Potent pheromonotropic/myotropic activity of a carboranyl pseudotetrapeptide analogue of the insect pyrokinin/PBAN neuropeptide family administered via injection or topical application

Disruption of insect immunity using analogs of the pleiotropic insect peptide hormone Neb-colloostatin: a nanotech approach for pest control II

This work continues our studies on the pleiotropic activity of the insect peptide Neb-colloostatin in insects. In vivo immunological bioassays demonstrated that hemocytotoxic analogs of Neb-colloostatin injected into Tenebrio molitor significantly reduced the number of hemocytes in the hemolymph and impaired phagocytosis, nodulation and phenoloxidase activities in the insects. Among the analogs tested, [Ala¹]-,[Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin were particularly potent in disrupting cellular immunity in larvae, pupae and adult insects. This result suggests that the most effective analogs showed increases in the bioactivity period in the hemolymph of insects when compared to Neb-colloostatin. Recently, we demonstrated that it is possible to introduce Neb-colloostatin through the cuticle of an insect into the hemolymph when the peptide is coupled with nanodiamonds. In this study, we showed that [Ala¹]-, [Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin, when complexed with nanodiamonds, may also pass through the cuticle into the hemolymph and induce long-term impairments of immunity in T. molitor at all developmental stages. Studies on the tissue selectivity and effectiveness of Neb-colloostatin analogs and efficient methods for their introduction into insects may contribute to the development of eco-friendly pest control methods based on bioactive peptidomimetics.

Inhibitors of CA IX Enzyme Based on Polyhedral Boron Compounds

This review describes recent progress in the design and development of inhibitors of human carbonic anhydrase IX (CA IX) based on space-filling carborane and cobalt bis(dicarbollide) clusters. CA IX enzyme is known to play a crucial role in cancer cell proliferation and metastases. The new class of potent and selective CA IX inhibitors combines the structural motif of a bulky inorganic cluster with an alkylsulfamido or alkylsulfonamido anchor group for Zn²⁺ ion in the enzyme active site. Detailed structure-activity relationship (SAR) studies of a large series containing 50 compounds uncovered structural features of the cluster-containing inhibitors that are important for efficient and selective inhibition of CA IX activity. Preclinical evaluation of selected compounds revealed low toxicity, favorable pharmacokinetics and ability to reduce tumor growth. Cluster-containing inhibitors of CA IX can thus be considered as promising candidates for drug development and/or for combination therapy in boron neutron capture therapy (BNCT).

Impairment of the immune response after transcuticular introduction of the insect gonadoinhibitory and hemocytotoxic peptide Neb-colloostatin: A nanotech approach for pest control

This article shows that nanodiamonds can transmigrate through the insect cuticle easily, and the doses used were not hemocytotoxic and did not cause inhibition of cellular and humoral immune responses in larvae, pupae and adults of Tenebrio molitor. The examination of the nanodiamond biodistribution in insect cells demonstrated the presence of nanodiamond aggregates mainly in hemocytes, where nanoparticles were efficiently collected as a result of phagocytosis. To a lesser extent, nanodiamond aggregates were also detected in fat body cells, while they were not observed in Malpighian tubule cells. We functionalized nanodiamonds with Neb-colloostatin, an insect hemocytotoxic and gonadoinhibitory peptide, and we showed that this conjugate passed through the insect cuticle into the hemolymph, where the peptide complexed with the nanodiamonds induced apoptosis of hemocytes, significantly decreased the number of hemocytes circulating in the hemolymph and inhibited cellular and humoral immune responses in all developmental stages of insects. The results indicate that it is possible to introduce a peptide that interferes with the immunity and reproduction of insects to the interior of the insect body by means of a nanocarrier. In the future, the results of these studies may contribute to the development of new pest control agents.

Icosahedral boron clusters as modifying entities for biomolecules

INTRODUCTION

Icosahedral boron clusters have unique properties useful in medicinal chemistry: rigidity, chemical stability, and three-dimensional aromaticity. Furthermore, these abiotic compounds have low toxicity and are stable in the biological environment. All these features ultimately give them the ability to interact with biological molecules in a different mode than organic compounds.

AREAS COVERED

In the present article, we aim to introduce boron clusters as a class of entities suitable for modifications of biomolecules to obtain a specific biological effect. We will focus on icosahedral boron clusters, as well as metallacarboranes, and their biological activity and interaction with the biological environment.

EXPERT OPINION

Boron clusters are suitable for altering structural and functional features of biomolecules and can be used in the development of new drugs and drug delivery systems. The high affinity of boron clusters, especially metallacarboranes, to albumin creates a new possibility to use them to optimize the pharmacokinetics of biologically active peptides. Boron clusters have high potential in biological and medicinal applications. Due to their peculiar properties, they can be used to optimize parameters critical for the biological activity of therapeutic substances and their affinity toward biological targets.

Selecting and validating reference genes for quantitative real-time PCR in Plutella xylostella (L.)

Gene expression analysis provides important clues regarding gene functions, and quantitative real-time PCR (qRT-PCR) is a widely used method in gene expression studies. Reference genes are essential for normalizing and accurately assessing gene expression. In the present study, 16 candidate reference genes (ACTB, CyPA, EF1-α, GAPDH, HSP90, NDPk, RPL13a, RPL18, RPL19, RPL32, RPL4, RPL8, RPS13, RPS4, α-TUB, and β-TUB) from Plutella xylostella were selected to evaluate gene expression stability across different experimental conditions using five statistical algorithms (geNorm, NormFinder, Delta Ct, BestKeeper, and RefFinder). The results suggest that different reference genes or combinations of reference genes are suitable for normalization in gene expression studies of P. xylostella according to the different developmental stages, strains, tissues, and insecticide treatments. Based on the given experimental sets, the most stable reference genes were RPS4 across different developmental stages, RPL8 across different strains and tissues, and EF1-α across different insecticide treatments. A comprehensive and systematic assessment of potential reference genes for gene expression normalization is essential for post-genomic functional research in P. xylostella, a notorious pest with worldwide distribution and a high capacity to adapt and develop resistance to insecticides.

Development of neuropeptide analogs capable of traversing the integument: A case study using diapause hormone analogs in Helicoverpa zea

Diapause hormone and its analogs terminate pupal diapause in Helicoverpa zea when injected, but if such agents are to be used as effective diapause disruptors it will be essential to develop simple techniques for administering active compounds that can exert their effect by penetrating the insect epidermis. In the current study, we used two molecules previously shown to have high diapause-terminating activity as lead molecules to rationally design and synthesize new amphiphilic compounds with modified hydrophobic components. An assay for diapause termination identified 13 active compounds with EC50's ranging from 0.9 to 46.0 pmol per pupa. Three compounds, Decyl-1963, Dodecyl-1967, and Heptyl-1965, selected from the 13 compounds most active in breaking diapause following injection, also successfully prevented newly-formed pupae from entering diapause when applied topically. These compounds feature straight-chain, aliphatic hydrocarbons from 7 to 12 carbons in length; DH analogs with either a short-chain length of 4 or an aromatic phenethyl group failed to act topically. Compared to a high diapause incidence of 80-90% in controls, diapause incidence in pupae receiving a 10 nmole topical application of Decyl-1963, Dodecyl-1967, or Heptyl-1965 dropped to 30-45%. Decyl-1963 and Dodecyl-1967 also remained effective when topically applied at the 1 nmole level. These results suggest the feasibility of developing DH agonists that can be applied topically and suggest the identity of new lead molecules for development of additional topically-active DH analogs. The ability to penetrate the insect epidermis and/or midgut lining is critical if such agents are to be considered for future use as pest management tools.

Pyrokinin β-neuropeptide affects necrophoretic behavior in fire ants (S. invicta), and expression of β-NP in a mycoinsecticide increases its virulence

Fire ants are one of the world's most damaging invasive pests, with few means for their effective control. Although ecologically friendly alternatives to chemical pesticides such as the insecticidal fungus Beauveria bassiana have been suggested for the control of fire ant populations, their use has been limited due to the low virulence of the fungus and the length of time it takes to kill its target. We present a means of increasing the virulence of the fungal agent by expressing a fire ant neuropeptide. Expression of the fire ant (Solenopsis invicta) pyrokinin β-neuropeptide (β-NP) by B. bassiana increased fungal virulence six-fold towards fire ants, decreased the LT(50), but did not affect virulence towards the lepidopteran, Galleria mellonella. Intriguingly, ants killed by the β-NP expressing fungus were disrupted in the removal of dead colony members, i.e. necrophoretic behavior. Furthermore, synthetic C-terminal amidated β-NP but not the non-amidated peptide had a dramatic effect on necrophoretic behavior. These data link chemical sensing of a specific peptide to a complex social behavior. Our results also confirm a new approach to insect control in which expression of host molecules in an insect pathogen can by exploited for target specific augmentation of virulence. The minimization of the development of potential insect resistance by our approach is discussed.

Bioavailability of beta-amino acid and C-terminally derived PK/PBAN analogs

The ability of linear beta-amino acid substituted peptides (PK-betaA-1: Ac-YFT[beta(3)P]RLa; PK-betaA-2: Ac-Y[beta(3)homoF]TPRLa; PK-betaA-3: Ac-Y[beta(3)F]TPRLa; PK-betaA-4: Ac-[beta(3)F]FT[beta(3)P]RLa) and unsubstituted analogs (Ac-YFTPRLa and YFTPRLa) of the pyrokinin(PK)/pheromone biosynthesis-activating neuropeptide (PBAN) family to penetrate the insect cuticle and exert biological activity (i.e., stimulate sex pheromone biosynthesis), was tested by topical application on Heliothis peltigera moths. The present results clearly indicate that small linear synthetic peptides can penetrate the cuticle very efficiently by contact application and activate their target organ. The time responses of the peptides applied in DDW and DMSO were tested and the activities of topically applied and injected peptides were compared. The results clearly indicate that PK-betaA-4 and PK-betaA-3 exhibited high bioavailability (ability to penetrate through the cuticle and exertion of bioactivity) with the latter showing longer persistence in both solvents than any other analog in the study; indicative that incorporation of a beta-amino acid at the Phe(2) position can enhance longevity in topical PK/PBAN analogs. PK-betaA-4 was significantly more active in DMSO than in DDW, and significantly more active than the parent peptide LPK in DMSO. PK-betaA-1 and PK-betaA-2 exhibited negligible activity. Interestingly, Ac-YFTPRLa was highly potent in both solvents; its activity in DDW did not differ from that of PK-betaA-4 and PK-betaA-3, and was higher than that of LPK. Even the unacylated peptide YFTPRLa was active in both solvents, at a similar level to LPK. Topically applied PK-betaA-4 and Ac-YFTPRLa exhibited significantly higher activity than the injected peptides. PK-betaA-3 and YFTPRLa were equally potent in both routes of administration.

Bioavailability of insect neuropeptides: the PK/PBAN family as a case study

The ability of unmodified linear peptides to penetrate the insect cuticle and exert bioactivity (e.g., stimulation of sex pheromone biosynthesis) was tested by topical application onto Heliothis peltigera moths of four insect neuropeptides (Nps) of the pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) family: Helicoverpa zea PBAN (Hez-PBAN), Pseudaletia (Mythimna) separata pheromonotropin (PT), Leucophaea maderae PK (LPK) and Locusta migratoria myotropin (Lom-MT-II). The time kinetic of the peptides applied in double distilled water (DDW) or dimethylsulfoxide (DMSO) was tested and the activities of topically applied and injected peptides were compared. The results clearly indicated that all four peptides were highly potent but with differing activities in the two solvents: PBAN was most active in water, and PT in DMSO. The activity of PBAN in DDW lasted up to 8h post-application and its activity in this solvent showed a faster onset and a longer persistence than in DMSO. LPK and MT differed less in their kinetics between the two solvents. Topically applied PBAN at 1 nmol exhibited an equivalent or even significantly higher potency than the injected peptide at several different times post-treatment. Similar results were obtained with topically applied and injected LPK. The present results add important information on the bioavailability of unmodified linear peptides in moths, clearly indicate that linear hydrophilic peptides can penetrate the cuticle by contact application in aqueous solutions and in organic solvents very efficiently, reach their target organ and activate it.

An amphiphilic, PK/PBAN analog is a selective pheromonotropic antagonist that penetrates the cuticle of a heliothine insect

A linear pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) antagonist lead (RYF[dF]PRLa) was structurally modified to impart amphiphilic properties to enhance its ability to transmigrate the hydrophobic cuticle of noctuid moth species and yet retain aqueous solubility in the hemolymph to reach target PK/PBAN receptors within the internal insect environment. The resulting novel PK/PBAN analog, Hex-Suc-A[dF]PRLa (PPK-AA), was synthesized and evaluated as an antagonist in a pheromonotropic assay in Heliothis peltigera against 4 natural PK/PBAN peptide elicitors (PBAN; pheromonotropin, PT; myotropin, MT; leucopyrokinin, LPK) and in a melanotropic assay in Spodoptera littoralis against 3 natural PK/PBAN peptide elicitors (PBAN, PT, LPK). The analog proved to be a potent and efficacious inhibitor of sex pheromone biosynthesis elicited by PBAN (84% at 100 pmol) and PT (54% at 100 pmol), but not by MT and LPK. PPK-AA is a selective pure antagonist (i.e., does not exhibit any agonistic activity) as it failed to inhibit melanization elicited by any of the natural PK/PBAN peptides. The analog was shown to transmigrate isolated cuticle dissected from adult female Heliothis virescens moths to a high extent of 25-30% (130-150 pmol), representing physiologically significant quantities. PPK-AA represents a significant addition to the arsenal of tools available to arthropod endocrinologists studying the endogenous mechanisms of PK/PBAN regulated processes, and a prototype for the development of environmentally friendly pest management agents capable of disrupting the critical process of reproduction.

Diapause hormone in the corn earworm, Helicoverpa zea: optimum temperature for activity, structure-activity relationships, and efficacy in accelerating flesh fly pupariation

Diapause hormone (DH) effectively terminated pupal diapause in Helicoverpa zea. This effect was temperature-dependent, with an optimum of 21 degrees C. The dose-response curve indicated an ED50 of DH for diapause termination of approximately 100 pmol. The core sequence and essential amino acids were determined by bioassays using modified and truncated DH analogs. A C-terminal hepta-peptide, LWFGPRLa, was the core sequence required for diapause termination. Activity was lost when Alanine was substituted for any of the amino acids in the hepta-peptide, with the exception of Glycine. A fragment series of analogs suggested that the amide and Arginine were the most important components needed for terminating diapause. Leucine, Tryptophan, and Phenylalanine at the N-terminus of the hepta-peptide were also critical for activity. The C-terminal Leucine was less important: deletion resulted in decreased activity, although it could not be substituted by Alanine. The fact that a portion of the DH sequence is similar to the pyrokinin that accelerates fly pupariation prompted us to also evaluate the capability of DH to accelerate development in the flesh fly, Sarcophaga bullata. The threshold dose of DH essential to accelerate fly pupariation was 5 pmol for immobilization/retraction and longitudinal contraction and 10 pmol for tanning, approximately one or two orders of magnitude lower than the effective dose required for diapause termination in H. zea. Tensiometric measurements revealed that DH affected neuromuscular patterns of pupariation behavior and associated cuticular changes in a manner similar to that of the fly pyrokinins and their analogs.

Synthesis and evaluation of transthyretin amyloidosis inhibitors containing carborane pharmacophores

Carboranes represent a potentially rich but underutilized class of inorganic and catabolism-inert pharmacophores. The regioselectivity and ease of derivatization of carboranes allows for facile syntheses of a wide variety of novel structures. The steric bulk, rigidity, and ease of B- and C-derivatization and lack of pi-interactions associated with hydrophobic carboranes may be exploited to enhance the selectivity of previously identified bioactive molecules. Transthyretin (TTR) is a thyroxine-transport protein found in the blood that has been implicated in a variety of amyloid related diseases. Previous investigations have identified a variety of nonsteroidal antiinflammatory drugs (NSAIDs) and structurally related derivatives that imbue kinetic stabilization to TTR, thus inhibiting its dissociative fragmentation and subsequent aggregation to form putative toxic amyloid fibrils. However, the cyclooxygenase (COX) activity associated with these pharmaceuticals may limit their potential as long-term therapeutic agents for TTR amyloid diseases. Here, we report the synthesis and evaluation of carborane-containing analogs of the promising NSAID pharmaceuticals previously identified. The replacement of a phenyl ring in the NSAIDs with a carborane moiety greatly decreases their COX activity with the retention of similar efficacy as an inhibitor of TTR dissociation. The most promising of these compounds, 1-carboxylic acid-7-[3-fluorophenyl]-1,7-dicarba-closo-dodecaborane, showed effectively no COX-1 or COX-2 inhibition at a concentration more than an order of magnitude larger than the concentration at which TTR dissociation is nearly completely inhibited. This specificity is indicative of the potential for the exploitation of the unique properties of carboranes as potent and selective pharmacophores.

Boron Units as Pharmacophores - New Applications and Opportunities of Boron Cluster Chemistry

Carboranes (dicarba-closo-dodecaboranes) are a class of carbon-containing polyhedral boron-cluster compounds showing remarkable hydrophobic character, chemical and thermal stability, and resistance to catabolism in biological environment. These features allow application of boron clusters as new hydrophobic core structure in biologically active molecules that interact hydrophobically with proteins, thus facilitating new drug design. A review with 45 references.

Enhanced oral availability/pheromonotropic activity of peptidase-resistant topical amphiphilic analogs of pyrokinin/PBAN insect neuropeptides

The peptide bond between active core residues Pro and Arg is the primary site of susceptibility for the pyrokinin/PBAN neuropeptides to insect tissue-bound peptidases, and incorporation of modified Pro residues can enhance resistance to peptidase hydrolysis. An Hyp-containing amphiphilic analog (Hex-FT[Hyp]RLa) is shown to operate as a topically active tissue-bound peptidase-resistant analog of the pyrokinin/PBAN class of insect neuropeptides in adult Heliothis virescens moths. An Oic amphiphilic analog (Hex-FT[Oic]RLa) is ineffective topically, but proves to be a superior tissue-bound, peptidase-resistant pyrokinin/PBAN analog for oral administration; outperforming both the Hyp analog and the orally inactive natural hormone PBAN in the moths. The Oic analog is effective in penetrating an isolated, ligated foregut preparation, but less successful in transmigrating an isolated midgut preparation; whereas the opposite behavior is observed for the Hyp analog. The success of the Oic analog via oral administration may be related to its ability to effectively penetrate the foregut, thereby bypassing the hostile environment of the midgut region.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

A brominated-fluorene insect neuropeptide analog exhibits pyrokinin/PBAN-specific toxicity for adult females of the tobacco budworm moth

An analog of the insect pyrokinin/PBAN class of neuropeptides, which features a 2-amino7-bromofluorene attached to the carboxy-terminal bioactive core of the insect pyrokinin/PBAN class of neuropeptides (Phe-Thr-Pro-Arg-Leu-NH(2)), via a succinnic acid linker, was tested in adult H. virescens moths. This analog was found to induce pheromone production when injected into or applied topically to moths. Topical application of as much as 1 nmol of the analog to moths induced production of significant amounts of pheromone for only 1-2 h, whereas injection of 500 pmol induced pheromone production for up to 20 h. All insects died within 24 h after injection of 500 pmol of the analog. Mortality studies indicated that the LD(50) for the analog was 0.7 pmol when injected. A non-pyrokinin/PBAN peptide analog formed by attachment of 2-amino-7-bromofluorene to Ala-Ala-Arg-Ala-Ala-NH(2) (via the succinnic acid linker) did not induce mortality when injected at 1 nmol. Similarly no mortality was found when up to 2 nmol of an analog containing a non-brominated fluorene ring, formed by attachment of 9-fluoreneacetic acid to Phe-Thr-Pro-Arg-Leu-NH(2,) was injected into moths. The data indicated that both the bromine and active core of the pyrokinin neuropeptides (Phe-Thr-Pro-Arg-Leu-NH(2)) were critical for a specific toxic action and suggested that the brominated analog poisoned the moths by interacting with pyrokinin receptors.

Myostimulatory neuropeptides in cockroaches: structures, distribution, pharmacological activities, and mimetic analogs

In this brief overview we give the historical background on the discovery of myostimulatory neuropeptides in cockroaches. Related peptides were later found in other insect groups as well. We summarize the current knowledge on primary structures, localization, physiological and pharmacological effects of the different cockroach neuropeptides, including kinins, sulfakinins, pyrokinins, tachykinin-related peptides, periviscerokinins, corazonin, and proctolin. In addition, we briefly comment on the development of mimetic pseudopeptide analogs in the context of their possible use in insect pest management.

Synthesis of 3-(12-hydroxy-p-carboranyl)propionic acid, a hydrophobic, N-terminal tyrosine-mimetic for peptides

A new, p-carborane containing analog of tyrosine, namely 3-[1-hydroxy-1,12-dicarba-closo-dodecaboran(12)-12-yl]propionic acid was prepared from p-carborane in five steps involving hydroxypropylation of O-protected 1-hydroxy-p-carborane as the key transformation. The simple tyrosine mimetic can function as a hydrophobic surrogate for an N-terminal tyrosine residue in insect and mammalian neuropeptides to enhance the lipophilicity, and therefore, the cuticle and/or tissue permeability properties of mimetic analogs.

Comparative topical pheromonotropic activity of insect pyrokinin/PBAN amphiphilic analogs incorporating different fatty and/or cholic acid components

This study presents a comparison of the topical pheromonotropic activity in the tobacco budworm moth of a series of amphiphilic pseudopeptide analogs of the insect pyrokinin/PBAN peptide class incorporating fatty acids of varying chain lengths. While the C16 analog fails to penetrate the moth cuticle, and the C12 only moderately so, shorter chain analogs transmigrate the moth cuticle readily with decreasing cuticle-retention properties. A cholic acid analog topically induces twice the maximal pheromone titer of injected native hormone. From a pest management perspective, these non-aromatic hydrophobic components are expected to be more environmentally benign than benzenoid components previously used in topical insect peptide analogs.

Antimicrobial activity of o-carboranylalanine

Functionalized polyhedral carboranes, including amino acid analogs, have unique physicochemical properties and are used as experimental anticancer agents. However, our current knowledge on their effect in nonmammalian biological systems is limited. We investigated the activity spectrum in vitro of o-carboranylalanine (o-Cba), considered to be a highly lipophilic analog of phenylalanine, against representative plant pathogenic bacteria and fungi of various taxonomic position. The antibacterial effect of o-Cba against some species was comparable to that of the widely used agricultural antibiotic, streptomycin. The sensitivity of individual bacterial species to o-Cba within the same genus varied to a greater extent than the average sensitivity of various genera. In general, this carborane-containing amino acid was more toxic to Gram positive bacteria (Bacillus, Corynebacterium, Curtobacterium, Micrococcus, Rhodococcus, and Staphylococcus) than to Gram negative ones (Agrobacterium, Erwinia, Escherichia, Pseudomonas, Rhizobium, and Xanthomonas). Compared to the commercial fungicide, prochloraz, o-Cba was weakly toxic against various fungi (Zygo- and Ascomycota). It was also inferior to the commercial fungicide metalaxyl in inhibiting the vegetative growth of oomyceteous plant pathogens (Pythium irregulare, Phytophthora cryptogea and Plasmopara halstedii). Against the asexual spores of P. halstedii, o-Cba, however, was over a thousandfold more active than tridemorph, a selective zoospore inhibitor fungicide. For all taxonomic groups, the observed antimicrobial effect of o-Cba could be diminished with histidine, but not with phenylalanine. In studies on healthy and mildew-infected sunflower and tobacco plants o-Cba showed neither fungicidal nor phytotoxic effects at 500 ppm. This is the first report on the biological activity spectrum of a carborane-containing amino acid.

Development of amphiphylic mimics of insect neuropeptides for pest control

Insect neuropeptides regulate virtually all aspects of insect life and are excellent candidates for development of new methods for pest control. However, they do not penetrate insect cuticle and are degraded by enzymes both in the digestive system and hemolymph. We have designed mimics of model neuropeptides by attachment of various lipidic moieties to the amino terminus of the bioactive core of the neuropeptides. These mimics have amphiphylic characteristics that allowed them to penetrate the hydrophobic insect cuticle. The mimics also induced prolonged physiological responses (up to 20 hours) and were resistant to peptidase attack. This knowledge has been used to develop a novel, species-specific approach to insect control.

Comparison of rates of penetration through insect cuticle of amphiphylic analogs of insect pyrokinin neuropeptides

Rates of penetration through the cuticle of amphiphylic analogs, synthesized by addition of 6-phenylhexanoic acid or 9-fluoreneacetic acid or 1-pyrenebutyric acid to the amino terminus of the pentapeptide Phe-Thr-Pro-Arg-Leu-amide, were assessed by quantitative analysis using reversed phase liquid chromatography. The analogs effectively penetrated the cuticle of both the adult American cockroach and tobacco budworm moth. However, the amounts of analogs that penetrated the cuticle of the cockroach were significantly lower and the rates of penetration were slower than for moth cuticle. Penetration of the analogs through the cuticle was dependent upon the size of the lipidic attachment to the pentapeptide. The 6-phenylhexanoic acid analog penetrated most rapidly followed by the 9-fluoreneacetic acid analog and the 1-pyrenebutyric acid analog penetrated slowest. All of the analogs exhibited an initial rapid period of penetration lasting 2-3 h followed by the establishment of a steady slow release state which lasted between 9-24 h and was dependent upon both the size and surface area of the aromatic lipidic portion of the analog and species of insect to which the analog was applied. The results confirmed the hypothesis that the insect cuticle could be employed as a slow release device for delivery of analogs of insect neuropeptides.

Minimum structure of diapause hormone required for biological activity

Diapause hormone is a 24-amino acid peptide amide, and its C-terminal penta-peptide amide structure of FGPRL-NH2 is believed to be essential for biological activity. The penta-peptide amide, the shorter peptide amides, and their derivatives and analogs were prepared to determine the minimal structure for biological activity. The C-terminal amide group of penta-peptide amide was not replaced with the other functional groups, but Gly, the 4th amino acid from the C terminal, could be substituted with an other amino acid while maintaining the biological activity. The shorter peptide amide, PRL-NH2, possessed low but significant activity, indicating the minimum structure of diapause hormone. By modifying its N-terminal, the aromatic ring of Phe is shown to enhance the activity of PRL-NH2.

Synthesis, biological activity, and conformational studies of insect allatostatin neuropeptide analogues incorporating turn-promoting moieties

Allatostatins are 6-18 amino acid peptides synthezed by insects to control production of juvenile hormones, which in turn regulate functions including metamorphosis and egg production. Four insect allatostatin neuropeptide analogues incorporating turn-promoting pseudopeptide moieties in the region responsible for biological activity were prepared by solid phase peptide synthetic methods. Bioassay indicated that activities approached those of the natural neuropeptides, and molecular models based on NMR data showed similar conformations and the presence of a beta-turn in the active core region for the four analogues. Differences in activity are believed to be due to differences in bulk and relative position of atoms in the unnatural portion of the analogues, and their differing degrees of conformational freedom. The studies support the feasibility of development of neuropeptide-based insect control agents resistant to peptidase deactivation.

Peptidergic control of the corpus cardiacum-corpora allata complex of locusts

The brain-corpora cardiaca-corpora allata complex of insects is the physiological equivalent of the brain-hypophysis axis of vertebrates. In locusts there is only one corpus cardiacum as a result of fusion, while most other insect species have a pair of such glands. Like the pituitary of vertebrates, the corpus cardiacum consists of a glandular lobe and a neurohemal lobe. The glandular lobe synthesizes and releases adipokinetic hormones. In the neurohemal part many peptide hormones, which are produced in neurosecretory cells in the brain, are released into the hemolymph. The corpora allata, which have no counterpart in vertebrates, synthesize and release juvenile hormones. The control of the locust corpus cardiacum-corpora allata complex appears to be very complex. Numerous brain factors have been reported to have an effect on biosynthesis and release of juvenile hormone or adipokinetic hormone. Many neuropeptides are present in nerves projecting from the brain into the corpora cardiaca-corpora allata complex, the most important ones being neuroparsins, ovary maturating parsin, insulin-related peptide, diuretic peptide, tachykinins, FLRFamides, FXPRLamides, accessory gland myotropin I, crustacean cardioactive peptide, and schistostatins. In this paper, the cellular distribution, posttranslational processing, peptide-receptor interaction, and inactivation of these peptides are reviewed. In addition, the signal transduction pathways in the release of adipokinetic hormone and juvenile hormone from, respectively, the corpora cardiaca and corpora allata are discussed.

Isolation of periviscerokinin-2 from the abdominal perisympathetic organs of the American cockroach, Periplaneta americana

Using the isolated hyperneural muscle as bioassay, a novel myotropin was isolated from the abdominal perisympathetic organs of Periplaneta americana. This is the second neuropeptide identified from insect perisympathetic organs. Peptide sequence analysis and mass spectrometry yielded the following structure: Gly-Ser-Ser-Ser-Gly-Leu-Ile-Ser-Met-Pro-Arg-Val-NH2. This peptide, named periviscerokinin-2, was confirmed to be amidated by chemical synthesis, bioassay, and comparison of retention times between native and synthetic peptides. A highly specific antiserum was used to determine sites of synthesis in the abdominal ganglia. Besides periviscerokinin-1, periviscerokinin-2 is the only putative myotropic neurohormone from the abdominal perisympathetic organs that is effective in the nanomolar range. This confirms the hypothesis that the neurohormonal system of the ventral nerve cord is remarkably different from that of the brain.

Prolonged pheromonotropic activity of pseudopeptide mimics of insect pyrokinin neuropeptides after topical application or injection into a moth

Amphiphilic pseudopeptide analogs of Phe-Thr-Pro-Arg-Leu-NH2, representing the active C-terminal core pentapeptide of the pyrokinin class of insect neuropeptides, were synthesized by replacement of phenylalanine with hydrocinnamic acid (Hca-Thr-Pro-Arg-Leu-NH2), or addition of 1-pyrenebutyric acid (Pba-Phe-Thr-Pro-Arg-Leu-NH2) or 9-fluoreneacetic acid (Fla-Phe-Thr-Pro-Arg-Leu-NH2). The pseudopeptides were found to stimulate sex pheromone biosynthesis when injected into females of the moth Heliothis virescens. Optimal pheromonotropic responses were obtained by injection of 0.25 pmol of Hca-Thr-Pro-Arg-Leu-NH2, 2.5 pmol of Pba-Thr-Pro-Arg-Leu-NH2 and 0.5 pmol of Fla-Thr-Pro-Arg-Leu-NH2. Topical application of each of the pseudopeptides in water to the cuticle of moths stimulated significant production of pheromone at a dose of 50 pmol with optimal stimulation occurring when 500 pmol were applied. The parent peptide, Phe-Thr-Pro-Arg-Leu-NH2, failed to stimulate significant production of pheromone when applied topically at a dose as high as 2000 pmol. Temporal studies indicated that Hca-Thr-Pro-Arg-Leu-NH2 stimulated significant production of pheromone for only 4 h after application where as continuous pheromone production for 18 h was observed when either Pba-Phe-Thr-Pro-Arg-Leu-NH2 or Fla-Phe-Thr-Pro-Arg-Leu-NH2 were applied to the abdomen. The results show that modification of the C-terminal active core of the insect pyrokinins, by addition of hydrophobic moieties, can result in production of pseudopeptides which effectively penetrate the insect cuticle and have prolonged physiological effects making them favorable candidates for use in development of alternative strategies for pest insect control.

Structure-activity relationships in C-terminal fragment analogs of pheromone biosynthesis activating neuropeptide in Helicoverpa zea

A number of analogs of the C-terminal hexapeptide of PBAN were prepared and tested in vivo for pheromonotropic activity in Helicoverpa zea. Peptides prepared with longer-chain omega-aminocarboxylic acids (Tyr-6-aminocaproyl-Leu-NH2 and Tyr-7-aminoheptanoyl-NH2) were active at 25 and 2.5 nmol. Acetyl-Pro-Arg-Leu-NH2 was active at 1,000 pmol and represents a new minimum active fragment in the PBAN system. Addition of a bulky, hydrophobic tail (4-octylphenoxyacetyl) to the C-terminal hexapeptide of PBAN gave an analog that was active at all concentrations tested from 1 to 1,000 pmol when injected, had slight oral activity, but had no activity when applied topically. Glu-Tyr-Phe-Ser-Pro-Arg-Leu-NH2 was active at 1,000 but not at 100 pmol; at the latter dose it synergised the activity of 5 pmol of PBAN.