Intraperitoneal injection of antisense peptide nucleic acids targeted to the mu receptor decreases response to morphine and receptor protein levels in rat brain

Pharmacodynamic and pharmacokinetic profiles of a neurotensin receptor type 2 (NTS2) analgesic macrocyclic analog

The current opioid crisis highlights the urgent need to develop safe and effective pain medications. Thus, neurotensin (NT) compounds represent a promising approach, as the antinociceptive effects of NT are mediated by activation of the two G protein-coupled receptor subtypes (i.e., NTS1 and NTS2) and produce potent opioid-independent analgesia. Here, we describe the synthesis and pharmacodynamic and pharmacokinetic properties of the first constrained NTS2 macrocyclic NT(8-13) analog. The Tyr¹¹ residue of NT(8-13) was replaced with a Trp residue to achieve NTS2 selectivity, and a rationally designed side-chain to side-chain macrocyclization reaction was applied between Lys⁸ and Trp¹¹ to constrain the peptide in an active binding conformation and limit its recognition by proteolytic enzymes. The resulting macrocyclic peptide, CR-01-64, exhibited high-affinity for NTS2 (K_i 7.0 nM), with a more than 125-fold selectivity over NTS1, as well as an improved plasma stability profile (t_1/2 > 24 h) compared with NT (t_1/2 ~ 2 min). Following intrathecal administration, CR-01-64 exerted dose-dependent and long-lasting analgesic effects in acute (ED₅₀ = 4.6 µg/kg) and tonic (ED₅₀ = 7.1 µg/kg) pain models as well as strong mechanical anti-allodynic effects in the CFA-induced chronic inflammatory pain model. Of particular importance, this constrained NTS2 analog exerted potent nonopioid antinociceptive effects and potentiated opioid-induced analgesia when combined with morphine. At high doses, CR-01-64 did not cause hypothermia or ileum relaxation, although it did induce mild and short-term hypotension, all of which are physiological effects associated with NTS1 activation. Overall, these results demonstrate the strong therapeutic potential of NTS2-selective analogs for the management of pain.

Intrathecal administration of NTS1 agonists reverses nociceptive behaviors in a rat model of neuropathic pain

Chronic neuropathic pain arising from peripheral nerve damage is a severe clinical issue where there is a major unmet medical need. We previously demonstrated that both neurotensin (NT) receptor subtypes 1 (NTS1) and 2 (NTS2) are involved in mediating the naloxone-insensitive antinociceptive effects of neurotensin in different analgesic tests including hotplate, tail-flick, and tonic pain. However, the role of these receptors in neuropathic pain management has been poorly investigated. In the present study, we therefore examined whether intrathecal delivery of NTS1 agonists was effective in reducing neuropathic pain symptoms in rats. Neuropathy was induced by sciatic nerve constriction (CCI model), and the development of mechanical allodynia and thermal hyperalgesia on the ipsi- and contralateral hind paws was examined 3, 7, 14, 21, and 28 days post-surgery. CCI-operated rats exhibited significant increases in thermal and mechanical hypersensitivities over a 28-day testing period. Spinal injection of NT to CCI rats alleviated the behavioral responses to radiant heat and mechanical stimuli, with a maximal reversal of 91% of allodynia at 6 μg/kg. Intrathecal administration of the NTS1-selective agonist, PD149163 (30-90 μg/kg) also produced potent anti-allodynic and anti-hyperalgesic effects in nerve-injured rats. Likewise, heat hyperalgesia and tactile allodynia produced by CCI of the sciatic nerve were fully reversed by the NTS1 agonist, NT69L (5-25 μg/kg). Altogether, these results support the idea that the NTS1 receptor subtype is involved in pain modulation, and the potential use of NTS1 agonists for the treatment of painful neuropathies.

Altered morphine-induced analgesia in neurotensin type 1 receptor null mice

Both neurotensin (NT) and opioid agonists have been shown to induce antinociception in rodents after central administration. Besides, previous studies have revealed the existence of functional interactions between NT and opioid systems in the regulation of pain processing. We recently demonstrated that NTS1 receptors play a key role in the mediation of the analgesic effects of NT in long-lasting pain. In the present study, we therefore investigated whether NTS1 gene deletion affected the antinociceptive action of mu opioid drugs. To this end, pain behavioral responses to formalin were determined following systemic administration of morphine in both male and female NTS1 knockout mice. Acute injection of morphine (2 or 5 mg/kg) produced strong antinociceptive effects in both male and female wild-type littermates, with no significant sex differences. On the other hand, morphine analgesia was considerably reduced in NTS1-deficient mice of both sexes compared to their respective controls, indicating that the NTS1 receptor actively participates in mu opioid alleviating pain. By examining specifically the flinching, licking and biting nociceptive behaviors, we also showed that the functional crosstalk between NTS1 and mu opioid receptors influences the supraspinally-mediated behaviors. Interestingly, sexual dimorphic action of morphine-induced pain inhibition was found in NTS1 null mice in the formalin test, suggesting that the endogenous NT system interacts differently with the opioid network in male and female mice. Altogether, these results demonstrated that NTS1 receptor activation operates downstream to the opioidergic transmission and that NTS1-selective agonists combined with morphine may act synergistically to reduce persistent pain.

Down-regulation of amyloid precursor protein by peptide nucleic acid in vivo

Alzheimer's disease (AD) is a neurodegenerative disease associated with increased expression of amyloid precursor protein (APP) and the deposition of its proteolytic cleavage products, the amyloid-beta peptides, Abeta(1-40) and Abeta(1-42). Peptide nucleic acids (PNAs) have been shown to block the expression of proteins at transcriptional and translational levels. In this study we used a sense and an antisense PNA specifically targeted to APP to inhibit the transcription and translation of APP by complementary binding to DNA or mRNA, respectively. Using Western blotting, APP showed a drastic decrease (50% and 90% reduction, in two separate experiments, as compared with saline control) with the injection of sense APP. mRNA levels were higher at the same time point after injection of APP sense PNA, most probably because of a compensatory mechanism in response to the drop of APP that might have occurred at an earlier time point (0-1 h) and was reflected in a drop at the protein level at 1 h. The injection of antisense PNA showed about 70% decrease in APP as measured by Western blotting. Unmodified PNA can be used in vivo to reduce the levels of APP, which plays a critical role in the development of AD.

Pharmacologically selective block of mu opioid antinociception by peptide nucleic acid antisense in absence of detectable ex vivo knockdown

The goal of this study was to determine the neuroanatomical extent of mu opioid receptor knockdown in central nervous system (CNS) following intracerebroventricular (i.c.v.) administration of peptide nucleic acid antisense. Rats received subchronic i.c.v. injections of anti-mu opioid receptor antisense, mismatch or vehicle, and were tested for paw pressure latency following i.c.v. mu opioid receptor agonist ([D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin; DAMGO) or delta opioid receptor agonist ((+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide; SNC80). The anti-mu opioid receptor antisense (but not mismatch) sequence abolished DAMGO-induced antinociception with no reduction in the delta opioid receptor-mediated response. In contrast, postmortem receptor autoradiographic analysis of CNS areas revealed no change in mu opioid receptor functional response ([35S]GTPgammaS assay) or receptor labelling ([125I]FK-33824 and mu opioid receptor immunoautoradiography). These results provide further evidence for antisense-induced knockdown at the behavioural level in the absence of clear changes at the tissue level.

Peptide nucleic acids targeted to the amyloid precursor protein

The depositing in brain of amyloid beta peptide (Abeta), which is formed by the cleavage of amyloid precursor protein (APP), is likely an etiologic factor in Alzheimer's disease (AD). Of the different forms of Abeta, Abeta(1-42) causes fibril formation and increases aggregation at elevated levels, which can lead to neuronal death. It is hypothesized that if the levels of Abeta, particularly Abeta(1-42), were reduced, then the onset of AD would be slowed or possibly prevented. Therefore, we are using peptide nucleic acids (PNAs) targeted to APP, as well as other key proteins, to try to decrease plasma and brain levels of Abeta(1-40) and Abeta(1-42). This research project was designed to utilize the expertise of our laboratory in the use of PNAs, a third-generation antisense or antigene molecule, to knock down proteins in brain. Antisense compounds specifically knock down the expression of a particular protein by inhibiting translation at the level of mRNA. On the other hand, antigene compounds knock down expression at the level of transcription. For experiments involving antisense strategies, there are several advantages to using PNAs as opposed to the traditional oligonucleotide molecules. We report here the ongoing studies with mice and rats with PNAs targeting APP, as well as BACE.

The pain of antisense: in vivo application of antisense oligonucleotides for functional genomics in pain and analgesia

As the genomic revolution continues to evolve, there is an increasing demand for efficient and reliable tools for functional characterization of individual gene products. Antisense oligonucleotide-mediated knockdown has been used successfully as a functional genomics tool in animal models of pain and analgesia yet skepticism regarding the validity and utility of antisense technology remains. Contributing to this uncertainty are the lack of systematic studies exploring antisense oligonucleotide use in vivo and the many technical and methodological challenges intrinsic to the method. This article reviews the contributions of antisense oligonucleotide-based studies to the field of pain and analgesia and the general principles of antisense technology. A special emphasis is placed on technical issues surrounding the successful application of antisense oligonucleotides in vivo, including sequence selection, antisense oligonucleotide chemistry, DNA controls, route of administration, uptake, dose-dependence, time-course and adequate evaluation of knockdown.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

The potential of antisense as a CNS therapeutic

Antisense offers a precise and specific means of knocking down expression of a target gene, and is a major focus of research in neuroscience and other areas. It has application as a tool in gene function and target validation studies and is emerging as a therapeutic technology in its own right. It has become increasingly obvious, however, that there are a number of hurdles to overcome before antisense can be used effectively in the CNS, most notably finding suitable nucleic acid chemistries and an effective delivery vehicle to transport antisense oligonucleotides (AS-ODNs) across the blood-brain barrier (BBB) to their site of action. Despite these problems, a number of potential applications of AS-ODNs in CNS therapeutics have been validated in vitro and, in some cases, in vivo. Here the authors outline available nucleic acid chemistries and review progress in the development of non-invasive delivery vehicles that may be applicable to CNS therapeutics. Further to this, they discuss a number of experimental applications of AS-ODNs to CNS research and speculate on the development of antisense techniques to treat CNS disease.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Antiproliferative effect in chronic myeloid leukaemia cells by antisense peptide nucleic acids

Peptide nucleic acid (PNA) is a synthetic DNA analogue that is resistant to nucleases and proteases and binds with exceptional affinity to RNA. Because of these properties PNA has the potential to become a powerful therapeutic agent to be used in vivo. Until now, however, the use of PNA in vivo has not been much investigated. Here, we have attempted to reduce the expression of the bcr/abl oncogene in chronic myeloid leukaemia KYO-1 cells using a 13mer PNA sequence (asPNA) designed to hybridise to the b2a2 junction of bcr/abl mRNA. To enhance cellular uptake asPNA was covalently linked to the basic peptide VKRKKKP (NLS-asPNA). Moreover, to investigate the cellular uptake by confocal microscopy, both PNAs were linked by their N-terminus to fluorescein (FL). Studies of uptake, carried out at 4 and 37 degrees C on living KYO-1 cells stained with hexidium iodide, showed that both NLS-asPNA-FL and asPNA-FL were taken up by the cells, through a receptor-independent mechanism. The intracellular amount of NLS-asPNA-FL was about two to three times higher than that of asPNA-FL. Using a semi-quantitative RT- PCR technique we found that 10 micro M asPNA and NLS-asPNA reduced the level of b2a2 mRNA in KYO-1 cells to 20 +/- 5% and 60 +/- 10% of the control, respectively. Western blot analysis showed that asPNA promoted a significant inhibition of p210(BCR/ABL) protein: residual protein measured in cells exposed for 48 h to asPNA was approximately 35% of the control. Additionally, asPNA impaired cell growth to 50 +/- 5% of the control and inhibited completion of the cell cycle. In summary, these results demonstrate that a PNA 13mer is taken up by KYO-1 cells and is capable of producing a significant and specific down-regulation of the bcr/abl oncogene involved in leukaemogenesis.

Using peptide nucleic acids as gene-expression modifiers to reduce beta-amyloid levels

The deposition of amyloid beta peptide (A beta) is an early and critical aspect of Alzheimer's disease. A beta is formed by the cleavage of amyloid precursor protein (APP). Studies of familial forms of Alzheimer's disease indicate that elevated secretion of A beta, particularly A beta(1-42), is likely to be an etiologic agent in the disease. A beta(1-42) is known to cause fibril formation and at elevated levels increases aggregation, which can lead to neuronal death. It has, therefore, been hypothesized that if the levels of A betaB, particularly A beta(1-42), could be reduced that onset of Alzheimer's disease could be slowed or possibly prevented. We, therefore, propose using PNAs targeted to APP to decrease plasma and brain levels of A beta(1-40) and A beta(1-42). This research project is designed to expand upon the discovery in our laboratory that systemic administration of antisense or antigene treatments utilizing peptide nucleic acids (PNAs) can be used to target and shut down proteins. Antisense strategies are methods of specifically targeting a particular protein by inhibiting translation by complementary binding to mRNA, while antigene methods inhibit transcription by complementary binding to DNA. For experiments involving antisense strategies, there are several advantages to using PNAs as opposed to the traditional oligonucleotide approaches. We initially preformed our studies in rats and identified a PNA sequence that was able to significantly reduce the levels of A beta(1-41) in rat brain compared to vehicle control rats. We have switched to mice so that we can prepare to perform our experiments in a transgenic animal model of Alzheimer's disease. We have, however, run into several technical difficulties with using mice compared to rats. In spite of this, we have identified one PNA sequence that specifically lowers mouse brain A beta(1-40) A beta(1-42) by 37% and 47%, respectively.

Antisense as a neuroscience tool and therapeutic agent

Gene expression in the mammalian brain is highly complex and requires an immensely powerful functional genomics tool to unravel it. Antisense has the potential to meet this requirement, but has always been plagued by biological and technological hurdles that have made the technology unreliable. With recent progress in developing potent, low-toxicity nucleic acid chemistries and novel drug delivery methods to cross the blood-brain barrier, the use of antisense is gathering momentum.

Telomerase - strategies to exploit an important chemotherapeutic target

Telomeres, unique protein-DNA complexes located at the chromosome ends, have important functions involving both DNA protection and cellular signalling. Telomere structure is very dynamic yet tightly controlled. One important factor is the presence of telomerase, a telomere-specific DNA polymerase activated in a majority of cancer cells. Cancer and normal cell telomeres may have dissimilar structures due to variances in telomere length, telomerase activity and levels of telomere binding proteins. In designing compounds to strictly target cancer cells, these distinctions should be investigated. Much of the recent focus has been on the development of highly effective telomerase inhibitors. Another novel group of small molecules target telomere DNA, thereby disrupting both telomerase activity and telomere structure. This class of compounds should have an immediate impact on cell growth and viability. Since many molecular characteristics of telomeres are unknown, small molecules should also be useful in probing differences in telomere dynamics unique to cancer cells.