The use of porcupine inhibitors to target Wnt-driven cancers.

Over the past decade, academic groups and pharmaceutical companies have uncovered several components and targets for intervention in the Wnt pathway. One approach is to block Wnt signalling through the use of orally bioavailable small molecules that prevent Wnt ligand secretion. In recent years, the membrane bound O-acyl transferase (MBOAT) porcupine (PORCN) has emerged as a molecular target of interest in the search for clinical options to treat Wnt-driven cancers. This review shall provide an overview of the reported small molecule inhibitors for PORCN and discuss the progress made in identifying human disease models that are responsive to PORCN inhibitors.

Pharmacophore Model for Wnt/Porcupine Inhibitors and Its Use in Drug Design.

Porcupine is a component of the Wnt pathway which regulates cell proliferation, migration, stem cell self-renewal, and differentiation. The Wnt pathway has been shown to be dysregulated in a variety of cancers. Porcupine is a membrane bound O-acyltransferase that palmitoylates Wnt. Inhibiting porcupine blocks the secretion of Wnt and effectively inhibits the Wnt pathway. Using high throughput screening, we have identified a number of novel porcupine inhibitors with diverse scaffolds. The pharmacophore requirements for our porcupine inhibitors were elucidated, and a pharmacophore model is proposed. Our compounds as well as all currently published porcupine inhibitors may be fitted to this model in low energy conformations with good superimposition of the pharmacophore elements. The model also explains the stereochemical requirements of our chiral porcupine inhibitors. The pharmacophore model was successfully used for designing 3 new series of porcupine inhibitors having a tricyclic xantine, a phtalimide, or a piperidine-maleimide scaffold.

[µ-1,1'-Bis(diphenyl-phosphino)ferrocene]bis-{[(Z)-O-ethyl N-phenyl-thio-carbamato-κS]gold(I)} dichloro-methane solvate.

The binuclear title compound, [Au(2)Fe(C(9)H(10)NOS)(2)(C(17)H(14)P)(2)]·CH(2)Cl(2), which has the Fe atom located on a crystallographic centre of inversion, crystallizes as a 1:1 dichloro-methane solvate, which is disordered about a centre of inversion. There is a small deviation from linearity defined by the SP donor set [S1-Au-P1 angle is 175.35 (5) °] which is due to an intra-molecular Au⋯O contact [3.080 (5) Å]. The primary inter-molecular contacts between binuclear mol-ecules are of the type C-H⋯π, and are arranged so as to form columns in the a-axis direction in which the disordered solvent mol-ecules reside.

[µ-1,2-Bis(diphenyl-phosphino)methane-κP:P']bis-{[(Z)-O-ethyl N-(4-nitro-phen-yl)thio-carbamato-κS]gold(I)}.

Each gold atom in the binuclear title compound, [Au(2)(C(9)H(9)N(2)O(3)S)(2)(C(25)H(22)P(2))], is coordinated within an S,P-donor set that defines a slightly distorted linear geometry [S-Au-P angles = 172.77 (6) and 173.84 (6)°], with the distortion due in part to a close intra-molecular Au⋯O contact [2.968 (11) and 2.963 (4) Å]. The mol-ecule adopts a U-shaped conformation allowing for the formation of an aurophilic Au⋯Au inter-action [3.2320 (5) Å]. Mol-ecules are consolidated in the crystal structure by C-H⋯π inter-actions. Disorder was noted for one of the eth-oxy groups with two orientations being resolved in a 0.679 (16):0.321 (16) ratio.

[(Z)-Isopropoxy(4-nitrophenylimino)methanethiolato-κS](tricyclo-hexyl-phosphine-κP)gold(I).

In the title compound, [Au(C(10)H(11)N(2)O(3)S)(C(18)H(33)P)], the gold(I) atom is linearly coordinated within a SP donor set. The distortion from linearity [S-Au-P = 177.54 (3)°] can be traced to an intra-molecular Au⋯O contact of 3.009 (3) Å. In the crystal, layers of mol-ecules are stabilized by a combination of C-H⋯O and C-H⋯π inter-actions.

[(Z)-O-Ethyl N-(4-nitro-phen-yl)thio-carbamato-κS](triethyl-phosphine-κP)gold(I).

In the title compound, [Au(C(9)H(9)N(2)O(3)S)(C(6)H(15)P)], two virtually identical mol-ecules comprise the asymmetric unit. These are connected by Au⋯Au [3.6796 (4) Å] and Au⋯S [3.6325 (18) and 3.5471 (18) Å] contacts, forming a dimeric aggregate. The presence of intra-molecular Au⋯O contacts [2.993 (5) and 2.957 (5) Å] is responsible for the slight deviations from the ideal linear coordination environments about the Au(I) ions. The conformation about the central C=N double bond is Z. Supra-molecular chains sustained by π-π [3.573 (4) Å] and C-H⋯π inter-actions are evident in the crystal structure. These are connected into layers via weak inter-molecular C-H⋯O inter-actions involving the nitro-group O atoms.

µ-1,1'-Bis(diphenyl-phosphino)ferrocene-κP:P'-bis-{[(Z)-O-isopropyl N-(4-nitro-phen-yl)thio-carbamato-κS]gold(I)} chloro-form disolvate.

The dinuclear title mol-ecule, [Au(2)Fe(C(10)H(11)N(2)O(3)S)(2)(C(17)H(14)P)(2)]·2CHCl(3), has crystallographic twofold symmetry with the Fe atom (bonded to two η(5)-cyclo-penta-dienyl rings) situated on the rotation axis. The Au atom exists within a linear geometry defined by an S,P-donor set with a deviation from linearity [S-Au-P = 176.86 (6)°] due to the close approach of the thio-carbamate O atom [Au⋯O = 3.108 (5) Å]. The mol-ecule has a U-shaped geometry which facilitates the formation of an intra-molecular Au⋯Au inter-action [3.0231 (5) Å]. In the crystal, the presence of C-H⋯O(nitro) contacts leads to the formation of layers with substantial voids; these are occupied by the solvent mol-ecules of crystallization, which are held in place by C-H⋯S contacts.

[(Z)-O-Ethyl N-(4-nitro-phen-yl)thio-carbamato-κS](triphenyl-phosphine-κP)gold(I) dichloro-methane solvate.

An S,P-donor set in the title solvate, [Au(C(9)H(9)N(2)O(3)S)(C(18)H(15)P)]·CH(2)Cl(2), defines a linear geometry for the Au(I) atom [S-Au-P = 177.75 (7)°], with the minor distortion ascribed to the influence of an intra-molecular Au⋯O contact [3.019 (6) Å]. In the crystal, the packing is stabilized by a network of C-H⋯S, C-H⋯N and C-H⋯O contacts.

Discovery of dual GyrB/ParE inhibitors active against Gram-negative bacteria.

Even though many GyrB and ParE inhibitors have been reported in the literature, few possess activity against Gram-negative bacteria. This is primarily due to limited permeability across Gram-negative bacterial membrane as well as bacterial efflux mechanisms. Permeability of compounds across Gram-negative bacterial membranes depends on many factors including physicochemical properties of the inhibitors. Herein, we show the optimization of pyridylureas leading to compounds with potent activity against Gram-negative bacterial species such as P.aeruginosa, E.coli and A.baumannii.

Fragment-Based Drug Discovery of Potent Protein Kinase C Iota Inhibitors.

Protein kinase C iota (PKC-ι) is an atypical kinase implicated in the promotion of different cancer types. A biochemical screen of a fragment library has identified several hits from which an azaindole-based scaffold was chosen for optimization. Driven by a structure-activity relationship and supported by molecular modeling, a weakly bound fragment was systematically grown into a potent and selective inhibitor against PKC-ι.

Scaffold Hopping and Optimization of Maleimide Based Porcupine Inhibitors.

Porcupine is an O-acyltransferase that regulates Wnt secretion. Inhibiting porcupine may block the Wnt pathway which is often dysregulated in various cancers. Consequently porcupine inhibitors are thought to be promising oncology therapeutics. A high throughput screen against porcupine revealed several potent hits that were confirmed to be Wnt pathway inhibitors in secondary assays. We developed a pharmacophore model and used the putative bioactive conformation of a xanthine inhibitor for scaffold hopping. The resulting maleimide scaffold was optimized to subnanomolar potency while retaining good physical druglike properties. A preclinical development candidate was selected for which extensive in vitro and in vivo profiling is reported.

Discovery and Optimization of a Porcupine Inhibitor.

Wnt proteins regulate various cellular functions and serve distinct roles in normal development throughout life. Wnt signaling is dysregulated in various diseases including cancers. Porcupine (PORCN) is a membrane-bound O-acyltransferase that palmitoleates the Wnts and hence is essential for their secretion and function. The inhibition of PORCN could serve as a therapeutic approach for the treatment of a number of Wnt-dependent cancers. Herein, we describe the identification of a Wnt secretion inhibitor from cellular high throughput screening. Classical SAR based cellular optimization provided us with a PORCN inhibitor with nanomolar activity and excellent bioavailability that demonstrated efficacy in a Wnt-driven murine tumor model. Finally, we also discovered that enantiomeric PORCN inhibitors show very different activity in our reporter assay, suggesting that such compounds may be useful for mode of action studies on the PORCN O-acyltransferase.

Fragment-based ligand design of novel potent inhibitors of tankyrases.

Tankyrases constitute potential drug targets for cancer and myelin-degrading diseases. We have applied a structure- and biophysics-driven fragment-based ligand design strategy to discover a novel family of potent inhibitors for human tankyrases. Biophysical screening based on a thermal shift assay identified highly efficient fragments binding in the nicotinamide-binding site, a local hot spot for fragment binding. Evolution of the fragment hit 4-methyl-1,2-dihydroquinolin-2-one (2) along its 7-vector yields dramatic affinity improvements in the first cycle of expansion. A crystal structure of 7-(2-fluorophenyl)-4-methylquinolin-2(1H)-one (11) reveals that the nonplanar compound extends with its fluorine atom into a pocket, which coincides with a region of the active site where structural differences are seen between tankyrases and other poly(ADP-ribose) polymerase (PARP) family members. A further cycle of optimization yielded compounds with affinities and IC50 values in the low nanomolar range and with good solubility, PARP selectivity, and ligand efficiency.

Luminescent phosphine gold(I) thiolates: correlation between crystal structure and photoluminescent properties in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}2] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc).

X-ray crystallography shows the gold atoms in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph; 1-3, respectively) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}(2)] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc; 4-8, respectively) are linearly coordinated by phosphorus and thiolate-sulfur; weak intramolecular Au...O interactions are featured in all structures. The smaller ethyl substituents in 1 allow for supramolecular association via Au...S and Au...Au interactions that are not found in 2 and 3, which contain larger phosphorus-bound Cy and Ph groups, respectively. Intramolecular Au...Au interactions are found in the dppm, dppe, dppp, and Fc structures but not in the dppp analogue, for which an anti conformation was found. The structures have been correlated with the results from photophysical study conducted in the solid state. Thus, photoexcitation of 1-7 with lambda > 350 in the solid state and in solution produces green and blue luminescence, respectively. The spectra in each medium are remarkably similar to each other, and so the emission energy and excitation maxima observed for 1-7 appear to be independent of the nature of the ancillary phosphines, as well as the presence or absence of Au...Au interactions, either intermolecularly or intramolecularly.

Cytotoxicity profiles for a series of triorganophosphinegold(I) dithiocarbamates and triorganophosphinegold(I) xanthates.

A series of triorganophosphinegold(1) dithiocarbamate (R(3)PAuS(2)CNR'(2)) and xanthate (R(3)PAuS(2)COR') complexes have been prepared and characterised spectroscopically. Based on crystallographic evidence, the molecules feature linear gold(1) geometries defined by sulphur and phosphorus donors. The complexes, along with a series of known anti-cancer agents, have been screened against a panel of seven human cancer cell lines. Uniformly, the dithiocarbamate derivatives are more active than their xanthate counterparts, with the most active complex being Et(3)PAu(S(2)CNEt(2)), and are more active than cisplatin in all cell lines screened but, not as potent as taxol.