Overriding the blockade of antinociceptive actions of opioids in rats treated with extended-release naltrexone.

A monthly extended-release formulation of the opioid antagonist naltrexone (XR-NTX) is approved for treatment of alcohol dependence. There is little research regarding overriding chronic (>21 days) competitive opioid receptor blockade with opioids for acute pain. Using the hot plate test after XR-NTX or placebo microsphere administration, rats were treated with an opioid analgesic to determine the dose required to produce the maximum response latency (MRL; 60 s). Rats were later treated with the same opioid to determine any potential effects on respiration rate or locomotor activity. In naïve rats, 15 mg/kg morphine, 0.1 mg/kg fentanyl and 8 mg/kg hydrocodone produced MRL. In XR-NTX treated rats, morphine produced 36% and 46% MRL at 90 mg/kg on days 4 and 19 and 96% MRL at 45 mg/kg on day 39. Fentanyl produced 100% MRL at 2.0 mg/kg on days 4 and 19 and at 0.5 mg/kg on day 39. Hydrocodone (80 mg/kg) produced 69%, 80% and 100% MRL on days 4, 19 and 39. Compared to placebo, these doses did not further depress respiration or alter locomotor activity. Thus, opioid receptor blockade with XR-NTX can be overcome in rats with higher doses of opioids without further affecting respiration or locomotor activity.

BIIB042, a novel γ-secretase modulator, reduces amyloidogenic Aß isoforms in primates and rodents and plaque pathology in a mouse model of Alzheimer's disease.

Reducing the production of larger aggregation-prone amyloid ß-peptides (Aß) remains an untested therapeutic approach for reducing the appearance and growth of Aß plaques in the brain, which are a hallmark pathological feature of Alzheimer's disease. γ-Secretase modulators (GSMs) are therapeutics that impact γ-secretase-dependent cleavage of amyloid precursor protein to promote the production of shorter Aß peptides that are less prone to aggregation and plaque deposition. This is accomplished without inhibiting overall γ-secretase function and cleavage of other substrates, which is believed to be a source of deleterious side effects. Here, we report the pharmacokinetic and pharmacodynamic properties of BIIB042, a novel bioavailable and brain-penetrant GSM. In cell-based assays, BIIB042 reduced the levels of Aß42, increased the levels of Aß38 and had little effect on the levels of Aß40, the most abundant Aß species. Similar pharmacodynamic properties were confirmed in the central nervous system and in plasma of mice and rats, and also in plasma of cynomolgus monkeys after a single oral dose of BIIB042. BIIB042 reduced Aß42 levels and Aß plaque burden in Tg2576 mice, which overexpress human amyloid precursor protein and serve as a model system for Alzheimer's disease. BIIB042 did not inhibit cleavage of other γ-secretase substrates in cell-based and in vivo signaling and cleavage assays. The pharmacodynamic effects of lowering Aß42 in the central nervous system coupled with demonstrated efficacy in reducing plaque pathology suggests modulation of γ-secretase, with molecules like BIIB042, is a compelling therapeutic approach for the treatment of Alzheimer's disease.