Phenolic modification as an approach to improve the pharmacology of the 3-acyloxy-2-benzylpropyl homovanillic amides and thioureas, a promising class of vanilloid receptor agonists and analgesics

Crystal structure of 1-(1,3-benzo-thia-zol-2-yl)-3-(4-bromo-benzo-yl)thio-urea

The chemical reaction of 4-bromo-benzoyl-chloride and 2-amino-thia-zole in the presence of potassium thio-cyanate yielded a white solid formulated as C15H10BrN3OS2, which consists of 4-bromo-benzamido and 2-benzo-thia-zolyl moieties connected by a thio-urea group. The 4-bromo-benzamido and 2-benzo-thia-zolyl moieties are in a trans conformtion (sometimes also called s-trans due to the single bond) with respect to the N-C bond. The dihedral angle between the mean planes of the 4-bromo-phenyl and the 2-benzo-thia-zolyl units is 10.45 (11)°. The thio-urea moiety, -C-NH-C(=S) -NH- fragment forms a dihedral angle of 8.64 (12)° with the 4-bromo-phenyl ring and is almost coplanar with the 2-benzo-thia-zolyl moiety, with a dihedral angle of 1.94 (11)°. The mol-ecular structure is stabilized by intra-molecular N-H⋯O hydrogen bonds, resulting in the formation of an S(6) ring. In the crystal, pairs of adjacent mol-ecules inter-act via inter-molecular hydrogen bonds of type C-H⋯N, C-H⋯S and N-H⋯S, resulting in mol-ecular layers parallel to the ac plane.

Effects of in-vitro modulation of TRPV1 activity on immune response of mice bearing metastatic breast carcinoma: Enhanced inflammatory response may hinder therapeutic potentials of TRPV1 agonists

AIMS

Activation of transient receptor potential vanilloid 1 (TRPV1) ion channels inhibits inflammation, enhance cytotoxic immune response, and may have therapeutic potential in treatment of cancer characterized by increased systemic inflammation. We here determined how activation of TRPV1 alters immune response of tumor-bearing mice.

MAIN METHODS

Three different metastatic subset of 4 T1 breast carcinoma cells were used to induce tumors in Balb-c mice. Mix leukocyte cultures (MLCs) using spleens and draining lymph nodes were prepared and stimulated with various challenges. Effects TRPV1 agonists including capsaicin, antagonist (AMG9810) and Gambogic Amide (GA), a TrkA agonist that sensitizes TRPV1, on secreted levels of cytokines were determined.

KEY FINDINGS

MLCs of tumor-bearing mice secreted markedly higher levels of IL-6 and lower levels of IFN-γ compared to control mice. We observed differential effects of TRPV1 agonists in control and mice bearing different subset of metastatic cells. TRPV1 increased IFN-γ and IL-17 secretion in control mice while they markedly increased IL-6 secretion and suppressed IFN--γ secretion in tumor-bearing mice. Unexpectedly, AMG9810 acted as an inverse agonist and did not antagonize the effects of TRPV1 agonists.

SIGNIFICANCE

Our results demonstrate constitutive activity of TRPV1 in immune cells, suggesting cross activation. To prevent excessive chronic activation of TRPV1 in immune cells in the presence of metastatic breast carcinoma, lower doses of TRPV1 agonist should be considered. Unexpected findings further document that a drug can have multiple intrinsic activities depending on surrounding factors can act on the same receptor as an agonist, antagonist or inverse agonist.

Direct arene C-H fluorination with 18F- via organic photoredox catalysis

Positron emission tomography (PET) plays key roles in drug discovery and development, as well as medical imaging. However, there is a dearth of efficient and simple radiolabeling methods for aromatic C-H bonds, which limits advancements in PET radiotracer development. Here, we disclose a mild method for the fluorine-18 (18F)-fluorination of aromatic C-H bonds by an [18F]F- salt via organic photoredox catalysis under blue light illumination. This strategy was applied to the synthesis of a wide range of 18F-labeled arenes and heteroaromatics, including pharmaceutical compounds. These products can serve as diagnostic agents or provide key information about the in vivo fate of the labeled substrates, as showcased in preliminary tracer studies in mice.

Exploiting Aryl Mesylates and Tosylates in Catalytic Mono-α-arylation of Aryl- and Heteroarylketones

The first general palladium catalyst for the catalytic mono-α-arylation of aryl- and heteroarylketones with aryl mesylates and tosylates is described. The newly developed indolyl-derived phosphine ligand L7 has been identified to promote this reaction efficiently. The key to success is attributed to the enhanced steric congestion of the catalyst and effective oxidative addition of the C(Ar)-OMs bond. In the presence of Pd(OAc)2 (0.25-2.5 mol %) and L7, selective monoarylations are achieved with ample reaction scope and product yields up to 95%. Importantly, we demonstrated the applicability of this protocol with the modification of biological phenolic compounds, rendering it amenable for functionalization of phenolic (pro)drugs.

The SAR analysis of TRPV1 agonists with the α-methylated B-region

A series of TRPV1 agonists with amide, reverse amide, and thiourea groups in the B-region and their corresponding α-methylated analogues were investigated. Whereas the α-methylation of the amide B-region enhanced the binding affinities and potencies as agonists, that of the reverse amide and thiourea led to a reduction in receptor affinity. The analysis indicated that proper hydrogen bonding as well as steric effects in the B-region are critical for receptor binding.

Structure-activity relationships of vanilloid receptor agonists for arteriolar TRPV1

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid 1 (TRPV1) plays a role in the activation of sensory neurons by various painful stimuli and is a therapeutic target. However, functional TRPV1 that affect microvascular diameter are also expressed in peripheral arteries and we attempted to characterize this receptor.

EXPERIMENTAL APPROACH

Sensory TRPV1 activation was measured in rats by use of an eye wiping assay. Arteriolar TRPV1-mediated smooth muscle specific responses (arteriolar diameter, changes in intracellular Ca(2+)) were determined in isolated, pressurized skeletal muscle arterioles obtained from the rat and wild-type or TRPV1(-/-) mice and in canine isolated smooth muscle cells. The vascular pharmacology of the TRPV1 agonists (potency, efficacy, kinetics of action and receptor desensitization) was determined in rat isolated skeletal muscle arteries.

KEY RESULTS

Capsaicin evoked a constrictor response in isolated arteries similar to that mediated by noradrenaline, this was absent in arteries from TRPV1 knockout mice and competitively inhibited by TRPV1 antagonist AMG9810. Capsaicin increased intracellular Ca(2+) in the arteriolar wall and in isolated smooth muscle cells. The TRPV1 agonists evoked similar vascular constrictions (MSK-195 and JYL-79) or were without effect (resiniferatoxin and JYL-273), although all increased the number of responses (sensory activation) in the eye wiping assay. Maximal doses of all agonists induced complete desensitization (tachyphylaxis) of arteriolar TRPV1 (with the exception of capsaicin). Responses to the partial agonist JYL-1511 suggested 10% TRPV1 activation is sufficient to evoke vascular tachyphylaxis without sensory activation.

CONCLUSIONS AND IMPLICATIONS

Arteriolar TRPV1 have different pharmacological properties from those located on sensory neurons in the rat.

Drug-induced mild therapeutic hypothermia obtained by administration of a transient receptor potential vanilloid type 1 agonist

Background

The use of mechanical/physical devices for applying mild therapeutic hypothermia is the only proven neuroprotective treatment for survivors of out of hospital cardiac arrest. However, this type of therapy is cumbersome and associated with several side-effects. We investigated the feasibility of using a transient receptor potential vanilloid type 1 (TRPV1) agonist for obtaining drug-induced sustainable mild hypothermia.

Methods

First, we screened a heterogeneous group of TRPV1 agonists and secondly we tested the hypothermic properties of a selected candidate by dose-response studies. Finally we tested the hypothermic properties in a large animal. The screening was in conscious rats, the dose-response experiments in conscious rats and in cynomologus monkeys, and the finally we tested the hypothermic properties in conscious young cattle (calves with a body weight as an adult human). The investigated TRPV1 agonists were administered by continuous intravenous infusion.

Results

Screening: Dihydrocapsaicin (DHC), a component of chili pepper, displayed a desirable hypothermic profile with regards to the duration, depth and control in conscious rats. Dose-response experiments: In both rats and cynomologus monkeys DHC caused a dose-dependent and immediate decrease in body temperature. Thus in rats, infusion of DHC at doses of 0.125, 0.25, 0.50, and 0.75 mg/kg/h caused a maximal ΔT (°C) as compared to vehicle control of -0.9, -1.5, -2.0, and -4.2 within approximately 1 hour until the 6 hour infusion was stopped. Finally, in calves the intravenous infusion of DHC was able to maintain mild hypothermia with ΔT > -3°C for more than 12 hours.

Conclusions

Our data support the hypothesis that infusion of dihydrocapsaicin is a candidate for testing as a primary or adjunct method of inducing and maintaining therapeutic hypothermia.

Different vanilloid agonists cause different patterns of calcium response in CHO cells heterologously expressing rat TRPV1

The vanilloid receptor subtype 1 (TRPV1 or VR1) is expressed in nociceptive primary afferents of the C-fiber 'pain' pathway and has attracted considerable attention as a therapeutic target. Here, using rat TRPV1 heterologously expressed in Chinese hamster ovary cells, we show that different agonists show different patterns of modulation of the intracellular Ca2+ concentration, monitored in individual cells by fura-2 Ca2+ imaging. We identified 5 parameters (potency, maximal response, latency of response, variability of latency of response among individual cells, and desensitization) which behaved differently for different compounds. The potencies of the compounds examined ranged from EC50 values of 80 pM to 9 microM. Peak levels of induced [Ca2+]i were observed either higher (RTX) or lower (anandamide) than for capsaicin. Significant latencies of response were observed for some (e.g. RTX) but not other derivatives, with great variation among individual cells in this latency. Marked desensitization after stimulation was detected in some cases (e.g. anandamide, capsaicin); for others, no desensitization was observed. We conclude that structurally diverse vanilloid agonists induce marked diversity in the patterns of Ca2+ response. This diversity of response may provide opportunities for pharmacological exploitation.

Natural and synthetic cage compounds incorporating the 2,9,10-trioxatricyclo[4.3.1.03,8]decane type moiety

The 2,9,10-trioxatricyclo[4.3.1.0(3,8)]decane moiety is a tetracyclic cage-like orthoester incorporated in the structure of a series of daphnane derivatives such as resiniferatoxin (RTX), kirkinine, synaptolepis factors, huratoxin etc., exhibiting various biological activities. The approaches to the preparation of cage-like orthoesters starting from partially acylated or unmodified 1,2,4-trihydroxycyclohexane moieties built onto natural as well as synthetic compounds are discussed. Orthoester derivatives of RTX analogs, Ceverathrum alkaloids, myoinositol and pyranoses are included. Stereochemical requirements to the formation of the orthoester unit are discussed. The biological activity of different compounds containing the cage-like orthoester structural fragment is given. The literature is reviewed till 2004.

Structure-activity relationships of simplified resiniferatoxin analogues with potent VR1 agonism elucidates an active conformation of RTX for VR1 binding

We previously described a series of N-(3-acyloxy-2-benzylpropyl) homovanillate and N'-(4-hydroxy-3-methoxybenzyl) thiourea derivatives that were potent VR1 agonists with high-affinities and excellent analgesic profiles. The design of these simplified RTX analogues was based on our RTX-derived pharmacophore model which incorporates the 4-hydroxy-3-methoxyphenyl (A-region), C(20)-ester (B-region), orthophenyl (C1-region) and C(3)-keto (C2-region) groups of RTX. For the purpose of optimizing the spatial arrangement of the four principal pharmacophores on the lead agonists (1-4), we have modified the distances in the parent C-region, 3-acyloxy-2-benzylpropyl groups, by lengthening or shortening one carbon to vary the distances between the pharmacophores. We find that two of the amides, 4 and 19, possess EC(50) values <1 nM for induction of calcium influx in the VR1-CHO cells. As observed previously, the structure-activity relations for inhibition of RTX binding to VR1 and for induction of calcium uptake were distinct, presumably reflecting both intrinsic and methodological factors. In order to find the active conformation of VR1 ligands, the energy-minimized conformations of seven selected agonists were determined and the positions of their four pharmacophores were matched with those of five low energy RTX conformations. The rms values for the overlaps in the pharmacophores were calculated and correlated with the measured binding affinities (K(i)) and calcium influx (EC(50)) values. The binding affinities of the agonists correlated best with the RMS values derived from RTX conformation E (r(2)=0.92), predicting a model of the active conformation of RTX and related vanilloids for binding to VR1. Poorer correlation was obtained between any of the conformations and the EC(50) values for calcium influx.

High-affinity partial agonists of the vanilloid receptor

The vanilloid receptor VR1 is a polymodal nociceptor sensitive to capsaicin, protons, and heat. Because VR1 represents an attractive therapeutic target for conditions ranging from long-term pain to bladder hyperreflexia, we and other groups have sought to develop novel ligands with enhanced potencies and novel pharmacological properties. Here, we characterize two compounds, N-[2-(3,4-dimethylbenzyl)-3-(pivaloyloxy)propyl]-N'-[4-(methylsulfonylamino)benzyl]thiourea (JYL827) and N-(4-tert-butylbenzyl)-N'-[3-methoxy-4-(methylsulfonylamino)benzyl]thiourea (JYL1511), that function as partial agonists for rat VR1 heterologously expressed in Chinese hamster ovary cells. Both compounds showed substantially enhanced potency, inhibiting [3H] resiniferatoxin binding with Ki values of 29.3 +/- 7.6 and 50.4 +/- 16.5 nM, respectively, compared with 1810 +/- 270 nM for capsaicin. The compounds showed different extents of partial agonism, 6.8 +/- 0.7% and 17.4 +/- 0.6%, respectively, and the expected corresponding degrees of partial antagonism (93.9 +/- 0.9 and 84.1 +/- 3.2%, respectively). Their IC50 values for antagonism of 45Ca2+ uptake in response to capsaicin were 67.3 +/- 24.9 nM and 3.4 +/- 0.5 nM, respectively. Protons, temperature, and protein kinase C all function as coactivators/modulators of rVR1. All enhanced the extent of partial agonism of JYL827 and JYL1511. Thus, at pH 5.5, for example, the extents of partial agonism increased to 54.9 +/- 2.5% and to 90.7 +/- 1.7%, respectively, relative to the response elicited by 300 nM capsaicin. The extents of partial antagonism decreased correspondingly. Compounds such as JYL827 and JYL1511 now permit exploration of the potential utility of partial agonists of rVR1 in animal models. Our results emphasize, moreover, the strong dependence of such partial agonists on other modulators of rVR1 and predict that their biological behavior will depend strongly on biological context.

High affinity antagonists of the vanilloid receptor

The vanilloid receptor VR1 has attracted great interest as a sensory transducer for capsaicin, protons, and heat, and as a therapeutic target. Here we characterize two novel VR1 antagonists, KJM429 [N-(4-tert-butylbenzyl)-N'-[4-(methylsulfonylamino)benzyl]thiourea] and JYL1421 [N-(4-tert-butylbenzyl)-N'-[3-fluoro-4-(methylsulfonylamino)benzyl]thiourea], with enhanced activity compared with capsazepine on rat VR1 expressed in Chinese hamster ovary (CHO) cells. JYL1421, the more potent of the two novel antagonists, inhibited [(3)H]resiniferatoxin binding to rVR1 with an affinity of 53.5 +/- 6.5 nM and antagonized capsaicin-induced calcium uptake with an EC(50) of 9.2 +/- 1.6 nM, reflecting 25- and 60-fold greater potencies than capsazepine. Both JYL1421 and KJM429 antagonized RTX as well as capsaicin and their mechanism was competitive. The responses to JYL1421 and KJM429 differed for calcium uptake by rVR1 induced by heat or pH. JYL1421 antagonized the response to both pH 6.0 and 5.5, whereas KJM429 antagonized at pH 6.0 but was an agonist at lower pH (<5.5). For heat, JYL1421 fully antagonized and KJM429 partially antagonized. Capsazepine showed only weak antagonism for both pH and heat. Responses of rVR1 to different activators could thus be differentially affected by different ligands. In cultured dorsal root ganglion neurons, JYL1421 and KJM429 likewise behaved as antagonists for capsaicin, confirming that the antagonism is not limited to heterologous expression systems. Finally, JYL1421 and KJM429 had little or no effect on ATP-induced calcium uptake in CHO cells lacking rVR1, unlike capsazepine. We conclude that JYL1421 is a competitive antagonist of rVR1, blocking response to all three of the agonists (capsaicin, heat, and protons) with enhanced potency relative to capsazepine.