Ketomethylene and methyleneamino pseudopeptide analogues of insect allatostatins inhibit juvenile hormone and vitellogenin production in the cockroach Blattella germanica

A short neuropeptide F analog (sNPF), III-2 may particularly regulate juvenile hormone III to influence Spodoptera frugiperda metamorphosis and development

Allatostatin (AS) or Allatotropin (AT) is a class of insect short neuropeptide F (sNPF) that affects insect growth and development by inhibiting or promote the synthesis of juvenile hormone (JH) in different insects. III-2 is a novel sNPF analog derived from a group of nitroaromatic groups connected by different amino acids. In this study, we found that III-2 showed high insecticidal activity against S. frugiperda larvae with a LC50 of 18.7 mg L-1. As demonstrated by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), III-2 particularly facilitated JH III and hindered 20E synthesis in S. frugiperda. The results of RNA-Seq and quantitative real-time polymerase chain reaction (qPCR) showed that III-2 treatment promoted the expression of key genes such as SfCYP15C1 in JH synthesis pathway and inhibited the expression of SfCYP314A1 and other genes in the 20E synthetic pathway. Significant differences were also observed in the expression of the genes related to cuticle formation. We report for the first time that sNPF compounds specifically interfere with the synthesis and secretion of a certain JH in insects, thus affecting the ecdysis and growth of insects, and leading to death. This study may provide a new plant conservation concept for us to seek the targeted control of certain insects based on specific interference with different JH.

Structure-Based Discovery of Nonpeptide Allatostatin Analogues for Pest Control

FGLamide allatostatins (ASTs) are regarded as possible insecticide candidates, although their lack of in vivo effects, rapid degradation, poor water solubility, and high production costs preclude their practical use in pest control. In contrast to previous research, the C-terminal tripeptide (FGLa) was selected as the lead compound in this study. Five nonpeptide AST analogues (2-amino-1-[3-oxo-3-(substituted-anilino)propyl]pyridinium nitrate derivatives) were designed on the basis of the structure-activity relationship and docking results of FGLa. All of the nonpeptide analogues (S1-S5) were more potent against juvenile-hormone (JH) biosynthesis than the lead compound. They significantly inhibited the biosynthesis of JH in vivo following injection. A pest-control application demonstrated that S1 and S3 have larvicidal effects following oral administration (the IC₅₀ values were 0.020 and 0.0016 mg/g, respectively). The good oral toxicities and excellent water solubilities of S1 and S3 suggest that they have considerable potential as insecticides for pest management.

A potential insect growth regulator for cockroach control: design, synthesis and bioactivity of N-terminal-modified allatostatin analogues

BACKGROUND

The FGLa-allatostatins (ASTs) are a family of neuropeptides that can inhibit juvenile hormone biosynthesis by the corpora allata (CA) in vitro, and therefore they are regarded as insect growth regulator (IGR) candidates for pest control. In our previous studies, an AST mimic, H17, was found to have a significant effect on JH biosynthesis by cockroach CA, both in vitro and in vivo. To discover new potential mimics and explore the substituent effect on the inhibition of JH biosynthesis, 30 analogues, modified with various substituents on the benzene ring at the N-terminus of lead compound H17, were designed and synthesised. Their bioactivity in inhibiting JH biosynthesis by the CA of Diploptera punctata and the potency of M9, M10 and M11 in activation of Dippu-AstR were evaluated.

RESULTS

All the analogues showed an effect on JH biosynthesis by CA in vitro. M9, M10 and M11 can activate the Dippu-AstR, albeit with much lower potency than that of AST 1. M11 also exhibited improved in vitro activity (IC₅₀ 6.98 nm) in comparison with the lead compound H17 (IC₅₀ 29.5 nm). In particular, M11 displayed good in vivo activity in inhibiting JH biosynthesis and basal oocyte growth.

CONCLUSION

The structure-activity relationship studies suggest that different positions of substituents on the benzene ring of the cinnamic acid can lead to different activities. The para-substitution on the benzene ring plays an important role in inhibiting JH biosynthesis in vitro. Moreover, M11 is considered to be a potential IGR for cockroach control. © 2016 Society of Chemical Industry.

Synthesis, biological activity, and conformational study of N-methylated allatostatin analogues inhibiting juvenile hormone biosynthesis

An allatostatin (AST) neuropeptide mimic (H17) is a potential insect growth regulator, which inhibits the production of juvenile hormone (JH) by the corpora allata. To determine the effect of conformation of novel AST analogues and their ability to inhibit JH biosynthesis, eight insect AST analogues were synthesized using H17 as the lead compound by N-methylation scanning, which is a common strategy for improving the biological properties of peptides. A bioassay using JH production by corpora allata of the cockroach Diploptera punctata indicated that single N-methylation mimics (analogues 1-4) showed more activity than double N-methylation mimics (analogues 5-8). Especially, analogues 1 and 4 showed roughly equivalent activity to that of H17, with IC50 values of 5.17 × 10(-8) and 6.44 × 10(-8) M, respectively. Molecular modeling based on nuclear magnetic resonance data showed that the conformation of analogues 1 and 4 seems to be flexible, whereas analogues 2 and 3 showed a type IV β-turn. This flexible linear conformation was hypothesized to be a new important and indispensable structural element beneficial to the activity of AST mimics.

Families of allatoregulator sequences: a 2011 perspective1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Three different peptide families have been named “allatostatins” (ASTs), based on their initial purifications which were based on their ability to inhibit juvenile hormone (JH) biosynthesis. These include (i) a family of peptides that have a consensus C-terminal sequence Y/FXFGL-NH2; (ii) a family of peptides with a conserved C-terminal sequence W(X)6W-NH2; and(iii) a family of peptides with C-terminal sequence PISCF, some of which are C-terminally-amidated. Each allatostatin family has functions distinct and apart from the inhibition of JH biosynthesis. A peptide family known as the “allatotropins” serve to stimulate JH biosynthesis. This family of peptides also has been proven to exert multiple effects dependent on the species in question. Genome and peptidome projects are uncovering new members of these families and it is clear that these structures are not just confined to Insecta but are found in a range of invertebrates. The receptors for these neuropeptides have been identified and tested experimentally for specific ligand binding. The Y/FXFGLa-ASTs exert their action through galanin-like receptors, W(X)6Wa-ASTs through a sex peptide-binding receptor, and PISCF-ASTs through somatostatin-like receptors. These receptors are conserved through evolutionary time and are being identified in numerous invertebrates by way of genome projects.

Design, synthesis and biological activity of peptidomimetic analogs of insect allatostatins

Allatostatins (ASTs) comprise a family of insect neuropeptides isolated from cockroaches and found to inhibit the production of juvenile hormone (JH) by the corpora allata (CA). For this reason, the ASTs can be regarded as possible IGR candidates for pest control. Six peptidomimetic analogs according to the C-terminal pentapeptide of ASTs were prepared by solid-phase organic synthetic methods in an attempt to obtain new simple substitution agents. Assays of inhibition of JH biosynthesis in vitro by corpora allata from the cockroach Diploptera punctata showed that the activity of analog I (IC(50): 0.09 μM) was more active than that of the C-terminal pentapeptide (Tyr-Xaa-Phe-Gly-Leu-NH(2), IC(50): 0.13 μM) it mimicked and the activity of the analog II (IC(50): 0.13 μM) proved roughly equivalent to the C-terminal pentapeptide. The results indicate that a new simple mimicry for Tyr-Xaa-Phe-Gly has been discovered; analog I may be a novel compound candidate for potential IGRs. This study will be useful for the design of new AST analogs for insect management.

Neuropeptide physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Synthesis, biological activity, and hologram quantitative structure-activity relationships of novel allatostatin analogues

Cockroach-type allatostatins (FGLamides) (ASTs) can inhibit the production of juvenile hormone in vitro, and they therefore are regarded as possible insect growth regulator (IGR) candidates for pest control. However, several shortcomings, such as the absence of in vivo effects, rapid degradation, and high production costs, preclude their practical use in pest management. To discover new IGRs, 25 novel analogues of pentapeptide (Y/FXFGLa) were designed and synthesized with different aromatic acids, fatty acids, and dicarboxylic acids as the Y/FX region replacements on the basis of previous results. Their bioactivities in vitro were determined, and the results showed that eight analogues (K14, K15, K17, K18, K19, K23, K24, and K25) were more active than the lead, core region pentapeptide. The IC(50) values of K15 and K24 (IC(50) = 1.79 and 5.32 nM, respectively) were even lower than that of the natural AST, Dippu-AST 1(IC(50) = 8 nM), which indicated both analogues have better activity than Dippu-AST 1; particularly, K15 has better activity than most natural Dippu-ASTs. A predictable and statistically meaningful hologram quantitative structure-activity relationship (HQSAR) model of 32 AST analogues (28 as training sets and 4 as test sets) was obtained. The final model suggested that a potent AST analogue should contain an aromatic group, a linker of appropriate length, and the FGLa portion. These results will be useful in the design of new AST analogues that are structurally related to the training set compounds.

A potential insect growth regulator: synthesis and bioactivity of an allatostatin mimic

Insect growth regulators play an important role in Integrated Pest Management systems. Cockroach-type allatostatins (FGLamides) (ASTs), which are a family of basic peptides first isolated from brains of Diploptera punctata were originally discovered on the basis of their ability to inhibit the production of juvenile hormone by the corpora allata. For this reason, the ASTs can be regarded as possible IGR candidates for pest control although the absence of effect in vivo, rapid degradation and high production costs of the natural peptides preclude their use in pest management. However, we have synthesized a new AST mimic, H17, from the pentapeptide C-terminal active core of the AST. This mimic is able to significantly inhibit the biosynthesis of JH by cockroach CA in vitro (IC(50) value: 12 nM) and in vivo following injection (IC(50) value: 33 nM). H17 also shows a highly significant inhibition of JH production in topical cuticular assays in vivo. Our results suggest that H17 has potential as an IGR for cockroach control.

The role of allatostatins in juvenile hormone synthesis in insects and crustaceans

Allatostatins are pleiotropic neuropeptides for which one function in insects is the inhibition of juvenile hormone synthesis. Juvenile hormone, an important regulator of development and reproduction in insects, is produced by the corpora allata. Mandibular organs, the crustacean homologs of insect corpora allata, produce precursors of juvenile hormone with putatively similar functions. Three types of allatostatins in insects have been isolated: FGLamides, W(X)(6)Wamides, and PISCFs. All act rapidly and reversibly; however, although these types occur in all groups of insects studied, they act as inhibitors of juvenile hormone production in only some groups. Only the FGLamide-type peptides have been isolated in crustaceans, in which they may function to stimulate production of hormone by the mandibular glands, as occurs in early cockroach embryos. Much remains to be learned in order to understand the role of allatostatins in the modulation of hormone production.

The study of solution conformation of allatostatins by 2-D NMR and molecular modeling

More than 70 allatostatins have been isolated from various insects and there is interest in the determination of their active conformation. We have synthesized Dippu-AST 1 (originally isolated from the cockroach Blattella germanica) and studied its conformation in solution by 2-D NMR and molecular modeling. Dippu-AST 1 belongs to the cockroach-type ASTs that have Y/FXFGL-NH(2) as the common C-terminal sequence. We found that Dippu-AST 1 forms a type I' beta-turn conformation in DMSO. We also studied the conformations of Dippu-AST 1 and six cockroach-type allatostatins in water using the molecular dynamics method. When the X amino acid in the consensus sequence Y/FXFGL-NH(2) is Ala or Ser, the allatostatin can form a typical type II beta-turn. If the X is Asp or Asn whose side chain contains a carbonyl, the allatostatin can form a type I, I' or IV beta-turn conformation; if the X is Gly, a closer gamma-turn is adopted. Our study indicates that the turn conformation is ubiquitous in cockroach-type allatostatins.

Identification of multiple peptides homologous to cockroach and cricket allatostatins in the stick insect Carausius morosus

Eighteen peptides were isolated from brain extracts of the stick insect Carausius morosus. The peptides were purified in four steps by high-performance liquid chromatography, monitored by their ability to inhibit juvenile hormone biosynthesis by corpora allata of the cricket Gryllus bimaculatus in vitro, and chemically characterised by Edman degradation and mass spectrometry. We obtained complete primary-structure information for nine peptides, four of which belong to the peptide family characterised by a common C-terminal pentapeptide sequence -YXFGLamide. The remaining five belong to the W(2)W(9)amide peptide family, nonapeptides characterised by having the amino acid tryptophan in positions 2 and 9. The amino-acid sequence of two other peptides could not be completely resolved by means of Edman degradation; however, these peptides could be allocated to the -YXFGLamide and the W(2)W(9)amide family, respectively, by comparison of retention times, co-elution and mass spectrometry. Both classes of neuropeptides strongly inhibit juvenile hormone biosynthesis in crickets but show no inhibiting effect on the corpora allata of the stick insect.

Injection of Dip-allatostatin or Dip-allatostatin pseudopeptides into mated female Diploptera punctata inhibits endogenous rates of JH biosynthesis and basal oocyte growth

Studies on the catabolism of allatostatins (ASTs) provided the rationale for the design of a series of Dip-allatostatin-derived pseudopeptide mimetic analogues. In vitro, the Dip-ASTs and pseudopeptides show varying degrees of resistance to catabolism and all show significant inhibition of juvenile hormone (JH) biosynthesis. This study was undertaken to determine whether potent Dip-ASTs and/or their pseudopeptide mimetic counterparts caused 'allatostatic' effects in vivo following injection into mated female Diploptera punctata. Animals injected with aqueous solvent or Dip-AST 7(1-7) N-terminal fragment, which excludes the active core region of the ASTs, were used as controls. An in vitro radiochemical assay revealed that injection of Dip-AST 5, 7 or pseudopeptide analogues 397-2 or AST(b)&phi;2 significantly inhibited the biosynthesis of JH (P<0.05). The results also indicate that basal oocyte growth was significantly inhibited by injection of these same compounds, with the exception of Dip-AST 7 (P<0.05). Analogues 396-1 and 419 did not significantly inhibit rates of JH biosynthesis but did significantly inhibit the growth of basal oocytes. Analyses of feeding, excretion and food absorption/utilization patterns of these same animals suggested that these compounds are not toxic to the insect; rather they directly inhibit the biosynthesis of JH by the corpora allata, and reduce the rate of growth of basal oocytes. Disruption of critical reproductive and/or developmental processes by pseudopeptide analogues of the ASTs could provide novel and selective strategies for future insect pest management.

Modulation of cardiac rhythm by allatostatins in the cockroach Blattella germanica (L.) (Dictyoptera, Blattellidae)

Cardiac rhythm was measured in Blattella germanica females during the reproductive cycle. The rate increased from day 0 to 1, remained constant during the vitellogenic period and fell by about 20% during the period of oothecal transport. The effects of allatostatins, allatostatin analogues and corazonin were tested on semi-isolated heart preparations. Allatostatins showed a rapid, reversible and dose-dependent cardioinhibitory activity. Blattella allatostatin 1 (BLAST-1: LYDFGL-NH(2)), was the most active, eliciting 76% inhibition at 10(-7) M and even 19% inhibition at 10(-9) M. BLAST-2 (DRLYSFGL-NH(2)), BLAST-3 (AGSDGRLYSFGL-NH(2)) and BLAST-4 (APSSAQRLYGFGL-NH(2)) were less active. An analogue of BLAST-2 with C-terminus in acid form and a pseudopeptide analogue of BLAST-2 with a methyleneamino Psi[CH(2)NH] peptide bond surrogate between residues L(3) and Y(4) were inactive. Corazonin elicited rapid, reversible and dose-dependent cardioacceleratory activity. When tested together with BLAST-1, corazonin overrode the cardioinhibitory effect of allatostatin. Our previous results had shown that high levels of allatostatin were maintained during the period of oothecal transport. This and the fact that physiological concentrations of allatostatins produce physiological levels of inhibition, suggest that allatostatins are involved in the modulation of cardiac rhythm in this cockroach.