Modern diuretics and the kidney

Design, synthesis and biological evaluation of a novel bioactive indane scaffold 2-(diphenylmethylene)c-2,3-dihydro-1H-inden-1-one with potential anticancer activity

Over the past decades, designing of privileged structures has emerged as a useful approach to the discovery and optimisation of novel biologically active molecules, and many have been successfully exploited across and within different target families. Examples include indole, quinolone, isoquinoline, benzofuran and chromone, etc. In the current study, we focus on synthesising a novel hybrid scaffold constituting naturally occurring benzophenone (14) and indanone (22) ring systems, leading to a general structure of 2-(diphenylmethylene)-2,3-dihydro-1H-inden-1-one (23). It was hypothesised this new hybrid system would provide enhanced anti-cancer activity owing to the presence of the common features associated with the tubulin binding small molecule indanocine (10) and the estrogen receptor (ER) antagonist tamoxifen (24). Key hybrid molecules were successfully synthesised and characterised, and the in vitro cytotoxicity assays were performed against cancer cell lines: MCF7 (breast) and SKBR3 (breast), DU145 (prostate) and A549 (lung). The methyl-, chloro- and methoxy-, para-substituted benzophenone hybrids displayed the greatest degree of cytotoxicity and the E-configuration derivatives 45, 47 and 49 being significantly most potent. We further verified that the second benzyl moiety of this novel hybrid scaffold is fundamental to enhance the cytotoxicity, especially in the SKBR3 (HER2+) by the E-methyl lead molecule 47, MCF7 (ER+) by 45 and 49, and A549 (NSCLC) cell lines by 49. These hybrid molecules also showed a significant accumulation of SKBR3 cells at S-phase of the cell cycle after 72 hrs, which demonstrates besides of being cytotoxic in vitro against SKBR3 cells, 47 disturbs the replication and development of this type of cancer causing a dose-dependent cell cycle arrest at S-phase. Our results suggest that DNA damage might be involved in the induction of SKBR3 cell death caused by the hybrid molecules, and therefore, this novel system may be an effective suppressor of HER2+/Neu-driven cancer growth and progression. The present study points to potential structural optimisation of the series and encourages further focussed investigation of analogues of this scaffold series toward their applications in cancer chemoprevention or chemotherapy.

SEC-TID: A Label-Free Method for Small-Molecule Target Identification

Bioactive small molecules are an invaluable source of therapeutics and chemical probes for exploring biological pathways. Yet, significant hurdles in drug discovery often come from lacking a comprehensive view of the target(s) for both early tool molecules and even late-stage drugs. To address this challenge, a method is provided that allows for assessing the interactions of small molecules with thousands of targets without any need to modify the small molecule of interest or attach any component to a surface. We describe size-exclusion chromatography for target identification (SEC-TID), a method for accurately and reproducibly detecting ligand-macromolecular interactions for small molecules targeting nucleic acid and several protein classes. We report the use of SEC-TID, with a library consisting of approximately 1000 purified proteins derived from the protein databank (PDB), to identify the efficacy targets tankyrase 1 and 2 for the Wnt inhibitor XAV939. In addition, we report novel interactions for the tumor-vascular disrupting agent vadimezan/ASA404 (interacting with farnesyl pyrophosphate synthase) and the diuretic mefruside (interacting with carbonic anhydrase XIII). We believe this method can dramatically enhance our understanding of the mechanism of action and potential liabilities for small molecules in drug discovery pipelines through comprehensive profiling of candidate druggable targets.

Diuretic drugs. Progress in clinical pharmacology

Oral diuretics are amongst the most widely used drugs in clinical practice today. Their discovery close on thirty years ago remains a major milestone in therapeutic progress. Though originally designed for treating heart failure, diuretics are more commonly prescribed, worldwide, in hypertension than for relief of oedema. Since the introduction of chlorothiazide, diuretic development has passed through a series of distinct stages. The thiazide era was followed by the 'high-ceiling' diuretics, the antikaliuretics and, more recently, polyvalent agents that cause both saluresis and uricosuria. Alongside these synthetic achievements, major advances have occurred in the knowledge of nephron function and ion transport mechanisms. These have acted as stimulus to the design of novel categories of diuretics. The practising clinician thus has a wide range of available diuretics to choose from. The most appropriate choice of an agent aimed at the relief of symptoms with minimal adverse effects requires an understanding of where and how diuretics act within their primary target organ, the kidney. Whereas various procedures, ranging from micropuncture to the study of brush border membrane vesicles, have been utilised experimentally, investigation of the mode and sites of action of diuretics in man has largely depended on application of clearance methodology. Refinements in analytical chemistry have encouraged study of the pharmacokinetic and metabolic fate of diuretics. Taken together, available evidence shows that most diuretics exert their saluretic action from the intraluminal aspect of the renal tubules. The time-course of drug delivery, as well as total quantity of drug transported into the lumen determine the cumulative drug response. Exceptions are muzolimine and the aldosterone antagonists which act at the peritubular membrane. Distinctive stereospecific effects on luminal tubular ion transport occur with indacrinone and etozoline. The clinical use of diuretics often involves concurrent administration with other drugs. The mechanisms involved in a number of the resulting pharmacodynamic and pharmacokinetic interactions have considerable relevance in patient management. Notable examples of these interactions are the blunting of diuretic action by non-steroidal anti-inflammatory agents and the diuretic-induced diminution in the renal clearance of lithium salts.

Piretanide. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Piretanide is a potent 'loop' diuretic whose principal site of action is in the thick ascending limb of the loop of Henle. When administered orally or intravenously to healthy volunteers it rapidly increases diuresis and electrolyte excretion, and the effects are short-lived. In comparative studies, piretanide has generally been found to be 5 to 7 times more potent than frusemide (furosemide) but only one-tenth as potent as bumetanide, on a weight-for-weight basis. Piretanide 6 to 12 mg/day, in conventional or sustained release formulations, has been shown to significantly lower elevated blood pressure in a large proportion of patients with mild to moderate hypertension. Comparative trials of up to 3 months duration indicate that at this dosage piretanide is of comparable antihypertensive efficacy as hydrochlorothiazide 50 to 100 mg/day, but has significantly less effect on serum potassium levels. Short term studies in patients with oedema caused by renal, hepatic or cardiac failure demonstrated that piretanide 6 to 9 mg is of similar diuretic potency as frusemide 40 mg and bumetanide 1 mg. In medium term trials in patients with congestive heart failure piretanide 6 mg/day produced equivalent symptomatic improvement as frusemide 40 mg/day. When used to treat oedema caused by liver disease, piretanide 12 to 24 mg/day was successful in only about 50% of patients, but spironolactone added to the treatment regimen greatly increased the response rate. Generally, piretanide has been well-tolerated in clinical trials, although the conventional tablet formulation has caused a relatively high incidence of acute adverse effects--these were greatly reduced with the introduction of the sustained release formulation. Serum concentrations of most electrolytes have not shown any consistent adverse trends and hyperuricaemia and hypokalaemia have been encountered infrequently. Thus, piretanide appears to offer an effective alternative to other 'loop' diuretics for the treatment of oedematous diseases and to hydrochlorothiazide for the management of mild to moderate hypertension. However, its relative place in therapy remains to be clarified with wider clinical experience.

Diuretics. Clinical pharmacology and therapeutic use (Part I)

25 years have elapsed since the introduction of the first effective oral diuretic, chlorothiazide. Diuretics are now amongst the most widely prescribed drugs in clinical practice worldwide. Availability of these drugs has not only brought therapeutic benefit to countless numbers of patients but it has at the same time provided valuable research tools with which to investigate the functional behaviour of the kidney and other electrolyte-transporting tissues. Despite many remaining gaps in our knowledge of the biochemical processes involved in diuretic drug action, available compounds can be divided into 5 groups on the basis of their preferential effects on different segments of the nephron involved in tubular reabsorption of sodium chloride and water. Firstly, there is heterogeneous group of chemicals that share the common property of powerful, short-lived diuretic effects that are complete within 4 to 6 hours. These agents act on the thick ascending limb of Henle's loop and are known as 'high ceiling' or 'loop' diuretics. The second group are the benzothiadiazines and their many related heterocyclic variants, all of which localise their effects to the early portion of the distal tubule. The third group comprises the potassium-sparing diuretics which act exclusively on the Na+-K+/H+ exchange mechanisms in the late distal tubule and cortical collecting duct. The action of drugs in groups 2 and 3 is prolonged to between 12 and 24 hours. The fourth group consists of diuretics that are chemically related to ethacrynic acid but have the unusual property of combining within the same molecule the property of saluresis and uricosuria. These compounds have actions, to different individual extents, in the proximal tubule, thick ascending limb, and early distal tubule and are known as 'polyvalent' diuretics. Finally, there is a mixed group of weak or adjunctive diuretics which includes the vasodilator xanthines such as aminophylline, and the osmotically active compounds such as mannitol. Available evidence on the molecular mechanisms of action of diuretics in each group is reviewed. The haemodynamic, humoral and physical factors involved in control of electrolyte and fluid handling by the kidney in normal conditions and pathological states are discussed in relation to rational choices of different diuretics in the treatment of various oedematous and non-oedematous conditions.

Indapamide. A review of its pharmacodynamic properties and therapeutic efficacy in hypertension

Indapamide is an orally active sulphonamide diuretic agent. Although some evidence appears to indicate that the antihypertensive action of indapamide is primarily a result of its diuretic activity, only a limited diuresis occurs with the usual antihypertensive doses of 2.5 mg daily, and in vitro and in vivo data suggest that it may also reduce blood pressure by decreasing vascular reactivity and peripheral vascular resistance. In mild to moderate hypertension it is as effective as thiazide diuretics and beta-adrenergic blocking agents in lowering blood pressure when used as the sole treatment. Indapamide has been successfully combined with beta-adrenergic blocking agents, methyldopa, and other anti-hypertensive agents. While such findings need confirmation, it appears that indapamide shares the potential with other diuretic agents to induce electrolyte and other metabolic abnormalities, although it may do so with less frequency or severity. Thus, indapamide appears to offer a suitable alternative to more established drugs as a 'first-line' treatment in patients with mild to moderate hypertension. Whether it differs significantly from other diuretics when used as antihypertensive therapy, either in its mode of action or its side effect profile, needs further clarification.