Sublethal effects of an indoxacarb enantiomer insecticide on Plutella xylostella caterpillar and Chrysoperla sinica predator

Plutella xylostella (L.) is a migratory species and an important insect pest of cruciferous crops worldwide, and Chrysoperla sinica (Tjeder) is a predaceous insect of agricultural and forest pests in the field. Indoxacarb has two enantiomers: (+)-S-indoxacarb and (-)-R-indoxacarb. This study was conducted to clarify the selective toxicity and sublethal effects of both enantiomers on P. xylostella and C. sinica. The (+)-S-indoxacarb isomer had greater acute toxicity to P. xylostella and C. sinica, while (-)-R-indoxacarb had less toxicity to P. xylostella and low toxicity to C. sinica. Lethal concentration 25 % (LC₂₅) of (+)-S-indoxacarb had significant effects on the development, population, and fecundity of P. xylostella and C. sinica. The LC₂₅ concentration of (-)-R-indoxacarb had a significant effect on the oviposition of P. xylostella. The field recommended concentration of (-)-R-indoxacarb significantly affected the pupal stage, adult survival rate, oviposition, and larval survival rate of C. sinica. Both enantiomers could significantly affect the search efficiency, successful attack rate, prey handling time, and maximum predation of C. sinica larvae, and the effects of (+)-S-indoxacarb alone were greater than those of (-)-R-indoxacarb. This study provided evidence of the different selective toxicity, sublethal effects of indoxacarb enantiomers on P. xylostella and C. sinica, which of the results could provide a basis for more rational use of indoxacarb in ecosystems.

Sublethal effects and reproductive hormesis of emamectin benzoate on Plutella xylostella

The diamondback moth (DBM), Plutella xylostella L., is an important pest of cruciferous vegetables, and population control mainly depends on chemical pesticides. Emamectin benzoate is a highly effective insecticide used for controlling DBM. However, it is unknown how the sublethal effects of low concentration residues of emamectin benzoate on DBM. So the population development sublethal effects of emamectin benzoate, at LC₅, LC₁₀, and LC₂₀ with concentrations of 0.014 mg/L, 0.024 mg/L and 0.047 mg/L, respectively, on adult DBM and their progeny were investigated in this study. The pupal weight, pupal period, female fecundity, and vitellin content of the F₀ DBM generation increased significantly compared to the control. And the single female oviposition number of DBM was increased by 20.21% with LC₂₀ treatment. The pupation rate, adult longevity and ovariole length of the treatment groups decreased significantly. The fecundity of DBM in the treatment groups increased, and this increased the population by a presumptive 13.84%. Treatment also led to the shortening of ovarioles and the reduction of egg hatching, and increased pupal weight in the F₁ generation. We concluded that the effects of sublethal/low concentration emamectin benzoate on the different life stages of DBM were variable, and the reproductive hormesis on DBM adults were attractive findings.

Sublethal effects of tolfenpyrad on the development, reproduction, and predatory ability of Chrysoperla sinica

The lacewing, Chrysoperla sinica, is a predaceous insect that is important in crop pest management. Chemical pesticides have adversely impacted predaceous insect species. Here we studied the effect of tolfenpyrad on C. sinica. The acute toxicity of tolfenpyrad to the second-instar larvae was determined and indicated that tolfenpyrad is a medium-risk insecticide. Sublethal concentrations (LC₁₀, LC₂₀, and LC₃₀) of tolfenpyrad had effects on the development, reproduction, and predatory ability of C. sinica. When the second-instar larvae of C. sinica were exposed to sublethal concentrations of tolfenpyrad, the activities of protective enzymes, such as superoxide dismutase, peroxidase, and catalase, and detoxification enzymes, including carboxylesterase, glutathione-S-transferase, and P450 monooxygenases, were increased with exposure time. The second-instar larvae of C. sinica exposed to sublethal concentrations of tolfenpyrad exhibited an oxidative stress response that increased the levels of malondialdehyde and reactive oxygen species (ROS). Within 48-120 h after treatment, the contents of mitochondrial respiratory chain complex I and adenosine triphosphate in the second-instar larvae were decreased. This resulted in an imbalance between the production and clearance of ROS and caused cellular damage.

Insecticide resistance and resistance mechanisms in the melon aphid, Aphis gossypii, in Shandong, China

The melon aphid, Aphis gossypii, is an important pest of vegetables. Insecticide resistance in A. gossypii has increased due to the frequent use of insecticides. We studied the levels and mechanisms of A. gossypii resistance to imidacloprid, acetamiprid and lambda-cyhalothrin here. The resistance levels of the three insecticides in 20 populations of A. gossypii varied. When compared to the susceptible strain (Lab-SS), there were two moderate resistance (MR) populations and nine low resistance (LR) populations to imidacloprid, respectively, two MR populations and two LR populations to acetamiprid, respectively, and, five MR populations and two LR populations to λ-cyhalothrin, respectively. Gene mutation detection in the MR level populations showed arginine to threonine substitution (R81T) in three populations and lysine to glutamine substitution (K264E) in the nicotinic acetylcholine receptor (nAChR) β1 subunit in one population, respectively. No valine to isoleucine substitution (V62I) was found in the nAChR β1 subunit in any of the tested populations. The leucine to phenylalanine substitution (L1014F) in sodium channel α subunit was found in five MR populations. The relative expression of the CYP6CY13 gene was significantly upregulated in the Daiyue and Shenxian populations. The CYP6CY14 gene was significantly upregulated in Daiyue, Dongchangfu, Shenxian, Mengyin and Anqiu populations. The CYP6CY19 gene was significantly upregulated in the Dongchangfu and Mengyin populations. The relative expressions of the esterase E4 or FE4 genes were significantly upregulated in most of the MR populations. These results provide insight into the current insecticide resistance of A. gossypii and may contribute to more effective resistance management strategies.

Mixtures of fluopyram and abamectin for management of Meloidogyne incognita in tomato

The southern root-knot nematode (RKN), Meloidogyne incognita, causes significant damage to vegetable production and is a major problem in greenhouse tomatoes. The effect of a combination of fluopyram and abamectin, at a mass ratio of 1:5, was studied for RKN control. Pot trials showed that fluopyram, abamectin, and their combination at three dosages increased the height, stem diameter, root fresh weight, shoot fresh weight, and the root length of tomato plants. The RKN control efficacy of the 1:5 combination at 450 g a.i./ha was 74.06% at 30 days after transplanting (DAT), and the control efficacy of the combination at 337.5 and 450 g a.i./ha differed significantly from those of other treatments at 60 DAT. The root-galling index (RGI) control efficacy of the combination at 450 g a.i./ha and of fluopyram (41.7% SC) only at 450 g a.i./ha were better than the control efficacies of other treatments, and these two treatments significantly increased root activity. Field trial results showed that the soil nematode control efficacy was similar to that of the pot trials at 30 and 60 DAT. The RGI control efficacy of the combination at 337.5 and 450 g a.i./ha and of fluopyram (41.7% SC) only at 450 g a.i./ha differed significantly from those of the two other treatments. The tomato yields of the 1:5 combination at 450 g a.i./ha were increased by 24.07 and 23.22% compared to the control in field trials during two successive years. The combination of fluopyram and abamectin provides good nematode measure, and it can increase tomato yields. It provides an effective solution for the integrated management of southern RKN.

Reduced fecundity and regulation of reproductive factors in flubendiamide-resistant strains of Plutella xylostella

Diamondback moth (DBM), Plutella xylostella, is an important pest of crucifers worldwide. The extensive use of flubendiamide has led to the development of resistance in field populations and reports of control failures. In this study, the lab-selected (R_f) and field-collected (R_b) flubendiamide-resistant strains of P. xylostella with LC₅₀ resistance ratios of 1890-fold and 1251-fold, respectively, were used, as well as a lab-reared flubendiamide-susceptible strain (S). The results showed that the fecundity of the R_f and R_b-resistant strains was significantly lower than that of S strain. The contents of vitellin and transcripts of P. xylostella vitellogenin (PxVg) and P. xylostella vitellogenin receptor (PxVgR) genes in the R_f and R_b strains were significantly higher than those of S strains at 0-48 h after adult eclosion. At 96 h after eclosion, the content of vitellin in the R_f and R_b strains did not differ significantly from those of S strains, whereas transcripts of the PxVg and PxVgR genes in the R_f and R_b strains were significantly lower than that of the S strain. The content of the juvenile hormone III (JH III), β-ecdysone (20E), and the gene expression level of P. xylostella methoprene tolerant (PxMet) in the R_f and R_b strains were significantly higher than that of the S strain. The activity of trehalase was significantly higher in the R_f and R_b strains than that of the S strain in the first to the third instar larvae, whereas in the fourth instar larvae, there was no significantly difference in the three strains. At different times after adult eclosion, the differences in trehalase activity were erratic between the strains. The transcripts of P. xylostella trehalase (PxTre) gene in the R_f and R_b strains were significantly higher than that of the S strain in most developmental stages. Here, we report differences in fecundity between flubendiamide-resistant and susceptible strains of P. xylostella and discuss gene expression of several reproductive factors, which provides a possible explanation for the mechanism of fecundity reduction concurrent with flubendiamide-resistance in P. xylostella.

Increased Responses of Phenoloxidase in Chlorantraniliprole Resistance of Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth (Plutella xylostella, DBM) is an important pest of cruciferous vegetables. The use of chlorantraniliprole has been essential in the management of the DBM. However, in many countries and areas, DBM has become highly resistant to chlorantraniliprole. Three different DBM strains, susceptible (S), chlorantraniliprole-selected (Rc), and field-collected (Rb) resistant strains/populations were studied for the role of phenoloxidase in resistance development to the insecticide. By assaying the activity of phenoloxidase (PO) in the three different DBM strains, the results showed that the PO activity in the Rc strain was increased significantly compared with the S strain. The synergistic effects of quercetin showed that the resistant ratio (RR) of the QRc larvae to chlorantraniliprole was decreased from 423.95 to 316.42-fold compared with the Rc larvae. Further studies demonstrated that the transcriptional and translational expression levels of PxPPO1 (P. xylostella prophenoloxidase-1 gene) and PxPPO2 (P. xylostella prophenoloxidase-2 gene) were increased to varying degrees compared with the S strain, such as the transcriptional expression levels of PxPPO2 were 24.02-fold that of the S strain. The responses of phenoloxidase were significantly different in chlorantraniliprole-resistant DBM.

Acute lethal and sublethal effects of four insecticides on the lacewing (Chrysoperla sinica Tjeder)

The lacewing, Chrysoperla sinica, is an important predatory insect, which plays an important role in the integrated pest management of agroforestry pests. However, the extensive use of insecticides negatively affects C. sinica. The acute toxicity, risk level, and, sublethal effects on growth and production, predation ability, protective enzyme activity and genotoxicity of four insecticides: indoxacarb, emamectin benzoate, imidacloprid and lambda-cyhalothrin to C. sinica were studied. The results showed that all four insecticides had lethal toxicity to larvae of C. sinica. Among them, emamectin benzoate had the highest toxicity with LC₅₀ value of 7.41 mg/L. The insecticides also had different effects on the growth and reproduction of C. sinica, of which lambda-cyhalothrin had the greatest impacts. Even at a very low LC₁ concentration (3.37 mg/L), it had strong impacts on the growth, reproduction and predatory ability of C. sinica. The four insecticides also caused a decrease in the predatory ability of the lacewing, of which lambda-cyhalothrin had the greatest effect. During the larval stage, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were significantly decreased by the four insecticides. At the pupal and adult stages, the effects of the four insecticides on the activities of protective enzymes were different, and the activities of SOD, CAT and POD decreased or increased. Indoxacarb and lambda-cyhalothrin exposure induced DNA damage in the haemocytes of C. sinica and produced obvious genotoxicity. These results provide important scientific basis for the rational use of these insecticides and the protection and utilization of lacewing.

Chromosomal deletions mediated by CRISPR/Cas9 in Helicoverpa armigera

Helicoverpa armigera, cotton bollworm, is one of the most disastrous pests worldwide, threatening various food and economic crops. Functional genomic tools may provide efficient approaches for its management. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system, dependent on a single guide RNA (sgRNA), has been used to induce indels for targeted mutagenesis in cotton bollworm. However, genomic deletions may be more desirable to disrupt the function of noncoding genes or regulatory sequences. By injecting two sgRNAs with Cas9 protein targeting different exons, we obtained predictable genomic deletions of several hundred bases. We achieved this type of modification with different combinations of sgRNA pairs, including HaCad and HaABCC2. Our finding indicated that CRISPR/Cas9 can be used as an efficient tool to engineer genomes with chromosomal deletion in H. armigera.

Molecular Characterization and Bioinformatics Analysis of a Prophenoloxidase-1 (PPO1) in Plutella xylostella

Phenoloxidase (PO) is an important enzyme in insect life, which is involved in important physical functions, such as defensive encapsulation and melanization of foreign organisms and wound healing. In this study, we obtained a cDNA sequence of 2838 bp with 2049 open reading frames encoding 682 amino acids. The protein sequence deduced from the cDNA has high homology with the known PPO1 sequences of other lepidopterous insects. There were three conserved regions, including the two copper-binding sites characteristic of arthropod PPOs. The whole PxPPO1 DNA was also obtained with 7202 bp when the five fragments were stitched together and the overlapping sequences were deleted. The PxPPO1 DNA consists of 11 introns and 12 exons, and the homology is 99.9% when the exons are compared with the above cDNA. Moreover, the gene expression levels were also determined by semiquantitative polymerase chain reaction (PCR), Western blotting, and real-time quantitative PCR; the results indicated that PxPPO1 transcripts in the eggs and the fourth instar larvae were more abundant, followed by the second and the third instar larvae, prepupae, and pupa.

Flubendiamide resistance and Bi-PASA detection of ryanodine receptor G4946E mutation in the diamondback moth (Plutella xylostella L.)

The extensive application of flubendiamide has led to increasingly prominent development of resistance in diamondback moth, Plutella xylostella. Here we report that the moderate and high level resistance to flubendiamide was identified in a laboratory-selected and two field-collected strains of P. xylostella. The resistance ratios were tested in the lab-selected resistant strains (R), and two field strains (BY and ZC). Compared with the S strain, the R strain showed extended larval development time, decreased pupation rate, emergencing rate, and male adult longevity. The realized heritability (h(2)=0.135) implies the high risk of flubendiamide resistance development in P. xylostella. A Bi-PASA (bi-directional PCR amplification of specific allele)-based method was successfully developed to detect the point mutation (G4946E) potentially causing flubendiamide resistance in diamondback moth, in which different fragments 866 bp + 340 bp, 866 bp+568 bp, and 866 bp+568 bp+340 bp were presented in SS, RR and RS stains, respectively. The predominant genotype was 83.33% SS homozygote in the S strain, 80.77% RR homozygote in ZC population, and 73.08% RS heterozygote in BY population, respectively. Current results showed the significant correlation between the frequencies of the allele carrying G4946E mutation (51.92%, 55.77% and 90.38% for R, BY and ZC, respectively) and the resistance ratios (40.72, 24.24 and 1779.24-folds for R, BY and ZC, respectively) in the three strains/populations. In addition, the relative PxRyR mRNA transcript level in the R strain was 2.938 ± 0.53 folds as compared with the S strain (1.0-fold).

Chlorantraniliprole resistance in the diamondback moth (Lepidoptera: Plutellidae)

The wide application of chlorantraniliprole, which selectively targets insect ryanodine receptors (RyR), for control of the diamondback moth, Plutella xylostella (L.), has led to increasingly prominent development of resistance to this insecticide. Although much work has been carried out on the structure and function of RyR, the molecular mechanisms of resistance to chlorantraniliprole in diamondback moth still needs further investigation. P. xylostella strains with medium and high resistance to chlorantraniliprole were obtained by laboratory selection and field collection. The biological activity of chlorantraniliprole against the third-instar larvae of susceptible and resistant strains was tested, and resistance development and biological fitness were investigated. The realized heritability (h2) of resistance showed the diamondback moth has a high risk of resistance to chlorantraniliprole. RyR transcript levels were lower in resistant strains than in susceptible strains, indicating that decreased expression of PxRyR may be associated with chlorantraniliprole resistance in P. xylostella. A 4,400 bp fragment of the RyR cDNA, which encodes most of the functional domains of RyR, was cloned and characterized from four strains (S, F18, BY, and ZC). A 14 amino acid (Q4546-S4559) deletion was found in three resistant strains (F18, BY, and ZC). A point mutation resulting in a glycine to glutamate substitution, as reported in a previously published article, was also found in the carboxyl-terminal region of two resistant strains (BY and ZC). These results indicated that decreased transcriptional level of RyR mRNA and combined with the site mutation might be related to chlorantraniliprole resistance in P. xylostella.

3D-QSAR and molecular docking studies of benzaldehyde thiosemicarbazone, benzaldehyde, benzoic acid, and their derivatives as phenoloxidase inhibitors

Phenoloxidase (PO), also known as tyrosinase, is a key enzyme in insect development, responsible for catalyzing the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones. Inhibition of PO may provide a basis for novel environmentally friendly insecticides. In the present study, we determined the inhibitory activities and IC50 values of 57 compounds belonging to the benzaldehyde thiosemicarbazone, benzaldehyde, and benzoic acid families against phenoloxidase from Pieris rapae (Lepidoptera) larvae. In addition, the inhibitory kinetics of 4-butylbenzaldehyde thiosemicarbazone against PO was measured in air-saturated solutions for the oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA). The results indicated that the compound is a reversible noncompetitive inhibitor. The bioactivity results were used to construct three-dimensional quantitative structure-activity relationship (3D-QSAR) models using two molecular field analysis techniques: comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). After carrying out superimposition using common substructure-based alignment, robust and predictive 3D-QSAR models were obtained from CoMFA (q2=0.926, r2=0.986) and CoMSIA (q2=0.933, r2=0.984) with six optimum components. The 3D-QSAR model built here will provide hints for the design of novel PO inhibitors. The molecular interactions between the ligands and the target were studied using a flexible docking method (FlexX). The best scored candidates were docked flexibly, and the interaction between the representative compound 4-butylbenzaldehyde thiosemicarbazone and the active site was elucidated in detail.

Discovery of macrocyclic hydroxamic acids containing biphenylmethyl derivatives at P1', a series of selective TNF-alpha converting enzyme inhibitors with potent cellular activity in the inhibition of TNF-alpha release

SAR exploration at P1' using an anti-succinate-based macrocyclic hydroxamic acid as a template led to the identification of several bulky biphenylmethyl P1' derivatives which confer potent porcine TACE and anti-TNF-alpha cellular activities with high selectivity versus most of the MMPs screened. Our studies demonstrate for the first time that TACE has a larger S1' pocket in comparison to MMPs and that potent and selective TACE inhibitors can be achieved by incorporation of sterically bulky P1' residues.

Design, synthesis, and structure-activity relationships of macrocyclic hydroxamic acids that inhibit tumor necrosis factor alpha release in vitro and in vivo

To search for TNF-alpha (tumor necrosis factor alpha) converting enzyme (TACE) inhibitors, we designed a new class of macrocyclic hydroxamic acids by linking the P1 and P2' residues of acyclic anti-succinate-based hydroxamic acids. A variety of residues including amide, carbamate, alkyl, sulfonamido, Boc-amino, and amino were found to be suitable P1-P2' linkers. With an N-methylamide at P3', the 13-16-membered macrocycles prepared exhibited low micromolar activities in the inhibition of TNF-alpha release from LPS-stimulated human whole blood. Further elaboration in the P3'-P4' area using the cyclophane and cyclic carbamate templates led to the identification of a number of potent analogues with IC(50) values of </=0.2 microM in whole blood assay (WBA). Although the P3' area can accommodate a broad array of structurally diversified functional groups including polar residues, hydrophobic residues, and amino and carboxylic acid moieties, in both the cyclophane series and the cyclic carbamate series, a glycine residue at P3' was identified as a critical structural component to achieve both good in vitro potency and good oral activity. With a glycine residue at P3', an N-methylamide at P4' provided the best cyclophane analogue, SL422 (WBA IC(50) = 0.22 microM, LPS-mouse ED(50) = 15 mg/kg, po), whereas a morpholinylamide at P4' afforded the most potent and most orally active cyclic carbamate analogue, SP057 (WBA IC(50) = 0.067 microM, LPS-mouse ED(50) = 2.3 mg/kg, po). Further profiling for SL422 and SP057 showed that these macrocyclic compounds are potent TACE inhibitors, with K(i) values of 12 and 4.2 nM in the porcine TACE assay, and are broad-spectrum MMP inhibitors. Pharmacokinetic studies in beagle dogs revealed that SL422 and SP057 are orally bioavailable, with oral bioavailabilities of 11% and 23%, respectively.

Aggrecanase. A target for the design of inhibitors of cartilage degradation

In arthritic diseases there is a gradual erosion of cartilage that leads to a loss of joint function. Aggrecan, which provides cartilage with its properties of compressibility and elasticity, is the first matrix component to undergo measurable loss in arthritis. This loss of aggrecan appears to be due to an increased rate of degradation, that can be attributed to proteolytic cleavage of the core protein within the interglobular domain (IGD). Two major sites of cleavage have been identified within the IGD. One, between the amino acids Asn341-Phe342, where the matrix metalloproteinases (MMPs) have been shown to clip; and the other, between Glu373-Ala374, which is attributed to a novel protease, "aggrecanase." We have generated aggrecanase in conditioned media from IL-1-stimulated bovine nasal cartilage and have used an enzymatic assay to evaluate this proteinase activity. In these studies we follow the generation of aggrecanase and MMPs in response to IL-1 in this system and examine the contribution of these enzymes in aggrecan degredation. Our data suggest that aggrecanase is a key enzyme in cartilage aggrecan degradation that represents a novel target for cartilage protection therapy in arthritis.

P1, P2'-linked macrocyclic amine derivatives as matrix metalloproteinase inhibitors

A novel series of 13- and 14-membered macrocyclic amines was developed by linking the P1 and P2' groups. The synthesis entails stereoselective Frater alkylation to install the anti-succinate configuration and macrocyclic amination via nucleophilic displacement. This strategy resulted in a new class of conformationally constrained inhibitors that are potent and selective for MMP-8 and 9 over MMP-1 and 3.

Macrocyclic hydroxamate inhibitors of matrix metalloproteinases and TNF-alpha production

Several macrocyclic, hydroxamate derivatives were synthesized and evaluated as inhibitors of matrix metalloproteinases (MMPs) and tumour necrosis factor-alpha (TNF-alpha) production. These macrocycles are anti-succinate based inhibitors linked from P1 to P2'. A variety of functionality was installed at the P1-P2' linkage, which gave inhibitors that displayed excellent MMP inhibition and good TNF-alpha suppression.

Synthesis and antiplatelet effects of an isoxazole series of glycoprotein IIb/IIIa antagonists

Despite the excellent in vitro potency of a series of benzamide glycoprotein IIb/IIIa antagonists, which have been reported previously, poor in vivo potency in the inhibition of platelet aggregation was observed when the most potent inhibitor XU057 was dosed intravenously to dogs. In this communication, we report that replacement of the benzamide in XU057 with an isoxazolecarboxamide resulted in significant improvement in in vivo potency. More importantly, the analogue XU065 showed an excellent oral antiplatelet effect in dogs.

Discovery of an orally active series of isoxazoline glycoprotein IIb/IIIa antagonists

Using isoxazoline XR299 (1a) as a starting point for the design of highly potent, long-duration GPIIb/IIIa antagonists, the effect of placing lipophilic substituents at positions alpha and beta to the carboxylate moiety was evaluated. Of the compounds studied, it was found that the n-butyl carbamate 24u exhibited superior potency and duration of ex vivo antiplatelet effects in dogs. Replacement of the benzamidin-4-yl moiety with alternative basic groups, elimination of the isoxazoline stereocenter, and reversal of the orientation of the isoxazoline ring resulted in lowered potency and/or duration of action.

Design, synthesis, and in vitro activities of benzamide-core glycoprotein IIb/IIIa antagonists: 2,3-diaminopropionic acid derivatives as surrogates of aspartic acid

In an effort to discover novel nonpeptide glycoprotein IIb/IIIa (GPIIb/IIIa, alpha IIb/beta 3) inhibitors, we investigated RGD mimetics featuring a 3-substituted benzoic acid as the core, benzamidine as the basic moiety, and a series of beta- and alpha-substituted beta-alanine derivatives as aspartic acid surrogates. It was found that the use of beta-methyl beta-alanine slightly improved the anti-aggregant potency in human platelet-rich plasma over the unsubstituted beta-alanine compound, while beta-substitution with a trifluoromethyl group resulted in considerable loss in activity. Significant enhancement (up to 100-fold) in potency was obtained when the beta-alanine was replaced with N2-substituted 1-2,3-diaminopropionic acid derivatives. Among the three types of alpha-substituents (carbamate, amide, and sulfonamide) investigated, no apparent preference was observed with respect to in vitro potency. However, alkyl groups were more favorable than arylalkyl groups (Cbz) in the carbamate analogues. We also investigated piperidine, piperazine, and N-formamidinopiperidine as replacements for the benzamidine moiety. The former two replacements led to a drop in potency while the latter replacement resulted in maintenance of activity as compared with the corresponding benzamidine analogue.

Novel nonpeptide antiplatelet glycoprotein IIb/IIIa receptor antagonist, DMP754: receptor binding affinity and specificity

OBJECTIVE

To define the antiplatelet efficacy and specificity of the glycoprotein IIb/IIIa complex (GPIIb/IIIa) antagonist prodrug DMP754 and its free acid form, XV459.

METHODS AND MATERIALS

DMP754 has an IC50 > 1 mumol/l, and, upon its conversion with esterases to its free acid form, demonstrated high potency (IC50 20-45 nmol/l) in inhibiting human platelet aggregation induced by 10 mumol/l adenosine diphosphate, 20 micrograms/ml collagen, 1 mmol/l epinephrine, 10 mumol/l platelet activating factor or 0.5 IU/ml thrombin. The in-vitro rate of hydrolysis of DMP754 or XV459 is much faster with human or canine liver esterases (t 1/2 = 2.4-23 min) than with plasma esterases (t 1/2 = 5.5-7.6 h). Platelet GpIIb/IIIa integrin binding affinity and specificity for XV459 were determined using cell binding/adhesion assays.

RESULTS

The range of IC50 values of XV459 in inhibiting platelet aggregation in platelet-rich plasma obtained from 12 subjects was 0.035-0.069 mumol/l with a mean IC50 of 0.050 +/- 0.003 mumol/l. Additionally, XV459 inhibited platelets obtained from mongrel dogs, baboons, sheep, guinea pigs, and mice with IC50 in the range 0.024-0.06 mumol/l, and IC50 in the range 0.16-5.8 mumol/l in pigs, rabbits, and rats. XV459 inhibited [125I]-fibrinogen binding to activated human platelets with an IC50 of 0.011 +/- 0.003 mumol/l. XV459 demonstrated a high degree of selectivity in specifically inhibiting fibrinogen binding to the platelet integrin, GPIIb/IIIa (IC50 = 0.00025 +/- 0.00005 mumol/l) compared with inhibiting other integrins (alpha v beta 3, IC50 > 10 mumol/l; or alpha v beta 5, alpha 5 beta 1, or alpha 4 beta 1, for which the IC50 exceeded 100 mumol/l).

CONCLUSION

DMP754 is a potent antiplatelet agent in inhibiting platelet aggregation, and has a high specificity and affinity for human platelet GPIIb/IIIa receptors.

Probing the functional conformation of the tridecapeptide mating pheromone of Saccharomyces cerevisiae through study of disulfide-constrained analogs

Analogs of the Saccharomyces cerevisiae alpha-mating factor, Trp-His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr, where Lys7 and Gln10 were replaced with Cys, Cys(CH3), or Ser, were synthesized using solid-phase procedures on a phenylacetamidomethyl resin. Cyclo7,10[Cys7,X9,Cys10,Nle12]alpha-factor , where X=D-Val, D-Ala, L-Ala and Gly, were prepared by on-resin cyclization using thallic trifluoroacetate in yields of 20-30%. Linear sulfhydryl-containing peptides were generated from their corresponding cyclic peptide by treatment with dithioerythritol in basic solution. In the linear analogs, replacement of both Lys7 and Gln10 with a cysteine residue resulted in an over 100-fold loss of the biological activity when compared with the native pheromone. The corresponding cyclic disulfides were 5-10-fold more active than their sulfhydryl-containing homologs, and cyclo7,10[Cys7,L-Ala9,Cys10,Nle12] alpha-factor was 50-fold more potent than linear analogs containing Ser or Cys(CH3) in positions 7 and 10. Binding competition studies indicated that all analogs had low affinity for the alpha-factor receptor and there was a poor correlation between binding and activity in a growth arrest assay. A cyclic analog in which residues 8 and 9 were replaced by 5-aminopentanoic acid was not biologically active. Based on NMR studies, all cyclic peptides have a higher tendency to form beta-turns spanning residues 7-10 than their less active linear counterparts. The results provide strong evidence that this beta-turn is important for optimal signal transduction by alpha-factor.

Molecular determinants of bioactivity of the Saccharomyces cerevisiae lipopeptide mating pheromone

The a-factor of Saccharomyces cerevisiae (YIIKGVF-WDPAC(Farnesyl)-OCH3) is a peptide pheromone in which post-translational modification with a farnesyl isoprenoid and carboxyl methyl group is required for export and bioactivity. Truncated and carboxyl-terminal modified analogs of the a-factor were synthesized in order to determine the effect of such modifications on bioactivity. Bioactivity studies on carboxyl-terminal analogs in which the chirality, the cysteine thioether, and the carboxyl ester were varied in an attempt to study the influence of topology on a-factor activity indicate that the hydrophobicity conferred by the farnesyl moiety and not its specific spatial orientation is a key determinant of a-factor potency. Analyses on truncated a-factors suggest that sequential removal of NH2-terminal residues leads to a gradient of potency loss, with some amino acids exhibiting a slightly greater contribution to bioactivity than others. Random oligonucleotide-targeted mutagenesis of the gene encoding a-factor was coupled to a biological screen to identify altered a-factor peptides which are secreted yet exhibit a loss of a-factor bioactivity. Transformants exhibiting this phenotype were examined to identify codon changes presumably responsible for the altered phenotype, thus indicating residues that may contribute significantly to a-factor bioactivity.

NMR investigation of cyclo7,10[C7,X9,C10,Nle12] analogues of the alpha-factor from Saccharomyces cerevisiae

The cyclo7,10[Cys7,Cys10,Nle12], cyclo7,10[Cys7,D-Ala9,Cys10,Nle12], and cyclo7,10[Cys7,L-Ala9,Cys10,Nle12] analogues of the alpha-factor mating pheromone (WHWLQLKPGQPMY) of the yeast Saccharomyces cerevisiae were studied in DMSO/water (80:20) and aqueous solution by nmr spectroscopy. In addition, the cyclo7,10[Cys7,D-Val9,Cys10,Nle12]alpha-fa ctor was examined in DMSO/water. Nuclear Overhauser effect (NOE) and NH d delta/dT data indicate that the cyclo7,10[Cys7,D-Val9,Cys10,Nle12]alpha-fa ctor adopts a type II beta-turn in DMSO/water and that the cyclo7,10[Cys7,D-Ala9,Cys10,Nle12]- and cyclo7,10[Cys7,L-Ala9,Cys10,Nle12]alpha-fa ctor analogues adopt type II and type I/III beta-turns, respectively, in both DMSO/water and aqueous solutions. In aqueous solution, residues 8 and 9 of the cyclo7,10[Cys7,Nle12] alpha-factor appear to adopt at least two distinct conformations, one of these being identified as a type I/III beta-turn. In contrast, the cyclo7,10[Cys7,Cys10,Nle12] alpha-factor appears to adopt predominately a type II beta-turn in DMSO/water. Quantitative NOE measurements of the cyclo7,10[Cys7,Cys10,Nle12]-, cyclo7,10[Cys7,D-Val9,Cys10,Nle12]-, and cyclo7,10[Cys7,L-Ala9,Cys10,Nle12] alpha-factors in DMSO/water were used to derive three-dimensional structures of the cyclo7,10[Cys7,Pro8,X9,Cys10] portion of these analogues.

Chemical synthesis of the M-factor mating pheromone from Schizosaccharomyces pombe

Conjugation in the fission yeast Schizosaccharomyces pombe is controlled by the reciprocal action of mating pheromones. We recently showed that M-factor, the pheromone released by cells of the cellular mating type Minus, is a nonapeptide in which the C-terminal cysteine residue is carboxyl-methylated and S-alkylated, probably with a farnesyl residue (Davey, 1992): Tyr-Thr-Pro-Lys-Val-Pro-Tyr-Met-Cys(S-farnesyl)- OCH3. Here we describe the chemical synthesis of this modified peptide and show that it exhibits all of the properties of the native pheromone. These results confirm the structure of the M-factor while the production of relatively large amounts of pure pheromone will be invaluable for studying the mating response in this yeast.

Role of prenylation in the interaction of the a-factor mating pheromone with phospholipid bilayers

We have studied the interaction between phospholipids and a-factor (YIIKGVFWDPAC-[Farn]OMe), S-alkylated forms of a-factor with the farnesyl group substituted by methyl, hexadecanyl, or benzyl groups, and truncated forms of this lipopeptide. Circular dichroism studies suggest that, despite its lack of farnesylation, S-methyl-a-factor is incorporated into vesicles of dimyristoylphosphatidylcholine in a conformation similar to that which a-factor adopts in this membrane. However, studies of the intrinsic fluorescence of the Trp residues of these peptides indicate that this residue is more deeply imbedded into the bilayer in the case of the farnesylated peptide. The a-factor is more effective in raising the bilayer to the hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine than is the S-methyl-a-factor. This bilayer-stabilizing ability is also reflected in a-factor inhibiting leakage from vesicles of N-methyldioleoylphosphatidylethanolamine. Studies on a-factor analogs permit the conclusion that the bilayer-stabilizing effect of a-factor is not solely a consequence of its greater partitioning into the membrane but is also a consequence of the degree of penetration into the bilayer and the specific conformation of the peptide at the membrane interface. These results indicate that the farnesyl group alone, in the absence of cellular factors, bestows a particular physical interaction with membranes.

Studies on the yeast alpha-mating factor: a model for mammalian peptide hormones

Small peptides initiate sexual conjugation in the yeast Saccharomyces cerevisiae and this phenomenon is an ideal paradigm for studying the mode of action of mammalian peptide hormones. 1H-nmr spectroscopy was used to examine the conformation of linear and cyclic analogues of the alpha-factor (WHWLQLKPGQPMY) in aqueous solution. In all cases peptides that exhibit nmr parameters expected for a type II beta-turn have higher biological activities than those that do not appear to assume this conformation. Based on a simple model for the interaction of the pheromone with its receptor, we prepared fragments of the alpha-factor. Several of these fragments either antagonize or potentiate the activity of the alpha-factor. The latter represent the first example of peptide fragments that synergize the activity of the parent pheromone.

Antagonistic and synergistic peptide analogues of the tridecapeptide mating pheromone of Saccharomyces cerevisiae

Biologically inactive, truncated analogues of the Saccharomyces cerevisiae alpha-mating factor (WHWLQLKPGQPMY) either antagonized or synergized the activity of the native pheromone. An amino-terminal truncated pheromone [WLQLKPGQP(Nle)Y] had no activity by itself, but the analogue acted as an antagonist by competing with binding and activity of the mating factor. In contrast, a carboxyl-terminal truncated pheromone [WHWLQLKPGQP] was not active by itself nor did the peptide compete with alpha-factor for binding to the alpha-factor receptor, but it acted as a synergist by causing a marked increase in the activity of alpha-factor. The observation that residues near the amino terminus may be involved in signal transduction whereas those near the carboxyl terminus influence binding allows us to separate binding and signal transduction in the yeast pheromone response pathway. If found for other hormone-receptor systems, synergists may have potential as therapeutic compounds.

The conformation of a-factor is not influenced by the S-prenylation of Cys12

Two-Dimensional NMR was used to examine the solution conformation of the lipopeptide a-factor, YIIKGVFWDPAC (S-farnesyl) OCH3, from the yeast Saccharomyces cerevisiae and five analogues containing various S-alkylated cysteines in DMSO-d6. NOESY data, NH temperature coefficients, and 3J alpha NH coupling constants indicate that the a-factor is a predominantly unstructured peptide in DMSO. Similar results were obtained for the other peptides indicating that S-prenylation of Cys12 does not affect the conformation of these peptides.

Significance of C-terminal cysteine modifications to the biological activity of the Saccharomyces cerevisiae a-factor mating pheromone

We have undertaken total synthesis of the Saccharomyces cerevisiae a-factor (NH2-YIIKGVFWDPAC[S-farnesyl]-COOCH3) and several Cys-12 analogs to determine the significance of S-farnesylation and carboxy-terminal methyl esterification to the biological activity of this lipopeptide mating pheromone. Replacement of either the farnesyl group or the carboxy-terminal methyl ester by a hydrogen atom resulted in marked reduction but not total loss of bioactivity as measured by a variety of assays. Moreover, both the farnesyl and methyl ester groups could be replaced by other substituents to produce biologically active analogs. The bioactivity of a-factor decreased as the number of prenyl units on the cysteine sulfur decreased from three to one, and an a-factor analog having the S-farnesyl group replaced by an S-hexadecanyl group was more active than an S-methyl a-factor analog. Thus, with two types of modifications, a-factor activity increased as the S-alkyl group became bulkier and more hydrophobic. MATa cells having deletions of the a-factor structural genes (mfal1 mfa2 mutants) were capable of mating with either sst2 or wild-type MAT alpha cells in the presence of exogenous a-factor, indicating that it is not absolutely essential for MATa cells to actively produce a-factor in order to mate. Various a-factor analogs were found to partially restore mating to these strains as well, and their relative activities in the mating restoration assay were similar to their activities in the other assays used in this study. Mating was not restored by addition of exogenous a-factor to a cross of a wild-type MAT alpha strain and a MATaste6 mutant, indicating a role of the STE6 gene product in mating in addition to its secretion of a-factor.

Synthesis of S-alkyl and C-terminal analogs of the Saccharomyces cerevisiae a-factor. Influence of temperature on the stability of Fmoc and OFm groups toward HF

The a-mating factor of Saccharomyces cerevisiae Tyr-Ile-Ile-Lys-Gly-Val-Phe-Trp-Asp-Pro-Ala-Cys(farnesyl)OCH3, and 10 analogs modified at the cysteine side chain and/or the terminal carboxyl were synthesized using a combination of solid phase and solution phase methodologies. The strategy of synthesis involved the condensation of an amine terminal protected decapeptide with a carboxyl terminal S-alkylated dipeptide ester or amide using benzotriazol-l-yloxy-tris(methylamino)-phosphonium hexafluorophosphate as the coupling agent. The protected decapeptide was assembled on a PAM-resin using 9-fluorenylmethoxycarbonyl (Fmoc) for the protection of the Tyr alpha-amine and Lys epsilon-amine and 9-fluorenylmethyl ester (OFm) for the protection of the Asp beta-carboxyl. Premature loss of the OFm group from the HF cleavage was observed at 0-2 degrees, whereas no loss occurred when the cleavage reaction was conducted at -5 degrees. In contrast to these results, the OFm group in Asp(OFm) was partially removed by HF at -5 degrees and was completely stable to HF only at -20 degrees. The S-alkylated dipeptide esters were prepared, in yields from 64% to 88%, via thioalkylation of amine protected or unprotected dipeptide esters using potassium fluoride dihydrate as the base. The use of a tertiary amine as the base of thiohexadecanylation resulted in low reactivity.

A novel reagent, dialkylphosphite, for peptide synthesis

The same dialkylphosphite reagent can be used for both N protection and C activation of amino acids. Two N-diisopropyloxyphosphinyl (Dipp) tripeptide esters were prepared, and nine N-Dipp-dipeptide acids were synthesized through the activated amide intermediate. The positive ion FAB-MS of N-Dipp-tripeptide showed novel cleavage patterns in that only the N-phosphoryl fragment ions gave intense peaks while the C-terminal series ions did not appear. This novel character might be useful for peptide sequence analysis. In addition, dialkyloxyphosphinyl group can be examined by 31P-NMR for peptide conformational analysis and inspection for the degree of racemization during the coupling reaction.

Mass spectrometric signature of S-prenylated cysteine peptides

The fast atom bombardment mass spectra of peptides containing S-prenylated cysteine display signature fragmentations characteristic of this modified amino acid. The fragmentation is independent of the nature of the cysteine carbonyl substituent, easily differentiates prenyl from nonprenyl alkylation, and readily identifies the oligomer count of the prenyl. This screening method, which requires little time, effort, or material (compared with previous analysis methods based on chemical degradation), greatly facilitates the identification of these prenylated proteins.

Total in vitro maturation of the Saccharomyces cerevisiae a-factor lipopeptide mating pheromone

The a-factor mating pheromone, produced by Saccharomyces cerevisiae a haploid cells, is post-translationally modified in a manner analogous to that of the ras proto-oncogene product. A consensus C-terminal amino acid sequence, -CAAX (C is cysteine, A is aliphatic amino acid, and X is any amino acid), is the target of these modifications, which include isoprenylation (essential for Ras function), proteolysis of the -AAX sequence, and carboxy methyl esterification. Recently, the RAM/DPR1 gene product was shown to be a component of the activity responsible for isoprenylation of both Ras and a-factor. In this report, we present an in vitro assay which not only detects a-factor isoprenylation, but also proteolysis and carboxy methyl esterification, and directly demonstrates, biochemically, the order of these processing events. This a-factor maturation assay may prove useful for screening agents which block any of the steps involved in the post-translational modification of the a-factor and Ras -CAAX sequences. Such agents would be potential anti-Ras-related cancer therapeutic drugs.

Solution phase synthesis of Saccharomyces cerevisiae a-mating factor and its analogs

The solution phase synthesis of the Saccharomyces cerevisiae a-mating factor and nonfarnesylated and nonmethylated a-factor analogs are reported. The a-factor, a lipopeptide with the sequence Tyr-Ile-Ile-Lys-Gly-Val-Phe-Trp-Asp-Pro-Ala-Cys(S-Farnesyl)OCH3 was synthesized by the condensation of the amine terminal protected decapeptide with the carboxyl terminal farnesylated dipeptide using benzotriazol-l-yloxy-tris-(dimethylamino)-phosphonium hexafluorophosphate (BOP reagent) as the coupling agent. The synthesis of the decapeptide involved 5 + 5 fragment coupling with the BOP reagent and the successful application of 9-fluorenylmethyl ester(OFm) and 9-fluorenylmethoxycarbonyl(Fmoc) groups for the protection of Asp and Lys side chains and Tyr alpha-amine and of phenacyl esters (OPa) for alpha-carboxyl protection. The OFm and Fmoc groups tolerated repeated couplings and were completely stable to zinc powder in acetic acid, a condition under which the OPa group was removed. The synthesis of the nonfarnesylated alpha-factor was accomplished by the coupling of the decapeptide with tetrapeptide (Ala-CysOCH3)2 followed by the deprotection of the OFm and Fmoc groups with piperidine and the cleavage of the disulfide bond with zinc powder in acetic acid. The nonmethylated a-factor was prepared by 10 + 2 fragment coupling using OFm protection of the dipeptide carboxyl group followed by removal of all protecting groups with piperidine. Attempts to saponify a-factor were not successful. The synthetic nonfarnesylated and nonmethylated a-mating pheromones were 100-1000 times less active than the a-factor, indicating that although the methyl ester and the farnesyl group are not essential for biological activity, they are necessary for high potency.

Synthetic probes for the alpha-factor receptor

The binding of the tridecapeptide yeast mating pheromone, alpha-factor, to its receptor represents an excellent model for the investigation of peptide hormone-receptor interactions. In this paper we present a number of strategies to probe the binding site of the alpha-factor receptor, and discuss the synthesis of probes containing radioactive and affinity tags. Preferential acylation of the alpha- or epsilon-amine in [Nle12]-alpha-factor was accomplished using 3-[3,5-diiodo-4-hydroxyphenyl] propanoic acid hydroxysuccinimide ester (diiodo Bolton-Hunter reagent). At pH 8.0 in a N-N-dimethylformamide/water mixture the ratio of epsilon- to alpha-acylation was 2.15 to 1, whereas at pH 6.5 in a 1,2-dimethoxyethane/water mixture alpha-acylation was favored by more than 3 to 1. The product distribution was found to depend on pH, organic cosolvent, and the ratio of organic solvent and aqueous buffer. Product distributions were followed using analytical high performance liquid chromatography and the products were characterized enzymatically and by mass spectrometry. Citraconic anhydride preferentially alpha-acylated [Nle12]-alpha-factor and served as a temporary masking group during the synthesis of epsilon-Bolton-Hunter acylated pheromone. Biotin or diiodo Bolton-Hunter reagents were also directly incorporated into [Nle12]-alpha-factor or Lys[Nle12]-alpha-factor during peptide synthesis. The peptides were assembled on a chloromethyl polystyrene resin or on a (phenylacetamido)methyl resin, and cleaved using anhydrous hydrogen fluoride (HF). Probes were inserted on amino groups either prior (biotin) or subsequent (Bolton-Hunter reagent) to HF cleavage. The biological activity of the synthetic peptides was characterized using growth arrest assays.(ABSTRACT TRUNCATED AT 250 WORDS)

A covalently constrained congener of the Saccharomyces cerevisiae tridecapeptide mating pheromone is an agonist

An analog of alpha-factor, the Saccharomyces cerevisiae tridecapeptide mating pheromone (Trp-His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr), in which the side chains of Lys7 and Gln10 were covalently linked, was synthesized using solid phase methodologies. The yield of the purified cyclic analog cyclo7,10[Nle12]alpha-factor was 30%, and its structure was verified by amino acid analysis, peptide sequencing, fast atom bombardment-mass spectrometry, and proton nuclear magnetic resonance spectroscopy. Cyclo7,10[Nle12]alpha-factor caused growth arrest and morphological alterations in S. cerevisiae MATa cells qualitatively identical to those induced by linear pheromone and was one-fourth to one-twentieth as active as the linear alpha-factor depending upon the S. cerevisiae strain tested. Consistent with the relative activities of the linear and cyclic peptides, binding competition studies indicated that cyclo7,10[Nle12]alpha-factor had approximately 20-40-fold less affinity for the alpha-factor receptor. Hydrolysis of the cyclic peptide by the target cells did not lead to opening of the ring and was less rapid than that of linear alpha-factor. The alpha-factor antagonist des-Trp1-[Ala3,Nle12]alpha-factor reversed the activity of the cyclic analog, and cyclo7,10[Nle12]alpha-factor was not active at the restrictive temperature in a temperature-sensitive receptor mutant. These results support the conclusion that the cyclic alpha-factor occupies the same binding site within the receptor as is occupied by the natural pheromone. The cyclic alpha-factor represents a rare example of an agonist among covalently constrained congeners of small linear peptide messengers.

Total synthesis of the lipopeptide a-mating factor of Saccharomyces cerevisiae

The a-mating factor of Saccharomyces cerevisiae was synthesized using both solution phase and solid phase strategies. Structure of the final peptide was confirmed using amino acid analysis, fast atom bombardment mass spectroscopy and 400 MHz proton NMR. The synthetic farnesylated dodecapeptide, YIIKGVFWDPAC (S-farnesyl) OCH3, exhibited chromatographic and spectroscopic properties identical to the natural pheromone and had significant biological activity at nanomolar concentrations.