Sequence-dependent antiproliferative effects of cytotoxic drugs and epidermal growth factor receptor inhibitors

BACKGROUND

Epidermal growth factor receptor (EGFR) inhibitors are in clinical development in cancer treatment. Preclinical studies have shown potential antitumor efficacy of these agents in combination with chemotherapy or with radiotherapy. However, controversial results have been obtained in different clinical trials.

MATERIALS AND METHODS

The effects on proliferation, cell cycle distribution and induction of apoptosis of three different anti-EGFR agents (gefitinib, ZD6474, cetuximab) were evaluated in different sequences of combination with either a platinum derivative (cisplatin, carboplatin, oxaliplatin) or a taxane (docetaxel, paclitaxel) in KYSE30 cells, a model of a human cancer cell line with a functional EGFR autocrine pathway.

RESULTS

The combination of a cytotoxic drug with an EGFR inhibitor caused different antiproliferative effects on KYSE30 cancer cells depending on the treatment schedule. An antagonistic effect was observed when treatment with each EGFR inhibitor was done before chemotherapy. In contrast, a synergistic antiproliferative activity was obtained when chemotherapy was followed by treatment with EGFR antagonists. This effect was accompanied by potentiation of apoptosis and arrest of the surviving cancer cells in the G(2)/M phases of the cell cycle.

CONCLUSIONS

This study provides a rationale for the evaluation of a potentially synergistic sequence of cytotoxic drugs and EGFR inhibitors in a clinical setting.

Inhibition of NF-kappaB activation by the histone deacetylase inhibitor 4-Me2N-BAVAH induces an early G1 cell cycle arrest in primary hepatocytes

OBJECTIVE

Benzoylaminoalkanohydroxamic acids, including 5-(4-dimethylaminobenzoyl)aminovaleric acid hydroxamide (4-Me(2)N-BAVAH), are structural analogues of Trichostatin A, a naturally occurring histone deacetylase inhibitor (HDACi). 4-Me(2)N-BAVAH has been shown to induce histone hyperacetylation and to inhibit proliferation in Friend erythroleukaemia cells in vitro. However, the molecular mechanisms have remained unidentified.

MATERIALS AND METHODS

In this study, we evaluated the effects of 4-Me(2)N-BAVAH on proliferation in non-malignant cells, namely epidermal growth factor-stimulated primary rat hepatocytes.

RESULTS AND CONCLUSION

We have found that 4-Me(2)N-BAVAH inhibits HDAC activity at non-cytotoxic concentrations and prevents cells from responding to the mitogenic stimuli of epidermal growth factor. This results in an early G(1) cell cycle arrest that is independent of p21 activity, but instead can be attributed to inhibition of cyclin D1 transcription through a mechanism involving inhibition of nuclear factor-kappaB activation. In addition, 4-Me(2)N-BAVAH delays the onset of spontaneous apoptosis in primary rat hepatocyte cultures as evidenced by down-regulation of the pro-apoptotic proteins Bid and Bax, and inhibition of caspase-3 activation.

Ionic liquids as advantageous solvents for headspace gas chromatography of compounds with low vapor pressure

The potential of ionic liquids as solvents for headspace gas chromatography was investigated. Three compounds with boiling points above 200 degrees C were selected to demonstrate the feasibility of the concept described. 2-Ethylhexanoic acid, formamide, and tri-n-butylamine as examples of acidic, neutral, and basic analytes were dissolved in acidic 1-n-butyl-3-methylimidazolium hydrogen sulfate (1), neutral 1-n-butyl-2,3-dimethylimidazolium dicyanamide (2), and 2 containing 1,8-diazabicyclo[5.4.0]undec-7-ene to adjust basic conditions. All analytes could be determined with limits of detection and limits of quantification in the low-ppm concentration range.

A Metabolic Screening Study of Trichostatin A (TSA) and TSA-Like Histone Deacetylase Inhibitors in Rat and Human Primary Hepatocyte Cultures

Hydroxamic acid (HA)-based histone deacetylase (HDAC) inhibitors, with trichostatin A (TSA) as the reference compound, are potential antitumoral drugs and show promise in the creation of long-term primary cell cultures. However, their metabolic properties have barely been investigated. TSA is rapidly inactivated in rodents both in vitro and in vivo. We previously found that 5-(4-dimethylaminobenzoyl)aminovaleric acid hydroxyamide or 4-Me2N-BAVAH (compound 1) is metabolically more stable upon incubation with rat hepatocyte suspensions. In this study, we show that human hepatocytes also metabolize TSA more rapidly than compound 1 and that similar pathways are involved. Furthermore, structural analogs of compound 1 (compounds 2-9) are reported to have the same favorable metabolic properties. Removal of the dimethylamino substituent of compound 1 creates a very stable but 50% less potent inhibitor. Chain lengthening (4 to 5 carbon spacer) slightly improves both potency and metabolic stability, favoring HA reduction to hydrolysis. On the other hand, Calpha-unsaturation and spacer methylation not only reduce HDAC inhibition but also increase the rate of metabolic inactivation approximately 2-fold, mainly through HA reduction. However, in rat hepatocyte monolayer cultures, compound 1 is shown to be extensively metabolized by phase II conjugation. In conclusion, this study suggests that simple structural modifications of amide-linked TSA analogs can improve their phase I metabolic stability in both rat and human hepatocyte suspensions. Phase II glucuronidation, however, can compensate for their lower phase I metabolism in rat hepatocyte monolayers and could play a yet unidentified role in the determination of their in vivo clearance.

Role of metalloproteinase-7 in oxaliplatin acquired resistance in colorectal cancer cell lines

20042

Background: Mechanisms responsible for acquired resistance in colorectal cancer (CRC) tumors are not well understood. Anticancer drugs have been shown to enhance FASL expression by NF-kB induction. Additionally Metalloproteinase (MMP)-7 is over-expressed in CRC and has been shown to inhibit apoptosis by cleavage of FASL. We have previously shown in vivo that, sFASL increment was associated with acquired chemoresistance. Therefore we speculate that inhibition of MMP-7 or NF-kB can reverse chemoresistance in CRC cell lines. Methods: We generated an oxaliplatin-resistant cells (HT29R) from a p53 mutated (HT29) cell line. Both cell lines were cultured for 72h with different concentrations of oxaliplatin, BAY11–7085 (inhibitor of NF-kB activation), 0.01 mM of the MMP-7 inhibitor 1,10-Phenanthroline monohydrate (1,10-PM) and 100 ng/ml of DX2 monoclonal antibody. Different drug combinations were performed. Citotoxicity was determined by the MTS method, and cell cycle was analysed at 72h. Cell lines were characterized for MMP-7 expression (ELISA), NF-KB (Western-Blot), Fas expression (immunohistochemistry) and FasL expression (Western-Blot). Results: FAS was down-expressed in HT29R compared to HT29. The HT29R cells showed a IC50 for oxaliplatin 2-fold higher than normal cells. Treatment with 1,10-PM decrease MMP-7 levels (p < 0.005) compared with untreated cells. Additionally, inhibition of MMP-7, restore IC50 values after oxaliplatin treatment in HT29R without changes in NF-KB expression. This oxaliplatin-resistant cell line, presents also sensibility for BAY11–7085, without affecting MMP-7 levels. Finally the addition of oxaliplatin to the MMP-7 inhibitor, increase FAS-mediated apoptosis (induced by DX2 antibody), suggesting that FASL cleavage is responsable of sensitivity. Conclusions: Reversal of oxaliplatin chemo-resistance can be obtained either by MMP-7 or NF-kB inhibition. Both drugs induced sFASL decrement, by inhibiting cleavage or expression, respectively.

No significant financial relationships to disclose.

Crystal structure of (E)-2-ruthenocenylethenylcobaltocenium hexafluorophosphate, [(C5H5)Ru(C12H10)Co(C5H5)][PF6]

C22H20CoF6PRu, monoclinic, P121/c1 (no. 14), a = 9.9053(2) Å, b = 11.4730(3) Å, c = 18.5156(5) Å, β = 94.940(2)°, V = 2096.4 Å3, Z = 4, Rgt(F) = 0.041, wRref(F2) = 0.094, T = 233 K.

Major phase I biotransformation pathways of Trichostatin a in rat hepatocytes and in rat and human liver microsomes

Phase I biotransformation of Trichostatin A (TSA), a histone deacetylase inhibitor with promising antifibrotic and antitumoral properties, was investigated in rat and human liver microsomes and in suspensions of rat hepatocytes. TSA (50 micro M) was readily and completely metabolized by rat hepatocytes in suspension (2 x 10(6) cells/ml), whereafter its phase I metabolites were separated by high-performance liquid chromatography and detected with simultaneous UV and electrospray ionization mass spectrometry (ESI-MS). ESI tandem mass spectrometry (ESI-MS/MS) was used to identify the metabolites. Two major phase I biotransformation pathways in rat hepatocytes were shown to be N-demethylation and reduction of the hydroxamic acid function to its corresponding amide. N-monodemethylated TSA and TSA amide were preferentially formed during the first 20 min of exposure, and N-monodemethylated TSA amide appeared as the main metabolite after a 30 min incubation period. At this time, virtually all TSA had been metabolized. Trichostatic acid, N-monodemethylated Trichostatic acid, and N-didemethylated TSA were identified as minor metabolites. Longer incubation led to the formation of N-didemethylated TSA amide as the main metabolite. Lower concentrations of TSA (5 and 25 micro M) formed relatively higher amounts of N-demethylated, nonreduced metabolites. Incubations of TSA with rat and human microsomal suspensions, however, led to an incomplete biotransformation with the formation of two major metabolites, N-mono- and N-didemethylated TSA. Traces of Trichostatic acid, TSA amide, N-mono- and N-didemethylated TSA amide were also detected. This study is the first to show that TSA undergoes intensive phase I biotransformation in rat hepatocytes. This has important consequences for its potential development as a drug, since rapid biotransformation resulting in a short exposure to the pharmacologically active parent compound, and a complex mixture of metabolites is usually not desired. Further biotransformation studies of TSA and structural analogs with antitumoral and antifibrotic properties need to be performed in cultured intact hepatocytes, in particular since one of the major phase I biotransformation pathways is catalyzed by nonmicrosomal enzymes.

Development of a downstream process for the isolation of Staphylococcus aureus arsenate reductase overproduced in Escherichia coli

Arsenate reductase (ArsC) encoded by Staphylococcus aureus arsenic-resistance plasmid pI258 reduces intracellular As(V) (arsenate) to the more toxic As(III) (arsenite). In order to study the structure of ArsC and to unravel biochemical and physical properties of this redox enzyme, wild type enzyme and a number of cysteine mutants were overproduced soluble in Escherichia coli. In this paper we describe a novel purification method to obtain high production levels of highly pure enzyme. A reversed-phase method was developed to separate and analyze the many different forms of ArsC. The oxidation state and the methionine oxidized forms were determined by mass spectroscopy.

The essential catalytic redox couple in arsenate reductase from Staphylococcus aureus

Arsenate reductase (ArsC) encoded by Staphylococcus aureus arsenic-resistance plasmid pI258 reduces intracellular As(V) (arsenate) to the more toxic As(III) (arsenite), which is subsequently extruded from the cell. ArsC couples to thioredoxin, thioredoxin reductase, and NADPH to be enzymatically active. A novel purification method leads to high production levels of highly pure enzyme. A reverse phase method was introduced to systematically analyze and control the oxidation status of the enzyme. The essential cysteinyl residues and redox couple in arsenate reductase were identified by a combination of site-specific mutagenesis and endoprotease-digest mass spectroscopy analysis. The secondary structures, as determined with CD, of wild-type ArsC and its Cys mutants showed a relatively high helical content, independent of the redox status. Mutation of Cys 10, 82, and 89 led to redox-inactive enzymes. ArsC was oxidized in a single catalytic cycle and subsequently digested with endoproteinases ArgC, AspN, and GluC. From the peptide-mass profiles, cysteines 82 and 89 were identified as the redox couple of ArsC necessary to reduce arsenate to arsenite.

Liquid chromatographic study of the enzymatic degradation of endomorphins, with identification by electrospray ionization mass spectrometry

The recently discovered native endomorphins play an important role in opioid analgesia, but their metabolic fate in the organism remains relatively little known. This paper describes the application of high-performance liquid chromatography combined with electrospray ionization mass spectrometry to identify the degradation products resulting from the incubation of endomorphins with proteolytic enzymes. The native endomorphin-1, H-Tyr-Pro-Trp-Phe-NH2 (1), and endomorphin-2, H-Tyr-Pro-Phe-Phe-NH2 (2), and an analog of endomorphin-2, H-Tyr-Pro-Phe-Phe-OH (3), were synthetized, and the levels of their resistance against carboxypeptidase A, carboxypeptidase Y, aminopeptidase M and proteinase A were determined. The patterns of peptide metabolites identified by this method indicated that carboxypeptidase Y first hydrolyzes the C-terminal amide group to a carboxy group, and then splits the peptides at the Trp3-Phe4 or Phe3-Phe4 bond. The remaining fragment peptides are stable against the enzymes investigated. Carboxypeptidase A degrades only analog 3 at the Phe3-Phe4 bond. Aminopeptidase M cleaves the peptides at the Pro2-Trp3 or Pro2-Phe3 bond. The C-terminal fragments hydrolyze further, giving amino acids and Phe-NH2-s while the N-terminal part displays a resistance to further aminopeptidase M digestion. Proteinase A exhibits a similar effect to carboxypeptidase Y: the C-terminal amide group is first converted to a carboxy group, and one amino acid is then split off from the C-terminal side.

Uncaria tomentosa (Willd.) DC.--ethnomedicinal use and new pharmacological, toxicological and botanical results

The medicinal system of the Asháninka Indians in Perú is portrayed. Three categories of medical disorders and healers are recognized. A human is viewed to consist of a physical and a spiritual being who communicate with each other by means of a regulating element. The significance of Uncaria tomentosa (Willd.) DC. (Rubiaceae), locally known as unã de gato, in traditional medicine is emphasized by its exclusive use by priests to influence this regulation. Pharmacological and toxicological results obtained with extracts or isolated compounds are summarized. Pentacyclic oxindole alkaloids stimulate endothelial cells in vitro to produce a lymphocyte-proliferation-regulating factor. Tetracyclic oxindole alkaloids act as antagonists. A significant normalization of lymphocyte percentage was observed in vivo although total leucocyte numbers did not change.

Pentacyclic oxindole alkaloids from Uncaria tomentosa induce human endothelial cells to release a lymphocyte-proliferation-regulating factor

In the present study we show that pentacyclic but not tetracyclic oxindole alkaloids from Uncoria tomentosa (Willd.) DC. (Rubiaceae) induced EA.hy926 endothelial cells to release some yet to be determined factor(s) into the supernatant; this factor was shown to significantly enhance proliferation of normal human resting or weakly activated B and T lymphocytes. In contrast, proliferation of normal human lymphoblasts and of both the human lymphoblastoid B cell line Raji and the human lymphoblastoid T cell line Jurkat was inhibited significantly while cell viability was not affected. Tetracyclic oxindole alkaloids dose-dependently reduce the activity of pentacyclic oxindole alkaloids on human endothelial cells.

Reconsidering the energetics of ribonuclease catalysed RNA hydrolysis

In principle, all biochemical reactions are reversible, though some are more reversible than others. The classical ribonuclease mechanism involves a reversible transphosphorylation step, followed by quasi irreversible hydrolysis of the cyclic intermediate. We performed isotope-exchange and intermediate-trapping experiments showing that the second hydrolysis step is readily reversible in the presence of RNase A or RNase T1. As a consequence, the equilibrium between a phosphodiester and a 2',3'-cyclophosphate accounts for all catalysed reactions, even if the leaving/attacking group is a water molecule. Therefore, ribonucleases are transferases rather than hydrolases. The equilibrium constant for the catalysed interconversion is close to 1 M. From this result, we estimate the effective concentration of the 2'-hydroxyl nucleophile in the cyclization step to be 10(7) M. The high effective concentration of the vicinal hydroxyl group balances the strain-associated and solvation-associated instability of the pentacyclic phosphodiester.

Location of the three disulfide bonds in an antimicrobial peptide from Amaranthus caudatus using mass spectrometry

The disulfide bridge pairing of Ac-AMP2, a 30-residue peptide isolated from the seeds of Amaranthus caudatus, is determined using a fast method involving enzymatic fragmentation followed by identification of the fragments with FAB mass spectrometry. The results confirm the location of the three disulfide bridges as previously established by NMR spectroscopy and molecular modelling.

Liquid chromatography studies on the enzymatic degradation of luteinizing hormone-releasing hormone analogues with off-line identification by mass spectrometry

Several agonists of luteinizing hormone-releasing hormone (LHRH) are currently used for different therapeutic purposes, but relatively little is known about their metabolic fate after administration. This paper describes the application of high-performance liquid chromatography combined with off-line fast atom bombardment mass spectrometry to identify the degradation products resulting from the incubation of LHRH analogues with proteolytic enzymes. Three analogues, containing a psi(E,CH = CH) pseudo-peptide bond were synthesized and afforded to the assay to determine the resistance against alpha-chymotrypsin and subtilisin: [Tyr5 psi(E,CH = CH)Gly6]LHRH, [Gly6 psi(E,CH = CH)D,L-Leu7]LHRH and [Pro9 psi(E,CH = CH)Gly10 ]LHRH. The pattern of peptide metabolites identified by this method indicates that alpha-chymotrypsin degrades LHRH analogues at the Trp3-Ser4 and Tyr5-Gly6 bond, while subtilisin hydrolyzes only the Tyr5-Gly6 linkage. The results also indicate a possible stabilization of native amide bonds against enzymatic degradation by neighbouring psi(E, CH = CH) modifications.

An evaluation of microwave heating for the rapid hydrolysis of peptide samples for chiral amino acid analysis

The hydrolysis of peptide samples in 6 N deuterium chloride by microwave heating has been investigated. The influence of the power and time of heating on the recovery of the amino acids and on their racemization was studied. A high recovery of sensitive amino acids and minimal racemization, as determined by the amount of deuterium incorporation, is obtained by using an intermediate irradiation power and 30 min reaction time.

Determination of the chiral purity of dipeptide isosteres containing a reduced peptide bond by gas chromatographic analysis

The stereochemical purity of psi (CH2-NH) dipeptides has been determined using gas chromatography-mass spectrometry. Different structures were found due to the derivatization procedures. A selective preparation of the linear bistrifluoroacetylated derivative and the monotrifluoroacetylated lactam makes it possible to monitor the chiral purity of the pseudodipeptides synthesized. Racemization occurring during peptide hydrolysis can be differentiated from racemization during the synthesis by using deuterium labelling. The method allows the optimization of the synthesis protocols and will be useful for further monitoring of the chiral purity of the pseudopeptides synthesized.