In vivo profiling of seven common opioids for antinociception, constipation and respiratory depression: no two opioids have the same profile.

BACKGROUND AND PURPOSE: For patients experiencing inadequate analgesia and intolerable opioid-related side effects on one strong opioid analgesic, pain relief with acceptable tolerability is often achieved by rotation to a second strong opioid. These observations suggest subtle pharmacodynamic differences between opioids in vivo. This study in rats was designed to assess differences between opioids in their in vivo profiles. EXPERIMENTAL APPROACH: Male Sprague Dawley rats were given single i.c.v. bolus doses of morphine, morphine-6-glucuronide (M6G), fentanyl, oxycodone, buprenorphine, DPDPE ([D-penicillamine(2,5) ]-enkephalin) or U69,593. Antinociception, constipation and respiratory depression were assessed using the warm water tail-flick test, the castor oil-induced diarrhoea test and whole body plethysmography respectively. KEY RESULTS: These opioid agonists produced dose-dependent antinociception, constipation and respiratory depression. For antinociception, morphine, fentanyl and oxycodone were full agonists, buprenorphine and M6G were partial agonists, whereas DPDPE and U69,593 had low potency. For constipation, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, morphine produced a bell-shaped dose-response curve, whereas DPDPE and U69,593 were inactive. For respiratory depression, morphine, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, whereas DPDPE and U69,593 were inactive. The respiratory depressant effects of fentanyl and oxycodone were of short duration, whereas morphine, M6G and buprenorphine evoked prolonged respiratory depression. CONCLUSION AND IMPLICATIONS: For the seven opioids we assessed, no two had the same profile for evoking antinociception, constipation and respiratory depression, suggesting that these effects are differentially regulated. Our findings may explain the clinical success of 'opioid rotation'. LINKED ARTICLES: This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

The relationship of glucokinase activator-induced hypoglycemia with arteriopathy, neuronal necrosis, and peripheral neuropathy in nonclinical studies.

Glucokinase activators (GKAs) are being developed for the treatment of type 2 diabetes. The toxicity of 4 GKAs (PF-04279405, PF-04651887, piragliatin, and PF-04937319) was assessed in mice, rats, dogs, and/or monkeys. GKAs were administered for 2 to 8 weeks. Standard endpoints, glucose, and insulin were assessed. All compounds produced varying degrees of hypoglycemia in all species. Brain neuronal necrosis and/or peripheral neuropathy were observed with most compounds. These findings are consistent with literature reports linking hypoglycemia with nervous system effects. Arteriopathy, mainly of cardiac vessels, was observed at a low frequency in monkey and/or dog. Arteriopathy occurred only at doses that produced severe and prolonged periods of repeated hypoglycemia. Since this lesion occurred in multiple studies with structurally distinct GKAs, these results suggested arteriopathy was related to GKA pharmacology. The morphological characteristics of the arteriopathy were consistent with that produced by experimental catecholamine administration. We hypothesize that the prolonged periods of hypoglycemia resulted in increased local and/or systemic concentrations of catecholamines via a counterregulatory and/or stress-related mechanism. Alternatively, prolonged hypoglycemia may have resulted in endothelial dysfunction leading to arteriopathy. This risk can be managed in human patients in clinical studies by careful glucose monitoring and intervention to avoid prolonged episodes of hypoglycemia.

Lipoamide channel-binding sulfonamides selectively inhibit mycobacterial lipoamide dehydrogenase.

Tuberculosis remains a global health emergency that calls for treatment regimens directed at new targets. Here we explored lipoamide dehydrogenase (Lpd), a metabolic and detoxifying enzyme in Mycobacterium tuberculosis (Mtb) whose deletion drastically impairs Mtb's ability to establish infection in the mouse. Upon screening more than 1.6 million compounds, we identified N-methylpyridine 3-sulfonamides as potent and species-selective inhibitors of Mtb Lpd affording >1000-fold selectivity versus the human homologue. The sulfonamides demonstrated low nanomolar affinity and bound at the lipoamide channel in an Lpd-inhibitor cocrystal. Their selectivity could be attributed, at least partially, to hydrogen bonding of the sulfonamide amide oxygen with the species variant Arg93 in the lipoamide channel. Although potent and selective, the sulfonamides did not enter mycobacteria, as determined by their inability to accumulate in Mtb to effective levels or to produce changes in intracellular metabolites. This work demonstrates that high potency and selectivity can be achieved at the lipoamide-binding site of Mtb Lpd, a site different from the NAD⁺/NADH pocket targeted by previously reported species-selective triazaspirodimethoxybenzoyl inhibitors.

Effects of kappa opioids in an assay of pain-depressed intracranial self-stimulation in rats.

RATIONALE: Selective, centrally acting kappa opioid agonists produce antinociception in a wide range of preclinical assays, but these compounds perform poorly as analgesics in humans. This discrepancy may be related to the behavioral depressant effects of kappa agonists. Kappa antagonists do not typically produce antinociception, but they produce antidepressant-like effects in some preclinical assays. OBJECTIVE: The objective of this study was to test the hypothesis that the kappa agonist U69,593 and the kappa antagonist norbinaltorphimine would produce pronociceptive and antinociceptive effects, respectively, in an assay of pain-depressed behavior. METHODS: Effects of U69,593 (0.056-0.56 mg/kg), norbinaltorphimine (10-32 mg/kg), and morphine (3.2 mg/kg) were evaluated on the stimulation of a stretching response and the depression of intracranial self-stimulation (ICSS) of the medial forebrain bundle produced in rats by a common noxious stimulus (intraperitoneal administration of dilute lactic acid). RESULTS: U69,593 produced a dose-dependent blockade of acid-stimulated stretching but only exacerbated acid-induced depression of ICSS. Thus, U69,593 produced antinociception in the assay of pain-stimulated behavior but pronociceptive effects in the assay of pain-depressed behavior. Norbinaltorphimine did not alter acid-stimulated stretching or acid-induced depression of ICSS. The mu opioid agonist morphine blocked both acid-stimulated stretching and acid-induced depression of ICSS. CONCLUSIONS: These results support the hypothesis that prodepressant effects of kappa agonists may limit their clinical utility as analgesics. These results do not support the use of kappa antagonists to treat depressant effects of pain. These findings illustrate the potential value of using complementary assays of pain-stimulated and pain-depressed behaviors for preclinical evaluation of candidate analgesics.

Targeted therapy with antineoplastons A10 and AS2-1 of high-grade, recurrent, and progressive brainstem glioma.

BACKGROUND: Brainstem glioma carries the worst prognosis of all malignancies of the brain. Most patients with brainstem glioma fail standard radiation therapy and chemotherapy and do not survive longer than 2 years. Treatment is even more challenging when an inoperable tumor is of high-grade pathology (HBSG). The objective of this report is to summarize the outcome of patients with HBSG treated with antineoplastons in 4 phase 2 trials. PATIENTS: The following group of 18 patients was evaluable: 4 patients with glioblastomas and 14 patients with anaplastic HBSG. Fourteen patients had diffuse intrinsic tumors. Twelve patients suffered from recurrence, and 6 patients did not have radiation therapy or chemotherapy. METHODS: Antineoplastons, which consist of antineoplaston A10 (A10I) and AS2-1 injections, were given in escalating doses by intravenous injections. The median duration of antineoplaston administration was 5 months, and the average dosage of A10I was 9.22 g/kg/d and of AS2-1 was 0.31 g/kg/d. Responses were assessed by gadolinium-enhanced magnetic resonance imaging and positron emission tomography. RESULTS: The overall survival at 2 and 5 years was 39% and 22%, respectively, and maximum survival was more than 17 years for a patient with anaplastic astrocytoma and more than 5 years for a patient with glioblastoma. Progression-free survival at 6 months was 39%. Complete response was achieved in 11%, partial response in 11%, stable disease in 39%, and progressive disease in 39% of patients. Antineoplastons were tolerated very well with 1 case of grade 4 toxicity (reversible anemia). CONCLUSION: Antineoplastons contributed to more than a 5-year survival in recurrent diffuse intrinsic glioblastomas and anaplastic astrocytomas of the brainstem in a small group of patients.

Long-term survival of high-risk pediatric patients with primitive neuroectodermal tumors treated with antineoplastons A10 and AS2-1.

Primitive neuroectodermal tumors (PNETs) are usually successfully treated with craniospinal radiation and chemotherapy; however, difficulties with standard treatment can be encountered in very young children, in adult patients at high risk of complication from standard treatment, and in patients with recurrent tumors. Thirteen children, either with recurrent disease or high risk, were treated in phase II studies with antineoplastons (ANP). The median age of patients was 5 years, 7 months (range, 1-11). Medulloblastoma was diagnosed in 8 patients, pineoblastoma in 3 patients, and other PNET in 2 patients. Previous treatments included surgery in 12 patients (1 had biopsy only, suboccipital craniotomy), chemotherapy in 6 patients, and radiation therapy in 6 patients. Six patients had not received prior chemotherapy or radiation. The treatment consisted of intravenous infusions of 2 formulations of ANP, A10 and AS2-1, and was administered for an average of 20 months. The average dosage of A10 was 10.3 g/kg/d and of AS2-1 was 0.38 g/kg/d. Complete response was accomplished in 23%, partial response in 8%, stable disease in 31%, and progressive disease in 38% of cases. Six patients (46%) survived more than 5 years from initiation of ANP; 5 were not treated earlier with radiation therapy or chemotherapy. The serious side effects included single occurrences of fever, granulocytopenia, and anemia. The study is ongoing and accruing additional patients. The percentage of patients' response is lower than for standard treatment of favorable PNET, but long-term survival in poor-risk cases and reduced toxicity makes ANP promising for very young children, patients at high risk of complication of standard therapy, and patients with recurrent tumors.