Pharmacology/Drug Development

Opioid therapeutics, such as morphine, that act at the mu-opioid receptor (MOR) are the clinical standard for patients struggling to manage symptoms associated with pain. It is widely understood that although opioids are effective at treating pain, their use leads to the development of severe adverse effects, such as constipation, addiction, and respiratory depression. Thus, there is a clear need for a safer alternative to manage pain. One such alternative is to enhance the effects of the body's endogenous opioid system by positive allosteric modulation (PAM) of MOR. A known PAM, BMS-986122, enhances MOR agonist potency in cellular models and MOR agonist mediated antinociception in vivo. In addition, this PAM is active alone in a variety of mouse pain assays by promoting the activity of endogenous opioid peptides. Moreover, at an effective antinociceptive dose, BMS-986122 alone produces less severe adverse effects than morphine as determined by measures of constipation, respiratory depression, and conditioned place preference. However, we do not yet know how the overall pharmacology of opioids is affected by PAMs or if all opioid drugs are equally sensitive to PAM modulation. Here we compare the ability of BMS-986122 to enhance the action of three structurally diverse opioid drugs, morphine, methadone, and fentanyl, in an acute pain assay and in an assay examining respiratory depression using CD-1 male and female mice. We show that BMS-986122 increases the antinociceptive effects of the opioid therapeutics in the warm water tail withdrawal assay without promoting the ability of the drugs to lower blood oxygen levels or heart rate. Future work will assess the effects of BMS-986122 in additional acute and chronic pain models and with a more diverse group of opioids. If additional experiments support the concept that BMS-986122 enhances MOR-mediated antinociception but not MOR-mediated respiratory depression, this will validate the development of MOR-PAMs as standalone pain medications and support the use of PAMs as opioid-sparing drugs for the effective management of pain.

Neuropathic pain is a debilitating health concern and there is an urgent need for non-opioid analgesic targets. Our group has identified GPR183 as a novel potential therapeutic target for neuropathic pain. GPR183 is a G-protein coupled receptor that promotes the migration of immune cells in response to its ligand, 7α,25-dihydroxycholesterol (7α,25-OHC). We have shown that GPR183 is upregulated in the dorsal horn spinal cord during neuropathic pain states in rodents and intrathecal injections of 7α,25-OHC is able to induce allodynia in mice in a GPR183-dependent manner. However, the mechanism by which GPR183 activation leads to pain is unknown. These studies aim to elucidate the molecular signaling pathways that contribute to 7α,25-OHC-induced hypersensitivity. Based on previous literature, we hypothesized that GPR183 activation in the spinal cord would activate mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK) and p38, leading to the production of neuroexcitatory cytokines contributing to hypersensitivity.

To assess the long-term efficacy and safety of erenumab in the subgroup of patients with chronic migraine (CM) in whom prior preventive treatments had failed (TF) (≥1, ≥2, and ≥3 TF medication categories) and never failed (preventive naïve or prior preventive treatments had not failed), using the data from a 52-week, open-label treatment period (OLTP) of the parent study.

The objective of this paper is to present a narrative review of the use of triptans in the treatment of trigeminal neuralgia (TN), as well as to outline possible therapeutic mechanisms of action.

Promising new therapeutic treatments using the fatty acid amide hydrolase (FAAH) inhibitor can be used to relieve symptoms in a patient suffering from a variety of conditions, including but not limited to insomnia, anxiety, fibromyalgia, migraines, arthritis, and other chronic pain conditions. FAAH is responsible for breaking down anandamide, which is an endogenous agonist of the CB1 cannabinoid receptor and analgesic neurotransmitter. The FAAH protein contains a catalytic triad of Ser 241, Ser 217, Lys 142 embedded in its center. The FAAH monomer assumes a twisted 11 strand β-sheet in the middle of the monomer and 24 α-helices surrounding the β-sheets. The Divine Savior Holy Angels MAPS (Modeling A Protein Story) Team modeled the catalytic domain of FAAH using 3D technology. Inhibitors of the FAAH molecules perform better through noncovalent interactions with the triad active site. The inhibitors stop FAAH activity through hydrophobic interactions that result from the active site changing its shape. Noncovalent and reversible inhibitors bring higher selectivity and less unwanted side effects than already studied covalent inhibitors. Non-covalent FAAH inhibitors are currently in development as analgesics lacking the adverse effects of opioid-based analgesics. Further studies are being conducted with selective and potent FAAH inhibitors in order to reduce neurological pain suppression, reduction of cancer cells, and increase feeling of motivation. Currently, the United States is in an opioid crisis that caused 100,000 deaths in the last year, which is why new treatments involving FAAH inhibitors prove promising because they reduce the extreme effects opioid-based drugs present.

Most patients with head and neck squamous cell carcinoma (HNSCC) experience pain and pain is associated with a poor prognosis. Despite the frequency and severity of HNSCC pain, current treatments fail to adequately control pain. Cancer-derived small extracellular vesicles (sEVs, size 30-150 nm) are well-positioned to be a mediator of communication between cancer cells and neurons. We hypothesize that cancer-derived sEVs contribute to cancer pain. Mouse oropharyngeal cells were retrovirally transduced to stably express HPV16 viral oncogenes, E6 and E7, H-Ras and luciferase and therefore called mEERL cells. Implantation of mEERL cells into WT mice induces evoked and spontaneous pain. Administration of the sEV release inhibitor GW4869 attenuates the pain in tumor-bearing mice. Additionally, blocking sEV release specifically in the cancer cells, by deleting Rab27a and Rab27b, two proteins required for exosome release, significantly delayed the development of pain hypersensitivity. To test whether cancer-derived sEVs are sufficient to induce pain, we isolated sEVs from mEERL culture and injected them subcutaneously. Injection of isolated sEVs triggers pain hypersensitivity in both sexes. NSAID ketoprofen has no effect on sEVs-induced pain hypersensitivity. In contrast blocking nociceptor neuron activity with the membrane-impermeant lidocaine derivate QX-314 alleviates sEVs-induced pain hypersensitivity. In primary culture of trigeminal ganglion neurons, addition of cancer-derived sEVs induces expression of the neuronal injury marker activating transcription factor 3 (ATF3) and calcium influx measured by calcium imaging in Trpv1 :GCaMP6 mice. Given that sEVs activate TRPV1+ neurons (mostly nociceptors), we examine the impact of TRP1V1+ neuron ablation on cancer pain. Chemical ablation of TRPV1+ neurons by resiniferatoxin (RTX) treatment prevents the development of evoked and spontaneous pain in tumor-bearing mice. Finally, to further explore the potential mechanism of nociception triggered by sEVs, we used published human RNA-sequencing data to investigate the change in gene expression in human cultured sensory neurons exposed to sEVs. Ingenuity pathways analysis (IPA) identified several pathways linked to the initiation of translation, a pathway known to contribute to nociception and neuroplasticity associated with chronic pain. Pharmacological inhibition of translation by rapamycin (mTOR inhibitor), and narciclasine (AMPK activator), alleviates and prevents pain in tumor-bearing mice respectively. In summary, our study shows that cancer-derived sEVs directly activate TRPV1+ neurons to trigger cancer pain and identify new actionable pharmacological targets.

Chemotherapy-induced peripheral neuropathy (CIPN) is a problematic side effect in patients receiving chemotherapeutic cancer treatments. Clinical use of approved analgesic drugs often does not adequately control the pathological pain arising from CIPN and does not account for potential abuse with opioid therapeutics. Mitragyna speciosa (kratom) contains the alkaloid mitragynine, which exhibits analgesic properties. However, the underlying pharmacological mechanisms that underlie these analgesic properties are complex and not completely understood. Male and female C57bl/6 mice received 8 mg/kg intraperitoneal injections of paclitaxel, a taxane class chemotherapeutic, every other day over the course of 7 days. To confirm the development of CIPN, the von Frey assay was utilized to determine the onset mechanical allodynia, which arises when a previously non-painful stimulus is perceived as painful. Intraperitoneal mitragynine and the prototypical opioid agonist morphine both dose-relatedly reversed CIPN-induced mechanical allodynia. Effective doses (ED) were as follows – morphine: 7.02 (6.56 – 7.51) mg/kg, mitragynine: 109.80 (104.27 – 115.62) mg/kg. Pretreatment with the opioid antagonist naltrexone 0.032 mg/kg, intraperitoneally produced a rightward shift in both morphine and mitragynine dose-response curves. Effective doses (ED) were as follows – naltrexone + morphine: 27.93 (24.84 – 31.40), naltrexone + mitragynine: 245.41 (211.76 – 284.39), resulting in a 3.98 and 2.24 fold shift of dose response curves, respectively. Here we show that mitragynine reverses mechanical allodynia associated with paclitaxel CIPN. We also show that opioid receptors mediate such activity, though additional data suggest a role for adrenergic and serotonin receptors as well. Mitragynine may be an effective analgesic treatment option for patients experiencing painful CIPN.

The antinociceptive effects of major cannabinoids such as ∆9-tetrahydrocannabinol (THC) and cannabidiol (CBD) have been extensively studied in rats. These studies have led to formulations of THC and CBD for human use; however, humans use different strains of Cannabis that contain several hundred different compounds. The contribution of these compounds to pain relief produced by Cannabis is unclear. ß-caryophyllene (BCP) is one compound found in the essential oils of Cannabis. Despite some early studies, the extent to which these compounds produce pain relief in assays of pain-evoked behaviors (i.e., von Frey and Hargreaves tests) and pain-depressed behaviors (i.e., home cage wheel running) is unclear. We hypothesized that BCP would inhibit mechanical allodynia and thermal hyperalgesia as well as restore depressed wheel running activity in male Sprague-Dawley rats with inflammatory pain. Three different doses of BCP (10, 30, and 100 mg/kg) or vehicle were administered to rats via an intraperitoneal injection after hindpaw inflammation induced by an intraplantar injection of Complete Freund's Adjuvant (CFA). Neither the low dose (10 mg/kg) nor the medium dose (30 mg/kg) of BCP reversed mechanical allodynia of the inflamed hindpaw after intraperitoneal injection. However, a high dose of BCP (100 mg/kg) reversed mechanical allodynia on the von Frey test; however, this dose did not reverse thermal hyperalgesia. A hindpaw injection of 0.1 mL CFA decreased wheel running activity as is consistent with a painful stimulus. However, neither 30 mg/kg BCP nor 100 mg/kg BCP restored pain-depressed wheel running in injured rats. These same doses of BCP did not affect wheel running in uninjured control rats. Therefore, a high dose BCP produces pain relief, although it only does so against mechanical allodynia. BCP does not restore normal activity. This suggests that although pain may be eliminated following BCP administration, a return to normal levels of activity may not be possible which raises questions about the utility of BCP to treat pain. Future studies of the pain-relieving effects of Cannabis constituents must include tests of many pain-related behaviors to understand dose-response relationships and their therapeutic potential.

Chronic pain remains a serious issue, affecting millions in the United States. Opioids serve as the most powerful therapeutic option but show limited efficacy in neuropathic pain and consequential side-effects, such as tolerance, addiction, and respiratory depression. Development of novel drugs to treat pain, though, continues to stagnate. Additionally, in conditions in which opioids are required, adjuvants to reduce opioid-induced neuroplasticity is critical. Agmatine has been shown to reduce neuropathic pain behavior and opioid tolerance, but use remains limited due to potentially reduced CNS penetration due to its hydrophilicity. Therefore, we have developed a series of agmatine-based compounds that exhibit greater lipophilicity while exhibiting equivalent pharmacological responses (Figure 1). The goal of this study was to assess differences in pharmacokinetics and dynamics of 4 of these strategically substituted agmatines (SSAs). Our hypothesis is that these compounds will have an increased plasma half-life and CNS distribution compared to agmatine, with equivalent reductions in neuropathic pain and opioid tolerance. Analysis of the pharmacokinetics in rat plasma was done using serial sampling via jugular catheter. All in vivo experiments were reviewed and approved by the University of Minnesota IACUC and the ACURO of the Department of Defense. After intravenous administration, the SSAs exhibit 2-phase distribution and elimination and have an increased elimination half-life over agmatine (9 minutes), with SSA3 and SSA4 showing the longest (Table 1). This increased half-life aligns with the increased lipophilicity of these compounds. Additionally, SSA2 and SSA4 show large volumes of distribution, suggesting increased CNS distribution. To test the impact of these compounds in vivo, we induced neuropathic pain by performing spared nerve injury (SNI). SNI drives robust tactile hypersensitivity measured using the von Frey assay in the ipsilateral hind-paw, with the contralateral paw serving as a non-injured control. Following intravenous administration, SSA2-4 reduced SNI-induced hypersensitivity at similar doses to agmatine, showing equivalent pharmacological activity. Additionally, after chronic morphine treatment alongside co-treatment with SSA1 and SSA2, opioid reduction in the warm water (52.5°C) tail flick response was preserved, representing a prevention of opioid tolerance. In conclusion, these chemical alterations to agmatine are able to improve pharmacokinetic parameters while maintaining the pharmacological reduction in neuropathic pain and opioid tolerance, suggesting potential as novel therapeutics to replace opioids in pain treatment.