Yishai Karton

M1 Agonists for the Treatment of Alzheimer's Disease.

The AF series compounds, AF102B and congeners of AF150(S), are functionally selective agonists for m1 muscarinic receptors (m1AChRs). This is shown in stable transfected CHO and PC12 cells (PC12M1) with m1‐m5AChRs and m1AChRs, respectively. AF102B and AF150(S) are partial agonists, but AF150, AF151, and AF151(S) are full agonists in stimulating phosphoinositides hydrolysis or arachidonic acid release in these cells. Yet, all these compounds behave as antagonists when compared with carbachol in elevating cAMP levels. In PC12M1 cells, unlike carbachol, the AF series compounds induce only minimal to moderate neurite outgrowth. Yet, these agonists synergize strongly with NGF, which by itself mediates only a mild response. Stimulation of m1AChRs by AF102B, AF150(S) and AF151(S) in PC12M1 cells enhances secretion of β/A4 amyloid precursor protein derivatives (APPs). The enhanced APPs secretion induced by AF102B is potentiated by NGF. AF102B also stimulates APPs secretion from rat cortical slices. Stimulation of m1AChR in PC12M1 cells with carbachol or AF102B decreases tau phosphorylation as indicated by specific tau‐1 mAb and alkaline phosphatase treatment. Due to the above mentioned properties m1 agonists may be of unique value in delaying the progression of Alzheimers disease (AD). The AF series compounds show a wide safety margin and improve memory and learning deficits in animal models for AD. There is a dearth of clinical reports on m1 agonists. These include studies on AF102B and xanomeline, another m1 selective agonist. We tested AF102B in escalating doses of 20, 40, 60 mg, tid, po, (each dose for 2 weeks) for a total of 10 weeks. This was a single‐blind placebo‐controlled, parallel‐group study in patients with probable AD. AFl02B was signiticantly effective at 40 and 60 mg, tid in the ADAS, ADAS‐cognitive and ADAS‐word recognition scales.

Selective Signaling via Unique Ml Muscarinic Agonistsa

Rigid analogs of acetylcholine (ACh) were designed for selective actions at muscarinic receptor (mAChR) subtypes and distinct second messenger systems. AF102B, AF150, and AF151 are such rigid analogs of ACh. AF102B, AF150 and AF151 are centrally active M1 agonists. AF102B has a unique agonistic profile showing, inter alia: only part of the M1 electrophysiology of ACh and unusual binding parameters to mAChRs. AF150 and AF151 are more efficacious agonists than AP102B for M1 AChRS in rat cortex and in CHO cells stably transfected with the ml AChR subtype. Notably, the selectivity of the new ml agonists is reflected also by activation of select second messenger systems via distinct G‐proteins. These compounds reflect a new pharmacological concept, tentatively defined as ligand‐selective signaling. Thus, agonist/m1AChR complexes may activate different combinations of signaling pathways, depending on the ligand used. Rigid agonists may activate a limited repertoire of signaling systems. In various animal models for Alzheimers disease (AD) the agonists AF102B, AF150 and AF151, exhibited positive effects on mnemomic processes and a wide safety margin. Such agonists, and especially AF102B, can be considered as a rational treatment strategy for AD.

Gastro intestinal tracking and gastric emptying of solid dosage forms in rats using X-ray imagining

The aim of this research was to study the gastrointestinal transit and gastric emptying of non-disintegrating solid dosage forms in rats using X-ray imaging. Commercial gelatin minicapsules were filled with barium sulfate and enterically coated using Eudragit S100. The capsules were administered orally to rats followed by a solution of iodine based contrast agent iopromide. Images were obtained using a standard X-ray camera and digital film processing. Capsules were followed through the GI tract from the stomach to the small intestine, cecum and large intestine and the capsule location could be easily identified. Gastric emptying of different sized capsules was studied. The effect of fasting and time of administration on gastric retention was also studied. It was found that shortened capsules of 3.5 and 4.8mm length were emptied from the stomach whereas the commercial length 7.18mm capsules were retained. Surprisingly, 2.5h post administration more rats retained the capsules in the stomach in the fasted state than in the fed state. We found that X-ray imaging can be used for simple visualization and localization of solid dosage forms in rats in the fed state using shortened commercial minicapsules on rats.

NGF-dependent neurotrophic-like effects of AF102B, an M1 muscarinic agonist, in PC12M1 cells.

The non-selective muscarinic agonist oxotremorine induces atropine-sensitive neurite outgrowth in PC12 cells stably transfected with m1 muscarinic receptors. In contrast, AF102B, an M1-selective muscarinic agonist, mediated minimal neurite outgrowth in these cells. In the presence of nerve growth factor (NGF) however, it induced atropine-sensitive neurite outgrowth in almost half the cell population. AF102B mediated phosphoinositide hydrolysis, but unlike carbachol, it did not stimulate cyclic AMP accumulation in these cells. These signals were not affected by NGF, indicating that they were not directly responsible for the cholinergic neurotrophic-like response. Our observations suggest that AF102B may improve neuronal responsiveness to neurotrophic factors, and thus may provide another beneficial aspect for treating Alzheimers disease.

Novel m1 muscarinic agonists in treatment and delaying the progression of Alzheimer's disease: An unifying hypothesis

M1 selective agonists from the AF series (e.g. AF102B, AF150(S)), via m1 muscarinic receptors, activate distinct signal transductions, enhance amyloid precursors proteins secretion from transfected cells and primary cell cultures, show neurotrophic effects and are beneficial in a variety of animal models for Alzheimers disease. Such m1 agonists may be effective in the treatment and therapy of Alzheimers disease.

Novel salicylazo polymers for colon drug delivery: Dissolving polymers by means of bacterial degradation

Novel azo polymers were prepared for colonic drug delivery with a release mechanism based on structural features of azo derivatives designed for rapid bacterial degradation leading to soluble polymers. Two Salicylazo derivatives were prepared and conjugated as side chains at different ratios to methacrylic acid-methyl methacrylate copolymers (Eudragits). The azo compounds were designed to have a hydrophilic and a hydrophobic part on opposite sides of the azo bond. Upon reduction of the azo bonds, the hydrophobic part is released, resulting in a more water soluble polymer. The solubility of the polymeric films was studied relative to Eudragit S known to dissolve toward the end of the small intestine. One of the two azo derivatives prepared gave rise to polymers, which showed reduced solubility relative to Eudragit S. These polymers were subjected to reduction tests in anaerobic rat cecal suspensions by following the release of the hydrophobic product. Reduction rate was found to be rapid, comparable to that of Sulfasalazine. Studies on the azopolymeric films in anaerobic rat cecal suspensions, showed that these polymers dissolve faster than in sterilized suspensions. Solid dosage forms may be coated with these polymers to provide an efficient delivery system to the colon with a rapid release mechanism.

Selective Signaling Via Novel Muscarinic Agonists: Implications for Alzheimer’s Disease Treatments and Clinical Update

Five human muscarinic acetylcholine receptors (mAChR) (ml–m5), have been cloned and expressed in suitable cell systems (reviewed by Hulme et al., 1990). * mAChRs have two binding domains, a ligand-binding extracellular (and including membrane-spanning) domain and a G-protein binding intracellular domain. This second domain, by interaction with various G-proteins, controls and modulates second messenger systems (Hulme et al., 1990).

High affinity acylating antagonists for muscarinic receptors

The muscarinic antagonists pirenzepine and telenzepine were derivatized as alkylamino derivatives at a site on the molecules corresponding to a region of bulk tolerance in receptor binding. The distal primary amino groups were coupled to the cross-linking reagent meta-phenylene diisothiocyanate, resulting in two isothiocyanate derivatives that were found to inhibit muscarinic receptors irreversibly and in a dose-dependent fashion. Preincubation of rat forebrain membranes with an isothiocyanate derivative followed by radioligand binding using [3H]N-methylscopolamine diminished the Bmax value, but did not affect the Kd value. The receptor binding site was not restored upon repeated washing, indicating that irreversible inhibition had occurred. IC50 values for the irreversible inhibition at rat forebrain muscarinic receptors were 0.15 nM and 0.19 nM, for derivatives of pirenzepine and telenzepine, respectively. The isothiocyanate derivative of pirenzepine was non-selective as an irreversible muscarinic inhibitor, and the corresponding derivative prepared from telenzepine was 5-fold selective for forebrain (mainly m1) vs. heart (m2) muscarinic receptors.

Ambident Electrophilicity of 5-Membered Ring Phosphate Triesters

The reactions of 2-alkoxy-1,3,2-dioxaphospholane 2-oxide with various nucleophiles were studied both experimentally and theoretically. These studies show that 5-membered ring phosphate triesters act as ambident electrophiles: hard and bulky nucleophiles attack at the phosphorus while soft nucleophiles attack at the ring carbon.

Ml Muscarinic Agonists: From Treatment Toward Delaying Progression of Alzheimer’s Disease

Alzheimer’s disease (AD) is characterized, inter alia, by synaptic loss, neurofibrillary tangles, amyloid plaques containing the β-amyloid peptide (Aβ), and degeneration of cholinergic neurons that ascend from the basal forebrain to cortical and hippocampal areas (reviewed by Court and Perry, 1991). A presynaptic cholinergic hypofunction, as one of the major neuronal events in AD, is reflected, inter alia, in reduced levels of acetylcholine (ACh), acetylcholinesterase (AChE) and choline acetyltransferase (ChAT). As a result of neuronal degeneration, the density of presynaptic M2 muscarinic receptors (mAChR) is significantly decreased in AD, yet post-synaptic Ml mAChR are relatively unchanged in AD (review by Court and Perry, 1991) (vide infra for further discussion). Degeneration of cholinergic neurons in AD is presumably a principal cause of the dementia. The “cholinergic hypothesis’.in AD implies that a cholinergic replacement therapy might be beneficial in alleviating some of the cognitive dysfunctions in this disorder (Court and Perry, 1991). Highly selective ml agonists, producing cellular excitation, should be beneficial in AD, regardless of the extent of degeneration of presynaptic cholinergic projections to the frontal cortex or hippocampus. This represents the most relevant approach of cholinergic treatment due to the role of Ml mAChRs in memory and learning processing (Fisher and Barak, 1994, Fisher, 1997). The present overview is an attempt to address some of these findings and to propose an unifying hypotheses regarding ml selective agonists aimed at treatment and therapy of AD.