Progressive plasticity during colorectal cancer metastasis

Metastasis is the principal cause of cancer death, yet we lack an understanding of metastatic cell states, their relationship to primary tumor states, and the mechanisms by which they transition. In a cohort of biospecimen trios from same-patient normal colon, primary and metastatic colorectal cancer, we show that while primary tumors largely adopt LGR5 + intestinal stem-like states, metastases display progressive plasticity. Loss of intestinal cell states is accompanied by reprogramming into a highly conserved fetal progenitor state, followed by non-canonical differentiation into divergent squamous and neuroendocrine-like states, which is exacerbated by chemotherapy and associated with poor patient survival. Using matched patient-derived organoids, we demonstrate that metastatic cancer cells exhibit greater cell-autonomous multilineage differentiation potential in response to microenvironment cues than their intestinal lineage-restricted primary tumor counterparts. We identify PROX1 as a stabilizer of intestinal lineage in the fetal progenitor state, whose downregulation licenses non-canonical reprogramming.

History and perspectives of A2A adenosine receptor antagonists as potential therapeutic agents

Growing evidence emphasizes that the purine nucleoside adenosine plays an active role as a local regulator in different pathologies. Adenosine is a ubiquitous nucleoside involved in various physiological and pathological functions by stimulating A1 , A2A , A2B , and A3 adenosine receptors (ARs). At the present time, the role of A2A ARs is well known in physiological conditions and in a variety of pathologies, including inflammatory tissue damage and neurodegenerative disorders. In particular, the use of selective A2A antagonists has been reported to be potentially useful in the treatment of Parkinson's disease (PD). In this review, A2A AR signal transduction pathways, together with an analysis of the structure-activity relationships of A2A antagonists, and their corresponding pharmacological roles and therapeutic potential have been presented. The initial results from an emerging polypharmacological approach are also analyzed. This approach is based on the optimization of the affinity and/or functional activity of the examined compounds toward multiple targets, such as A1 /A2A ARs and monoamine oxidase-B (MAO-B), both closely implicated in the pathogenesis of PD.

Discovery of 7-oxopyrazolo[1,5-a]pyrimidine-6-carboxamides as potent and selective CB(2) cannabinoid receptor inverse agonists

We recently described the medicinal chemistry of a new series of heteroaryl-4-oxopyridine/7-oxopyrimidines as CB2 receptor partial agonists, showing that the functionality of these ligands is controlled by the nature of the heteroaryl function condensed with the pyridine ring. We describe herein the design and synthesis of the 7-oxopyrazolo[1,5-a]pyrimidine-6-carboxamides, structural isomers of our previously reported pyrazolo[3,4-b]pyridines. All of the new compounds showed high affinity and selectivity for the CB2 receptor in the nanomolar range. In 3,5-cyclic adenosine monophosphate (cAMP) assays, the novel series shows stimulatory effects on forskolin-induced cAMP production acting as inverse agonists.

Skin permeability and pharmacokinetics of diclofenac epolamine administered by dermal patch in Yorkshire-Landrace pigs

Purpose

This study compared the pharmacokinetic profile, and systemic and local absorption of diclofenac, following dermal patch application and oral administration in Yorkshire-Landrace pigs.

Patients and methods

Twelve anesthetized, female, Yorkshire-Landrace pigs were randomized to receive either the dermal patch (FLECTOR^® patch, 10 × 14 cm; Alpharma Pharmaceuticals, a subsidiary of Pfizer Inc, New York, NY) or 50 mg oral diclofenac (Voltaren^®; Novartis, East Hanover, NJ). Tissue (skin area of 2 × 2 cm and underlying muscles approximately 2–3 cm in depth) and blood (10 mL) samples were collected at timed intervals up to 11.5 hours after initial patch application or oral administration. The concentrations of diclofenac in plasma, skin, and muscle samples were analyzed using validated ultra performance liquid chromatography tandem mass spectrometric methods.

Results

Peak systemic exposure of diclofenac was very low by dermal application compared with oral administration (maximum concentration [C_max] values of 3.5 vs 9640 ng/mL, respectively). Absorption of diclofenac into underlying muscles beneath the dermal patch was sustained, and followed apparently zero-order kinetics, with the skin serving as a depot with elevated concentrations of diclofenac. Concentrations of diclofenac in muscles beneath the patch application site were similar to corresponding tissues after oral administration (C_max values of 879 and 1160 ng/mL, respectively). In contrast to the wide tissue distribution of diclofenac after oral administration, dermal patch application resulted in high concentrations of diclofenac only on the treated skin and immediate tissue underneath the patch. Low concentrations of diclofenac were observed in the skin and muscles collected from untreated areas contralateral to the site of dermal patch application.

Conclusion

Dermal patch application resulted in low systemic absorption and high tissue penetration of diclofenac compared with oral administration.

Water-soluble pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines as human A₃ adenosine receptor antagonists

A relevant problem of the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine nucleus, an attractive scaffold for the preparation of adenosine receptor antagonists, is the low water solubility. We originally functionalized the C(5) position with a salifiable 4-pyridylcarbamoyl moiety that conferred good water solubility at low pH (<4.0) but poor solubility at physiologic pH, indicative of the dissociation of the pyridinium species. Here we replaced the pyridin-4-yl moiety with a 1-(substituted)piperidin-4-yl ring to exploit the higher basicity of this nucleus and for the the possibility to generate stable, water-soluble salts. The hydrochloride salt of the 1-(cyclohexylmethyl)piperidin-4-yl derivative (10, K(i)(hA(3)) = 9.7 nM, IC(50)(hA(3)) = 30 nM, K(i)(hA(1)/hA(3)) = 351, K(i)(hA(2A)/hA(3)) > 515, IC(50)(hA(2B)) > 5 μM) showed a solubility of 8 mg/mL at physiological pH and gave a stable aqueous system suitable for intravenous infusion. Molecular modeling studies were helpful in rationalizing the available structure-activity relationships and the selectivity profile of the new ligands.

Novel 1,3-dipropyl-8-(3-benzimidazol-2-yl-methoxy-1-methylpyrazol-5-yl)xanthines as potent and selective A₂B adenosine receptor antagonists

Molecular modeling studies, including the comparative molecular field analysis (CoMFA) method, on 52 antagonists of the A(2B) adenosine receptor with known biological activity were performed to identify the three-dimensional features responsible for A(2B) adenosine receptor antagonist activity. On the basis of these and previous results on the potent antagonist effect of 8-pyrazolyl-xanthines at human A(2B)AR, a new series of compounds was synthesized and evaluated in binding studies against the human A(1), A(2A), A(3), and A(2B)ARs. A remarkable improvement in selectivity with respect to the previous series, maintaining the potency at human A(2B) receptor, was achieved, as exemplified by the 8-[3-(4-chloro-6-trifluoromethyl-1H-benzoimidazol-2-yl-methoxy)-1-methyl-1H-pyrazol-5-yl]-1,3-dipropyl-3,7-dihydro-purine-2,6-dione derivative 66: K(i) A(2B) = 9.4 nM, IC(50) hA(2B) = 26 nM hA(1)/hA(2B) = 269, hA(2A)/hA(2B) > 106, hA(3)/hA(2B) >106. This study also led to the identification of a series of pyrazole-xanthine compounds with a simplified structure, exemplified by 8-(3-hydroxy-1-methyl-1H-pyrazol-5-yl)-xanthine 80 displaying very high affinity at A(2B)AR with good selectivity over AR subtypes (K(i) = 4.0 nM, IC(50) hA(2B) = 20 nM hA(1)/hA(2B) = 183, hA(2A),hA(3)/hA(2B) > 250).

Structure-activity relationships of 2-amino-3-aroyl-4-[(4-arylpiperazin-1-yl)methyl]thiophenes. Part 2: Probing the influence of diverse substituents at the phenyl of the arylpiperazine moiety on allosteric enhancer activity at the A₁ adenosine receptor

In a preliminary article, we reported the potent allosteric enhancer activity at the A(1) adenosine receptor of a small series of 2-amino-3-(4-chlorobenzoyl)-4-[4-(aryl)piperazin-1-yl)methyl]thiophene derivatives bearing electron-withdrawing or electron-releasing groups at the para-position of the phenylpiperazine moiety. In the present study, we report the development of the compounds previously studied by modifying both the number and position of substituents on the phenylpiperazine moiety, aimed at establishing a structure-activity relationship identifying additional compounds with improved activity. The nature and the position of substituents on the phenyl ring tethered to the piperazine seemed to exert a fundamental influence on the allosteric enhancer activity, with the 3,4-difluoro 4i, 3-chloro-4-fluoro 4o, and 4-trifluoromethoxy 4ak derivatives being the most active compounds in binding (saturation and competition experiments) and functional cAMP studies. This study shows that it is also possible to obtain a good separation between allosteric enhancement and antagonistic activity at the A(1) adenosine receptor.

Pyrrolo- and pyrazolo-[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as adenosine receptor antagonists

The discovery and development of adenosine receptor antagonists have represented for years an attractive field of research from the perspective of identifying new drugs for the treatment of widespread disorders such as inflammation, asthma and Parkinson's disease. The present work can be considered as an extension of our structure-activity relationship studies on the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine (PTP) nucleus, extensively investigated by us as a useful template, in particular, for the identification of A(2A) and A(3) adenosine receptor antagonists. In order to explore the role of the nitrogen at the 7-position, we performed a new synthetic strategy for the preparation of pyrrolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives which can be considered as 7-deaza analogues of the parent PTPs. We also synthesised a novel series of pyrazolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as junction isomers of the reference compounds. In both cases we obtained some examples of potent antagonists (K(i) in the low nanomolar range) with variable selectivity profiles in relation to the nature of substituents introduced at the C(5)-, N(8)- and/or N(9)-positions. The pyrrolo-triazolo-pyrimidine derivative 9b appeared to be a potent A(3) adenosine receptor antagonist (K(i)=10 nM) with good selectivity over hA(1) (74-fold) and hA(2A) (20-fold) adenosine receptors combined with low activity at the hA(2B) subtype (IC(50)=906 nM). Moreover, some examples of high-affinity A(1)/A(2A) dual antagonists have been identified in both series. This work constitutes a new and important contribution for the comprehension of the interaction between PTPs and adenosine receptors.

New 2-heterocyclyl-imidazo[2,1-i]purin-5-one derivatives as potent and selective human A3 adenosine receptor antagonists

A series of 4-allyl/benzyl-7,8-dihydro-8-methyl/ethyl-2-[(substituted)isoxazol/pyrazol-3/5-yl]-1H-imidazo[2,1-i]purin-5(4H)-ones has been synthesized and evaluated in radioligand binding assays to determine their affinities at the human A(1), A(2A), and A(3) adenosine receptors. Efficacy at the hA(2B) AR and antagonism of selected ligands at the hA(3) AR were also assessed through cAMP experiments. All of the synthesized molecules exhibited high affinity at the hA(3) AR (K(i) values ranging from 1.46 to 44.8 nM), as well as remarkable selectivity versus A(1), A(2A), and A(2B) AR subtypes. Compound (R)-4-allyl-8-ethyl-7,8-dihydro-2-(3-methoxy-1-methyl-1H-pyrazol-5-yl)-1H-imidazo[2,1-i]purin-5(4H)-one (R-33) was found to be the most potent and selective ligand of the series (K(i) hA(3) = 1.46 nM, K(i) hA(2A)/K(i) hA(3) > 3425; IC(50) hA(2B)/K(i) hA(3) > 3425; K(i) hA(1)/K(i) hA(3) = 1729). Molecular modeling studies were helpful in rationalizing the available structure-activity relationships along with the selectivity profiles of the new series of ligands.

Allosteric enhancers for A1 adenosine receptor

Allosteric enhancers at the adenosine A(1) receptor have received attention as anti-arrhythmic cardiac agents, and, more recently, as anti-lipolytic agents. In addition, allosteric modulators at the adenosine A(1) receptor have therapeutic potential as analgesics and neuroprotective agents. In particular, the compounds with improved potency as enhancers and reduced antagonist properties are mentioned.

From tyrosine to glycine: synthesis and biological activity of potent antagonists of the purinergic P2X7 receptor

The characterization of the native and recombinant P2X7 receptor continues to be hindered by the lack of specific and subtype-selective antagonists with a "druglike" profile. However, a tyrosine derivative named KN-62 exhibits selective P2X7 receptor-blocking properties. As a molecular simplification of KN-62, the present study was designed to evaluate the functional antagonistic properties of a novel series of glycine derivatives characterized by the presence of different phenyl-substituted piperazine moieties. Antagonistic activity of these glycine derivatives was tested on HEK293 cells transfected with the human P2X7 receptor. The most potent P2X7 receptor antagonist identified in this study (compound 4g) contains an o-fluorine substituent on the phenylpiperazine moiety and had an IC50 of 12.1 nM. The biological responses investigated were ATP-dependent Ca2+ influx across the plasma membrane and ethidium bromide uptake.

Synthesis and biological evaluation of novel 1-deoxy-1-[6-[((hetero)arylcarbonyl)hydrazino]- 9H-purin-9-yl]-N-ethyl-beta-D-ribofuranuronamide derivatives as useful templates for the development of A2B adenosine receptor agonists

The lack of molecules endowed with selective and potent agonistic activity toward the hA2B adenosine receptors has limited the studies on this pharmacological target and consequently the evaluation of its therapeutic potential. We report the design and the synthesis of the first potent (EC50 in the nanomolar range) and selective hA2B adenosine receptor agonists consisting of 1-deoxy-1-[6-[((hetero)arylcarbonyl)hydrazino]-9H-purin-9-yl]-N-ethyl-beta-D-ribofuranuronamide derivatives. The concurrent effect of 6-substitution of the purine nucleus with a ((hetero)arylcarbonyl)hydrazino function and a 2-chloro substitution has been investigated in such NECA derivatives.

N(6)-[(hetero)aryl/(cyclo)alkyl-carbamoyl-methoxy-phenyl]-(2-chloro)-5'-N-ethylcarboxamido-adenosines: the first example of adenosine-related structures with potent agonist activity at the human A(2B) adenosine receptor

A new series of N(6)-[(hetero)aryl/(cyclo)alkyl-carbamoyl-methoxy-phenyl]-(2-chloro)-5'-N-ethylcarboxamido-adenosines (24-43) has been synthesised and tested in binding assays at hA(1), hA(2A) and hA(3) adenosine receptors, and in a functional assay at the hA(2B) subtype. The examined compounds displayed high potency in activating A(2B) receptors with good selectivity versus A(2A) subtypes. The introduction of an unsubstituted 4-[(phenylcarbamoyl)-methoxy]-phenyl chain at the N(6) position of 5'-N-ethylcarboxamido-adenosine led us to the recognition of compound 24 as a full agonist displaying the highest efficacy of the series (EC(50) hA(2B)=7.3 nM). These compounds represent the first report about adenosine-related structures capable of activating hA(2B) subtype in the low nanomolar range.

Microwave-assisted synthesis of thieno[2,3-c]pyridine derivatives as a new series of allosteric enhancers at the adenosine A(1) receptor

The microwave-assisted aromatization method has been used for the synthesis of a series of novel thieno[2,3-c]pyridines. This rapid method produces compounds in good yield within minutes in comparison with conventional heating method. The synthesized molecules have been evaluated as a potential new series of allosteric enhancers acting at the adenosine A(1) receptor. In a functional assay, one compound (3h) showed activity comparable with that of reference compound PD 81,723.

Synthesis and biological characterization of [3H] (2-amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-(4-chlorophenyl)-methanone, the first radiolabelled adenosine A1 allosteric enhancer

Among the adenosine A(1) allosteric enhancers reported so far, compound (2-amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-(4-chlorophenyl)-methanone 1 (named T-62) has shown biological properties similar to those of PD 81,723, the reference A(1) allosteric enhancer and it has been more fully pharmacologically investigated. The preparation of the radiolabelled form of compound 1 and its characterization by saturation binding experiments are reported. These studies allowed us to demonstrate for the first time the existence of a specific, allosteric site on the A(1) receptor.

Triglyceride modulation by acifran analogs: activity towards the niacin high and low affinity G protein-coupled receptors HM74A and HM74

Niacin is known to exert profound beneficial effects on cholesterol levels in humans, although its use is somewhat hampered by the gram quantities necessary to exert effects and the prevalence of compliance-limiting skin flushing side effects that occur. Recently, two G protein-coupled receptors (GPCRs) for niacin were identified and characterized as high (HM74A; GPR109A) and low (HM74; GPR109B) affinity receptors based on the binding affinities of niacin. These receptors also bind acifran (AY-25,712), which is known to modulate lipid levels like niacin, with similar affinities. Twelve analogs of acifran were chemically synthesized. One analogue demonstrated a dose-dependent decrease in serum triglycerides in rats within 3h of oral administration. Next, the acifran analogs were assessed for their activity towards the high and low affinity niacin receptors expressed in CHO-K1 cells. Constructs expressing HM74A or HM74 were stably transfected into CHO-K1 cells and shown to elicit phosphorylation of p42 and p44 mitogen-activated protein kinase (ERK1/ERK2) phosphorylation upon addition of niacin or acifran. The presence of functionally coupled GPCRs was further confirmed using Pertussis toxin, which completely inhibited the ability of either niacin or acifran to elicit phospho-ERK1/ERK2. The EC(50) of p-ERK1/ERK2 for niacin for the high and low affinity receptors was 47nM and indeterminate (i.e., >100microM), respectively, while the EC(50) for acifran was 160 and 316nM, respectively. Two chemical analogs of acifran demonstrated robust phosphorylation of ERK1/ERK2. Collectively, these data suggest that the synthesis of acifran analogs may be a suitable path for developing improved HM74A agonists.

New 2-arylpyrazolo[4,3-c]quinoline derivatives as potent and selective human A3 adenosine receptor antagonists

In this paper we report the synthesis and biological evaluation of a new class of 2-phenyl-2,5-dihydro-pyrazolo[4,3-c]quinolin-4-ones as A(3) adenosine receptor antagonists. We designed a new route based on the Kira-Vilsmeier reaction for the synthesis of this class of compounds. Some of the synthesized compounds showed A(3) adenosine receptor affinity in the nanomolar range and good selectivity as evaluated in radioligand binding assays at human (h) A(1), A(2A), A(2B), and A(3) adenosine receptor subtypes. We introduced several substituents on the 2-phenyl ring. In particular substitution at the 4-position by methyl, methoxy, and chlorine gave optimal activity and selectivity 6c (K(i)hA(1), A(2A)>1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 9 nM), 6d (K(i)hA(1), A(2A)>1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 16 nM), 6b (K(i)hA(1), A(2A) >1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 19 nM). In conclusion, the 2-phenyl-2,5-dihydro-pyrazolo[4,3-c]quinolin-4-one derivatives described herein represent a new family of in vitro selective antagonists for the adenosine A(3) receptor.

New pyrrolo[2,1-f]purine-2,4-dione and imidazo[2,1-f]purine-2,4-dione derivatives as potent and selective human A3 adenosine receptor antagonists

Compounds presenting an additional fused ring on the xanthine nucleus have been reported to exhibit antagonistic activity with various levels of affinity and selectivity toward the four adenosine receptors subtypes A(1), A(2A), A(2B), and A(3). This paper reports synthesis and biological evaluation of new 1-benzyl-3-propyl-1H,6H-pyrrolo[2,1-f]purine-2,4-diones and 1-benzyl-3-propyl-1H,8H-imidazo[2,1-f]purine-2,4-diones, among which we identified potent and selective A(3) adenosine receptors antagonists. In particular, 1-benzyl-7-methyl-3-propyl-1H,8H-imidazo[2,1-f]purine-2,4-dione (11e) shows a K(i) (hA(3)) value from binding assay of 0.8 nM.

Synthesis, radiolabeling, and preliminary biological evaluation of [3H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine, a potent antagonist radioligand for the P2X7 receptor

The design, synthesis, and preliminary biological evaluation of the first potent radioligand antagonist for the P2X(7) receptor, named [(3)H]-1-[(S)-N,O-bis-(isoquinolinesulfonyl)-N-methyl-tyrosyl]-4-(o-tolyl)-piperazine (compound 13), are reported. This compound bound to human P2X(7) receptors expressed in HEK transfected cells with K(D) and B(max) value of 3.46+/-0.1 nM and 727+/-73 fmol/mg of protein, respectively. The high affinity and facile labeling makes it a promising radioligand for a further characterization of P2X(7) receptor subtype.

Synthesis of 2-amino-3-heteroaroylthiophenes and evaluation of their activity as potential allosteric enhancers at the human A1 receptor

2-Amino-3-benzoylthiophenes are allosteric enhancers of agonist binding to the adenosine A(1) receptor. New compounds bearing an heteroaroyl instead of the benzoyl moiety at the 3-position of the thiophene were synthesized. The phenyl ring was replaced with heterocycles that possess heteroatoms able to form hydrogen bonds (2-furanyl, 2-benzofuranyl, 2-pyridinyl in compounds 2-13) or with a thienyl moiety as isoster of the phenyl ring (2-thienyl, 3-thienyl and 5-halo-2-thienyl in compounds 14-29). The effect of several alkyl substituents at positions 4 and 5 of the thiophene ring to increase enhancer activity was determined. The ability of the new molecules to reduce the cAMP content in CHO cells expressing the human adenosine A(1) receptor was evaluated. Compounds 2-13 with hydrogen bond-forming heteroatoms did not show significant activity as allosteric enhancers. On the other hand, compounds 15-16 and 19-20 with an unsubstituted thienyl moiety as replacement for the phenyl ring were nearly as efficacious as PD 81,723, the prototypical A(1) allosteric enhancer. Alkyl substituents at positions 4 and 5 of the thiophene ring were tolerated while a substituted piperidine ring was not tolerated. We conclude that hydrogen bonds could not be formed in the domain of the receptor that accommodates the phenyl ring of 2-amino-3-benzoylthiophene derivatives, indicating that this domain is hydrophobic.

[3H]-MRE 2029-F20, a selective antagonist radioligand for the human A2B adenosine receptors

MRE 2029-F20 [N-benzo[1,3]dioxol-5-yl-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]-acetamide] is a selective antagonist ligand of A2B adenosine receptors. For use as a radioligand, 1,3-diallyl-xanthine, the precursor of [3H]-MRE 2029-F20, was synthesized, and tritiated on the allyl groups. [3H]-MRE 2029-F20 bound to human A2B receptors expressed in CHO cells showed a KD value of 1.65+/-0.10 nM and Bmax value of 36+/-4 fmol/mg protein. [3H]-MRE2029-F20 represents a useful tool for the pharmacological characterization of human A2B adenosine receptor subtype.

Design, synthesis, and biological evaluation of new 8-heterocyclic xanthine derivatives as highly potent and selective human A2B adenosine receptor antagonists

Here we report the synthesis of 8-heterocycle-substituted xanthines as potent and selective A(2B) adenosine receptor antagonists. The structure-activity relationships (SAR) of the xanthines synthesized in binding to recombinant human A(2B) adenosine receptors (ARs) in HEK-293 cells (HEK-A(2B)) and at other AR subtypes were explored. The synthesized compounds showed A(2B) adenosine receptor affinity in the nanomolar range and good levels of selectivity evaluated in radioligand binding assays at human (h) A(1), A(2A), A(2B), and A(3) ARs. We introduced several heterocycles, such as pyrazole, isoxazole, pyridine, and pyridazine, at the 8-position of the xanthine nucleus and we have also investigated different spacers (substituted acetamide, oxyacetamide, and urea moieties) on the heterocycle introduced. Various groups at the 3- and 4-positions of phenylacetamide moiety were studied. This study allowed us to identify the derivatives 2-(3,4-dimethoxyphenyl)-N-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yl]acetamide (29b, MRE2028F20) [K(i)(hA(2B)) = 38 nM, K(i)(hA(1),hA(2A),hA(3)) >1000 nM], N-benzo[1,3]dioxol-5-yl-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]acetamide (62b, MRE2029F20) [K(i)(hA(2B)) = 5.5 nM, K(i)(hA(1),hA(2A),hA(3)) > 1000 nM], and N-(3,4-dimethoxyphenyl)-2-[5-(2,6-dioxo-1,3-dipropyl-2,3,6,7-tetrahydro-1H-purin-8-yl)-1-methyl-1H-pyrazol-3-yloxy]acetamide (72b, MRE2030F20) [K(i)(hA(2B) = 12 nM, K(i)(hA(1),hA(2A), hA(3)) > 1000 nM], which showed high affinity at the A(2B) receptor subtype and very good selectivity vs the other ARs. Substitution of the acetamide with an urea moiety afforded bioisosteric xanthines with good affinity and selectivity comparable to the acetamide derivatives. Substitution at the para-position of a 4-benzyloxy group of the phenylacetamido chain enhanced affinity at the A(2B) receptor [compound 30b (K(i)(hA(2B)) = 13 nM) vs compound 21b (K(i)(hA(2B) = 56 nM)] but did not favor selectivity. The derivatives with higher affinity at human A(2B) AR proved to be antagonists, in the cyclic AMP assay, capable of inhibiting the stimulatory effect of NECA (100 nM) with IC(50) values in the nanomolar range, a trend similar to that observed in the binding assay (62b, IC(50) = 38 nM; 72b, IC(50) = 46 nM). In conclusion, the 8-pyrazolo-1,3-dipropyl-1H-purine-2,6-dione derivatives described herein represent a new family of selective antagonists for the adenosine A(2B) receptor.

New strategies for the synthesis of A3 adenosine receptor antagonists

New A(3) adenosine receptor antagonists were synthesized and tested at human adenosine receptor subtypes. An advanced synthetic strategy permitted us to obtain a large amount of the key intermediate 5 that was then submitted to alkylation procedures in order to obtain the derivatives 6-8. These compounds were then functionalised into ureas at the 5-position (compounds 9-11, 18 and 19) to evaluate their affinity and selectivity versus hA(3) adenosine receptor subtype; in particular, compounds 18 and 19 displayed a value of affinity of 4.9 and 1.3 nM, respectively. Starting from 5, the synthetic methodologies employed permitted us to perform a rapid and a convenient divergent synthesis. A further improvement allowed the regioselective preparation of the N(8)-substituted compound 7. This method could be used as an helpful general procedure for the design of novel A(3) adenosine receptor antagonists without the difficulty of separating the N(8)-substituted pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidines from the corresponding N(7)-isomers.

Synthesis and biological effects of novel 2-amino-3-naphthoylthiophenes as allosteric enhancers of the A1 adenosine receptor

The current study describes the synthesis and biological evaluation of a novel series of 2-amino-3-naphthoylthiophenes, with variable modifications at the 4- and 5-position of the thiophene as well as the naphthoyl ring. Allosteric enhancer activity was measured in several ways: (1) evaluating the effect on forskolin-stimulated cAMP accumulation in the presence of an A(1)-adenosine agonist (CPA) in Chinese hamster ovary (CHO) cells expressing the cloned human A(1)-adenosine receptor (hA(1)AR); (2) ability of these compounds to displace the binding of [(3)H]DPCPX, [(3)H]ZM 241385, and [(3)H]MRE 3008F20 to the ligand binding site of CHO cells expressing the hA(1), hA(2A), and hA(3) adenosine receptors, respectively; (3) effect on the binding of [(3)H]CCPA to membranes from CHO cells expressing hA(1)AR, to rat brain and human cortex membrane preparations containing native adenosine A(1) receptors; (4) kinetics of the dissociation of [(3)H]CCPA from CHO-hA1 membranes. The pharmacological assays compared the various activities to that of the reference compound PD 81,723 (compound 1). Several compounds appeared to be better than PD 81,723 to enhance the effect of CPA (and thus reduce cAMP content) in the CHO:hA(1) assay. The effect of these compounds at a concentration of 10 microM was slightly greater than that of the same concentration of the PD 81,723 and substantially greater than that of PD 81,723 when responses to 1 microM of each compound were compared. These include compounds 23, 25-29, 31-34, 38, 39, 43, and 58. Cycloalkylthiophenes tended to be more potent then their 4,5-dimethyl analogues, and in the series of cycloalkylthiophenes, tetrahydrobenzo[b]thiophene derivatives appeared to be more potent than the dihydrocyclopentadien[b]thiophene counterparts. Some of the most potent compounds were tested at a concentration of 10 microM for their affinity as competitors to the antagonist binding site of CHO cells expressing hA(1), hA(2A), and hA(3) adenosine receptors. None inhibited binding at the hA(2A)AR, but most of them inhibited binding to the hA(1)AR to varying extents (0-19%) as well as to the hA(3)AR to a substantial degree (0-57%). At a concentration of 10 microM, the compounds 31, 34, 37, 38, and 39 were more active than PD 81,723 to increase the binding of [(3)H]CCPA to CHO:hA(1), human brain and rat cortex membranes. Compound 37 was the most active compound increasing the binding to CHO:hA(1), human brain, and rat cortex membranes by 149, 43, and 27%, respectively (51, 15, and 22%, respectively, for PD 81,723). A good correlation was found between the increments [(3)H]CCPA binding to A(1) receptors expressed in different systems. Unlike the effect on agonist binding, the tested compounds did not increase the binding of the antagonist [(3)H]DPCPX on hCHO-A(1) membranes. Ligand dissociation studies revealed that two compounds (22 and 39) were more potent than 1 to slow the dissociation of [(3)H]CCPA from CHO:hA(1)AR membranes. No clear-cut structure-activity relationship can be observed based on data from the functional assay, but we have identified several compounds, in particular 37 and 39, which appeared to be more potent than 1 and that may be selected for further development.

Suicide inactivation of chymotrypsin by benzoxazinones

The benzoxazinones 2-ethoxy-4H-3,1- benzoxazin -4-one (1a) and 2-(trifluoromethyl)-4H-3,1- benzoxazin -4-one (1d) inactivate chymotrypsin. The inactivation is stoichiometric and proceeds with rate constants of 7 X 10(5) M-1 min-1 and greater than 4 X 10(6) M-1 min-1, respectively. The inactivated enzyme recovers catalytic activity slowly, k = 2.3 X 10(-3) min-1 and 3.7 X 10(-2) min-1 (pH 7.1). When the enzyme regains catalytic activity, 2-[N-(ethoxycarbonyl)amino]benzoic acid is released from enzyme inactivated with 1a and N-(trifluoroacetyl)anthranilic acid from enzyme inactivated with 1d. The mechanism of inactivation involves attack of the active site serine on the C-4 carbonyl of the inactivator which leads to ring opening and formation of an ortho-substituted benzoylchymotrypsin , which hydrolyzes slowly due to electron releasing ability of the substituents. The rate of hydrolysis of the benzoylchymotrypsin from 1a or 1d is in close agreement with those predicted from the Hammett parameters (sigma, rho) for hydrolysis of their para-substituted analogues [ Caplow , M., & Jencks , W. P. (1962) Biochemistry 1, 883-893]. The inactivation of chymotrypsin by 2-methyl-4H-3,1- benzoxazin -4-one (1b) is an equilibrium process (kinact = 1 X 10(4) M-1 min-1 and Keq = 2 X 10(6) M-1). Formation of a benzoylchymotrypsin is demonstrated by spectral changes and methanol trapping. The benzoylchymotrypsin can also decay by direct hydrolysis to N- acetylanthranilic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

The structure of human aldose reductase bound to the inhibitor IDD384

The crystallographic structure of the complex between human aldose reductase (AR2) and one of its inhibitors, IDD384, has been solved at 1.7 A resolution from crystals obtained at pH 5.0. This structure shows that the binding of the inhibitor's hydrophilic head to the catalytic residues Tyr48 and His110 differs from that found previously with porcine AR2. The difference is attributed to a change in the protonation state of the inhibitor (pK(a) = 4.52) when soaked with crystals of human (at pH 5.0) or pig lens AR2 (at pH 6.2). This work demonstrates how strongly the detailed binding of the inhibitor's polar head depends on its protonation state.

Di- and triester prodrugs of the varicella-zoster antiviral agent 6-methoxypurine arabinoside

6-Methoxypurine arabinoside (9-beta-D-arabinofuranosyl-6-methoxy-9H-purine, 1) has potent and selective activity against varicella-zoster virus in vitro. An unfavourable metabolic profile observed with oral dosing in the rat led to the preparation of a variety of 2',3',5'-triesters (2a-n) and several 2',3'-, 2',5'-, and 3',5'-diesters of this arabinoside (3a-n, 4a-f, and 5a-j, respectively). The compounds were evaluated as prodrugs by measuring the urinary levels of 1 in rat urine after oral dosing. With the exception of triacetate 2a, the triesters failed to significantly enhance bioavailability. Administration of compound 2a resulted in a 3-fold increase in systemic availability of 1, possibly because of its increased water solubility (1.6 times more soluble than 1) and only slightly increased relative log P value (1.93 vs 0.50 for 1). The longer chain aliphatic triesters and aromatic triesters had lower water solubilities and increased lipophilic partitioning. These factors might account for the lower systemic bioavailability of these compounds. In contrast, the diesters, especially the aliphatic diesters, showed significantly improved systemic availability. This might be a consequence of the higher aqueous solubilities and enhanced partition coefficients seen with these compounds. 2',3'-Diacetate 3a showed the best combination of high systemic availability and water solubility of all the prodrugs of 1.

Antiprotozoal activity of 3'-deoxyinosine. Inverse correlation to cleavage of the glycosidic bond

Two nucleosides related to the known antiprotozoal agent 1-(beta-D-ribofuranosyl)-1,5-dihydro-4H-pyrazolo-[3,4-d]pyrimidine-4-one (allopurinol riboside, 1) were prepared and evaluated against Leishmania donovani, Trypanosoma cruzi, and Trypanosoma gambiense. 3'-Deoxyinosine (2) exhibited potent antiprotozoal activity against the three protozoal pathogens with minimal toxicity for host cells. It was found to be especially effective against the Columbia strain of T. cruzi reported to be resistant to 1. The antiprotozoal activity of 2 appeared to be inversely related to the rate of cleavage of the glycosidic bond, as shown by metabolic profiles of 2 in the various pathogenic hemoflagellates and host cells. Combining the key structural elements of 1 and 2 led to the synthesis of 1-(3-deoxy-beta-D-erythro-pentofuranosyl)-1,5-dihydro-4H-pyrazolo[3,4-d] pyrimidin-4-one (3'-deoxy-allopurinol riboside, 3). which was found to be inactive as an antiprotozoal agent.

Nucleotide analogue inhibitors of purine nucleoside phosphorylase

The diphosphate of the antiherpetic agent acyclovir [9-[(2-hydroxyethoxy)methyl]guanine] has been shown to inhibit purine nucleoside phosphorylase with unique potency (Tuttle, J. V., and Krenitsky, T. A. (1984) J. Biol. Chem. 259, 4065-4069). A major factor contributing to the superior inhibition by this diphosphate over the corresponding mono- and triphosphates is revealed here. Homologues of acyclovir mono- and diphosphate that extend the ethoxy moiety by one to four methylene groups were synthesized. These homologues were evaluated for their ability to inhibit human purine nucleoside phosphorylase. Within the diphosphate series, the Ki values increased progressively with increasing chain length. With the monophosphates, the Ki values reached a minimum with the homologue containing a pentoxy moiety. A plot of chain length versus Ki values for both mono- and diphosphates showed that both series had similar optimal distances between the aminal carbon and the terminal oxygen anion. Monophosphates with optimal positioning were somewhat less potent than diphosphates with similar positioning. Nevertheless, it was clear that a major factor in determining potency of inhibition was the distance of the terminal phosphate from the guanine moiety.