Reversal of resistance in multidrug resistance protein (MRP1)-overexpressing cells by LY329146.

The benzothiophene LY329146 reverses the drug resistance phenotype in multidrug resistance protein (MRP1)-overexpressing cells when dosed in combination with MRP1-associated oncolytics doxorubicin and vincristine. Additionally, LY329146 inhibited MRP1-mediated uptake of the MRP1 substrate LTC4 into membrane vesicles prepared from MRP1-overexpressing cells.

Discovery and synthesis of [6-hydroxy-3-[4-[2-(1-piperidinyl)ethoxy]phenoxy]-2-(4-hydroxyphenyl)]b enzo[b]thiophene: a novel, highly potent, selective estrogen receptor modulator.

Raloxifene,[2-(4-hydroxyphenyl)-6-hydroxybenzo[b]thien-3-yl] [4-[2-(1-piperidinyl)ethoxy]phenyl]methanone hydrochloride (2), is representative of a class of compounds known as selective estrogen receptor modulators (SERMs) that possess estrogen agonist-like actions on bone tissues and serum lipids while displaying potent estrogen antagonist properties in the breast and uterus. As part of ongoing SAR studies with raloxifene, we found that replacement of the carbonyl group with oxygen ([6-hydroxy-3-[4-[2-(1-piperidinyl)ethoxy]phenoxy]-2-(4-hydroxyphenyl)]b enzo[b]thiophene hydrochloride, 4c) resulted in a substantial (10-fold) increase in estrogen antagonist potency relative to raloxifene in an in vitro estrogen dependent cell proliferation assay (IC50 = 0.05 nM) in which human breast cancer cells (MCF-7) were utilized. In vivo, 4c potently inhibited the uterine proliferative response to exogenous estrogen in immature rats following both sc and oral dosing (ED50 of 0.006 and 0.25 mg/kg, respectively). In ovariectomized aged rats, 4c produced a significant maximal decrease (45%) in total cholesterol at 1.0 mg/kg (p.o.) and showed a protective effect on bone relative to controls with maximal efficacy at 1.0 mg/kg (p.o.). These data identify 4c as a novel SERM with greater potency to antagonize estrogen in uterine tissue and in human mammary cancer cells compared to raloxifene, tamoxifen or ICI-182,780.

Structural evolution and pharmacology of a novel series of triacid angiotensin II receptor antagonists.

cis-4-(4-Phenoxy)-1-[1-oxo-2(R)-[4-[(2-sulfobenzoyl)amino)-1H- imidazol-1-yl]octyl]-L-proline derivatives represent a novel class of potent nonpeptide angiotensin II (Ang II) receptor antagonists. These compounds evolved from directed structure-activity relationship (SAR) studies on a lead identified by random screening. Further SAR studies revealed that acidic modification of the 4-phenoxy ring system produced a series of triacid derivatives possessing oral activity in pithed rats. The most potent compound, cis-4-[4-(phosphonomethyl)phenoxy]-1-[1-oxo-2(R)-[4-[(2-sulfobenzoyl+ ++) amino]-1H-imidazol-1-yl]octyl]-L-proline (1e), inhibited the pressor response to exogenously administered Ang II for periods up to 8 h following oral dosing. The antihypertensive activity of 1e was evaluated in the Lasix-pretreated conscious spontaneously hypertensive rat (SHR) where it produced a dose-dependent fall in blood pressure following oral dosing lasting > 12 h. Antagonists such as 1e may serve as useful therapeutic agents for the treatment of hypertension as well as for studying the role of Ang II in various disease states.

Developmental changes in high-affinity uptake of GABA by cultured neurons.

High-affinity uptake of [3H]gamma-aminobutyric acid (GABA) was studied in cultures of neonatal rat cortical neurons grown on pre-formed monolayers of non-neuronal (glial) cells. Both the maximum rate (Vmax) and, to a smaller extent, the Km of [3H]GABA uptake increased with time. In addition, in parallel with these changes, 2,4-diaminobutyric acid and cis-3-aminocyclohexane-1-carboxylic acid (ACHC), compounds which are considered typical substrate/inhibitors of GABA uptake in neurons, became progressively stronger inhibitors of [3H]GABA uptake. Consequently, the present results may mean that the studies using uptake of [3H]GABA, [3H]ACHC, or [3H]DABA as a specific marker for GABAergic neurons differentiating during the ontogenetic development of the central nervous system may have to be interpreted with caution.

Alteration of central alpha 2- and beta-adrenergic receptors in the rat after DSP-4, a selective noradrenergic neurotoxin.

A peripheral injection of DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] produced a marked, selective, and lasting depletion of norepinephrine in certain regions of the rat central nervous system. This depletion at 10 days after injection was associated with regional alterations in some, but not all, adrenergic binding sites (receptors) as determined by in vitro [3H]prazosin (alpha 1), [3H]p-aminoclonidine (alpha 2), and [3H]dihydroalprenolol (beta) binding. The neocortical alpha 1-receptor was not changed. The alpha 2-receptor in several regions was altered as indicated by an increase in ligand affinity; additionally, the density of this receptor was slightly decreased in some regions. Depending on the region, the beta-receptor either increased in density or was unchanged. The increased density of this receptor in neocortex corresponded to an increased activity of isoproterenol-sensitive adenylate cyclase. These two changes were not affected by subchronic treatment with desipramine, a norepinephrine uptake inhibitor. The changes were, however, partially or completely reversed by subchronic administration of clenbuterol, a centrally-acting beta-receptor agonist. The dopaminergic receptor in various regions was unaltered as assessed by in vivo and/or in vitro binding of [3H]spiperone. The in vivo binding of this ligand also indicated that the serotoninergic receptor in frontal neocortex was unchanged. Assessment of adrenergic receptors in neocortex at 50 days after injection indicated only the above affinity change of the (presumably postsynaptic) alpha 2-receptor. The alpha 1-receptor remained unaltered. The density of the beta-receptor had normalized, as had the activity of isoproterenol-sensitive adenylate cyclase. Implicit in these findings is the following rank order of receptor sensitivity to chronic norepinephrine depletion: alpha 2 greater than beta greater than alpha 1. The use of DSP-4 has clear advantages over other methods of depleting central norepinephrine. This neurotoxin can be administered by intraperitoneal injection, the depletion of norepinephrine can be readily checked by absence of the post-decapitation reflex, and the changes in other neurotransmitter concentrations are relatively minor or nonexistent. The alteration of alpha 2- and beta-receptors, as a consequence of DSP-4 treatment, may form the basis of a new animal model of adrenergic receptor supersensitivity. Such a model may clarify the importance of these central receptors to physiological and behavioral processes.

Subchronic infusion of clenbuterol, a beta-adrenergic agonist, decreases the cerebellar beta receptor.

Subchronic, peripheral infusion of clenbuterol, a beta-adrenergic agonist, markedly reduced beta receptor density and isoproterenol-sensitive adenylate cyclase activity in the cerebellum of the rat. In contrast, infusion of salbutamol, isoproterenol or desipramine did not alter the beta receptor. The result of clenbuterol administration demonstrates, for the first time, a significant alteration of the cerebellar beta 2 receptor to a pharmacologic manipulation. This alteration may influence physiological and behavioral processes regulated by the cerebellum.

Differential decrease of the central beta-adrenergic receptor in the rat after subchronic infusion of desipramine and clenbuterol.

The effect of subchronic infusion of desipramine, a norepinephrine uptake inhibitor, and clenbuterol, a beta-adrenergic agonist, on the central beta receptor of the rat was determined using in vitro [(3)H]dihydroalprenolol binding. Desipramine produced significant decreases of the receptor in neocortex and hippocampal formation, and clenbuterol effected such decreases in corpus striatum and cerebellum. Both drugs caused a marked decrease in the activity of isoproterenol-sensitive adenylate cyclase in neocortex. The alpha(2) receptor of neocortex and cerebellum was unchanged by either drug as assessed by in vitro[ (3)H ]p- aminoclonidine binding. The results are discussed in terms of the different mechanisms of action of desipramine and clenbuterol, and the efficacy of these two drugs in the treatment of depression.