Design and synthesis of novel cyanoguanidine ATP-sensitive potassium channel openers for the treatment of overactive bladder

Targeting mast cells: Uncovering prolific therapeutic role in myriad diseases

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases.

Structure-activity relationship analysis of cytotoxic cyanoguanidines: selection of CHS 828 as candidate drug

Background

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N''-4-pyridyl guanidine) (CHS 828) is the first candidate drug from a novel group of anti-tumour agents – the pyridyl cyanoguanidines, shown to be potent compounds interfering with cellular metabolism (inhibition of nicotinamide phosphoribosyl transferase) and NF-κB signalling. Substituted cyanoguanidines are also found in anti-hypertensive agents such as the potassium channel opener pinacidil (N-cyano-N'-(4-pyridyl)-N''-(1,2,2-trimethylpropyl)guanidine) and histamine-II receptor antagonists (e.g. cimetidine, N-cyano-N'-methyl-N''-[2-[[(5-methylimidazol-4-yl]methyl]thio]ethyl)guanidine). In animal studies, CHS 828 has shown very promising activity, and phase I and II studies resulted in further development of a with a water soluble prodrug.

Findings

To study the structural requirements for cyanoguanidine cytotoxicity a set of 19 analogues were synthesized. The cytotoxic effects were then studied in ten cell lines selected for different origins and mechanisms of resistance, using the fluorometric microculture cytotoxicity assay (FMCA). The compounds showed varying cytotoxic activity even though the dose-response curves for some analogues were very shallow. Pinacidil and cimetidine were found to be non-toxic in all ten cell lines. Starting with cyanoguanidine as the crucial core it was shown that 4-pyridyl substitution was more efficient than was 3-pyridyl substitution. The 4-pyridyl cyanoguanidine moiety should be linked by an alkyl chain, optimally a hexyl, heptyl or octyl chain, to a bulky end group. The exact composition of this end group did not seem to be of crucial importance; when the end group was a mono-substituted phenyl ring it was shown that the preferred position was 4-substitution, followed by 3- and, finally, 2-substitution as the least active. Whether the substituent was a chloro, nitro or methoxy substituent seemed to be of minor importance. Finally, the activity patterns in the ten cell lines were compared. Substances with similar structures correlated well, whilst substances with large differences in molecular structure demonstrated lower correlation coefficients.

Conclusion

According to this structure-activity relationship (SAR) study, CHS 828 meets the requirements for optimal cytotoxic activity for this class of compounds.

Selective P2X(7) receptor antagonists for chronic inflammation and pain

ATP, acting on P2X₇ receptors, stimulates changes in intracellular calcium concentrations, maturation, and release of interleukin-1β (IL-1β), and following prolonged agonist exposure, cell death. The functional effects of P2X₇ receptor activation facilitate several proinflammatory processes associated with arthritis. Within the nervous system, these proinflammatory processes may also contribute to the development and maintenance of chronic pain. Emerging data from genetic knockout studies have indicated specific roles for P2X₇ receptors in inflammatory and neuropathic pain states. The discovery of multiple distinct chemical series of potent and highly selective P2X₇ receptor antagonists have enhanced our understanding of P2X₇ receptor pharmacology and the diverse array of P2X₇ receptor signaling mechanisms. These antagonists have provided mechanistic insight into the role(s) P2X₇ receptors play under pathophysiological conditions. In this review, we integrate the recent discoveries of novel P2X₇ receptor-selective antagonists with a brief update on P2X₇ receptor pharmacology and its therapeutic potential.

Functional and molecular identification of pH-sensitive K+ channels in murine urinary bladder smooth muscle

OBJECTIVE

To examine the role of pH-sensitive K(+) channels in setting the resting membrane potential in murine bladder smooth muscle, as bladder contractility is influenced by the resting membrane potential, which is mainly regulated by background K(+) conductances.

MATERIALS AND METHODS

Using conventional microelectrode recordings, isometric tension measurements, patch-clamp recordings, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry, we assessed bladder smooth muscle cells and tissues.

RESULTS

Acidic pH (pH 6.5) depolarized the resting membrane potential of murine bladder smooth muscles and increased muscle tone and contractility. The pH-induced changes were not abolished by neuronal blockers or classical K(+)-channel antagonists. Lidocaine (1 mM) and bupivacaine (100 microm) mimicked the effects of acidifying the external solution, and in the presence of lidocaine no further increase in contractility was induced by reducing the pH to 6.5. Voltage-clamp experiments on freshly dispersed bladder myocytes showed that pH 6.5 decreased the outward current. Pre-treatment of bladder myocytes with the classical K(+) antagonists tetraethylammonium (10 mm), 4-aminopyridine (5 mM), glibenclamide (10 microm) or apamin (300 nM) did not inhibit the effects of low pH on outward current. However, treatment with lidocaine (1 mM) abolished the effects of acidic pH on outward current. RT-PCR showed the expression of the acid-sensitive K(+) channel (TASK)-1 and TASK-2 gene transcripts in murine bladder, and immunohistochemistry and Western blot analysis showed TASK-1 and TASK-2 channel expression and distribution in smooth muscle tissues and cells.

CONCLUSION

TASK channels are expressed in bladder smooth muscle and contribute to the basal K(+) conductances responsible for resting membrane potential.

Structure-activity studies of novel cyanoguanidine ATP-sensitive potassium channel openers for the treatment of overactive bladder

A series of novel cyanoguanidine derivatives was designed and synthesized. Condensation of N-(1-benzotriazol-1-yl-2,2-dichloropropyl)-substituted benzamides with N-(substituted-pyridin-3-yl)-N'-cyanoguanidines furnished N-{2,2-dichloro-1-[N'-(substituted-pyridin-3-yl)-N''-cyanoguanidino]propyl}-substituted benzamide derivatives. These agents were glyburide-reversible potassium channel openers and hyperpolarized human bladder cells as assessed by the FLIPR membrane potential dye (KATP-FMP). These compounds were also potent full agonists in relaxing electrically stimulated pig bladder strips, an in vitro model of overactive bladder. The most active compound 9 was evaluated for in vivo efficacy and selectivity in a pig model of bladder instability. Preliminary pharmacokinetic studies in dog demonstrated excellent oral bioavailability and a t1/2 of 15 h. The synthesis, SAR studies, and biological properties of these agents are discussed.

Overactive bladder treatments in early phase clinical trials

'Overactive bladder' (OAB) is a syndrome that is characterised by symptoms of urgency, with or without urge urinary incontinence, usually with frequency and nocturia [1] . It is a highly prevalent condition affecting 17% of the general population, with a significant negative effect on quality of life, impairing several areas with physical, social, emotional and sexual limitations. The prevalence of OAB increases with age in both men and women [2,3] . The pathophysiology is multifactorial and not yet fully understood. Non-surgical treatment is the mainstay of therapy for OAB. The available options include biofeedback, electrical stimulation, bladder training, pharmacotherapy or a combination of these options. Nevertheless pharmacotherapy is still the treatment of choice for OAB symptoms [4] . The pharmacological treatment of OAB is generally directed towards the central or the peripheral neural control pathways or the detrusor muscle [5] . The antimuscarinic drugs are the most commonly used. In the US, approved antimuscarinics include oxybutynin, tolterodine, trospium chloride, solifenacin and darifenacin. Although this class of drugs has been shown to be more effective than placebo in specific meta-analyses [6] , it has been reported that < or = 80% of the patients discontinue the treatment within 6 months, mainly for the low drug compliance due to the high incidence of side effects [7] . Therefore, there is a strong need to identify drugs with novel mechanisms of action, which could provide equal or even better efficacy and overall greater acceptability than antimuscarinic drugs. At present, several other specific molecular targets identified within detrusor muscle and/or neural systems are under investigation for the development of more specific treatments of OAB. This article provides an up-to date review of drugs that are in investigational preclinical and early stage (Phase I and II) clinical trials for the treatment of OAB.

Characterization of a novel ATP-sensitive K+ channel opener, A-251179, on urinary bladder relaxation and cystometric parameters

BACKGROUND AND PURPOSE

ATP-sensitive K(+) channels (K(ATP)) play a pivotal role in contractility of urinary bladder smooth muscle. This study reports the characterization of 4-methyl-N-(2,2,2-trichloro-1-(3-pyridin-3-ylthioureido)ethyl)benzamide (A-251179) as a K(ATP) channel opener.

EXPERIMENTAL APPROACH

Glyburide-sensitive membrane potential, patch clamp and tension assays were employed to study the effect of A-251179 in vitro. The in vivo efficacy of A-251179 was characterized by suppression of spontaneous contractions in obstructed rat bladder and by measuring urodynamic function of urethane-anesthetized rat models.

KEY RESULTS

A-251179 was about 4-fold more selective in activating SUR2B-Kir6.2 derived K(ATP) channels compared to those derived from SUR2A-Kir6.2. In pig bladder smooth muscle strips, A-251179 suppressed spontaneous contractions, about 27- and 71-fold more potently compared to suppression of contractions evoked by low-frequency electrical stimulation and carbachol, respectively. In vivo, A-251179 suppressed spontaneous non-voiding bladder contractions from partial outlet-obstructed rats. Interestingly, in the neurogenic model where isovolumetric contractions were measured by continuous transvesical cystometry, A-251179 at a dose of 0.3 micromol kg(-1), but not higher, was found to increase bladder capacity without affecting either the voiding efficiency or changes in mean arterial blood pressure.

CONCLUSIONS AND IMPLICATIONS

The thioureabenzamide analog, A-251179 is a potent novel K(ATP) channel opener with selectivity for SUR2B/Kir6.2 containing K(ATP) channels relative to pinacidil. The pharmacological profile of A-251179 is to increase bladder capacity and to prolong the time between voids without affecting voiding efficiency and represents an interesting characteristic to be explored for further investigations of K(ATP) channel openers for the treatment of overactive bladder.

Synthesis and analgesic activity evaluation of some agmatine derivatives

A series of N,N'-disubstituted-2-nitroethene-1,1-diamine and N,N'-disubstituted- N''-cyanoguanidine derivatives were prepared and evaluated for in vivo analgesic activity. The blood brain barrier (BBB) VolSurf model was used to predict the BBB permeation profiles of our synthesized compounds. Some compounds show both remarkable analgesic activity and good BBB permeation profiles, and these compounds might be developed for treatment of opioid tolerance and dependence.

Potassium channel subtypes as molecular targets for overactive bladder and other urological disorders

Potassium channels have re-emerged as attractive targets for overactive bladder and other urological diseases in recent years, in part due to an enhanced understanding of their molecular heterogeneity, tissue distribution, functional roles and regulation in physiological and pathological states. Cloning and heterologous expression analysis, coupled with the advancement of improved high-throughput screening techniques, have enabled expeditious identification of selective small-molecule openers and blockers for ATP-sensitive K+ channels, Ca2+-activated K+ channels and voltage-dependent K+ channel-KQT-like subfamily (KCNQ) members, and has paved the way in the assessment of efficacy and adverse effects in preclinical models. This review focuses on the rationale for molecular targeting of K+ channels, the current status of target validation, including preclinical proof-of-concept studies, and provides perspectives on the limitations and hurdles to be overcome in realising the potential of these targets for diverse urological indications such as overactive bladder, erectile dysfunction and prostate diseases.