Current Medicinal Chemistry - Immunology, Endocrine & Metabolic Agents - Volume 2, Issue 3, 2002

The genetics of Alzheimer's disease (AD) is complex. Three genes-amyloid precursor protein, presenilin 1 (PS1), and presenilin 2 (PS2)- have been described in the relatively rare, early-onset, autosomal dominant familial form of AD. In the common, nonfamilial (sporadic) late-onset AD, the major known genetic risk factor is the e4 allele of the Apolipoprotein E (APOE) gene, but at least half of the people who develop AD do not carry this allele. Therefore, other genes are risk factors for sporadic AD or modify the association with APOE ε4 allele. Nine candidate genes that have been implicated in the pathophysiology of AD, although none is as widely accepted as APOE, are the human leucocyte antigen (HLA)-A2, PS1 and PS2, butyrylcholinesterase (BCHE), endothelial nitric oxide synthase (NOS3), cathepsine D (catD), prion protein (PRNP), low density lipoprotein-related protein (LRP), and interleukin-1A (IL-1A). Positive-association studies with these candidate genes have not been consistently confirmed. This fact has prompted a search of these 9 candidate genes and APOE gene in a large case-control study utilizing a clinically well-defined group of 311 sporadic AD patients and 346 control subjects. Risk for AD was increased with one copy (odds ratio -OR- 5.3) or two copies of APOE ε4 allele (OR 49.8), and with two copies of IL-1A allele 2 (OR 3.1), homozygosity for either the 1 allele of PS1 or the C allele of PS2 increased the risk conferred by APOE ε4 allele, homozygous for the T allele of -491 APOE promoter and carriers of the K allele of BCHE were at reduced risk of AD (OR 0.1 and 0.4, respectively), HLA-A2 anticipated in 2.7 years the age at onset of AD, LRP, catD, NOS3, and PRNP were not associated with AD.

The discovery of a G-protein-coupled calcium-sensing receptor (CaR) almost a decade ago has provided incontrovertible evidence of the receptor's role in the critical maintenance of systemic calcium homeostasis. Situated on the chief cells of the parathyroid glands, CaR “senses” the extracellular calcium concentration and, in turn, alters the rate of secretion of parathyroid hormone (PTH). CaR is also functionally expressed in bone, kidney, and gut-the three major organs involved in calcium homeostasis. Intracellular signal pathways to which the CaR couples include, but are not limited to, phospholipase C (PLC), Gα / Gq11, and mitogen-activated protein kinases. The receptor is widely expressed in various tissues and likely serves important cellular functions beyond the realm of maintaining systemic calcium homeostasis, i.e., cellular proliferation, differentiation, and membrane polarization etc. Functionally important mutations in the receptor have been found to cause disorders in calcium homeostasis that are due to changes in the set point for PTH secretion as well as the control of renal calcium excretion. These mutations cause hypocalcemia when the mutation activates the receptor and hypercalcemia when the mutation inactivates the receptor. Recent studies have shown the same clinical presentation caused by the presence of circulating autoantibodies to the CaR. A drug that stimulates the receptor (calcimimetic) has been effective as a medical treatment for renal secondary hyperparathyroidism.

In order to survive and maintain cellular homeostasis the different cells of the central nervous system (CNS) must continually adapt to a wide variety of genetic and environmental stimuli. Heat shock proteins (HSPs) are a class of proteins that are rapidly elevated in response to stress, aiding in protein folding, protein unfolding, and protein trafficking. The proteasome is a large intracellular protease that is responsible for the majority of intracellular protein degradation in the CNS. In particular, the proteasome is responsible for the degradation of most oxidized, aggregated, and damaged proteins. Increasing evidence suggests that HSPs may play important roles in the targeting of proteins to the proteasomal and lysosomal proteolytic pathways. Additionally, HSPs may play an important role in protein unfolding necessary for proteasome-mediated proteolytic degradation. Because the proteasome appears to become inhibited in a wide variety of neurodegenerative conditions, and possibly contribute to neurodegeneration in those conditions, studies must be conducted to determine how alterations in HSPs may contribute to proteasome inhibition in neurodegenerative disorders. The focus of this review is to outline what is currently known about HSPs and proteasome function in normal and neurodegenerative settings, and to discuss the possible therapeutic benefit of maintaining a robust HSP-proteasome interplay within the CNS.

In addition to supplying cholesterol, the mevalonate pathway is also responsible for providing other intermediates essential for the regulation of cell functions. Products from the mevalonate pathway include the isoprenoid family, such as farnesyl or geranylgeranyl derivatives that are required for the prenylation of small proteins regulating cell growth such as Ras. The hypocholesterolemic class of drugs statins that are competitive inhibitors of HMG-CoA Reductase, have displayed antiproliferative activity in vitro.As part of a search for novel inhibitors of the mevalonate pathway as therapeutic agents, a series of 1,1-bisphosphonate esters (I) was prepared for pharmacological screening. The alkyl- and alkoxy-substituted phenol derivatives with a variety of vinylidene or alkylidene linkages were prepared by condensation of the appropriate aldehydes with the corresponding methylenebisphosphonate esters, followed by reduction. In our primary screening assay, the di-tert-butyl phenol-1,1- bisphosphonate esters were shown to inhibit cholesterol synthesis with IC50s in the submicromolar range in cultured human-derived intestinal cells (CaCo-2). The inhibition of proliferation of H-Ras transfected cell lines PAP-2, as well as other cell lines such as HL-60 and SW-620, was selected as the subsequent screening assays. Test results showed that the most active compounds for decreasing cholesterol synthesis, the di-tert-butylphenol-1,1-bisphosphonates, were also the most effective for inhibiting cell growth. The most potent analogue, compound 36, decreased cholesterol synthesis with an IC50 of 0.08 mM and inhibited cell growth with IC50s of 5 μM (PAP-2), 12 μM (HL-60) and 16 μM (SW-620), respectively.Based on these findings and the results from further pharmacological evaluation, compound 36 (Apomine, SR-45023A), tetraisopropyl 2-(3,5-di-tert-butyl-4-hydroxyphenyl) ethylidene-1,1-bisphosphonate, was selected for development as an antineoplastic agent.

Secretory output of insulin from the pancreatic beta cell is regulated in a sophisticated manner by nutrients, hormones and neurotransmitters,having impact on the different stages of the sequential events leading to release into the blood to maintain glucose homeostasis. Although the final step of the secretory process, exocytosis, has relatively been well investigated, the significance of pre-exocytotic processes such as granule movement and interaction with the plasma membrane has received less attention. Recently, we and a few other groups directly analysed the nature of intracellular traffic of insulin granules as well as their distribution. Glucose, the most important insulin secretagogue, was found to activate pre-exocytotic events as well as actual exocytosis, whereas some hormones, neurotransmitters and pharmacological substances were found to act solely on the earlier stages to potentiate insulin release. Mechanisms regulating granule traffic, access, docking and priming were found to be distinct from those for granule exocytosis, which dominantly depends on Ca2+ influx from the extracellular space. Recent studies have suggested that overloading of Ca2+may cause apoptotic death of the beta cell. We, therefore, suggest here that elucidation of the pre-exocytotic steps may allow an increase in insulin output with a minimal rise in the intracellular Ca2+ concentration, which would be helpful to prevent beta-cell loss and maintain beta cell functions under diabetic conditions.