Exploration of the nicotinamide-binding site of the tankyrases, identifying 3-arylisoquinolin-1-ones as potent and selective inhibitors in vitro.

Tankyrases-1 and -2 (TNKS-1 and TNKS-2) have three cellular roles which make them important targets in cancer. Using NAD(+) as a substrate, they poly(ADP-ribosyl)ate TRF1 (regulating lengths of telomeres), NuMA (facilitating mitosis) and axin (in wnt/ß-catenin signalling). Using molecular modelling and the structure of the weak inhibitor 5-aminoiso quinolin-1-one, 3-aryl-5-substituted-isoquinolin-1-ones were designed as inhibitors to explore the structure-activity relationships (SARs) for binding and to define the shape of a hydrophobic cavity in the active site. 5-Amino-3-arylisoquinolinones were synthesised by Suzuki-Miyaura coupling of arylboronic acids to 3-bromo-1-methoxy-5-nitro-isoquinoline, reduction and O-demethylation. 3-Aryl-5-methylisoquinolin-1-ones, 3-aryl-5-fluoroisoquinolin-1-ones and 3-aryl-5-methoxyisoquinolin-1-ones were accessed by deprotonation of 3-substituted-N,N,2-trimethylbenzamides and quench with an appropriate benzonitrile. SAR around the isoquinolinone core showed that aryl was required at the 3-position, optimally with a para-substituent. Small meta-substituents were tolerated but groups in the ortho-positions reduced or abolished activity. This was not due to lack of coplanarity of the rings, as shown by the potency of 4,5-dimethyl-3-phenylisoquinolin-1-one. Methyl and methoxy were optimal at the 5-position. SAR was rationalised by modelling and by crystal structures of examples with TNKS-2. The 3-aryl unit was located in a large hydrophobic cavity and the para-substituents projected into a tunnel leading to the exterior. Potency against TNKS-1 paralleled potency against TNKS-2. Most inhibitors were highly selective for TNKSs over PARP-1 and PARP-2. A range of highly potent and selective inhibitors is now available for cellular studies.

Structure-based design, synthesis and evaluation in vitro of arylnaphthyridinones, arylpyridopyrimidinones and their tetrahydro derivatives as inhibitors of the tankyrases.

The tankyrases are members of the PARP superfamily; they poly(ADP-ribosyl)ate their target proteins using NAD(+) as a source of electrophilic ADP-ribosyl units. The three principal protein substrates of the tankyrases (TRF1, NuMA and axin) are involved in replication of cancer cells; thus inhibitors of the tankyrases may have anticancer activity. Using structure-based drug design and by analogy with known 3-arylisoquinolin-1-one and 2-arylquinazolin-4-one inhibitors, series of arylnaphthyridinones, arylpyridinopyrimidinones and their tetrahydro-derivatives were synthesised and evaluated in vitro. 7-Aryl-1,6-naphthyridin-5-ones, 3-aryl-2,6-naphthyridin-1-ones and 3-aryl-2,7-naphthyridin-1-ones were prepared by acid-catalysed cyclisation of the corresponding arylethynylpyridinenitriles or reaction of bromopyridinecarboxylic acids with ß-diketones, followed by treatment with NH3. The 7-aryl-1,6-naphthyridin-5-ones were methylated at 1-N and reduced to 7-aryl-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-ones. Cu-catalysed reaction of benzamidines with bromopyridinecarboxylic acids furnished 2-arylpyrido[2,3-d]pyrimidin-4-ones. Condensation of benzamidines with methyl 1-benzyl-4-oxopiperidine-3-carboxylate and deprotection gave 2-aryl-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-4-ones, aza analogues of the known inhibitor XAV939. Introduction of the ring-N in the arylnaphthyridinones and the arylpyridopyrimidinones caused >1000-fold loss in activity, compared with their carbocyclic isoquinolinone and quinazolinone analogues. However, the 7-aryl-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-ones showed excellent inhibition of the tankyrases, with some examples having IC50=2nM. One compound (7-(4-bromophenyl)-1-methyl-1,2,3,4-tetrahydro-1,6-naphthyridin-5-one) showed 70-fold selectivity for inhibition of tankyrase-2 versus tankyrase-1. The mode of binding was explored through crystal structures of inhibitors in complex with tankyrase-2.

Initial development of a cytotoxic amino-seco-CBI warhead for delivery by prodrug systems.

Cyclopropabenzaindoles (CBIs) are exquisitely potent cytotoxins which bind and alkylate in the minor groove of DNA. They are not selective for cancer cells, so prodrugs are required. CBIs can be formed at physiological pH by Winstein cyclisation of 1-chloromethyl-3-substituted-5-hydroxy-2,3-dihydrobenzo[e]indoles (5-OH-seco-CBIs). Corresponding 5-NH2-seco-CBIs should also undergo Winstein cyclisation similarly. A key triply orthogonally protected intermediate on the route to 5-NH2-seco-CBIs has been synthesised, via selective monotrifluoroacetylation of naphthalene-1,3-diamine, Boc protection, electrophilic iodination, selective allylation at the trifluoroacetamide and 5-exo radical ring-closure with TEMPO. This intermediate has potential for introduction of peptide prodrug masking units (deactivating the Winstein cyclisation and cytotoxicity), addition of diverse indole-amide side-chains (enhancing non-covalent binding prior to alkylation) and use of different leaving groups (replacing the usual chlorine, allowing tuning of the rate of Winstein cyclisation). This key intermediate was elaborated into a simple model 5-NH2-seco-CBI with a dimethylaminoethoxyindole side-chain. Conversion to a bio-reactive entity and the bioactivity of this system were confirmed through DNA-melting studies (ΔTm=13°C) and cytotoxicity against LNCaP human prostate cancer cells (IC50=18nM).

The enone motif of (+)-grandifloracin is not essential for 'anti-austerity' antiproliferative activity.

We report the synthesis and biological evaluation of three analogues of the natural product (+)-grandifloracin (+)-1. All three analogues exhibit enhanced antiproliferative activity against PANC-1 and HT-29 cells compared to the natural product. The retention of activity in an analogue lacking the enone functional group, 9, implies this structural element is not an essential part of the (+)-grandifloracin pharmacophore.

α-Methylacyl-CoA racemase (AMACR): metabolic enzyme, drug metabolizer and cancer marker P504S.

α-Methylacyl-CoA racemase (AMACR; P504S) catalyzes a key chiral inversion step in the metabolism of branched-chain fatty acids, ibuprofen and related drugs. Protein levels are increased in all prostate and some other cancer cells and it is used as a marker (P504S). The enzyme requires no cofactors and catalyzes its reaction by a stepwise 1,1-proton transfer via an enolate intermediate. The biological role of AMACR in cancer is complex, linking lipid metabolism with nuclear receptor (e.g. FXR and PPAR) activity and expression of enzymes such as cyclooxygenase-2 (COX-2). The roles of the various splice variants and the effects of single-nucleotide polymorphisms (SNPs) in cancers are discussed. A number of rationally designed AMACR inhibitors have been reported in the literature as potential cancer treatments. The opportunities and challenges for development of acyl-CoA esters as inhibitors are discussed from a medicinal chemical viewpoint. Other challenges for drug development include the problems in assaying enzymatic activity and the prediction of structure-activity relationships (SAR). Inhibitors of AMACR have potential to provide a novel treatment for castrate-resistant prostate cancers but this potential can only be realized once the biology is well understood. Recent work on the role of AMACR in parasitic diseases is also reviewed.

Design and Discovery of 2-Arylquinazolin-4-ones as Potent and Selective Inhibitors of Tankyrases.

Tankyrases (TNKSs) are poly(ADP-ribose)polymerases (PARPs) that are overexpressed in several clinical cancers. They regulate elongation of telomeres, regulate the Wnt system, and are essential for the function of the mitotic spindle. A set of 2-arylquinazolin-4-ones has been designed and identified as potent and selective TNKS inhibitors, some being more potent and selective than the lead inhibitor XAV939, with IC50 = 3 nM vs. TNKS-2. Methyl was preferred at the 8-position and modest bulk at the 4-position of the 2-phenyl group; electronic effects and H-bonding were irrelevant, but charge in the 4'-substituent must be avoided. Molecular modeling facilitated initial design of the compounds and rationalization of the SAR of binding into the nicotinamide-binding site of the target enzymes. These compounds have potential for further development into anticancer drugs.

Chiral inversion of 2-arylpropionyl-CoA esters by human α-methylacyl-CoA racemase 1A (P504S)--a potential mechanism for the anti-cancer effects of ibuprofen.

Metabolic chiral inversion of 2-arylpropanoic acids (2-APAs;'profens'), such as ibuprofen, is important for pharmacological activity. Several 2-APA-CoA esters were good racemisation substrates for human AMACR 1A, suggesting a common chiral inversion pathway for all 2-APAs and an additional mechanism for their anti-cancer properties.

5-Benzamidoisoquinolin-1-ones and 5-(ω-carboxyalkyl)isoquinolin-1-ones as isoform-selective inhibitors of poly(ADP-ribose) polymerase 2 (PARP-2).

PARP-2 is a member of the poly(ADP-ribose) polymerase family, with some activities similar to those of PARP-1 but with other distinct roles. Two series of isoquinolin-1-ones were designed, synthesized, and evaluated as selective inhibitors of PARP-2, using the structures of the catalytic sites of the isoforms. A new efficient synthesis of 5-aminoisoquinolin-1-one was developed, and acylation with acyl chlorides gave 5-acylaminoisoquinolin-1-ones. By examination of isoquinolin-1-ones with carboxylates tethered to the 5-position, Heck coupling of 5-iodoisoquinolin-1-one furnished the 5-CH═CHCO(2)H compound for reduction to the 5-propanoic acid. Alkylation of 5-aminoisoquinolin-1-one under mildly basic conditions, followed by hydrolysis, gave 5-(carboxymethylamino)isoquinolin-1-one, whereas it was alkylated at 2-N with methyl propenoate and strong base. Compounds were assayed in vitro for inhibition of PARP-1 and PARP-2, using FlashPlate and solution-phase assays, respectively. The 5-benzamidoisoquinolin-1-ones were more selective for inhibition of PARP-2, whereas the 5-(ω-carboxyalkyl)isoquinolin-1-ones were less so. 5-Benzamidoisoquinolin-1-one is the most PARP-2-selective compound (IC(50(PARP-1))/IC(50(PARP-2)) = 9.3) to date, in a comparative study.

Inhibition of neutrophil infiltration into A549 lung tumors in vitro and in vivo using a CXCR2-specific antagonist is associated with reduced tumor growth.

Neutrophils are important innate immune cells that are involved in microbial clearance at sites of infection and in wound healing. The microenvironment of tumors often resembles that of chronic inflammation and increased numbers of neutrophils have been observed in several tumors and, in some cases, these positively correlate with poor prognosis. Neutrophil recruitment into tumors appears to be dependent on chemokines that bind to CXCR1 and CXCR2 expressed by neutrophils. In our study, we used lung adenocarcinoma A549 multicellular tumor spheroids and A549 tumor xenografts along with a CXCR2-specific small molecule inhibitor (AZ10397767) to investigate the recruitment and function of human neutrophils in tumors. We found that A549 spheroids constitutively secrete high levels of CXCL chemokines and that neutrophil recruitment into A549 tumors in vitro and in vivo is largely dependent on CXCR2 activation. AZ10397767 significantly reduced the numbers of infiltrating neutrophils into both in vitro and in vivo tumor models, which was associated with slower growing tumors. Neutrophil infiltration into A549 tumor spheroids increased their size compared to noninfiltrated spheroids and neutrophil-derived factors increased the proliferation of A549 tumor cells and induced endothelial cell tubule formation in vitro. In contrast, we saw no reduction in microvascular density in AZ10397767-treated A549 tumors or in tumors grown in CXCR2(-/-) mice, suggesting that angiogenesis in these tumors is CXCR2-independent. Our data show that neutrophils can contribute to lung tumor growth and that CXCR2 antagonists may be a useful therapeutic agent in the treatment of lung carcinomas.

Challenges associated with the synthesis of unusual o-carboxamido stilbenes by the Heck protocol: Intriguing substituent effects, their toxicological and chemopreventive implications.

The syntheses of fourteen unusual o-carboxamido stilbenes by the Heck protocol revealed surprising complexity related to intriguing substituent effects with mechanistic implications. The unexpected cytotoxic and chemopreventive properties also seem to be substituent dependent. For example, although stilbene 15d (with a 4-methoxy substituent) showed cytotoxicity on HT29 colon cancer cells with an IC(50) of 4.9 µM, the 3,4-dimethoxy derivative (15c) is inactive. It is interesting to observe that the 3,5-dimethoxy derivative (15e) showed remarkable chemopreventive activity in WRL-68 fetal hepatocytes, surpassing the gold standard, resveratrol. The resveratrol concentration needed to be 5 times higher than that of 15e to produce comparable elevation of NQO1.

A polyphosphate kinase 1 (ppk1) mutant of Pseudomonas aeruginosa exhibits multiple ultrastructural and functional defects.

Pseudomonas aeruginosa, of medical, environmental, and industrial importance, depends on inorganic polyphosphate (poly P) for a wide range of functions, especially survival. Mutants of PAO1 lacking poly P kinase 1, PPK1, the enzyme responsible for most poly P synthesis in Escherichia coli and other bacteria, are defective in motility, quorum sensing, biofilm formation, and virulence. We describe here multiple defects in the ppk1 mutant PAOM5, including a striking compaction of the nucleoid, distortion of the cell envelope, lack of planktonic motility and exopolymer production, and susceptibility to the beta-lactam antibiotic carbenicillin as well as desiccation. We propose that P. aeruginosa with reduced poly P levels undergoes ultrastructural changes that contribute to profound deficiencies in cellular functions.

Amoebae promote persistence of epidemic strains of MRSA.

The control of healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) infection is of concern worldwide. Given the evidence that several pathogenic species replicate within amoebae and emerge more virulent and more resistant and the abundance of amoebae in healthcare settings, we investigated interactions of Acanthamoeba polyphaga with epidemic MRSA isolates. MRSA proliferated in the presence of amoebae, attributable partly to intracellular replication. Following 24 h of co-culture, confocal microscopy revealed that c. 50% amoebae had viable MRSA within phago-lysosomes and 2% of amoebae were heavily infected with viable cocci throughout the cytoplasm. Infection control strategies should recognize the contribution of protozoa.