An open-label, dose-escalation, safety, and pharmacokinetics phase I study of ombrabulin, a vascular disrupting agent, administered as a 30-min intravenous infusion every 3 weeks in Japanese patients with advanced solid tumors

PURPOSE

To determine ombrabulin's maximum tolerated dose and dose recommended for Japanese patients with advanced solid tumors and to assess its antitumor activity and overall safety and pharmacokinetic profiles.

METHODS

This was a multi-center, open-label, sequential-cohort, dose-escalation phase I study of ombrabulin, a vascular disrupting agent, administered once every 3 weeks. Patients were treated with 15.5, 25, 35, or 50 mg/m(2) ombrabulin over a 30-min intravenous infusion. The recommended dose was the highest dose at which <33 % of all evaluable patients experienced dose-limiting toxicities (DLTs) during the first treatment cycle or 50 mg/m(2) (recommended in Caucasian patients) if the previous definition was not met.

RESULTS

Fifteen patients were treated. No DLT occurred with 15.5, 25, or 35 mg/m(2) ombrabulin. In the 50 mg/m(2) group, one patient had Grade 3 lymphopenia, and another experienced Grade 2 hypertension and Grade 3 diarrhea judged as DLTs. The most frequent related adverse events in this group were diarrhea, nausea, and hypertension. Two patients had Grade 3 anemia, one at the 15.5 mg/m(2) and the other at the 50 mg/m(2). No AEs necessitating dose reduction or Grade 4 AEs were observed. Overall, five patients had stable disease. Pharmacokinetic parameters were comparable to those in non-Japanese patients.

CONCLUSIONS

Ombrabulin treatment once every 3 weeks was well tolerated in Japanese patients with advanced solid tumors. The dose recommended is 50 mg/m(2), as in Caucasian patients. The safety and pharmacokinetic profiles were comparable between Japanese and Caucasian patients (funded by Sanofi; ClinicalTrials.gov number, NCT00968916).

Biochemical properties of nematode O-acetylserine(thiol)lyase paralogs imply their distinct roles in hydrogen sulfide homeostasis

O-Acetylserine(thiol)lyases (OAS-TLs) play a pivotal role in a sulfur assimilation pathway incorporating sulfide into amino acids in microorganisms and plants, however, these enzymes have not been found in the animal kingdom. Interestingly, the genome of the roundworm Caenorhabditis elegans contains three expressed genes predicted to encode OAS-TL orthologs (cysl-1-cysl-3), and a related pseudogene (cysl-4); these genes play different roles in resistance to hypoxia, hydrogen sulfide and cyanide. To get an insight into the underlying molecular mechanisms we purified the three recombinant worm OAS-TL proteins, and we determined their enzymatic activities, substrate binding affinities, quaternary structures and the conformations of their active site shapes. We show that the nematode OAS-TL orthologs can bind O-acetylserine and catalyze the canonical reaction although this ligand may more likely serve as a competitive inhibitor to natural substrates instead of being a substrate for sulfur assimilation. In addition, we propose that S-sulfocysteine may be a novel endogenous substrate for these proteins. However, we observed that the three OAS-TL proteins are conformationally different and exhibit distinct substrate specificity. Based on the available evidences we propose the following model: CYSL-1 interacts with EGL-9 and activates HIF-1 that upregulates expression of genes detoxifying sulfide and cyanide, the CYSL-2 acts as a cyanoalanine synthase in the cyanide detoxification pathway and simultaneously produces hydrogen sulfide, while the role of CYSL-3 remains unclear although it exhibits sulfhydrylase activity in vitro. All these data indicate that C. elegans OAS-TL paralogs have distinct cellular functions and may play different roles in maintaining hydrogen sulfide homeostasis.

Cyclopeptide alkaloids: stereochemistry and synthesis of the precursors of discarines C and D and myrianthine A

The stereochemistry of discarines C (1) and D (2) and myrianthine A (3), three cyclopeptide alkaloids isolated from Discaria febrifuga, was determined by a combination of NMR studies of 1-3, enantioselective gas chromatography, and comparison of NMR data with those of synthetic tripeptides. For the synthesis of peptides, the nonproteinogenic amino acid 3-phenylserine was also obtained in its four diastereoisomeric forms (l and d threo, obtained by recrystallization of the diastereoisomeric tripeptide, and l and d erythro, obtained by a Mitsunobu reaction with the threo-tripeptides). The general synthetic strategy described in this paper allows the tripeptide to be obtained with the free N-terminal extremity protected or dimethylated. This strategy also allows the synthesis of the corresponding peptide with an imidazolidinone ring.

Direct targeting of Arabidopsis cysteine synthase complexes with synthetic polypeptides to selectively deregulate cysteine synthesis

Biosynthesis of cysteine is one of the fundamental processes in plants providing the reduced sulfur for cell metabolism. It is accomplished by the sequential action of two enzymes, serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL). Together they constitute the hetero-oligomeric cysteine synthase (CS) complex through specific protein-protein interactions influencing the rate of cysteine production. The aim of our studies was to deregulate the CS complex formation in order to investigate its function in the control of sulfur homeostasis and optimize cysteine synthesis. Computational modeling was used to build a model of the Arabidopsis thaliana mitochondrial CS complex. Several polypeptides based on OAS-TL C amino-acid sequence found at SAT-OASTL interaction sites were designed as probable competitors for SAT3 binding. After verification of the binding in a yeast two-hybrid assay, the most strongly interacting polypeptide was introduced to different cellular compartments of Arabidopsis cell via genetic transformation. Moderate increase in total SAT and OAS-TL activities, but not thiols content, was observed dependent on the transgenic line and sulfur availability in the hydroponic medium. Though our studies demonstrate the proof of principle, they also suggest more complex interaction of both enzymes underlying the mechanism of their reciprocal regulation.

D-Serine facilitates the effectiveness of extinction to reduce drug-primed reinstatement of cocaine-induced conditioned place preference

Addiction is a disease that is characterized by compulsive drug-seeking and use despite negative health and social consequences. One obstacle in treating addiction is a high susceptibility for relapse which persists despite prolonged periods of abstinence. Relapse can be triggered by drug predictive stimuli such as environmental context and drug associated cues, as well as the addictive drug itself. The conditioned place preference (CPP) behavioral model is a useful paradigm for studying the ability of these drug predictive stimuli to reinstate drug-seeking behavior. The present study investigated the dose-dependent effects of D-serine (10 mg/kg, 30 mg/kg and 100 mg/kg) on extinction training and drug-primed reinstatement in cocaine-conditioned rats. In the first experiment, D-serine had no effect on the acquisition or development of cocaine-induced locomotor sensitization or CPP. In the second experiment, D-serine treatment resulted in significantly decreased time spent in the drug-paired compartment following completion of an extinction protocol. A cocaine-primed reinstatement test indicated that the combination of extinction training along with D-serine treatment resulted in a significant reduction of drug-seeking behavior. The third experiment assessed D-serine's long-term effects to diminish drug-primed reinstatement. D-serine treatment given during extinction was effective in reducing drug-seeking for more than four weeks of abstinence after the last cocaine exposure. These findings demonstrate that D-serine may be an effective adjunct therapeutic agent along with cognitive behavioral therapy for the treatment of cocaine addiction. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Local and systemic regulation of sulfur homeostasis in roots of Arabidopsis thaliana

Nutrients are limiting for plant growth and vigour. Hence, nutrient uptake and homeostasis must be adjusted to the needs of the plant according to developmental stages and environmental conditions. A split-root system was applied to analyse the systemic and local response of Arabidopsis thaliana to sulfur starvation. Arabidopsis thaliana plants in which only one root half was starved while the other root half was supplied with sulfate were analysed at the metabolic and transcriptional level. No systemic induction of sulfate uptake or expression of sulfate starvation marker genes was observed in split-roots sufficiently supplied with sulfate. Our data suggest that no activation of sulfur uptake takes part in sulfur-supplied root patches when the general sulfur status declines. When comparing roots of fully sulfate-starved plants with sulfate-starved split-root roots, expression of several potentially OAS responsive genes was attenuated in split-roots depending on the shoot sulfate status and the local root O-acetylserine concentration. In contrast, high-affinity sulfate transporters displayed similar expression in sulphate-starved split-roots and the corresponding controls. Feeding of (35) SO(4) (2-) to the shoot or to either part of a split-root system revealed that sulfate is the most prominent mobile sulfur-containing compound within the plant. Hence, we postulate a model whereby the soil sulfate availability regulates the sulfate uptake system of roots while the shoot sulfur status modulates the local O-acetylserine response in the root by passive 'plant sulfur status-dependent' transport of sulfate.

Transcripts of sulphur metabolic genes are co-ordinately regulated in developing seeds of common bean lacking phaseolin and major lectins

The lack of phaseolin and phytohaemagglutinin in common bean (dry bean, Phaseolus vulgaris) is associated with an increase in total cysteine and methionine concentrations by 70% and 10%, respectively, mainly at the expense of an abundant non-protein amino acid, S-methyl-cysteine. Transcripts were profiled between two genetically related lines differing for this trait at four stages of seed development using a high density microarray designed for common bean. Transcripts of multiple sulphur-rich proteins were elevated, several previously identified by proteomics, including legumin, basic 7S globulin, albumin-2, defensin, albumin-1, the Bowman-Birk type proteinase inhibitor, the double-headed trypsin inhibitor, and the Kunitz trypsin inhibitor. A co-ordinated regulation of transcripts coding for sulphate transporters, sulphate assimilatory enzymes, serine acetyltransferases, cystathionine β-lyase, homocysteine S-methyltransferase and methionine gamma-lyase was associated with changes in cysteine and methionine concentrations. Differential gene expression of sulphur-rich proteins preceded that of sulphur metabolic enzymes, suggesting a regulation by demand from the protein sink. Up-regulation of SERAT1;1 and -1;2 expression revealed an activation of cytosolic O-acetylserine biosynthesis. Down-regulation of SERAT2;1 suggested that cysteine and S-methyl-cysteine biosynthesis may be spatially separated in different subcellular compartments. Analysis of free amino acid profiles indicated that enhanced cysteine biosynthesis was correlated with a depletion of O-acetylserine. These results contribute to our understanding of the regulation of sulphur metabolism in developing seed in response to a change in the composition of endogenous proteins.

A novel in-gel assay and an improved kinetic assay for determining in vitro sulfite reductase activity in plants

Sulfite reductase (SiR; EC 1.8.7.1), an essential enzyme in the sulfate reduction pathway, catalyzes the reduction of sulfite to sulfide, as an intermediate for cysteine biosynthesis. The commonly used kinetic assay for the detection of in vitro SiR activity in plants is based on a coupled reaction, in which the sulfide produced is converted to cysteine through the presence, in the assay medium, of O-acetylserine sulfhydralase (EC 2.5.1.47) and its substrate, O-acetylserine. An improved kinetic assay for SiR activity in crude desalted protein extracts was developed. The improvement was based on pre-treatment of the protein with tungstate, which improved SiR activity in Arabidopsis and tomato leaf by 29 and 12%, respectively, and the addition of NADPH to the reaction medium, which increased SiR activity by 1.6- and 2.8-fold in Arabidopsis and tomato, respectively, in comparison with the current protocols. Despite the availability and reliability of the kinetic assay, there is currently no assay that enables the direct detection of SiR in relatively large numbers of samples. To meet this need, we developed a novel in-gel assay to detect SiR activity in crude extracts. The method is based on the detection of a brownish-black precipitated band of lead sulfide, formed by the reaction of lead acetate with sulfide. The in-gel assay for SiR activity is reliable, sensitive and technically simpler than the kinetic assay, and opens up the possibility for detecting active SiR isoenzymes and splice variants.

The vascular disrupting agent ombrabulin (AVE8062) enhances the efficacy of standard therapies in head and neck squamous cell carcinoma xenograft models

Targeting tumor vasculature is an emerging strategy in cancer treatment. Promising results have been shown in preclinical studies when vascular disrupting agents (VDAs) are used in combination with other anticancer therapies. Because radiation therapy with concurrent cisplatin or cetuximab has become standard treatment for patients with locally advanced head and neck squamous cell carcinoma (HNSCC), we investigated whether the VDA ombrabulin (AVE8062) could improve the antitumor activity of radiation plus cisplatin and radiation plus cetuximab combinations. HNSCC HEP2 or FaDu tumor bearing mice were treated with ombrabulin, cisplatin, cetuximab, local radiation therapy or combinations of these treatments. Ombrabulin attenuated tumor growth of HEP2 and FaDu xenografts compared to control tumors. A more pronounced tumor growth delay and tumor regression were induced when ombrabulin was added to local irradiation, cisplatin or cetuximab in FaDu tumors compared to single agent treatments. Finally, triple agent therapies combining ombrabulin, irradiation, and either cisplatin or cetuximab were more effective than double combination treatment regimens and increased tumor growth delay in both HEP2 and FaDu tumor models. Of note, complete tumor regression was achieved in FaDu tumor model for the triple combination including platinum. Immunohistochemistry on FaDu tumors demonstrated a specificity of ombrabulin towards intratumoral vessels, in contrast to peritumoral vasculature. Our results provide a rationale for the use of ombrabulin in combination with two standard treatment regimens that are concurrent cisplatin-based chemoradiation and cetuximab plus ionizing radiation therapies, for the treatment of HNSCC.

A convenient route to optically pure α-alkyl-β-(sec-amino)alanines

The cyclization of N-Boc-α-alkylserines to corresponding β-lactones under Mitsunobu reaction conditions and the ring opening with heterocyclic amines (pyrrolidine, piperidine, morpholine and thiomorpholine) produced N-Boc-α-alkyl-β-(sec-amino)alanines. The removal of the Boc group gives di-hydrochlorides of non-protein amino acids.

Additional role of O-acetylserine as a sulfur status-independent regulator during plant growth

O-acetylserine (OAS) is one of the most prominent metabolites whose levels are altered upon sulfur starvation. However, its putative role as a signaling molecule in higher plants is controversial. This paper provides further evidence that OAS is a signaling molecule, based on computational analysis of time-series experiments and on studies of transgenic plants conditionally displaying increased OAS levels. Transcripts whose levels correlated with the transient and specific increase in OAS levels observed in leaves of Arabidopsis thaliana plants 5-10 min after transfer to darkness and with diurnal oscillation of the OAS content, showing a characteristic peak during the night, were identified. Induction of a serine-O-acetyltransferase gene (SERAT) in transgenic A. thaliana plants expressing the genes under the control of an inducible promoter resulted in a specific time-dependent increase in OAS levels. Monitoring the transcriptome response at time points at which no changes in sulfur-related metabolites except OAS were observed and correlating this with the light/dark transition and diurnal experiments resulted in identification of six genes whose expression was highly correlated with that of OAS (adenosine-5'-phosphosulfate reductase 3, sulfur-deficiency-induced 1, sulfur-deficiency-induced 2, low-sulfur-induced 1, serine hydroxymethyltransferase 7 and ChaC-like protein). These data suggest that OAS displays a signalling function leading to changes in transcript levels of a specific gene set irrespective of the sulfur status of the plant. Additionally, a role for OAS in a specific part of the sulfate response can be deduced.

The key enzyme of sulfate assimilation, adenosine 5'-phosphosulfate reductase, is regulated by HY5 in Arabidopsis

Plant sulfate assimilation is regulated by demand for reduced sulfur, as is its key enzyme, adenosine 5'-phosphosulfate reductase (APR). In a genetic screen for mutants lacking this regulation, we identified the bZIP transcription factor LONG HYPOCOTYL 5 (HY5) as a necessary component of the regulatory circuit. Regulation of APR activity by the inhibitor of glutathione synthesis, buthionine sulfoximine, or by the precursor of cysteine, O-acetylserine, was disrupted in the hy5 mutant. When dark-adapted plants were re-illuminated, the rapid induction of APR1 and APR2 mRNA levels was attenuated in hy5 seedlings, but APR3 regulation was not affected. Chromatin immunoprecipitation revealed that HY5 binds directly to the APR1 and APR2 promoters but not to the APR3 promoter. Accordingly, the regulation of APR1 and APR2 by O-acetylserine was disturbed in hy5 roots. HY5 is also important for the coordination of nitrogen and sulfur assimilation, as, unlike the wild-type, hy5 mutants do not undergo a reduction in sulfate uptake and APR activity during nitrogen starvation. Altogether, these data show that HY5 plays an important role in regulation of APR gene expression and plant sulfate assimilation.

Cardiovascular toxicity profiles of vascular-disrupting agents

BACKGROUND

Vascular-disrupting agents (VDAs) represent a new class of chemotherapeutic agent that targets the existing vasculature in solid tumors. Preclinical and early-phase trials have demonstrated the promising therapeutic benefits of VDAs but have also uncovered a distinctive toxicity profile highlighted by cardiovascular events.

METHODS

We reviewed all preclinical and prospective phase I-III clinical trials published up to August 2010 in MEDLINE and the American Association of Cancer Research and American Society of Clinical Oncology meeting abstracts of small-molecule VDAs, including combretastatin A4 phosphate (CA4P), combretastatin A1 phosphate (CA1P), MPC-6827, ZD6126, AVE8062, and ASA404.

RESULTS

Phase I and II studies of CA1P, ASA404, MPC-6827, and CA4P all reported cardiovascular toxicities, with the most common cardiac events being National Cancer Institute Common Toxicity Criteria (version 3) grade 1-3 hypertension, tachyarrhythmias and bradyarrhythmias, atrial fibrillation, and myocardial infarction. Cardiac events were dose-limiting toxicities in phase I trials with VDA monotherapy and combination therapy.

CONCLUSIONS

Early-phase trials of VDAs have revealed a cardiovascular toxicity profile similar to that of their vascular-targeting counterparts, the angiogenesis inhibitors. As these agents are added to the mainstream chemotherapeutic arsenal, careful identification of baseline cardiovascular risk factors would seem to be a prudent strategy. Close collaboration with cardiology colleagues for early indicators of serious cardiac adverse events will likely minimize toxicity while optimizing the therapeutic potential of VDAs and ultimately enhancing patient outcomes.

[Spectral study on the interaction of [Cu(DPPZ)(L-Ser)]+ complex with DNA and its analytical application]

The characteristics of resonance light scattering (RLS), UV-visible absorption spectra and fluorescence spectra of [Cu(DPPZ)(L-Ser)]+ with DNA were studied and a RLS method for the determination of DNA was established. [Cu(DPPZ) (L-Ser)]+ could assemble on the surface of DNA through intercalation, and enhanced the RLS of DNA in the tris buffer of pH 7. 2. The maximum resonance light scattering peak appeared at 400 nm. Under the optimum conditions, the enhanced intensity of RLS was proportional to the concentration of DNA over the range of 0.42 - 4.2 ng x mL(-1), with a detection limit (3sigma/k) of 0.29 ng x mL(-1). The method was used for the determination of DNA samples with the recoveries between 97.8% and 106%.

Contrast ultrasonography: necessity of linear data processing for the quantification of tumor vascularization

PURPOSE

This study is intended to compare the value of uncompressed ultrasonic data, obtained after linear power detection of the ultrasonic radiofrequencies that we call linear data, with usual compressed video data for the quantification of tumor perfusion, particularly for monitoring antivascular therapy.

MATERIALS AND METHODS

To form a clinically useful ultrasonic image, the detected power of the received signals (linear data) is compressed in a quasi-logarithmic fashion in order to match the limited dynamic range of the video monitor. The resulting reduced range of signals from an injected contrast agent may limit the sensitivity to changes in the time-intensity curves. Following a theoretical evaluation of the effects of compression on time-intensity curves and as an in vivo example, we measured at different times the effects of an antivascular drug administered to mice bearing melanoma tumors. The mean time-intensity curves within the tumors after bolus injection of a contrast agent were determined using both linear and video data. Linearized data was recovered using the inverse of the true scanner's compression law, which was experimentally determined. Three features were extracted from the time-intensity curves: peak intensity (PI), time to peak intensity (TPI) and area under the curve in the wash-in phase (AUC (wash-in)). When contrast reached its maximum value, the coefficient of variation reflecting the heterogeneity of the intensity of contrast uptake within the tumor, was computed using both data sets.

RESULTS

TPI was found to be similar with either data set (r = 0.98, p < 0.05, factor of 1.09). Linear PI and AUC (wash-in) had significantly earlier decreases after drug administration than video data (p = 0.015 and p = 0.03, respectively). The coefficient of variation was significantly lower when using video rather than linear data (p < 10 (-4)).

CONCLUSION

In conclusion, the use of linear data is the only mathematically valid methodology for determining a tumor's time-intensity curve and, in practice, it allows earlier demonstration of responses to antivascular drugs.

[Advances in the study of the anti-tumor activity of small molecule vascular disrupting agents]

Vascular disrupting agents (VDAs) have presented a new kind of anti-cancer drug in recent years. VDAs take advantage of the weakness of established tumor endothelial cells and their supporting structures. In contrast to anti-angiogenic therapy, which inhibits the outgrowth of new blood vessels, vascular targeting treatments selectively attack the existing tumor vasculature. Here we summarized the anti-tumor activities, mechanisms and clinical applications of small molecule VDAs.

Overexpression of serine acetlytransferase produced large increases in O-acetylserine and free cysteine in developing seeds of a grain legume

There have been many attempts to increase concentrations of the nutritionally essential sulphur amino acids by modifying their biosynthetic pathway in leaves of transgenic plants. This report describes the first modification of cysteine biosynthesis in developing seeds; those of the grain legume, narrow leaf lupin (Lupinus angustifolius, L.). Expression in developing lupin embryos of a serine acetyltransferase (SAT) from Arabidopsis thaliana (AtSAT1 or AtSerat 2;1) was associated with increases of up to 5-fold in the concentrations of O-acetylserine (OAS), the immediate product of SAT, and up to 26-fold in free cysteine, resulting in some of the highest in vivo concentrations of these metabolites yet reported. Despite the dramatic changes in free cysteine in developing embryos of SAT overexpressers, concentrations of free methionine in developing embryos, and the total cysteine and methionine concentrations in mature seeds were not significantly altered. Pooled F(2) seeds segregating for the SAT transgene and for a transgene encoding a methionine- and cysteine-rich sunflower seed storage protein also had increased OAS and free cysteine, but not free methionine, during development, and no increase in mature seed total sulphur amino acids compared with controls lacking SAT overexpression. The data support the view that the cysteine biosynthetic pathway is active in developing seeds, and indicate that SAT activity limits cysteine biosynthesis, but that cysteine supply is not limiting for methionine biosynthesis or for storage protein synthesis in maturing lupin embryos in conditions of adequate sulphur nutrition. OAS and free methionine, but not free cysteine, were implicated as signalling metabolites controlling expression of a gene for a cysteine-rich seed storage protein.

Total synthesis of (+)-conagenin

A new approach for the synthesis of the (+)-conagenin has been achieved based on Evans asymmetry syn-aldol reaction and the self-regeneration of stereocenters strategy.

A genome-wide and metabolic analysis determined the adaptive response of Arabidopsis cells to folate depletion induced by methotrexate

Control of folate homeostasis is essential to sustain the demand for one-carbon (C1) units that are necessary for major biological functions, including nucleotide synthesis and methylation reactions. In this study, we analyzed the genome-wide and metabolic adaptive response of Arabidopsis (Arabidopsis thaliana) cells to folate depletion induced by the antifolate methotrexate. Drug treatment induced a response typical to xenobiotic stress and important changes in folate content and composition. This resulted in a reduction of cell division and primary energy metabolism that was likely associated with perturbation of nucleotide homeostasis. Through a modification of serine metabolism, folate depletion also induced O-acetylserine accumulation and mimicked sulfur deficiency response. The major adaptive response to folate limitation concerned the composition of the folate pool rather than the intracellular level of cofactors. Thus, no significant change in the expression of genes involved in cofactor synthesis, degradation, or trafficking was observed. However, changes in the distribution of C1 derivative pools and increased expression levels for transcripts coding enzymes manipulating C1 moieties in plastids suggested a reorientation of C1 units toward the synthesis of purine and thymidylate. Also, no genomic or metabolic adaptation was built up to counterbalance the major impairment of the methyl index, which controls the efficiency of methylation reactions in the cell. Together, these data suggested that the metabolic priority of Arabidopsis cells in response to folate limitation was to shuttle the available folate derivatives to the synthesis of nucleotides at the expense of methylation reactions.

Mitochondrial serine acetyltransferase functions as a pacemaker of cysteine synthesis in plant cells

Cysteine (Cys) synthesis in plants is carried out by two sequential reactions catalyzed by the rate-limiting enzyme serine acetyltransferase (SAT) and excess amounts of O-acetylserine(thiol)lyase. Why these reactions occur in plastids, mitochondria, and cytosol of plants remained unclear. Expression of artificial microRNA (amiRNA) against Sat3 encoding mitochondrial SAT3 in transgenic Arabidopsis (Arabidopsis thaliana) plants demonstrates that mitochondria are the most important compartment for the synthesis of O-acetylserine (OAS), the precursor of Cys. Reduction of RNA levels, protein contents, SAT enzymatic activity, and phenotype strongly correlate in independent amiSAT3 lines and cause significantly retarded growth. The expression of the other four Sat genes in the Arabidopsis genome are not affected by amiRNA-SAT3 according to quantitative real-time polymerase chain reaction and microarray analyses. Application of radiolabeled serine to leaf pieces revealed severely reduced incorporation rates into Cys and even more so into glutathione. Accordingly, steady-state levels of OAS are 4-fold reduced. Decrease of sulfate reduction-related genes is accompanied by an accumulation of sulfate in amiSAT3 lines. These results unequivocally show that mitochondria provide the bulk of OAS in the plant cell and are the likely site of flux regulation. Together with recent data, the cytosol appears to be a major site of Cys synthesis, while plastids contribute reduced sulfur as sulfide. Thus, Cys synthesis in plants is significantly different from that in nonphotosynthetic eukaryotes at the cellular level.

Recent advances in understanding plant response to sulfur-deficiency stress

Sulfur is an essential macronutrient for all living organisms. Plants are able to assimilate inorganic sulfur and incorporate it into organic compounds, while animals rely entirely on organic sources of sulfur. In the last decades sulfate availability in soils has become the major limiting factor for plant production in many countries due to significant reduction of anthropogenic sulfur emission forced by introducing stringent environmental legislation. The sulfur flux after transferring plants from optimal conditions to sulfur deficiency is regulated on multiple levels including transcription, translation and activity of enzymes needed for sulfate assimilation and synthesis of sulfur-containing metabolites. Most of these regulatory steps are not yet fully characterized. Plant responses to sulfur limitation are complex and can be divided into phases depending on the degree of sulfur shortage. The initial responses are limited to adaptations within sulfur metabolic pathway, while multiple metabolic pathways and developmental process are affected when sulfur shortage becomes more severe. The major aim of this work is a comprehensive review of recent progress in understanding the regulation of plant adaptations to sulfur deficit.

Comparative genomics and reverse genetics analysis reveal indispensable functions of the serine acetyltransferase gene family in Arabidopsis

Ser acetyltransferase (SERAT), which catalyzes O-acetyl-Ser (OAS) formation, plays a key role in sulfur assimilation and Cys synthesis. Despite several studies on SERATs from various plant species, the in vivo function of multiple SERAT genes in plant cells remains unaddressed. Comparative genomics studies with the five genes of the SERAT gene family in Arabidopsis thaliana indicated that all three Arabidopsis SERAT subfamilies are conserved across five plant species with available genome sequences. Single and multiple knockout mutants of all Arabidopsis SERAT gene family members were analyzed. All five quadruple mutants with a single gene survived, with three mutants showing dwarfism. However, the quintuple mutant lacking all SERAT genes was embryo-lethal. Thus, all five isoforms show functional redundancy in vivo. The developmental and compartment-specific roles of each SERAT isoform were also demonstrated. Mitochondrial SERAT2;2 plays a predominant role in cellular OAS formation, while plastidic SERAT2;1 contributes less to OAS formation and subsequent Cys synthesis. Three cytosolic isoforms, SERAT1;1, SERAT3;1, and SERAT3;2, may play a major role during seed development. Thus, the evolutionally conserved SERAT gene family is essential in cellular processes, and the substrates and products of SERAT must be exchangeable between the cytosol and organelles.

Tumor blood flow interruption after radiotherapy strongly inhibits tumor regrowth

To clarify the therapeutic significance of interrupting tumor blood flow after irradiation, we investigated X-irradiation-induced changes in hemodynamic parameters (blood flow, extravasation and washout of fluorescein isothiocyanate-dextran, and interstitial fluid pressure) in a variant of Yoshida sarcoma, LY80. Tumors in anesthetized male Donryu rats received local irradiation (10 Gy). At 48 h after irradiation, tumor blood flow increased significantly; at 72-96 h after irradiation, a 2-2.5-fold increase was observed. All parameters then consistently showed improved tumor microcirculation, which probably contributed to regrowth of cancer because certain cells survived irradiation. Rats received an intravenous dose (10 mg/kg) of a combretastatin derivative, AC7700 (AVE8062), which interrupts tumor blood flow and disrupts tumor vessels. At all times evaluated after irradiation, AC7700 completely stopped tumor blood flow. Radiotherapy efficacy was significantly enhanced when combined with AC7700: AC7700 given 48 h after irradiation, when tumor blood flow increased significantly, remarkably suppressed tumor regrowth compared with AC7700 given 48 h before irradiation. Also, postirradiation AC7700 completely inhibited not only primary tumor regrowth but also regional lymph node metastases in half of tumor-bearing rats and led to a significant improvement in survival. These results strongly suggest that the combination effect was enhanced via interruption of increased tumor blood flow after irradiation. This therapeutic combination and timing may have important benefits, even in tumors with low sensitivity to either treatment alone, because the effect was considerably greater than additive. Our data thus show that destruction of tumor microcirculation after irradiation is quite effective for preventing cancer recurrence.

LMP2-specific inhibitors: chemical genetic tools for proteasome biology

The immunoproteasome, having been linked to neurodegenerative diseases and hematological cancers, has been shown to play an important role in MHC class I antigen presentation. However, its other pathophysiological functions are still not very well understood. This can be attributed mainly to a lack of appropriate molecular probes that can selectively modulate the immunoproteasome catalytic subunits. Herein, we report the development of molecular probes that selectively inhibit the major catalytic subunit, LMP2, of the immunoproteasome. We show that these compounds irreversibly modify the LMP2 subunit with high specificity. Importantly, LMP2-rich cancer cells compared to LMP2-deficient cancer cells are more sensitive to growth inhibition by the LMP2-specific inhibitor, implicating an important role of LMP2 in regulating cell growth of malignant tumors that highly express LMP2.

Antitumor and antivascular effects of AVE8062 in ovarian carcinoma

The purpose of this study was to examine the therapeutic efficacy and underlying mechanisms of action of a vascular-disrupting agent, AVE8062, and to determine its effects on tumor metabolic activity. The in vitro and in vivo effects of AVE8062 alone and in combination with docetaxel were tested in chemotherapy-sensitive and chemotherapy-resistant ovarian cancer models. Tumors were analyzed for necrosis, microvessel density, endothelial cell apoptosis, and proliferation following treatment. The effect of AVE8062 on tumor regression and metabolic activity was examined by magnetic resonance (MR) or by [18F]fluorodeoxyglucose ([18F]FDG) uptake by positron emission tomography (PET) with MR imaging, respectively. AVE8062 monotherapy was effective in inhibiting tumor growth in all models (range 43-51% versus control; P < 0.05). Combination therapy was even more effective in inhibiting tumor growth (range 76-90% compared with controls, P < 0.01). AVE8062 in combination with chemotherapy significantly prolonged survival in HeyA8-injected mice (P < 0.001) compared with other groups. AVE8062-based therapy resulted in rapid development of central tumor necrosis, decreased microvessel density, decreased proliferation, and induction of apoptosis of tumor-associated endothelial cells. MR imaging showed regression of established HeyA8 ovarian tumors and [18F]FDG PET with MR showed rapid decrease in metabolic activity after AVE8062 therapy. Combination of AVE8062 plus docetaxel results in potent inhibition of ovarian cancer growth. These results suggest that AVE8062 may be useful as a clinical therapeutic approach for ovarian cancer patients and that functional [18F]FDG PET imaging may predict clinical response before an anatomic reduction in tumor size.