Abstract P4-04-04: Identification and development of oral estrogen receptor PROTAC degraders for breast cancer

ER-positive breast cancers comprise approximately 70-80% of all newly diagnosed cases. Downregulation or degradation of ER is a treatment approach currently used in the clinic to target estrogen receptor signaling. Faslodex, the only clinically-approved ER-downregulator, is administered as a monthly intramuscular injection with limiting pharmaceutical properties. Reasoning that an orally-available estrogen receptor degrader would be beneficial to patients, we have leveraged our experience in targeted protein degradation to generate and characterize novel proteolysis targeting chimeras (PROTACs) against estrogen receptor alpha. PROTACs are heterobifunctional molecules that facilitate the formation of a “trimer complex” comprised of the PROTAC, a pathogenic target protein of interest and an E3 ligase, which catalyzes the ubiquitylation and subsequent degradation of the target protein via the proteasome. To identify novel ER degraders (ER PROTACs), we have used several in vitro assays to characterize the extent of target engagement and receptor degradation. Potent ER PROTACs with good oral exposure and other pharmaceutical properties in multiple pre-clinical species were further evaluated in breast cancer xenograft models. Orally-administered ER PROTACs achieved >80% degradation of estrogen receptor alpha and demonstrated single agent tumor growth inhibition in these disease models. Further, combination with a CDK4/6 inhibitor resulted in the expected improvement in anti-proliferative activity.

Citation Format: Flanagan JJ, Qian Y, Gough SM, Andreoli M, Bookbinder M, Bradley J, Rousseau E, Willard R, Crews CM, Crew AP, Taylor I, Houston J. Identification and development of oral estrogen receptor PROTAC degraders for breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-04-04.

BET protein proteolysis targeting chimera (PROTAC) exerts potent lethal activity against mantle cell lymphoma cells

Bromodomain extraterminal protein (BETP) inhibitors transcriptionally repress oncoproteins and nuclear factor-κB (NF-κB) target genes that undermines the growth and survival of mantle cell lymphoma (MCL) cells. However, BET bromodomain inhibitor (BETi) treatment causes accumulation of BETPs, associated with reversible binding and incomplete inhibition of BRD4 that potentially compromises the activity of BETi in MCL cells. Unlike BETi, BET-PROTACs (proteolysis-targeting chimera) ARV-825 and ARV-771 (Arvinas, Inc.) recruit and utilize an E3-ubiquitin ligase to effectively degrade BETPs in MCL cells. BET-PROTACs induce more apoptosis than BETi of MCL cells, including those resistant to ibrutinib. BET-PROTAC treatment induced more perturbations in the mRNA and protein expressions than BETi, with depletion of c-Myc, CDK4, cyclin D1 and the NF-κB transcriptional targets Bcl-xL, XIAP and BTK, while inducing the levels of HEXIM1, NOXA and CDKN1A/p21. Treatment with ARV-771, which possesses superior pharmacological properties compared with ARV-825, inhibited the in vivo growth and induced greater survival improvement than the BETi OTX015 of immune-depleted mice engrafted with MCL cells. Cotreatment of ARV-771 with ibrutinib or the BCL2 antagonist venetoclax or CDK4/6 inhibitor palbociclib synergistically induced apoptosis of MCL cells. These studies highlight promising and superior preclinical activity of BET-PROTAC than BETi, requiring further in vivo evaluation of BET-PROTAC as a therapy for ibrutinib-sensitive or -resistant MCL.

Abstract S4-03: Targeted and selective degradation of estrogen receptor (ER) alpha by PROTACs

ERα-positive breast cancers comprise approximately 80% of all newly diagnosed cases. Current treatment approaches targeting ER signaling include antagonizing and/or downregulating ER or reducing estrogen levels. Faslodex (fulvestrant) is the only clinically-approved agent that is both a potent ER antagonist and downregulator but has limitations given its pharmacokinetics and route of administration. Over the past several years, targeted ER therapies have focused on developing selective estrogen receptor downregulators (SERDs, i.e, GDC-0810, GDC-0927, AZD9496, RAD1901). The mechanisms involved in ER downregulation by SERD binding are not completely understood, but evidence suggests that conformational changes in the receptor upon ligand binding combined with specific co-regulator interactions destabilize the receptor making it a target for passive proteasomal degradation. We hypothesized that the complex ER pharmacology required for SERD-based passive degradation might be different across various ER-positive cell lines and that targeted degradation of the receptor by actively recruiting the ubiquitin-proteasome machinery would provide a better approach for reducing ER levels. To test this hypothesis, we developed potent molecules directed against ER using our pioneering technology—proteolysis targeting chimeras (PROTACs). PROTACs are heterobifunctional molecules that actively recruit specific E3 ligases resulting in ubiquitylation and degradation of target proteins. When testing for ER degradation using several SERDs and ER PROTACs, we discovered that both fulvestrant and ER PROTACs provided robust degradation in all ER-positive lines (<1 nM 50% degradation; >90% reduction) whereas other SERDs did not degrade or only modestly degraded the receptor. Importantly, MCF-7 cells were uniquely sensitive to SERD-based degradation of ER compared to other cell lines. Subcutaneous administration of fulvestrant (1mpk) or ER PROTACs (10 mpk) reduced uterine ER alpha levels in immature rats (>65% reduction). PROTAC-mediated degradation of ER was also achieved in breast cancer xenografts. To further validate the PROTAC mechanism, incubation of ER-positive cells with ER PROTACs resulted in increased levels of poly-ubiquitylated ERα when compared to SERDs. Lastly, to demonstrate the specificity of PROTAC-mediated ERα degradation, we utilized a cellular expression proteomics-based approach to examine over 7,000 proteins. In this experiment, only ERα and several known proteins whose genes are regulated by ERα, were significantly reduced by PROTACs. It remains to be seen how the current class of investigational downregulators will perform in the clinic. More importantly, a better understanding of the therapeutic potential and benefit of degrading the receptor instead of inhibiting the receptor needs to be explored. To that end, we continue to develop and characterize novel ER PROTACs with the anticipation that targeted ERα degradation will provide a greater clinical benefit than receptor antagonism.

Citation Format: Flanagan JJ, Rossi AK, Anderoli M, Willard RR, Gordon D, Harling J, Churcher I, Smith I, Zinn N, Bantscheff M, Crews CM, Crew A, Coleman KG, Winkler JD, Qian Y. Targeted and selective degradation of estrogen receptor (ER) alpha by PROTACs [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S4-03.

Developments in mycotoxin analysis: an update for 2014-2015

This review summarises developments in the determination of mycotoxins over a period between mid-2014 and mid-2015. In tradition with previous articles of this series, analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone are covered in individual sections. Advances in proper sampling strategies are discussed in a dedicated section, as are new methods used to analyse botanicals and spices and newly developed LC-MS based multi-mycotoxin methods. The critical review aims to briefly discuss the most important developments and trends in mycotoxin determination as well as to address shortcomings of current methodologies.

Developments in mycotoxin analysis: an update for 2013-2014

This review highlights developments in the determination of mycotoxins over a period between mid-2013 and mid-2014. It continues in the format of the previous articles of this series, emphasising on analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone. The importance of proper sampling and sample preparation is briefly addressed in a dedicated section, while another chapter summarises new methods used to analyse botanicals and spices. As LC-MS/MS instruments are becoming more and more widespread in the determination of multiple classes of mycotoxins, another section is focusing on such newly developed multi-mycotoxin methods. While the wealth of published methods during the 12 month time span makes it impossible to cover every single one, this exhaustive review nevertheless aims to address and briefly discuss the most important developments and trends.

Developments in mycotoxin analysis: an update for 2012-2013

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2012 and mid-2013. It covers the major mycotoxins: aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone. A wide range of analytical methods for mycotoxin determination in food and feed were developed last year, in particular immunochemical methods and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)-based methods. After a section on sampling and sample preparation, due to the rapid spread and developments in the field of LC-MS/MS multimycotoxin methods, a separate section has been devoted to this area of research. It is followed by a section on mycotoxins in botanicals and spices, before continuing with the format of previous reviews in this series with dedicated sections on method developments for the individual mycotoxins.

Developments in mycotoxin analysis: an update for 2011-2012

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2011 and mid- 2012. It covers the major mycotoxins aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. A section on mycotoxins in botanicals and spices is also included. Methods for mycotoxin determination continue to be developed using a wide range of analytical systems ranging from rapid immunochemical-based methods to the latest advances in mass spectrometry. This review follows the format of previous reviews in this series (i.e. sections on individual mycotoxins), but due to the rapid spread and developments in the field of multimycotoxin methods by liquid chromatography-tandem mass spectrometry, a separate section has been devoted to advances in this area of research.

Analytical approaches for MCPD esters and glycidyl esters in food and biological samples: a review and future perspectives

Esters of 2 - and 3-monochloropropane-1,2-diol (MCPD) and glycidol esters are important contaminants of processed edible oils used as foods or food ingredients. This review describes the occurrence and analysis of MCPD esters and glycidol esters in vegetable oils and some other foods. The focus is on the analytical methods based on both direct and indirect methods. Methods of analysis applied to oils and lipid extracts of foods have been based on transesterification to free MCPD and determination by gas chromatography-mass spectrometry (indirect methods) and by high-performance liquid chromatography-mass spectrometry (direct methods). The evolution and performance of the different methods is described and their advantages and disadvantages are discussed. The application of direct and indirect methods to the analysis of foods and to research studies is described. The metabolism and fate of MCPD esters and glycidol esters in biological systems and the methods used to study these in body tissues studies are described. A clear understanding of the chemistry of the methods is important when choosing those suitable for the desired application, and will contribute to the mitigation of these contaminants.

Developments in mycotoxin analysis: an update for 2010-2011

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2010 and mid-2011. It covers the major mycotoxins: aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. Analytical methods for mycotoxins continue to be developed and published. Despite much interest in immunochemical methods and in the rapid development of LC-MS methodology, more conventional methods, sometimes linked to novel clean-up protocols, have also been the subject of research publications over the above period. Occurrence of mycotoxins falls outside the main focus of this review; however, where relevant to analytical method development, this has been mentioned.

Developments in mycotoxin analysis: an update for 2009-2010

This review highlights developments in mycotoxin analysis and sampling over a period between mid-2009 and mid-2010. It covers the major mycotoxins aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxin, patulin, trichothecenes, and zearalenone. New and improved methods for mycotoxins continue to be published. Immunological-based method developments continue to be of wide interest in a broad range of formats. Multimycotoxin determination by LC-MS/MS is now being targeted at the specific ranges of mycotoxins and matrices of interest or concern to the individual laboratory. Although falling outside the main emphasis of the review, some aspects of natural occurrence have been mentioned, especially if linked to novel method developments.

Targeting steroid hormone receptors for ubiquitination and degradation in breast and prostate cancer

Proteolysis targeting chimeric molecules (Protacs) target proteins for destruction by exploiting the ubiquitin-dependent proteolytic system of eukaryotic cells. We designed two Protacs that contain the peptide 'degron' from hypoxia-inducible factor-1alpha, which binds to the Von-Hippel-Lindau (VHL) E3 ubiquitin ligase complex, linked to either dihydroxytestosterone that targets the androgen receptor (AR; Protac-A), or linked to estradiol (E2) that targets the estrogen receptor-alpha (ERalpha; Protac-B). We hypothesized that these Protacs would recruit hormone receptors to the VHL E3 ligase complex, resulting in the degradation of receptors, and decreased proliferation of hormone-dependent cell lines. Treatment of estrogen-dependent breast cancer cells with Protac-B induced the degradation of ERalpha in a proteasome-dependent manner. Protac-B inhibited the proliferation of ERalpha-dependent breast cancer cells by inducing G(1) arrest, inhibition of retinoblastoma phosphorylation and decreasing expression of cyclin D1, progesterone receptors A and B. Protac-B treatment did not affect the proliferation of estrogen-independent breast cancer cells that lacked ERalpha expression. Similarly, Protac-A treatment of androgen-dependent prostate cancer cells induced G(1) arrest but did not affect cells that do not express AR. Our results suggest that Protacs specifically inhibit the proliferation of hormone-dependent breast and prostate cancer cells through degradation of the ERalpha and AR, respectively.

Stability and epimerisation behaviour of ergot alkaloids in various solvents

In this paper the stability and degree of epimerisation of six major ergot alkaloids at three different temperature levels (-20 °C, +4 °C and +20 °C) over periods of 18 hours and six weeks is reported for the first time. The behaviour of ergometrine, ergocornine, ergocristine, α-ergocryptine, ergosine and ergotamine was thoroughly studied in seven solvents which are employed for the preparation of calibrants and extraction mixtures, respectively. Moreover, the stability of the ergot alkaloids was tested in different cereal extracts (rye, wheat, barley, oats) for 1, 2 and 6 days. Of the toxins tested, the ergopeptide-type toxins ergosine, ergotamine, ergocornine, α-ergocryptine and ergocristine showed similar behaviour patterns. The simple lysergic acid derivative ergometrine was more stable and showed hardly any epimerisation to ergometrinine, with the sum of both epimers remaining constant in all seven solvents. The ergopeptides tested show variable epimerisation tendencies, and were also less stable during six weeks at 20 °C. Ergosine showed the highest degree of epimerisation (43% after 6 weeks at 20 °C). In general, the order of epimerisation promotion was methanol/dichloromethane > acetonitrile/buffer > extraction mix > stabilising solution > acetonitrile >> chloroform. Long-term storage at room temperature can only be carried out in chloroform, which showed no epimerisation for all toxins even at 20 °C and also kept the sum of R and S forms constant, which indicates no formation of aci-epimers or other degradation products. Long-term storage of ergot alkaloids in acetonitrile, the most convenient solvent with respect to HPLC analysis, should be carried out at temperatures of -20 °C or below. The constant epimer ratio of all ergot alkaloids in the extraction mixture acetonitrile/ammonium carbonate buffer (200 mg/l; 92:8, v/v) during an HPLC run (18 hours) demonstrates the stability of the toxins in this extraction mixture.

Neurocirculatory and nigrostriatal abnormalities in Parkinson disease from LRRK2 mutation

BACKGROUND

Patients with Parkinson disease (PD) often have cardiac sympathetic denervation and failure of neurocirculatory regulation by baroreflexes. Familial PD caused by mutation of the gene encoding alpha-synuclein or by alpha-synuclein gene triplication also features cardiac sympathetic denervation and baroreflex failure.

METHODS

Here we report results of cardiac sympathetic neuroimaging by 6-[(18)F]fluorodopamine PET, baroreflex testing based on beat-to-beat hemodynamic responses to the Valsalva maneuver, and nigrostriatal neuroimaging using 6-[(18)F] fluorodopa PET in a proband with mutation of the gene encoding leucine-rich repeat kinase 2 (LRRK2), the most common genetic abnormality identified so far in familial PD.

RESULTS

The patient had no detectable 6-[(18)F] fluorodopamine-derived radioactivity in the left ventricular myocardium, a progressive fall in blood pressure during the Valsalva maneuver and no pressure overshoot after release of the maneuver, and decreased 6-[(18)F] fluorodopa-derived radioactivity bilaterally in the putamen and substantia nigra.

CONCLUSION

This patient with Parkinson disease (PD) caused by LRRK2 mutation had evidence of cardiac sympathetic denervation, baroreflex-sympathoneural and baroreflex-cardiovagal failure, and nigrostriatal dopamine deficiency, a pattern resembling that in the sporadic disease. The results fit with the concept that in LRRK2 PD, parkinsonism, cardiac sympathetic denervation, and baroreflex failure can result from a common pathogenetic process.

Factors affecting the analysis of furan in heated foods

Various experimental factors, which could affect the measurement of furan by automated headspace gas chromatography/mass spectrometry, have been investigated. It was established that furan was not lost during sample heating through leakage or decomposition. Deuterium-labelled furan, used as an internal standard, was stable with respect to incubation in the presence of food and stable in model food systems at raised temperature. Saturation of the aqueous phase of the sample with ammonium sulphate improved the partitioning of furan from samples into the headspace. There was a very small decrease in the peak areas of both d0-furan and d4-furan when heated at acid pH. For food samples heated at normal headspace incubation temperature (50 degrees C), the level of furan was highest at the most acidic conditions used (pH 2.4) and did not differ significantly between pH 5 and 10. Under strong heating, production of furan decreased markedly at very high pH. Quantification based on standard additions or on external calibration gave comparable results for foods containing furan at relatively low, moderate and high levels.

Some factors affecting the formation of furan in heated foods

Levels of furan in various foods were measured before and after heating under heating and laboratory conditions. The effect of contact with can coatings, sealing gaskets and the epoxidized oils used in gasket manufacture on furan formation was studied. The objective was to identify factors affecting furan formation. Furan present in heat-processed food samples persisted during cooking. Furan was shown to form in foods on heating, although it did not accumulate to a significant degree on heating in an open vessel. There were no interactions between foods and cans, can coatings or gaskets that had a significant influence on furan formation. Furan accumulated particularly in heat-processed canned and jarred foods because they are sealed containers that receive a considerable thermal load. Heating epoxidized oils used in sealing gaskets formed furan. At the levels used in gaskets, however, epoxidized oils should not affect the formation of furan in foods.

Probing protein function with small molecules

The interface of chemistry and biology offers many opportunities to explore different aspects of cell biology. The emerging field of chemical genetics is providing the chemical means to understand biological systems not easily accessible using classical genetic manipulations. In this article, we will discuss how natural product mode of action studies and novel bio-organic manipulation of intracellular protein levels are proving useful in the exploration of cell biology.

Effects of storage time and temperature on the concentration of ethyl carbamate and its precursors in wine

A 3-year study was carried out on the effects of time and temperature on the concentration of ethyl carbamate in wine. The study monitored the changing concentration of ethyl carbamate and of urea and citrulline, which are two major precursors of ethyl carbamate in wine. In addition to the formation of ethyl carbamate, both urea and citrulline decayed in other reactions. Kinetic analysis was carried out to model the formation of ethyl carbamate and its dependence on the concentrations of ethanol, urea and citrulline. This led to the development of an equation that can be used to predict the concentration of ethyl carbamate in wine at the point of consumption, resulting from any given storage time and temperature profile. The results were in good agreement with data obtained from similar studies.

Survey of chloropropanols in soy sauces and related products purchased in the UK in 2000 and 2002

The results of surveys to investigate the levels of 3-monochloropropane-1,2-diol (3-MCPD) and 1,3-dichloropropanol (1,3-DCP) in UK retail samples of soy sauces and similar products are reported. The products, sampled in 2000 and 2002, were analysed for 3-MCPD using an established solvent extraction technique with a reporting limit of 0.01 mg kg(-1), which also detected 2-monochloropropane-1,2-diol (2-MCPD), and for 1,3-DCP by an automated headspace method with a reporting limit of 0.005 mg kg(-1), which also detected 2,3-dichloropropanol (2,3-DCP). In the 2000 survey, 3-MCPD was quantified in 32 of 100 samples. After normalization to 40% dry matter, it was quantified at or above 0.02 mg kg(-1) in 25 of the samples and in excess of 1 mg kg(-1) in 16 samples, the highest containing 82.8 mg kg(-1). 2-MCPD was found in 26 samples, at up to 17.6 mg kg(-1) after normalization to 40% dry matter. The presence of 1,3-DCP was detected in 17 of the samples, at levels between 0.006 and 0.345 mg kg(-1). 1,3-DCP was only detected where 3-MCPD was present, but the levels of 1,3-DCP and 3-MCPD were not correlated. 2,3-DCP was detected in 11 samples at levels ranging from 0.006 to 0.043 mg kg(-1). In the 2002 survey, 3-MCPD was quantified (> 0.01 mg kg(-1)) in only eight of 99 samples and 2-MCPD in three samples. After normalization to 40% dry matter, 3-MCPD was present at or above 0.02 mg kg(-1) in seven of these, the maximum level being 35.9 mg kg(-1). 1,3-DCP was detected in this sample alone, at 0.017 mg kg(-1).

Selective inhibitors of the osteoblast proteasome stimulate bone formation in vivo and in vitro

We have found that the ubiquitin-proteasome pathway exerts exquisite control of osteoblast differentiation and bone formation in vitro and in vivo in rodents. Structurally different inhibitors that bind to specific catalytic beta subunits of the 20S proteasome stimulated bone formation in bone organ cultures in concentrations as low as 10 nM. When administered systemically to mice, the proteasome inhibitors epoxomicin and proteasome inhibitor-1 increased bone volume and bone formation rates over 70% after only 5 days of treatment. Since the ubiquitin-proteasome pathway has been shown to modulate expression of the Drosophila homologue of the bone morphogenetic protein-2 and -4 (BMP-2 and BMP-4) genes, we examined the effects of noggin, an endogenous inhibitor of BMP-2 and BMP-4 on bone formation stimulated by these compounds and found that it was abrogated. These compounds increased BMP-2 but not BMP-4 or BMP-6 mRNA expression in osteoblastic cells, suggesting that BMP-2 was responsible for the observed bone formation that was inhibited by noggin. We show proteasome inhibitors regulate BMP-2 gene expression at least in part through inhibiting the proteolytic processing of Gli3 protein. Our results suggest that the ubiquitin-proteasome machinery regulates osteoblast differentiation and bone formation and that inhibition of specific components of this system may be useful therapeutically in common diseases of bone loss.

Occurrence of 3-chloro-propane-1,2-diol (3-MCPD) and related compounds in foods: a review

A critical review of the occurrence of 3-chloro-propane-1,2-diol (3-MCPD) in foods not known to contain hydrolysed vegetable proteins is presented. The review covers the properties and chemistry of 3-MCPD and the current methods of analysis in foodstuffs. The results of UK surveys of 3-MCPD occurrence in both retail foods and commercial food ingredients are discussed with particular reference to cereal, meat and dairy products. The possible mechanisms for the formation and decay of 3-MCPD in foods are suggested. The review does not cover the detailed toxicology of 3-MCPD and its occurrence in hydrolysed vegetable proteins, which have been considered elsewhere, nor possible issues such as in-vivo formation.

Determination of 1,3-dichloropropanol in soy sauces by automated headspace gas chromatography-mass spectrometry

There has been recent concern about the levels of carcinogenic chloropropanols in some soy sauces. We have devised and tested a new automated headspace GC-MS technique for the analysis of 1,3-dichloropropan-2-ol (1,3-DCP) in soy sauce and similar products. The method incorporates the use of cryogenic trapping and a deuterium-labelled internal standard. The limit of detection was 0.003 mg kg(-1). After in-house validation testing, the method was applied to soy sauce samples that had previously been analysed for the related contaminant 3-monochloropropanediol (3-MCPD). 1,3-DCP was detected in 10 of 40 sauces, all of which also contained 3-MCPD. The highest level was just >1 mg kg(-1). There was no correlation between the levels of 1,3-DCP and 3-MCPD.

Survey of 3-monochloropropane-1,2-diol (3-MCPD) in selected food groups, 1999-2000

A survey of the levels of 3-monochloropropane-1,2-diol (3-MCPD) in a range of selected food products available in the UK is reported. The survey was carried out on behalf of the Food Standards Agency (FSA) to identify the food groups that might provide a significant contribution to 3-MCPD exposure from the diet. Three hundred samples comprising meat, dairy, cereal, soup and miscellaneous products were purchased from retail outlets and analysed using a GC-MS procedure, which had been formally validated by an earlier collaborative trial. 3-MCPD was detected in 89 (30%) of the samples. Three samples, all crackers, contained levels of 3-MCPD > 0.1 mg kg(-1), the highest level being 0.134 mg kg(-1). Levels of 3-MCPD were generally slightly higher in foods after cooking. In all cases where 3-MCPD was detected in cooked foods, it was also present in the uncooked sample.

The anti-inflammatory natural product parthenolide from the medicinal herb Feverfew directly binds to and inhibits IkappaB kinase

BACKGROUND

Biologically active natural products continue to be useful in the exploration and control of intracellular signaling processes. For example, the sesquiterpene lactone parthenolide from the anti-inflammatory medicinal herb Feverfew (Tanacetum parthenium) appears to inhibit the pro-inflammatory signaling pathway. Parthenolide's direct molecular target, however, remains unknown. We set out to identify the molecular mechanisms of parthenolide's anti-inflammatory activity.

RESULTS

A parthenolide affinity reagent was synthesized and shown to bind directly to and inhibit IkappaB kinase beta (IKKbeta), the kinase subunit known to play a critical role in cytokine-mediated signaling. Mutation of cysteine 179 in the activation loop of IKKbeta abolished sensitivity towards parthenolide. Moreover, we showed that parthenolide's in vitro and in vivo anti-inflammatory activity is mediated through the alpha-methylene gamma-lactone moiety shared by other sesquiterpene lactones.

CONCLUSIONS

In recent years, the multi-subunit IKK complex has been shown to be responsible for cytokine-mediated stimulation of genes involved in inflammation and as such represents an attractive target for pharmaceutical intervention. Our finding that parthenolide targets this kinase complex provides a possible molecular basis for the anti-inflammatory properties of parthenolide. In addition, these results may be useful in the development of additional anti-inflammatory agents.

Protacs: chimeric molecules that target proteins to the Skp1-Cullin-F box complex for ubiquitination and degradation

The intracellular levels of many proteins are regulated by ubiquitin-dependent proteolysis. One of the best-characterized enzymes that catalyzes the attachment of ubiquitin to proteins is a ubiquitin ligase complex, Skp1-Cullin-F box complex containing Hrt1 (SCF). We sought to artificially target a protein to the SCF complex for ubiquitination and degradation. To this end, we tested methionine aminopeptidase-2 (MetAP-2), which covalently binds the angiogenesis inhibitor ovalicin. A chimeric compound, protein-targeting chimeric molecule 1 (Protac-1), was synthesized to recruit MetAP-2 to SCF. One domain of Protac-1 contains the I kappa B alpha phosphopeptide that is recognized by the F-box protein beta-TRCP, whereas the other domain is composed of ovalicin. We show that MetAP-2 can be tethered to SCF(beta-TRCP), ubiquitinated, and degraded in a Protac-1-dependent manner. In the future, this approach may be useful for conditional inactivation of proteins, and for targeting disease-causing proteins for destruction.

The ubiquitin-proteasome pathway and proteasome inhibitors

The ubiquitin-proteasome pathway has emerged as a central player in the regulation of several diverse cellular processes. Here, we describe the important components of this complex biochemical machinery as well as several important cellular substrates targeted by this pathway and examples of human diseases resulting from defects in various components of the ubiquitin-proteasome pathway. In addition, this review covers the chemistry of synthetic and natural proteasome inhibitors, emphasizing their mode of actions toward the 20S proteasome. Given the importance of proteasome-mediated protein degradation in various intracellular processes, inhibitors of this pathway will continue to serve as both molecular probes of major cellular networks as well as potential therapeutic agents for various human diseases.

Relationship between genotype, activity, and galactose sensitivity in yeast expressing patient alleles of human galactose-1-phosphate uridylyltransferase

Impairment of the human enzyme galactose-1-phosphate uridylyltransferase (GALT) results in the potentially lethal disorder galactosemia; the biochemical basis of pathophysiology in galactosemia remains unknown. We have applied a yeast expression system for human GALT to test the hypothesis that genotype will correlate with GALT activity measured in vitro and with metabolite levels and galactose sensitivity measured in vivo. In particular, we have determined the relative degree of functional impairment associated with each of 16 patient-derived hGALT alleles; activities ranged from null to essentially normal. Next, we utilized strains expressing these alleles to demonstrate a clear inverse relationship between GALT activity and galactose sensitivity. Finally, we monitored accumulation of galactose-1-P, UDP-gal, and UDP-glc in yeast expressing a subset of these alleles. As reported for humans, yeast deficient in GALT, but not their wild type counterparts, demonstrated elevated levels of galactose 1-phosphate and diminished UDP-gal upon exposure to galactose. These results present the first clear evidence in a genetically and biochemically amenable model system of a relationship between GALT genotype, enzyme activity, sensitivity to galactose, and aberrant metabolite accumulation. As such, these data lay a foundation for future studies into the underlying mechanism(s) of galactose sensitivity in yeast and perhaps other eukaryotes, including humans.

The effects of domestic cooking on the levels of 3-monochloropropanediol in foods

The results are reported of a study to determine the effect of domestic cooking procedures on the level of 3-monochloropropane-1,2-diol (3-MCPD) in selected foods. Samples of 23 foods comprising stock cubes, gravies, a cake mix, batters, breads, cheese and meats were subjected to a range of cooking procedures including grilling, toasting and microwaving. The resulting levels of 3-MCPD were compared with those present in the foods before cooking. Grilling and toasting produced substantial increases in the 3-MCPD content of bread, forming up to 0.3 mg/kg, and of most cheeses, resulting in levels of up to about 0.1 mg/kg. Microwave cooking produced elevated 3-MCPD levels in some cheeses. Frying laboratory-produced batters increased 3-MCPD levels to about 0.1 mg/kg whereas a retail batter contained no detectable 3-MCPD when fried. The remaining foods showed little or no discernible increase on cooking.

Determination of 3-chloro-1,2-propanediol in foods and food ingredients by gas chromatography with mass spectrometric detection: collaborative study

The results of a collaborative study are reported for the determination of 3-chloro-1,2-propanediol (3-monochloropropane-1,2-diol; 3-MCPD) in a wide range of foods and food ingredients, using gas chromatography with mass spectrometric detection and incorporating the use of a deuterated internal standard. After a pretrial study, 12 laboratories (6 United Kingdom, 1 Switzerland, 1 Japan, 2 United States, 1 The Netherlands, and 1 from the European Commission) were asked to analyze 12 test materials (as known duplicates or split-level samples) by using a prescribed procedure. The test materials consisted of duplicate samples of acid-hydrolyzed vegetable protein (containing 3-MCPD at 0.029 mg/kg), malt extract (0.055 mg/kg), wholemeal bread crumbs (0.030 mg/kg), salami (0.016 mg/kg), cheese alternative (0.043 mg/kg), and soup powder (split levels at 0.045 and 0.041 mg/kg). Repeatability ranged from 0.005 to 0.013 mg/kg and reproducibility, from 0.010 to 0.027 mg/kg, for the samples tested. Precision values were well within statistically predicted levels (HORRAT values of <1 for 5 of the 6 matrixes tested) and within method criteria prepared by a joint working group composed of the United Kingdom Ministry of Agriculture, Fisheries and Food and industry representatives. The study demonstrated the satisfactory validation of the method for quantifying 3-MCPD at levels of > or = 0.010 mg/kg. The limit of detection derived from separate in-house studies was estimated to be 0.005 mg/kg. The method was adopted First Action by AOAC INTERNATIONAL.

Lack of proteasome active site allostery as revealed by subunit-specific inhibitors

The chymotrypsin-like (CT-L) activity of the proteasome is downregulated by substrates of the peptidyl-glutamyl peptide hydrolyzing (PGPH) activity. To investigate the nature of such interactions, we synthesized selective alpha',beta'-epoxyketone inhibitors of the PGPH activity. In cellular proliferation and protein degradation assays, these inhibitors revealed that selective PGPH inhibition was insufficient to inhibit protein degradation, indicating that the CT-L and PGPH sites function independently. We also demonstrated that CT-L inhibition by a PGPH substrate does not require the occupancy of the PGPH site or hydrolysis of the PGPH substrate. Thus, these results support a model in which a substrate of one subunit regulates the activity of another via binding to a noncatalytic site(s) rather than through binding to an active site.

Cells adapted to the proteasome inhibitor 4-hydroxy- 5-iodo-3-nitrophenylacetyl-Leu-Leu-leucinal-vinyl sulfone require enzymatically active proteasomes for continued survival

The proteasome is the primary protease used by cells for degrading proteins and generating peptide ligands for class I molecules of the major histocompatibility complex. Based on the properties of cells adapted to grow in the presence of the proteasome inhibitor 4-hydroxy-5-iodo-3-nitrophenylacetyl-Leu-Leu-leucinal-vinyl sulfone (NLVS), it was proposed that proteasomes can be replaced by alternative proteolytic systems, particularly a large proteolytic complex with a tripeptidyl peptidase II activity. Here we show that NLVS-adapted cells retain sensitivity to a number of highly specific proteasome inhibitors with regard to antigenic peptide generation, accumulation of polyubiquitinated proteins, degradation of p53, and cell viability. In addition, we show that in the same assays (with a single minor exception), NLVS-adapted cells are about as sensitive as nonselected cells to Ala-Ala-Phe-chloromethylketone, a specific inhibitor of tripeptidyl peptidase II activity. Based on these findings, we conclude that proteasomes still have essential proteolytic functions in adapted cells that are not replaced by Ala-Ala-Phe-chloromethylketone-sensitive proteases.

The antiangiogenic agent TNP-470 requires p53 and p21CIP/WAF for endothelial cell growth arrest

Targeting the endothelial cell cycle as an antiangiogenic strategy has been difficult given the ubiquitous expression of critical cell cycle regulators. Here, we show that the antiangiogenic drug TNP-470 displays striking cell-type specificity insofar as it induces the expression of p21(CIP/WAF), a cyclin-dependent kinase inhibitor, in endothelial cells but not in embryonic or adult fibroblasts. Moreover, primary endothelial cells isolated from p53(-/-) and p21(CIP/WAF-/-) mice are resistant to the cytostatic activity of TNP-470. We also demonstrate that p21(CIP/WAF-/-) mice are resistant to the antiangiogenic activity of TNP-470 in the basic fibroblast growth factor corneal micropocket angiogenesis assay. We conclude that TNP-470 induces p53 activation through a unique mechanism in endothelial cells leading to p21(CIP/WAF) expression and subsequent growth arrest.

3-monochloropropane-1,2-diol (3-MCPD) in soy sauces and similar products available from retail outlets in the UK

A survey of the level of 3-monochloropropane-1,2-diol (3-MCPD) in soy sauces and similar products available in the UK is reported. The survey was carried out by the Joint Ministry of Agriculture, Fisheries and Food/Department of Health Food Safety and Standards Group (JFSSG) to check for compliance with the Food Advisory Committee's (FAC) recommended limit for 3-MCPD of 0.01 mg/kg following reports that soy sauces in several European countries had been found to contain high levels (up to 124 mg/kg) of 3-MCPD. Forty samples of soy sauce and similar products purchased from retail outlets were analysed using a GC-MS procedure which had been formally validated by an earlier collaborative trial. 3-MCPD was undetectable in 21 (52%) of samples analysed in the survey, with a further five samples containing very low levels of between 0.01 and 0.02 mg/kg. Five samples (13%) contained 3-MCPD at levels in the range 0.020-1 mg/kg while nine samples (23%) were found to contain 3-MCPD at levels greater than 1 mg/kg, with the highest level being 30.5 mg/kg.

An improved method for the measurement of added vegetable fats in chocolate

A method for identifying refined vegetable fats added to chocolate (cocoa butter equivalents, CBEs) was combined with established quantitative methods for determining the level of vegetable fat added to cocoa butter with the aim of providing improved precision. The identification of fats was based on the analysis of sterol and triterpene alcohol degradation products formed during the processing of the fat. The procedure was able to successfully discriminate between 95% of pairs of fats from a set (33) of CBE-type vegetable fats. Subsequent analysis of 80 mixtures of four CBEs with chocolate successfully identified, on cross-validation, 94% of the samples. Combining the qualitative procedure with established quantitative methodology, based on the analysis of triacylglycerols, improved the method precision from +/- 2.1% to +/- 0.3% (5% addition of CBE at 95% confidence). Identifying the fat analytically permits the use of quantitative methods for determining the level of added fat in chocolate that have improved precision in comparison with the measurement of an unidentified fat. This may obviate the need to use factory inspection as a means to identify the ingredients of a product and monitor compliance with proposed legislation.

Functional consequence of substitutions at residue 171 in human galactose-1-phosphate uridylyltransferase

Impairment of the human enzyme galactose-1-phosphate uridylyltransferase (hGALT) results in the potentially lethal disorder classic galactosemia. Although a variety of naturally occurring mutations have been identified in patient alleles, few have been well characterized. We have explored the functional significance of a common patient mutation, F171S, using a strategy of conservative substitution at the defined residue followed by expression of the wild-type and, alternatively, substituted proteins in a null-background strain of yeast. As expected from patient studies, the F171S-hGALT protein demonstrated <0.1% wild-type levels of activity, although two of three conservatively substituted moieties, F171L- and F171Y-hGALT, demonstrated approximately 10% and approximately 4% activity, respectively. The third protein, F171W, demonstrated severely reduced abundance, precluding further study. Detailed kinetic analyses of purified wild-type, F171L- and F171Y-hGALT enzymes, coupled with homology modeling of these proteins, enabled us to suggest that the effects of these substitutions resulted largely from altering the position of a catalytically important residue, Gln-188, and secondarily, by altering the subunit interface and perturbing hexose binding to the uridylylated enzyme. These results not only provide insight into the functional impact of a single common patient allele and offer a paradigm for similar studies of other clinically or biochemically important residues, but they further help to elucidate activity of the wild-type human GALT enzyme.

Small-molecule inhibitors of the cell cycle

The cell cycle remains an attractive target for the development of small-molecule inhibitors for use as both novel chemotherapeutics and research probes. Given the importance of cytoskeletal dynamics and cyclin-dependent kinases for cell-cycle progression, much interest has focused on the identification of anti-mitotic agents and kinase inhibitors. However recent advances in cell-based screening technologies and an increased interest in inhibitors with greater specificity are beginning to influence the search for novel cell-cycle inhibitors.

Benzene accumulation in horticultural crops

In this study apple, blackberry and cucumber crops were exposed to elevated levels of benzene under controlled conditions. Benzene was retained in fruits of all crops, but only accumulated in leaves of blackberries and apples. The retention by cucumber fruits is suggested to result from the longer pathway for the desorption of benzene as a consequence of their increased tissue depth compared to leaves. The process of accumulation in blackberry and apple leaves is unknown. The ingestion of benzene via the food-chain pathway on the basis of this study is concluded not to be significant.

Proteasome inhibition by the natural products epoxomicin and dihydroeponemycin: insights into specificity and potency

While two structurally related epoxyketone-containing antitumor natural products, epoxomicin and eponemycin, share the proteasome as a common intracellular target, they differ in their antiproliferative activity, proteasome subunit binding specificity, and rates of proteasome inhibition. As a first step towards understanding such differences and developing novel proteasome subunit-specific inhibitors, we report here the synthesis and characterization of epoxomicin/dihydroeponemycin chimerae.

Towards subunit-specific proteasome inhibitors: synthesis and evaluation of peptide alpha',beta'-epoxyketones

BACKGROUND

The proteasome is a large multicatalytic protease complex (700 kDa) involved in a number of highly regulated processes. It has three major catalytic activities: a chymotrypsin-like activity, a trypsin-like activity and a post-glutamyl peptide hydrolyzing (PGPH) activity. To be useful as molecular probes, which could help dissect the cellular functions of the proteasome, inhibitors should be specific for the proteasome, active in vivo and selectively block only one of the three catalytic activities. To date, few inhibitors fulfill these requirements so we set out to make novel proteasome inhibitors that incorporate these characteristics.

RESULTS

A panel of amino-terminally acetylated peptide alpha',beta'-epoxyketones with leucine in P1 and various aliphatic or aromatic amino acids in P2-P4 were prepared and evaluated. Most compounds selectively inhibited the chymotrypsin-like activity, while only weakly inhibiting the trypsin-like and PGPH activities. After optimization, one inhibitor, Ac-hFLFL-epoxide, was found to be more potent and selective for the inhibition of the chymotrypsin-like activity than several previously described inhibitors. This inhibitor also exhibited strong in vivo anti-inflammatory activity.

CONCLUSIONS

Optimization of amino-terminally acetylated peptide alpha',beta'-epoxyketones furnished a potent proteasome inhibitor, Ac-hFLFL-epoxide, that has an excellent selectivity for the chymotrypsin-like activity. The inhibitor also proved to be a potent antiproliferative and anti-inflammatory agent. The strong in vivo and in vitro activities suggest that this class of proteasome inhibitors could be both molecular probes and therapeutic agents.

Epoxomicin, a potent and selective proteasome inhibitor, exhibits in vivo antiinflammatory activity

The proteasome regulates cellular processes as diverse as cell cycle progression and NF-kappaB activation. In this study, we show that the potent antitumor natural product epoxomicin specifically targets the proteasome. Utilizing biotinylated-epoxomicin as a molecular probe, we demonstrate that epoxomicin covalently binds to the LMP7, X, MECL1, and Z catalytic subunits of the proteasome. Enzymatic analyses with purified bovine erythrocyte proteasome reveal that epoxomicin potently inhibits primarily the chymotrypsin-like activity. The trypsin-like and peptidyl-glutamyl peptide hydrolyzing catalytic activities also are inhibited at 100- and 1,000-fold slower rates, respectively. In contrast to peptide aldehyde proteasome inhibitors, epoxomicin does not inhibit nonproteasomal proteases such trypsin, chymotrypsin, papain, calpain, and cathepsin B at concentrations of up to 50 microM. In addition, epoxomicin is a more potent inhibitor of the chymotrypsin-like activity than lactacystin and the peptide vinyl sulfone NLVS. Epoxomicin also effectively inhibits NF-kappaB activation in vitro and potently blocks in vivo inflammation in the murine ear edema assay. These results thus define epoxomicin as a novel proteasome inhibitor that likely will prove useful in exploring the role of the proteasome in various in vivo and in vitro systems.

Total synthesis of the potent proteasome inhibitor epoxomicin: a useful tool for understanding proteasome biology

Epoxomicin (1), a peptide alpha',beta'-epoxyketone isolated from the actinomycete strain No.Q996-17, possesses potent in vivo anti-tumor and anti-inflammatory activities. In this paper, we report the first syntheses of epoxomicin, [3H]-epoxomicin, and a biotinylated epoxomicin analog as well as the absolute configuration of the epoxide stereocenter. The natural product and derivatives have permitted the first identification of the proteasome as the specific cellular target of epoxomicin.

Chemical genetics: exploring and controlling cellular processes with chemical probes

The new field of chemical biology brings together chemists and biologists who are seeking to understand and mimic the natural world. One research strategy in this new field is the development of biologically active small molecules as molecular probes. This approach, which has been called 'chemical' genetics, has allowed elucidation of several pathways that have been difficult to study using traditional genetic approaches.