(1).

OBJECTIVE

The objective of this study was to compare the outcome of double balloon catheter to normal packing method for epistaxis.

MATERIALS AND METHODS

An interventional study of 30 patients admitted in Kathmandu Medical College, Sinamangal, Kathmandu, Nepal from Baisak 2065 to Chaitra 2066 with bleeding from the nose were taken into study. These patients were analysed on the basis of duration of hospital stay, any related cause for epistaxis, modalities of treatment, success of balloon catheter etc.

RESULT

Results with double-balloon catheter showed less hospital stay and better compliance by the patient.

CONCLUSION

This study highlights that double-balloon catheter has a higher chance of acceptance by the patient and is better in the treatment of epistaxis. This method can be undertaken without anaesthetic assistance thus it is very feasible even in the most remote areas of our nation.

Diagnostic accuracy of fine needle aspiration cytology in thyroid swellings

BACKGROUND

Proper management of the disease depends upon accurate diagnosis. Fine Needle Aspiration Cytology has become the investigation of choice because of its high accuracy, simplicity, minimal-invasiveness, quick result and reliability.

METHODS

All the patients with thyroid disease, irrespective of age and gender, who underwent thyroid were studied. These patients had their fine needle aspiration Cytology was done in our centre. Detailed history, physical examination, routine investigations, radiological investigations (including CT scans when needed), hormonal assay, (T3, T4, TSH ), ultrasound of neck and FNAC were done. Pre- operative fine needle aspiration results were compared with histopathology results of operated specimen and then analyzed statistically to assess the sensitivity, specificity and accuracy of the result.

RESULTS

There were total of 51 patients. Age ranges from 21 to 62 years. The study duration was from May 2006 to February 2011. Out of 51 patients, 82.35% (n=42) were females and 17.64% (n=9) were males. In 43 patients, FNAC showed benign lesions, of which 40 were true negative (TN) and three false negative (FN), which on histopathology reported malignancy. Remaining eight cases were diagnosed as malignancy on histopathology of which seven cases were true positive (TP), one case of false positive (FP) was detected in our study. Over all Sensitivity was 70% and specificity was 97.5% and accuracy of FNAC was 92.1%.

CONCLUSIONS

FNAC should be performed in all cases of thyroid nodules because of its high sensitivity and specificity to differentiate benign from malignant lesions and counsel the patient as well as plan surgery accordingly. Expenditure, time and the hassle of revision surgery is minimized by the pre operative FNAC report.

Observation of hearing loss in patients with chronic suppurative otitis media tubotympanic type

BACKGROUND

It is acknowledged that size and site of tympanic membrane perforation is proportional to degree of hearing loss but there are many studies which suggests otherwise. Persistent ear discharge is also supposed to deteriorate hearing level with passage of time. This study is carried out to find out the relation between size and site of tympanic membrane perforation and duration of ear discharge on hearing loss.

OBJECTIVES

The objective of this study is to study the effect of size and site of tympanic membrane perforation and duration of ear discharge on hearing loss.

METHODS AND MATERIALS

This is a cross-sectional prospective study conducted at Kathmandu Medical College, department of ear nose and throat from January till July 2009. One hundred patients aged between 8 to 60 years with pars-tensa perforations were included in the study. Detail clinical examination and history was carried out followed by hearing evaluation by audiometry was done in all cases. All the data is collected, statistical analysis is done using SPSS program and documented for study.

RESULTS

One hundred patients with 119 perforated tympanic membrane, age ranged between 8 to 60 years, 44 males and 56 females were studied. Bilateral tympanic membrane perforation were seen in 19 patients, right sided perforation in 39 and left sided in 42 patients respectively. Large central perforation involving all four quadrants was the most common otologic findings seen in 72 ears (60.50%) whereas perforation in posterosuperior quadrant was the least common finding seen in 3 patients (2.52%). Significant relation is observed between site of perforation and degree of hearing loss; posterior placed perforations seem to have larger hearing loss. Ninety-five perforations (79.83%) showed more loss in low frequencies with larger air bone gap at low frequencies. The longer the duration of ear discharge, the more the hearing loss.

CONCLUSION

The larger the perforation, the greater the decibel loss in sound perception. The location of perforation on the tympanic membrane and the duration of ear discharge have significant effect on the magnitude of hearing loss.

Computed tomographic Assessment of Lateral Lamella of Cribiform Plate and Comparison of Depth of Olfactory Fossa

INTRODUCTION: Endoscopic sinus surgery is an upcoming branch in rhinological practice but with some major risks since it has to play around the skull base area. Lateral lamella of cribriform plate is the thinnest area of the skull base. Thus this study is undertaken to evaluate the height of lateral lamella of cribriform plate and the depth of olfactory fossae by the help of computed tomographic images. METHODS: Computed tomographic study of 50 patients was done in Advanced Imaging and Diagnostic center, Kathmandu Medical College. Coronal sections at the centre of infra-orbital foramina were taken as reference slide. The height of cribriform plate point was subtracted from the height of medial ethmoidal roof point to measure the length of lateral lamella of cribriform plates on both sides. RESULTS: The median height of LLCP in 100 slides was 2.8 mm. LLCP height was 0 to 3.9 mm in 86 slides, 4 to 7 mm in 12 slides and greater than 7mm in 2 slides. The LLCP length was greater in right side in 28 (56%) patients and was greater in left side in 19 (38%) patients. It was equal in both sides in only three patients (6%). CONCLUSIONS: As regards the length of LLCP; 0 to 3.9 mm length was most common. The olfactory fossa depth was more in the right side compared to the left side. Thus, right side is more vulnerable to injury during surgery. Thus adequate caution has to be exercised by the rhinological surgeon during endoscopic sinus surgery. Keywords: lateral lamella of Cribriform plate, medical ethmoidal roof, olfactory fossa.  

1,4-Thienodiazepine-2,5-diones via MCR (I): synthesis, virtual space and p53-Mdm2 activity

1,4-Thienodiazepine-2,5-diones have been synthesized via the Ugi-Deprotection-Cyclization (UDC) approach starting from Gewald 2-aminothiophenes in a convergent and versatile manner. The resulting scaffold is unprecedented, cyclic, and peptidomimetic with four points of diversity introduced from readily available starting materials. In addition to eighteen synthesized and characterized compounds, a virtual compound library was generated and evaluated for chemical space distribution and drug-like properties. A small focused compound library of 1,4-thienodiazepine-2,5-diones has been screened for the activity against p53-Mdm2 interaction. Biological evaluations demonstrated that some compounds exhibited promising antagonistic activity.

Computed tomographic assessment of lateral lamella of cribriform plate and comparison of depth of olfactory fossa

INTRODUCTION

Endoscopic sinus surgery is an upcoming branch in rhinological practice but with some major risks since it has to play around the skull base area. Lateral lamella of cribriform plate is the thinnest area of the skull base. Thus this study is undertaken to evaluate the height of lateral lamella of cribriform plate and the depth of olfactory fossae by the help of computed tomographic images.

METHODS

Computed tomographic study of 50 patients was done in Advanced Imaging and Diagnostic center, Kathmandu Medical College. Coronal sections at the centre of infra-orbital foramina were taken as reference slide. The height of cribriform plate point was subtracted from the height of medial ethmoidal roof point to measure the length of lateral lamella of cribriform plates on both sides.

RESULTS

The median height of LLCP in 100 slides was 2.8 mm. LLCP height was 0 to 3.9 mm in 86 slides, 4 to 7 mm in 12 slides and greater than 7mm in 2 slides. The LLCP length was greater in right side in 28 (56%) patients and was greater in left side in 19 (38%) patients. It was equal in both sides in only three patients (6%).

CONCLUSIONS

As regards the length of LLCP; 0 to 3.9 mm length was most common. The olfactory fossa depth was more in the right side compared to the left side. Thus, right side is more vulnerable to injury during surgery. Thus adequate caution has to be exercised by the rhinological surgeon during endoscopic sinus surgery.

Incidence of tuberculosis in enlarged neck nodes, our experience

OBJECTIVES

To determine the incidence of tuberculous lymphadenitis in enlarged neck nodes.

MATERIALS AND METHODS

Continuous prospective study is carried out in the department of otorhinolaryngology head & neck surgery, Kathmandu Medical College, Kathmandu, during two years, from January 2006 to January 2008. The study included a group of 155 patients with cervical lymphadenopathy. Each patient underwent a detail clinical Ear, Nose and Throat (ENT) examination and a battery of investigations which included Fine Needle Aspiration Cytology (FNAC) of the nodes, Montoux's test, blood Erythrocyte Sedimentation Rate (ESR) and chest X-ray. Those patients with tubercular lymphadenitis were referred to Directly Observed Therapy System (DOTS) clinic for anti-tubercular therapy. Others with reactive lymphadenitis were treated with antibiotic and those with metastatic neck nodes were treated accordingly.

RESULTS

Of the 155 cases with enlarged neck nodes, 83 (54%) had tubercular lymphadenitis. Fifty two (33%) cases had reactive lymphadenitis and 17 (11%) cases were diagnosed with metastatic neck nodes. Fine needle aspiration cytology was found to be highly effective in the diagnosis of tubercular lymphadenitis with 94% accuracy. Majority of patients were otherwise healthy adults, aged between 8 - 71 years. No difference was observed between male and female in this study. Posterior triangle (PT) nodes were most commonly affected group of nodes accounting for 35 (42%) cases and preauricular region 1 (1%) case being the least commonly affected site. Fifteen (18%) cases presented with abscess formation. Only 42 (50%) cases had family history of tuberculosis but 8 (9%) patients had previous history of various forms of tuberculosis. Twelve (14%) patients had positive chest X-ray findings suggesting of concurrent pulmonary tuberculosis. All the patients were referred to DOTS clinic and were treated with category (CAT) - III anti tubercular therapy (ATT). Others with concurrent pulmonary tuberculosis were treated with CAT I regime. None of the patients required surgical treatment.

CONCLUSION

There is high incidence of tubercular cervical lymphadenitis in patients with enlarged neck nodes in developing countries like Nepal. Involvement of cervical lymphnodes are the most commonly affected group of nodes. Therefore, it is important that otolaryngologists are aware of tuberculosis in the head and neck region.

Robust NMR screening for lead compounds using tryptophan-containing proteins

NMR-based drug screening methods provide the most reliable characterization of binding propensities of ligands to their target proteins. Unique to NMR is its capability to detect weak microM-mM bindings. NMR assays are, however, one of the least effective methods in terms of the amount of protein required and the time needed for acquiring NMR experiments. We have recently described a time efficient 1D proton NMR assay for studying the effect of antagonists on protein-protein interactions. The method, named AIDA-NMR (for Antagonist Induced Dissociation Assay-NMR), can provide information on whether an antagonist of a protein-protein interaction is strong enough to dissociate the complex and, in addition, whether its interaction is through denaturation, precipitation, or release of a protein in its functional folded state. AIDA requires a large protein fragment (larger than ca. 30 kDa) to bind to a small reporter protein (smaller than ca.12 kDa). Here, we present an extension of this method, named SEI AIDA (SEI, for Selective Excitation-Inversion). The SEI AIDA uses tryptophan-bearing proteins, and by selectively exciting only the proton NMR signals of the (N)H(epsilon) indole side chains of tryptophans, the acquisition time of the AIDA experiment can be reduced by an order of magnitude relative to the corresponding 1D AIDA that uses hard pulses. Thus, at 600 MHz, the (N)H(epsilon) signal of a 35 microM protein complex can be acquired in only 2.5 min, making the SEI AIDA suitable for high-throughput screening pipelines in drug discovery.

A novel member of the thermolysin family, cloning and biochemical characterization of metalloprotease from Staphylococcus pseudintermedius

Thermolysins constitute a family of secreted bacterial metalloproteases expressed, among others, by several pathogens. Strains of Staphylococcus pseudintermedius isolated from diseased dogs and judged as protease-positive, by skim milk agar plate culture, were investigated for protease content. No proteolytic activity was detected when the bacteria were grown in regular liquid media. Unexpectedly, supplementation of the medium with calcium ions resulted in expression of a metalloprotease and profound changes in the profile of extracellular proteins. On the basis of homology to other staphylococcal metalloproteases, the nucleotide sequence of the gene encoding this protease (Pst) and its flanking regions was determined. The full-length pst codes for a protein with an open reading frame of 505 amino acids. The internal region contains the HEXXH catalytic domain that is conserved in members of the thermolysin family. Regardless of the presence of calcium in the medium, the expression of the protease gene was of the same intensity. This suggests that regulation of the metalloprotease production by calcium ions is at a post-transcriptional level. Isolates of S. pseudintermedius exhibit a proteolytic phenotype due to the metalloprotease expression, however only in presence of calcium ions, which most probably stabilize the structure of the protease.

A novel member of the thermolysin family, cloning and biochemical characterization of metalloprotease from Staphylococcus pseudintermedius

Thermolysins constitute a family of secreted bacterial metalloproteases expressed, among others, by several pathogens. Strains of Staphylococcus pseudintermedius isolated from diseased dogs and judged as protease-positive, by skim milk agar plate culture, were investigated for protease content. No proteolytic activity was detected when the bacteria were grown in regular liquid media. Unexpectedly, supplementation of the medium with calcium ions resulted in expression of a metalloprotease and profound changes in the profile of extracellular proteins. On the basis of homology to other staphylococcal metalloproteases, the nucleotide sequence of the gene encoding this protease (Pst) and its flanking regions was determined. The full-length pst codes for a protein with an open reading frame of 505 amino acids. The internal region contains the HEXXH catalytic domain that is conserved in members of the thermolysin family. Regardless of the presence of calcium in the medium, the expression of the protease gene was of the same intensity. This suggests that regulation of the metalloprotease production by calcium ions is at a post-transcriptional level. Isolates of S. pseudintermedius exhibit a proteolytic phenotype due to the metalloprotease expression, however only in presence of calcium ions, which most probably stabilize the structure of the protease.

Surgery for recurrent lower lip carcinoma

A 38 year old gentleman presented with recurrent squamous cell carcinoma of lower lip. He had earlier undergone previous surgeries and radiotherapy. At the time that he presented in KMCTH his lower lip area was much scarred and the tongue was shrunk and unavailable for vermilion reconstruction. This case report is an account of the various treatment carried out to reconstruct the lip. It was done with co-operation of the ENT department.

Enzymatic activity of the Staphylococcus aureus SplB serine protease is induced by substrates containing the sequence Trp-Glu-Leu-Gln

Proteases are of significant importance for the virulence of Staphylococcus aureus. Nevertheless, their subset, the serine protease-like proteins, remains poorly characterized. Here presented is an investigation of SplB protease catalytic activity revealing that the enzyme possesses exquisite specificity and only cleaves efficiently after the sequence Trp-Glu-Leu-Gln. To understand the molecular basis for such selectivity, we solved the three-dimensional structure of SplB to 1.8 A. Modeling of substrate binding to the protease demonstrated that selectivity relies in part on a canonical specificity pockets-based mechanism. Significantly, the conformation of residues that ordinarily form the oxyanion hole, an essential structural element of the catalytic machinery of serine proteases, is not canonical in the SplB structure. We postulate that within SplB, the oxyanion hole is only formed upon docking of a substrate containing the consensus sequence motif. It is suggested that this unusual activation mechanism is used in parallel with classical determinants to further limit enzyme specificity. Finally, to guide future development, we attempt to point at likely physiological substrates and thus the role of SplB in staphylococcal physiology.

Tonsillar microbial flora: a comparison of infected and non-infected tonsils

OBJECTIVE

The main objective of this study was to find out the most common organism affecting the tonsils in recurrent tonsillitis.

METHODOLOGY

This was a prospective study consisting of total number of 50 patients, conducted in the ENT department of Dhulikhel Hospital, KUTH, Dhulikhel, Nepal. The study period was one year and three months (March 2004 to April 2005).

RESULTS

Total numbers of 50 patients were selected, of which 32 were of acute tonsillitis and 18 were taken as control. Among these males were 32 and females were 18. The age group was from 3 years to 64 years. Throat swabs of patients were taken by aseptic method and were sent to the laboratory immediately. Among the infected tonsils the most common organism was Streptococcus viridans followed by Streptococcus pneumoniae and Moraxella catarrhalis. The third most common was Beta haemolytic streptococci whereas Micrococcus was not isolated in any of the infected samples. Likewise in non-infected tonsils, the most common organism isolated was again Streptococcus viridans followed by Micrococcus and Diptheroids. In these specimen no Beta haemolytic streptococci was isolated from the control group.

CONCLUSION

Thus, the study is able to put forward the fact that most common organism affecting the tonsils in infected as well as non- infected state is Streptococcus viridans. Where as Beta haemolytic streptococci was not found in non-infected tonsils, likewise Micrococcus was not found in infected tonsils.