Functional neurotoxicity evaluation of noribogaine using video-EEG in cynomolgus monkeys.

INTRODUCTION: Continuous video-electroencephalographic (EEG) monitoring remains the gold standard for seizure liability assessments in preclinical drug safety assessments. EEG monitored by telemetry was used to assess the behavioral and EEG effects of noribogaine hydrochloride (noribogaine) in cynomolgus monkeys. Noribogaine is an iboga alkaloid being studied for the treatment of opioid dependence. METHODS: Six cynomolgus monkeys (3 per gender) were instrumented with EEG telemetry transmitters. Noribogaine was administered to each monkey at both doses (i.e., 160 and 320mg/kg, PO) with an interval between dosing of at least 6days, and the resulting behavioral and EEG effects were evaluated. IV pentylenetetrazol (PTZ), served as a positive control for induced seizures. RESULTS: The administration of noribogaine at either of the doses evaluated was not associated with EEG evidence of seizure or with EEG signals known to be premonitory signs of increased seizure risk (e.g., sharp waves, unusual synchrony, shifts to high-frequency patterns). Noribogaine was associated with a mild reduction in activity levels, increased scratching, licking and chewing, and some degree of poor coordination and related clinical signs. A single monkey exhibited brief myoclonic movements that increased in frequency at the high dose, but which did not appear to generalize, cluster or to be linked with EEG abnormalities. Noribogaine was also associated with emesis and partial anorexia. In contrast, PTZ was associated with substantial pre-ictal EEG patterns including large amplitude, repetitive sharp waves leading to generalized seizures and to typical post-ictal EEG frequency attenuation. INTERPRETATION: EEG patterns were within normal limits following administration of noribogaine at doses up to 320mg/kg with concurrent clinical signs that correlated with plasma exposures and resolved by the end of the monitoring period. PTZ was invariably associated with EEG paroxysmal activity leading to ictal EEG. In the current study, a noribogaine dose of 320mg/kg was considered to be the EEG no observed adverse effect level (NOAEL) in conscious freely moving cynomolgus monkeys.

Lost interest for existing compounds: New boosts.

Development of new drugs is typically thought of as a bottom-up endeavor where basic science identifies a target, various strategies are used to generate drugs that stimulate or inhibit the target, the drugs are first tested for safety and efficacy in animals and finally efficacy and safety are evaluated in a well defined clinical development process. However, this is not the only way that new drug products are developed. Many new products come from re-initiating development of discontinued drugs, finding new uses for existing drugs, creating a new product by obtaining marketing approval in expanded territories, obtaining approvals for new formulations or a single isomer of a previously approved racemic drug, converting products from prescription to over-the- counter use or converting folk medicines or vitamins to modern pharmaceuticals. Based on this long and successful history of contributions to modern therapeutics, these alternative sources of new products should not be neglected.

Cyclin-dependent kinase 8 mediates chemotherapy-induced tumor-promoting paracrine activities.

Conventional chemotherapy not only kills tumor cells but also changes gene expression in treatment-damaged tissues, inducing production of multiple tumor-supporting secreted factors. This secretory phenotype was found here to be mediated in part by a damage-inducible cell-cycle inhibitor p21 (CDKN1A). We developed small-molecule compounds that inhibit damage-induced transcription downstream of p21. These compounds were identified as selective inhibitors of a transcription-regulating kinase CDK8 and its isoform CDK19. Remarkably, p21 was found to bind to CDK8 and stimulate its kinase activity. p21 and CDK8 also cooperate in the formation of internucleolar bodies, where both proteins accumulate. A CDK8 inhibitor suppresses damage-induced tumor-promoting paracrine activities of tumor cells and normal fibroblasts and reverses the increase in tumor engraftment and serum mitogenic activity in mice pretreated with a chemotherapeutic drug. The inhibitor also increases the efficacy of chemotherapy against xenografts formed by tumor cell/fibroblast mixtures. Microarray data analysis revealed striking correlations between CDK8 expression and poor survival in breast and ovarian cancers. CDK8 inhibition offers a promising approach to increasing the efficacy of cancer chemotherapy.

Phenserine efficacy in Alzheimer's disease.

To gather preliminary evidence in Alzheimer's disease (AD) for the efficacy of phenserine, a non-competitive acetylcholinesterase inhibitor that has independent modulatory effects on amyloid-ß generation, a 12-week comparison of patients receiving phenserine (10 and 15 mg BID) or placebo was conducted under double-blind conditions. Patients who completed 12 weeks of the double-blind before others were continued in the double-blind to determine longer-term treatment effects. At 12 weeks, mean ADAS-cog (AD assessment scale-cognitive) changes from baseline were -2.5 and -1.9 for high-dose phenserine (n=83) and placebo (n=81) groups, respectively, a non-statistically significant improvement for the high-dose phenserine group relative to placebo. CIBIC+ (clinician's interview based impression of change + caregiver's input) values for the high-dose and placebo groups were similar at 12 weeks. For patients who received more than 12 weeks of therapy, the ADAS-cog changes were -3.18 and -0.66 for the high-dose phenserine (n=52) and placebo (n=63) groups, respectively, a difference achieving statistical significance (p=0.0286). After 12 weeks, CIBIC+ values were 3.59 and 3.95 for the high-dose (n=54) and placebo (n=66) groups respectively (p=0.0568). These results from this short-term study are consistent with phenserine potentially benefiting mild to moderate Alzheimer's disease symptomatically but do not address possible amyloid metabolic mediated effects on disease processes in AD.

Pharmacological concentrations of the HMG-CoA reductase inhibitor lovastatin decrease the formation of the Alzheimer beta-amyloid peptide in vitro and in patients.

Epidemiological studies demonstrate that hypercholesterolemia is a risk factor for Alzheimer's disease (AD). As the generation and accumulation of the beta-amyloid peptide (Abeta) in the brain appears to be significant for the initiation and progression of AD, it is possible that cholesterol levels regulate Abeta formation and/or clearance. To test the effects of altering cholesterol on Abeta formation, we incubated cells with or without lovastatin acid, the active metabolite of the HMG-CoA reductase inhibitor lovastatin, and measured the fraction of Abeta formed from its precursor under each condition. We observed that treatment with lovastatin acid led to a profound decrease in the levels of Abeta formed. This effect was observed at concentrations of 0.05-5 microM, ranges where this compound is effective at inhibiting HMG-CoA reductase. To examine the effects of lovastatin on Abeta in vivo, human subjects who had elevated low-density lipoprotein cholesterol were treated during a double-blind, randomized study with 10-60-mg once-daily doses of a controlled-release formulation of lovastatin, or matching placebo. Serum Abeta concentrations were measured before and after up to 3 months of treatment. Mean and median changes from baseline in serum Abeta concentrations showed a significant (p < 0.0348), dose-dependent decrease. Differences between the 40- and 60-mg dose groups and placebo were statistically significant (Dunnett's p< 0.05). Our results suggest a mechanism by which hypercholesterolemia may increase risk for AD and indicate that lovastatin reduces Abeta formation and may thereby be effective in delaying the onset and/or slowing the progression of AD.

Cholesterol depletion with physiological concentrations of a statin decreases the formation of the Alzheimer amyloid Abeta peptide.

Epidemiological studies have demonstrated that hypercholsterolemia is a significant risk factor for Alzheimer's disease (AD). The mechanism by which increased cholesterol may contribute to AD is unknown. However, as the generation and accumulation of the amyloid Abeta peptide in the brain appears to be significant for the initiation and progression of AD, it is possible that cholesterol levels can regulate Abeta formation and/or clearance. To test the effects of altering cholesterol on Abeta formation, we incubated cells in the presence of lipid depleted serum, with or without the active metabolite of the HMG-CoA reductase inhibitor lovastatin. After confirming that cholesterol was depleted in the cells, we then measured the fraction of Abeta formed from its precursor betaPP under each condition. We observed that cholesterol depletion led to a profound decrease in the levels of Abeta released from the cells. This effect of lovastatin acid was observed at concentrations of 0.05-5 &mgr;M, ranges where this compound is effective at inhibiting HMG-CoA reductase, thereby inhibiting cholesterol synthesis. In contrast, the release of an additional AbetaPP fragment, AbetaPPs, was only modestly reduced by cholesterol treatment. In further studies, we determined that the decreased release of Abeta was not due to its accumulation in the cell, but rather due to decreased formation of Abeta. Finally, we were able to exclude decreased maturation (glycosylation and sulfation) of newly synthesized AbetaPP as a cause for the effects of lovastatin acid on betaPP processing and Abeta formation. Our results demonstrate that reducing cellular cholesterol by the use of an HMG-CoA reductase inhibitor regulates Abeta formation. This effect may involve alterations in the trafficking of AbetaPP and/or alterations in the activity of the proteases that cleave AbetaPP. The results suggest a mechanism by which hypercholesterolemia may increase risk for AD and indicate that reduction in cholesterol may delay the onset and/or slow the progression of AD.