Synthesis and Characterization in Vitro and in Vivo of (l)-(Trimethylsilyl)alanine Containing Neurotensin Analogues

Neurotensin(8-13) analogs as dual NTS1 and NTS2 receptor ligands with enhanced effects on a mouse model of Parkinson's disease

The modulatory interactions between neurotensin (NT) and the dopaminergic neurotransmitter system in the brain suggest that NT may be associated with the progression of Parkinson's disease (PD). NT exerts its neurophysiological effects by interactions with the human NT receptors type 1 (hNTS1) and 2 (hNTS2). Therefore, both receptor subtypes are promising targets for the development of novel NT-based analogs for the treatment of PD. In this study, we used a virtually guided molecular modeling approach to predict the activity of NT(8-13) analogs by investigating the docking models of ligands designed for binding to the human NTS1 and NTS2 receptors. The importance of the residues at positions 8 and/or 9 for hNTS1 and hNTS2 receptor binding affinity was experimentally confirmed by radioligand binding assays. Further in vitro ADME profiling and in vivo studies revealed that, compared to the parent peptide NT(8-13), compound 10 exhibited improved stability and BBB permeability combined with a significant enhancement of the motor function and memory in a mouse model of PD. The herein reported NTS1/NTS2 dual-specific NT(8-13) analogs represent an attractive tool for the development of therapeutic strategies against PD and potentially other CNS disorders.

Unnatural amino acids: promising implications for the development of new antimicrobial peptides

The increasing incidence and rapid spread of bacterial resistance to conventional antibiotics are a serious global threat to public health, highlighting the need to develop new antimicrobial alternatives. Antimicrobial peptides (AMPs) represent a class of promising natural antibiotic candidates due to their broad-spectrum activity and low tendency to induce resistance. However, the development of AMPs for medical use is hampered by several obstacles, such as moderate activity, lability to proteolytic degradation, and low bioavailability. To date, many researchers have focussed on the optimization or design of novel artificial AMPs with desired properties. Unnatural amino acids (UAAs) are valuable building blocks in the manufacture of a variety of pharmaceuticals, and have been used to develop artificial AMPs with specific structural and physicochemical properties. Rational incorporation of UAAs has become a very promising approach to endow AMPs with strong and long-lasting activity but no toxicity. This review aims to summarize key approaches that have been used to incorporate UAAs to develop novel AMPs with improved properties and better performance. It is anticipated that this review will guide future design considerations for UAA-based antimicrobial applications.

Design, Synthesis, and Biological Evaluation of the First Radio-Metalated Neurotensin Analogue Targeting Neurotensin Receptor 2

Neurotensin receptor 2 (NTS₂) is a well-known mediator of central opioid-independent analgesia. Seminal studies have highlighted NTS₂ overexpression in a variety of tumors including prostate cancer, pancreas adenocarcinoma, and breast cancer. Herein, we describe the first radiometalated neurotensin analogue targeting NTS₂. JMV 7488 (DOTA-(βAla)₂-Lys-Lys-Pro-(D)Trp-Ile-TMSAla-OH) was prepared using solid-phase peptide synthesis, then purified, radiolabeled with ⁶⁸Ga and ¹¹¹In, and investigated in vitro on HT-29 cells and MCF-7 cells, respectively, and in vivo on HT-29 xenografts. [⁶⁸Ga]Ga-JMV 7488 and [¹¹¹In]In-JMV 7488 were quite hydrophilic (logD_7.4 = -3.1 ± 0.2 and -2.7 ± 0.2, respectively, p < 0.0001). Saturation binding studies showed good affinity toward NTS₂ (K _D = 38 ± 17 nM for [⁶⁸Ga]Ga-JMV 7488 on HT-29 and 36 ± 10 nM on MCF-7 cells; K _D = 36 ± 4 nM for [¹¹¹In]In-JMV 7488 on HT-29 and 46 ± 1 nM on MCF-7 cells) and good selectivity (no NTS₁ binding up to 500 nM). On cell-based evaluation, [⁶⁸Ga]Ga-JMV 7488 and [¹¹¹In]In-JMV 7488 showed high and fast NTS₂-mediated internalization of 24 ± 5 and 25 ± 11% at 1 h for [¹¹¹In]In-JMV 7488, respectively, along with low NTS₂-membrane binding (<8%). Efflux was as high as 66 ± 9% at 45 min for [⁶⁸Ga]Ga-JMV 7488 on HT-29 and increased for [¹¹¹In]In-JMV 7488 up to 73 ± 16% on HT-29 and 78 ± 9% on MCF-7 cells at 2 h. Maximum intracellular calcium mobilization of JMV 7488 was 91 ± 11% to that of levocabastine, a known NTS₂ agonist on HT-29 cells demonstrating the agonist behavior of JMV 7488. In nude mice bearing HT-29 xenograft, [⁶⁸Ga]Ga-JMV 7488 showed a moderate but promising significant tumor uptake in biodistribution studies that competes well with other nonmetalated radiotracers targeting NTS₂. Significant uptake was also depicted in lungs. Interestingly, mice prostate also demonstrated [⁶⁸Ga]Ga-JMV 7488 uptake although the mechanism was not NTS₂-mediated.

Opening the amino acid toolbox for peptide-based NTS2-selective ligands as promising lead compounds for pain management

Chronic pain is one of the most critical health issues worldwide. Despite considerable efforts to find therapeutic alternatives, opioid drugs remain the gold standard for pain management. The administration of μ-opioid receptor (MOR) agonists is associated with detrimental and limiting adverse effects. Overall, these adverse effects strongly overshadow the effectiveness of opioid therapy. In this context, the development of neurotensin (NT) ligands has shown to be a promising approach for the management of chronic and acute pain. NT exerts its opioid-independent analgesic effects through the binding of two G protein-coupled receptors (GPCRs), NTS1 and NTS2. In the last decades, modified NT analogues have been proven to provide potent analgesia in vivo. However, selective NTS1 and nonselective NTS1/NTS2 ligands cause antinociception associated with hypothermia and hypotension, whereas selective NTS2 ligands induce analgesia without altering the body temperature and blood pressure. In light of this, various structure-activity relationship (SAR) studies provided findings addressing the binding affinity of ligands towards NTS2. Herein, we comprehensively review peptide-based NTS2-selective ligands as a robust alternative for future pain management. Particular emphasis is placed on SAR studies governing the desired selectivity and associated in vivo results.

Novel Approaches, Drug Candidates, and Targets in Pain Drug Discovery

Because of the problems associated with opioids, drug discovery efforts have been employed to develop opioids with reduced side effects using approaches such as biased opioid agonism, multifunctional opioids, and allosteric modulation of opioid receptors. Receptor targets such as adrenergic, cannabinoid, P2X3 and P2X7, NMDA, serotonin, and sigma, as well as ion channels like the voltage-gated sodium channels Nav1.7 and Nav1.8 have been targeted to develop novel analgesics. Several enzymes, such as soluble epoxide hydrolase, sepiapterin reductase, and MAGL/FAAH, have also been targeted to develop novel analgesics. In this review, old and recent targets involved in pain signaling and compounds acting at these targets are summarized. In addition, strategies employed to reduce side effects, increase potency, and efficacy of opioids are also elaborated. This review should aid in propelling drug discovery efforts to discover novel analgesics.

Metabolically stable neurotensin analogs exert potent and long-acting analgesia without hypothermia

The endogenous tridecapeptide neurotensin (NT) has emerged as an important inhibitory modulator of pain transmission, exerting its analgesic action through the activation of the G protein-coupled receptors, NTS1 and NTS2. Whereas both NT receptors mediate the analgesic effects of NT, NTS1 activation also produces hypotension and hypothermia, which may represent obstacles for the development of new pain medications. In the present study, we implemented various chemical strategies to improve the metabolic stability of the biologically active fragment NT(8-13) and assessed their NTS1/NTS2 relative binding affinities. We then determined their ability to reduce the nociceptive behaviors in acute, tonic, and chronic pain models and to modulate blood pressure and body temperature. To this end, we synthesized a series of NT(8-13) analogs carrying a reduced amide bond at Lys⁸-Lys⁹ and harboring site-selective modifications with unnatural amino acids, such as silaproline (Sip) and trimethylsilylalanine (TMSAla). Incorporation of Sip and TMSAla respectively in positions 10 and 13 of NT(8-13) combined with the Lys⁸-Lys⁹ reduced amine bond (JMV5296) greatly prolonged the plasma half-life time over 20 h. These modifications also led to a 25-fold peptide selectivity toward NTS2. More importantly, central delivery of JMV5296 was able to induce a strong antinociceptive effect in acute (tail-flick), tonic (formalin), and chronic inflammatory (CFA) pain models without inducing hypothermia. Altogether, these results demonstrate that the chemically-modified NT(8-13) analog JMV5296 exhibits a better therapeutic profile and may thus represent a promising avenue to guide the development of new stable NT agonists and improve pain management.

Therapeutic approaches targeting the neurotensin receptors

Introduction: Neurotensin is a gut-brain peptide hormone, a 13 amino acid neuropeptide found in the central nervous system and in the GI tract. The neurotensinergic system is implicated in various physiological and pathological processes related to neuropsychiatric and metabolic machineries, cancer growth, food, and drug intake. NT mediates its functions through its two G protein-coupled receptors: neurotensin receptor 1 (NTS1/NTSR1) and neurotensin receptor 2 (NTS2/NTSR2). Over the past decade, the role of NTS3/NTSR3/sortilin has also gained importance in human pathologies. Several approaches have appeared dealing with the discovery of compounds able to modulate the functions of this neuropeptide through its receptors for therapeutic gain.Areas covered: The article provides an overview of over four decades of research and details the drug discovery approaches and patented strategies targeting NTSR in the past decade.Expert opinion: Neurotensin is an important neurotransmitter that enables crosstalk with various neurotransmitter and neuroendocrine systems. While significant efforts have been made that have led to selective agonists and antagonists with promising in vitro and in vivo activities, the therapeutic potential of compounds targeting the neurotensinergic system is still to be fully harnessed for successful clinical translation of compounds for the treatment of several pathologies.

Optimized Opioid-Neurotensin Multitarget Peptides: From Design to Structure-Activity Relationship Studies

Fusion of nonopioid pharmacophores, such as neurotensin, with opioid ligands represents an attractive approach for pain treatment. Herein, the μ-/δ-opioid agonist tetrapeptide H-Dmt-d-Arg-Aba-β-Ala-NH2 (KGOP01) was fused to NT(8-13) analogues. Since the NTS1 receptor has been linked to adverse effects, selective MOR-NTS2 ligands are preferred. Modifications were introduced within the native NT sequence, particularly a β3-homo amino acid in position 8 and Tyr11 substitutions. Combination of β3hArg and Dmt led to peptide 7, a MOR agonist, showing the highest NTS2 affinity described to date (Ki = 3 pM) and good NTS1 affinity (Ki = 4 nM), providing a >1300-fold NTS2 selectivity. The (6-OH)Tic-containing analogue 9 also exhibited high NTS2 affinity (Ki = 1.7 nM), with low NTS1 affinity (Ki = 4.7 μM), resulting in an excellent NTS2 selectivity (>2700). In mice, hybrid 7 produced significant and prolonged antinociception (up to 8 h), as compared to the KGOP01 opioid parent compound.

Data set describing the in vitro biological activity of JMV2009, a novel silylated neurotensin(8-13) analog

Neurotensin (NT) is a tridecapeptide displaying interesting antinociceptive properties through its action on its receptors, NTS1 and NTS2. Neurotensin-like compounds have been shown to exert better antinociceptive properties than morphine at equimolar doses. In this article, we characterized the molecular effects of a novel neurotensin (8-13) (NT(8-13)) analog containing an unnatural amino acid. This compound, named JMV2009, displays a Silaproline in position 10 in replacement of a proline in the native NT(8-13). We first examined the binding affinities of this novel NT(8-13) derivative at both NTS1 and NTS2 receptor sites by performing competitive displacement of iodinated NT on purified cell membranes. Then, we evaluated the ability of JMV2009 to activate NTS1-related G proteins as well as to promote the recruitment of β-arrestins 1 and 2 by using BRET-based cellular assays in live cells. We next assessed its ability to induce p42/p44 MAPK phosphorylation and NT receptors internalization using western blot and cell-surface ELISA, respectively. Finally, we determined the in vitro plasma stability of this NT derivative. This article is associated with the original article "Pain relief devoid of opioid side effects following central action of a silylated neurotensin analog" published in European Journal of Pharmacology[1]. The reader is directed to the associated article for results interpretation, comments, and discussion.

Insightful Backbone Modifications Preventing Proteolytic Degradation of Neurotensin Analogs Improve NTS1-Induced Protective Hypothermia

Therapeutic hypothermia represents a brain-protective strategy for multiple emergency situations, such as stroke or traumatic injury. Neurotensin (NT), which exerts its effects through activation of two G protein-coupled receptors, namely NTS1 and NTS2, induces a strong and long-lasting decrease in core body temperature after its central administration. Growing evidence demonstrates that NTS1 is the receptor subtype mediating the hypothermic action of NT. As such, potent NTS1 agonists designed on the basis of the minimal C-terminal NT(8-13) bioactive fragment have been shown to produce mild hypothermia and exert neuroprotective effects under various clinically relevant conditions. The high susceptibility of NT(8-13) to protease degradation (half-life <2 min) represents, however, a serious limitation for its use in pharmacological therapy. In light of this, we report here a structure-activity relationship study in which pairs of NT(8-13) analogs have been developed, based on the incorporation of a reduced Lys⁸-Lys⁹ bond. To further stabilize the peptide bonds, a panel of backbone modifications was also inserted along the peptide sequence, including Sip¹⁰, D-Trp¹¹, Dmt¹¹, Tle¹², and TMSAla¹³. Our results revealed that the combination of appropriate chemical modifications leads to compounds exhibiting improved resistance to proteolytic cleavages (>24 h; 16). Among them, the NT(8-13) analogs harboring the reduced amine bond combined with the unnatural amino acids TMSAla¹³ (4) and Sip¹⁰ (6) or the di-substitution Lys¹¹ - TMSAla¹³ (12), D-Trp¹¹-TMSAla¹³ (14), and Dmt¹¹-Tle¹² (16) produced sustained hypothermic effects (−3°C for at least 1 h). Importantly, we observed that hypothermia was mainly driven by the increased stability of the NT(8-13) derivatives, instead of the high binding-affinity at NTS1. Altogether, these results reveal the importance of the reduced amine bond in optimizing the metabolic properties of the NT(8-13) peptide and support the development of stable NTS1 agonists as first drug candidate in neuroprotective hypothermia.

Cell-penetrating pepducins targeting the neurotensin receptor type 1 relieve pain

Pepducins are cell-penetrating, membrane-tethered lipopeptides designed to target the intracellular region of a G protein-coupled receptor (GPCR) in order to allosterically modulate the receptor's signaling output. In this proof-of-concept study, we explored the pain-relief potential of a pepducin series derived from the first intracellular loop of neurotensin receptor type 1 (NTS1), a class A GPCR that mediates many of the effects of the neurotensin (NT) tridecapeptide, including hypothermia, hypotension and analgesia. We used BRET-based biosensors to determine the pepducins' ability to engage G protein signaling pathways associated with NTS1 activation. We observed partial Gα_q and Gα₁₃ activation at a 10 μM concentration, indicating that these pepducins may act as allosteric agonists of NTS1. Additionally, we used surface plasmon resonance (SPR) as a label-free assay to monitor pepducin-induced responses in CHO-K1 cells stably expressing hNTS1. This whole-cell integrated assay enabled us to subdivide our pepducin series into three profile response groups. In order to determine the pepducins' antinociceptive potential, we then screened the series in an acute pain model (tail-flick test) by measuring tail withdrawal latencies to a thermal nociceptive stimulus, following intrathecal (i.t.) pepducin administration (275 nmol/kg). We further evaluated promising pepducins in a tonic pain model (formalin test), as well as in neuropathic (Chronic Constriction Injury) and inflammatory (Complete Freund's Adjuvant) chronic pain models. We report one pepducin, PP-001, that consistently reduced rat nociceptive behaviors, even in chronic pain paradigms. Finally, we designed a TAMRA-tagged version of PP-001 and found by confocal microscopy that the pepducin reached the rat dorsal root ganglia post i.t. injection, thus potentially modulating the activity of NTS1 at this location to produce its analgesic effect. Altogether, these results suggest that NTS1-derived pepducins may represent a promising strategy in pain-relief.

Neurotensin Analogues Containing Cyclic Surrogates of Tyrosine at Position 11 Improve NTS2 Selectivity Leading to Analgesia without Hypotension and Hypothermia

Neurotensin (NT) exerts its analgesic effects through activation of the G protein-coupled receptors NTS1 and NTS2. This opioid-independent antinociception represents a potential alternative for pain management. While activation of NTS1 also induces a drop in blood pressure and body temperature, NTS2 appears to be an analgesic target free of these adverse effects. Here, we report modifications of NT at Tyr¹¹ to increase selectivity toward NTS2, complemented by modifications at the N-terminus to impair proteolytic degradation of the biologically active NT(8-13) sequence. Replacement of Tyr¹¹ by either 6-OH-Tic or 7-OH-Tic resulted in a significant loss of binding affinity to NTS1 and subsequent NTS2 selectivity. Incorporation of the unnatural amino acid β³hLys at position 8 increased the half-life to over 24 h in plasma. Simultaneous integration of both β³hLys⁸ and 6-OH-Tic¹¹ into NT(8-13) produced a potent and NTS2-selective analogue with strong analgesic action after intrathecal delivery in the rat formalin-induced pain model with an ED₅₀ of 1.4 nmol. Additionally, intravenous administration of this NT analogue did not produce persistent hypotension or hypothermia. These results demonstrate that NT analogues harboring unnatural amino acids at positions 8 and 11 can enhance crucial pharmacokinetic and pharmacodynamic features for NT(8-13) analogues, i.e., proteolytic stability, NTS2 selectivity, and improved analgesic/adverse effect ratio.

In Search of the Optimal Macrocyclization Site for Neurotensin

Neurotensin exerts potent analgesic effects following activation of its cognate GPCRs. In this study, we describe a systematic exploration, using structure-based design, of conformationally constraining neurotensin (8-13) with the help of macrocyclization and the resulting impacts on binding affinity, signaling, and proteolytic stability. This exploratory study led to a macrocyclic scaffold with submicromolar binding affinity, agonist activity, and greatly improved plasma stability.

New Insights in the Design of Bioactive Peptides and Chelating Agents for Imaging and Therapy in Oncology

Many synthetic peptides have been developed for diagnosis and therapy of human cancers based on their ability to target specific receptors on cancer cell surface or to penetrate the cell membrane. Chemical modifications of amino acid chains have significantly improved the biological activity, the stability and efficacy of peptide analogues currently employed as anticancer drugs or as molecular imaging tracers. The stability of somatostatin, integrins and bombesin analogues in the human body have been significantly increased by cyclization and/or insertion of non-natural amino acids in the peptide sequences. Moreover, the overall pharmacokinetic properties of such analogues and others (including cholecystokinin, vasoactive intestinal peptide and neurotensin analogues) have been improved by PEGylation and glycosylation. Furthermore, conjugation of those peptide analogues to new linkers and bifunctional chelators (such as AAZTA, TETA, TRAP, NOPO etc.), produced radiolabeled moieties with increased half life and higher binding affinity to the cognate receptors. This review describes the most important and recent chemical modifications introduced in the amino acid sequences as well as linkers and new bifunctional chelators which have significantly improved the specificity and sensitivity of peptides used in oncologic diagnosis and therapy.

Coarse-Grained Prediction of Peptide Binding to G-Protein Coupled Receptors

In this study, we used the Martini Coarse-Grained model with no applied restraints to predict the binding mode of some peptides to G-Protein Coupled Receptors (GPCRs). Both the Neurotensin-1 and the chemokine CXCR4 receptors were used as test cases. Their ligands, NTS_8-13 and CVX15 peptides, respectively, were initially positioned in the surrounding water box. Using a protocol based on Replica Exchange Molecular Dynamics (REMD), both opening of the receptors and entry of the peptides into their dedicated pockets were observed on the μs time-scale. After clustering, the most statistically representative orientations were closely related to the X-ray structures of reference, sharing both RMSD lower than 3 Å and most of the native contacts. These results demonstrate that such a model, that does not require access to tremendous computational facilities, can be helpful in predicting peptide binding to GPCRs as well as some of the receptor's conformational changes required for this key step. We also discuss how such an approach can now help to predict, de novo, the interactions of GPCRs with other intra- or extracellular peptide/protein partners.

Ventral Midbrain NTS1 Receptors Mediate Conditioned Reward Induced by the Neurotensin Analog, D-Tyr[11]neurotensin

The present study was aimed at characterizing the mechanisms by which neurotensin (NT) is acting within the ventral midbrain to induce a psychostimulant-like effect. In a first experiment, we determine which subtype(s) of NT receptors is/are involved in the reward-inducing effect of ventral midbrain microinjection of NT using the conditioned place-preference (CPP) paradigm. In a second study, we used in vitro patch clamp recording technique to characterize the NT receptor subtype(s) involved in the modulation of glutamatergic neurotransmission (excitatory post-synaptic current, EPSC) in ventral tegmental neurons that expressed (Ih+), or do not express (Ih-), a hyperpolarization-activated cationic current. Behavioral studies were performed with adult male Long-Evans rats while electrophysiological recordings were obtained from brain slices of rat pups aged between 14 and 21 days. Results show that bilateral ventral midbrain microinjections of 1.5 and 3 nmol of D-Tyr[¹¹]NT induced a CPP that was respectively attenuated or blocked by co-injection with 1.2 nmol of the NTS1/NTS2 antagonist, SR142948, and the preferred NTS1 antagonist, SR48692. In electrophysiological experiments, D-Tyr[¹¹]NT (0.01-0.5 μM) attenuated glutamatergic EPSC in Ih+ but enhanced it in Ih- neurons. The attenuation effect (Ih+ neurons) was blocked by SR142948 (0.1 μM) while the enhancement effect (Ih- neurons) was blocked by both antagonists (0.1 μM). These findings suggest that (i) NT is acting on ventral midbrain NTS1 receptors to induce a rewarding effect and (ii) that this psychostimulant-like effect could be due to a direct action of NT on dopamine neurons and/or an enhancement of glutamatergic inputs to non-dopamine (Ih-) neurons.