ABSTRACT
Converging lines of evidence implicate the beta-amyloid peptide (Ass) as causative in Alzheimer's disease. We describe a novel class of compounds that reduce A beta production by functionally inhibiting gamma-secretase, the activity responsible for the carboxy-terminal cleavage required for A beta production. These molecules are active in both 293 HEK cells and neuronal cultures, and exert their effect upon A beta production without affecting protein secretion, most notably in the secreted forms of the amyloid precursor protein (APP). Oral administration of one of these compounds, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester, to mice transgenic for human APP(V717F) reduces brain levels of Ass in a dose-dependent manner within 3 h. These studies represent the first demonstration of a reduction of brain A beta in vivo. Development of such novel functional gamma-secretase inhibitors will enable a clinical examination of the A beta hypothesis that Ass peptide drives the neuropathology observed in Alzheimer's disease.
Subject(s)
Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Brain/metabolism , Dipeptides/administration & dosage , Endopeptidases/metabolism , Administration, Oral , Alzheimer Disease/drug therapy , Alzheimer Disease/genetics , Amyloid Precursor Protein Secretases , Amyloid beta-Protein Precursor/genetics , Amyloid beta-Protein Precursor/metabolism , Animals , Aspartic Acid Endopeptidases , Brain/cytology , Brain/drug effects , Cells, Cultured , Disease Models, Animal , Dose-Response Relationship, Drug , Drug Evaluation, Preclinical , Endopeptidases/drug effects , Enzyme Inhibitors/administration & dosage , Female , Humans , Injections, Subcutaneous , Kidney/cytology , Kidney/drug effects , Kidney/metabolism , Male , Mice , Mice, Transgenic , Neurons/cytology , Neurons/drug effects , Neurons/metabolism , Peptide Fragments/metabolismABSTRACT
The lipophilic derivatives of the anticancer alkylating agent chlorambucil, chlorambucil-methyl, -isopropyl and -tertiary butyl esters, were synthesized and administered i.v. to anesthetized rats. Plasma and brain concentrations of these agents and of their active metabolites, chlorambucil and phenylacetic mustard, then were determined by high-performance liquid chromatography between 5 and 60 min. Whereas large amounts of chlorambucil-tertiary butyl ester entered and were maintained in brain, lower amounts of chlorambucil-isopropyl ester and no chlorambucil-methyl ester were found in brain. The comparative brain/plasma concentration-time integral ratios of the total active agents generated from chlorambucil-tertiary butyl, -isopropyl and -methyl esters were 0.85, 0.12 and 0.06, respectively, compared to a ratio of 0.02 for chlorambucil. In vitro alkylating activity of each ester was compared to that of equimolar chlorambucil, by reaction with 4-(p-nitrobenzyl)pyridine. Each ester possessed high intrinsic alkylating activity, equal to 38.4, 57.0 and 69.9% of chlorambucil activity, for the -tertiary butyl, -isopropyl and -methyl esters, respectively. Therefore each is an active antineoplastic agent irrespective of whether or not chlorambucil is regenerated. The rates of ester hydrolysis of these derivatives to chlorambucil were measured in fresh rat blood and in liver and brain homogenates at 37 degrees C. Chlorambucil-methyl and -isopropyl esters were hydrolysed quickly within 30 s in blood and liver, whereas chlorambucil-tertiary butyl ester was more stable with half-lives of approximately 7 h and 2 h, respectively. All proved to be relatively stable in brain homogenate. Steric hindrance around the ester linkage of chlorambucil-tertiary butyl ester reduces its affinity to and rate of hydrolysis by plasma and liver esterases, and allows it to accumulate within the brain. Chlorambucil-tertiary butyl ester maintains high levels in brain despite rapidly declining plasma concentrations and, due to these favorable pharmacokinetics and to its intrinsic anticancer activity, it possess promising characteristics for the treatment of malignant brain tumors.
Subject(s)
Antineoplastic Agents/pharmacokinetics , Brain Neoplasms/metabolism , Chlorambucil/analogs & derivatives , Alkylating Agents/pharmacokinetics , Animals , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/pharmacology , Blood-Brain Barrier/physiology , Brain/metabolism , Brain Neoplasms/drug therapy , Chlorambucil/pharmacokinetics , Chlorambucil/pharmacology , Drug Stability , Esters/chemical synthesis , Esters/metabolism , Esters/pharmacokinetics , Female , Injections, Intravenous , Nitrogen Mustard Compounds/pharmacokinetics , Rats , Rats, Wistar , SolubilityABSTRACT
The assembly of the collagen tailed A12 form of acetylcholinesterase (AChE) is regulated by muscle contraction. To begin to study this regulation, we derived antibody probes for the three subunits (100 kd, catalytic, and collagen tail) of AChE purified from Torpedo californica electric tissue. These included a polyclonal antiserum that recognizes all 3 subunits and 19 monoclonal antibodies; 16 of the monoclonals recognized the catalytic subunit, 2 recognized the tail subunit, and 1 recognized the 100 kd subunit on Western blots. We used immunohistochemical procedures to show that several of the anticatalytic and one of the antitail monoclonals cross-reacted with frog muscle AChE and Western blotting to show that several of the anticatalytic monoclonals cross-react with rat brain AChE. These antibodies were then used to immunoprecipitate AChE precursors from a cell-free translation system. There were generally three primary translation products, corresponding to the three enzyme subunits. Therefore, each subunit is probably derived from a separate mRNA. Occasionally there were two translation products corresponding to the catalytic subunit alone. The catalytic subunit was glycosylated following addition of canine microsomal membranes to the translation mix. The mRNA coding for this subunit appeared to be present in the poly(A)- RNA pool.
