Development of potent cholinesterase inhibitors based on a marine pharmacophore.

The management of neurological disorders such as dementia associated with Alzheimer's or Parkinson's disease includes the use of cholinesterase inhibitors. These compounds can slow down the progression of these diseases and can also be used in the treatment of glaucoma and myasthenia gravis. The majority of the cholinesterase inhibitors used in the clinic are derived from natural products and our current paper describes the use of a small marine pharmacophore to develop potent and selective cholinesterase inhibitors. Fourteen small inhibitors were designed based on recent discoveries about the inhibitory potential of a range of related marine secondary metabolites. The compounds were evaluated, in kinetic enzymatic assays, for their ability to inhibit three different cholinesterase enzymes and it was shown that compounds with a high inhibitory activity towards electric eel and human recombinant acetylcholinesterase (IC50 between 20-70 µM) could be prepared. It was also shown that this compound class was particularly active against horse serum butyrylcholinesterase, with IC50 values between 0.8-16 µM, which is an order of magnitude more potent than the clinically used positive control neostigmine. The compounds were further tested for off-target toxicity against both human umbilical vein endothelial cells and bovine and human erythrocytes and were shown to display a low mammalian cellular toxicity. Overall, the study illustrates how the brominated dipeptide marine pharmacophore can be used as a versatile natural scaffold for the design of potent, and selective cholinesterase inhibitors.

Phidianidine A and Synthetic Analogues as Naturally Inspired Marine Antifoulants.

Stationary and slow-moving marine organisms regularly employ a natural product chemical defense to prevent being colonized by marine micro- and macroorganisms. While these natural antifoulants can be structurally diverse, they often display highly conserved chemistries and physicochemical properties, suggesting a natural marine antifouling pharmacophore. In our current report, we investigate the marine natural product phidianidine A, which displays several chemical properties found in highly potent marine antifoulants. Phidianidine A and synthetic analogues were screened against the settlement and metamorphosis of Amphibalanus improvisus cyprids, and several of the compounds displayed inhibitory activities at low micromolar concentrations with IC50 values down to 0.7 µg/mL observed. The settlement study highlights that phidianidine A is a potent natural antifoulant and that the scaffold can be tuned to generate simpler and improved synthetic analogues. The bioactivity is closely linked to the size of the compound and to its basicity. The study also illustrates that active analogues can be prepared in the absence of the natural constrained 1,2,4-oxadiazole ring. A synthetic lead analogue of phidianidine A was incorporated in a coating and included in antifouling field trials, where it was shown that the coating induced potent inhibition of marine bacteria and microalgae settlement.

Heterocyclic cellular lipid peroxidation inhibitors inspired by the marine antioxidant barettin.

The marine environment remains a rich source for the discovery and development of novel bioactive compounds. The present paper describes the design, synthesis and biological evaluation of a library of small molecule heterocyclic mimetics of the marine 2,5-diketopiperazine barettin which is a powerful natural antioxidant. By mainly focusing on the influence from the brominated indole and heterocyclic core of barettin, a library of 19 compounds was prepared. The compounds comprised a heterocyclic core, either a 2,5 diketopiperazine, an imidazolidinedione or a thioxothiazolidinone, which were mainly monosubstituted with ranging bulky substituents. The prepared compounds were screened for activity in a cellular lipid peroxidation assay using HepG2 cells. Several of the synthetic compounds showed antioxidant properties superior to the positive control barettin. Two of the prepared compounds displayed inhibitory activity similar to commercial antioxidants with significant inhibition at low µg/mL concentrations. The toxicity of the compounds was also investigated against MRC-5 lung fibroblasts and none of the included compounds displayed any toxicity at 50 µg/mL.

New MKLP-2 inhibitors in the paprotrain series: Design, synthesis and biological evaluations.

Members of the kinesin superfamily are involved in key functions during intracellular transport and cell division. Their involvement in cell division makes certain kinesins potential targets for drug development in cancer chemotherapy. The two most advanced kinesin targets are Eg5 and CENP-E with inhibitors in clinical trials. Other mitotic kinesins are also being investigated for their potential as prospective drug targets. One recently identified novel potential cancer therapeutic target is the Mitotic kinesin-like protein 2 (MKLP-2), a member of the kinesin-6 family, which plays an essential role during cytokinesis. Previous studies have shown that inhibition of MKLP-2 leads to binucleated cells due to failure of cytokinesis. We have previously identified compound 1 (paprotrain) as the first selective inhibitor of MKLP-2. Herein we describe the synthesis and biological evaluation of new analogs of 1. Our structure-activity relationship (SAR) study reveals the key chemical elements in the paprotrain family necessary for MKLP-2 inhibition. We have successfully identified one MKLP-2 inhibitor 9a that is more potent than paprotrain. In addition, in vitro analysis of a panel of kinesins revealed that this compound is selective for MKLP-2 compared to other kinesins tested and also does not have an effect on microtubule dynamics. Upon testing in different cancer cell lines, we find that the more potent paprotrain analog is also more active than paprotrain in 10 different cancer cell lines. Increased selectivity and higher potency is therefore a step forward toward establishing MKLP-2 as a potential cancer drug target.

Optimization and structure-activity relationships of a series of potent inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase as novel antimicrobial agents.

A novel series of hydrazones were synthesized and evaluated as inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase (PK). PK has been identified as one of the most highly connected 'hub proteins' in MRSA. PK has been shown to be critical for bacterial survival which makes it a potential target for development of novel antibiotics and the high degree of connectivity implies it should be very sensitive to mutations and thus less able to develop resistance. PK is not unique to bacteria and thus a critical requirement for such a PK inhibitor would be that it does not inhibit the homologous human enzyme(s) at therapeutic concentrations. Several MRSA PK inhibitors (including 8d) were identified using in silico screening combined with enzyme assays and were found to be selective for bacterial enzyme compared to four human PK isoforms (M1, M2, R and L). However these lead compounds did not show significant inhibitory activity for MRSA growth presumably due to poor bacterial cell penetration. Structure-activity relationship (SAR) studies were carried out on 8d and led us to discover more potent compounds with enzyme inhibiting activities in the low nanomolar range and some were found to effectively inhibit bacteria growth in culture with minimum inhibitory concentrations (MIC) as low as 1 µg/mL. These inhibitors bind in two elongated flat clefts found at the minor interfaces in the homo-tetrameric enzyme complex and the observed SAR is in keeping with the size and electronic constraints of these binding sites. Access to the corresponding sites in the human enzyme is blocked.

Identification of pyruvate kinase in methicillin-resistant Staphylococcus aureus as a novel antimicrobial drug target.

Novel classes of antimicrobials are needed to address the challenge of multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). Using the architecture of the MRSA interactome, we identified pyruvate kinase (PK) as a potential novel drug target based upon it being a highly connected, essential hub in the MRSA interactome. Structural modeling, including X-ray crystallography, revealed discrete features of PK in MRSA, which appeared suitable for the selective targeting of the bacterial enzyme. In silico library screening combined with functional enzymatic assays identified an acyl hydrazone-based compound (IS-130) as a potent MRSA PK inhibitor (50% inhibitory concentration [IC50] of 0.1 µM) with >1,000-fold selectivity over human PK isoforms. Medicinal chemistry around the IS-130 scaffold identified analogs that more potently and selectively inhibited MRSA PK enzymatic activity and S. aureus growth in vitro (MIC of 1 to 5 µg/ml). These novel anti-PK compounds were found to possess antistaphylococcal activity, including both MRSA and multidrug-resistant S. aureus (MDRSA) strains. These compounds also exhibited exceptional antibacterial activities against other Gram-positive genera, including enterococci and streptococci. PK lead compounds were found to be noncompetitive inhibitors and were bactericidal. In addition, mutants with significant increases in MICs were not isolated after 25 bacterial passages in culture, indicating that resistance may be slow to emerge. These findings validate the principles of network science as a powerful approach to identify novel antibacterial drug targets. They also provide a proof of principle, based upon PK in MRSA, for a research platform aimed at discovering and optimizing selective inhibitors of novel bacterial targets where human orthologs exist, as leads for anti-infective drug development.

Structure-Activity Relationship Probing of the Natural Marine Antifoulant Barettin.

The sponge derived 2,5-diketopiperazine metabolite barettin is a potent antifouling compound effective against the settlement and metamorphosis of barnacles. Simplified derivatives of barettin have previously been shown to display similar inhibitory properties. The synthetic derivative benzo[g]dipodazine has been reported to display significantly improved antifouling properties in comparison with the native barettin with inhibitory activities as low a 0.034 µM reported against barnacle cyprid settlement. In the current study we report the antifouling activity of 29 synthetic analogs designed and inspired by the potent antifouling effect seen for benzo[g]dipodazine. The library contains mainly not only dipodazine derivatives but also disubstituted diketopiperazines and compounds incorporating alternative heterocyclic cores such as hydantoin, creatinine, and rhodanine. Several of the prepared compounds inhibit the settlement of Amphibalanus improvisus cyprids at low micromolar concentrations, in parity with the natural barettin. While several highly active compounds were prepared by incorporating the benzo[g]indole as hydrophobic substituent, the remarkable antifouling effect reported for benzo[g]dipodazine was not observed when evaluated in our study.

Evidence for oxylipin synthesis and induction of a new polyunsaturated fatty acid hydroxylase activity in Chondrus crispus in response to methyljasmonate.

Signaling cascades involving oxygenated derivatives (oxylipins) of polyunsaturated fatty acids (PUFAs) are known to operate in response to external stimuli. The marine red alga Chondrus crispus uses both oxygenated derivatives of C18 (octadecanoids) and C20 (eicosanoids) PUFAs as developmental or defense hormones. The present study demonstrates that methyljasmonate (MeJA) triggers a cascade of oxidation of PUFAs leading to the synthesis of prostaglandins and other oxygenated fatty acids. As a result of a lipoxygenase-like activation, MeJA induces a concomitant accumulation of 13-hydroxy-9Z,11E-octadecadienoic acid (13-HODE) and 13-oxo-9Z,11E-octadecadienoic acid (13-oxo-ODE) in a dose-dependent manner in C. crispus. Furthermore, MeJA increases the level of mRNA encoding a gluthatione S-transferase and induces the activity of a new enzyme catalyzing the regio- and stereoselective bisallylic hydroxylation of polyunsaturated fatty acids from C(18) to C(22). The enzyme selectively oxidized the omega minus 7 carbon position (omega-7) and generated the stereoselective (R)-hydroxylated metabolites with a large enantiomeric excess. The enzyme specificity for the fatty acid recognition was not dependent of the position of double bonds but at least requires a methylene interrupted double bond 1,4-pentadiene motif involving the omega-7 carbon.

Design and Biological Evaluation of Antifouling Dihydrostilbene Oxime Hybrids.

By combining the recently reported repelling natural dihydrostilbene scaffold with an oxime moiety found in many marine antifoulants, a library of nine antifouling hybrid compounds was developed and biologically evaluated. The prepared compounds were shown to display a low antifouling effect against marine bacteria but a high potency against the attachment and growth of microalgae down to MIC values of 0.01 µg/mL for the most potent hybrid. The mode of action can be characterized as repelling via a reversible non-toxic biostatic mechanism. Barnacle cyprid larval settlement was also inhibited at low µg/mL concentrations with low levels or no toxicity observed. Several of the prepared compounds performed better than many reported antifouling marine natural products. While several of the prepared compounds are highly active as antifoulants, no apparent synergy is observed by incorporating the oxime functionality into the dihydrostilbene scaffold. This observation is discussed in light of recently reported literature data on related marine natural antifoulants and antifouling hybrids as a potentially general strategy for generation of improved antifoulants.

Further investigation of inhibitors of MRSA pyruvate kinase: Towards the conception of novel antimicrobial agents.

Several novel series of compounds were synthesized and evaluated as inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase (PK). PK has been identified as a highly interconnected essential 'hub' protein in MRSA, with structural features distinct from the human homologs which makes it a novel antimicrobial target. Several MRSA PK inhibitors (including the hydrazide 1) were identified using in silico screening combined with enzyme assays and were found to be selective for bacterial enzyme compared to human PK isoforms. Structure-activity relationship (SAR) studies were carried out on the replacement of the hydrazide linker with 3-atoms, 2-atoms and 0-atom linkers and led us to discover more potent compounds with enzyme inhibiting activities in the low nanomolar range and some were found to effectively inhibit bacteria growth in culture with minimum inhibitory concentrations (MIC) as low as 1 µg/mL.

Further investigation of Paprotrain: Towards the conception of selective and multi-targeted CNS kinase inhibitors.

Starting from a known compound, identified as the first inhibitor of the kinesin MKLP-2 and named Paprotrain, we have investigated its reactivity to produce through photochemistry a potent nanomolar inhibitor of the kinase DYRK1A. Using similar and different chemical pathways, we have designed several families of compounds that have been screened on a panel of five protein kinases: CK1δ/ε, CDK5/p25, GSK3α/ß, DYRK1A and CLK1, all involved in neurodegenerative disorders such as Alzheimer's disease. We have identified a first group of multi-targeted compounds, a second group of dual inhibitors of DYRK1A & CLK1 and a last group of selective inhibitors of CLK1. Then, our best submicromolar to nanomolar inhibitors were evaluated towards the closest members of the aforementioned kinases: DYRK1B and CLK4, as well as the subfamily CLK2-3. Several compounds appear to be particularly promising for the development of tools in the battle against Alzheimer's disease.

Targeting the binding function 3 (BF3) site of the androgen receptor through virtual screening. 2. development of 2-((2-phenoxyethyl) thio)-1H-benzimidazole derivatives.

The human androgen receptor (AR) is a proven therapeutic target in prostate cancer. All current antiandrogens, such as Bicalutamide, Flutamide, Nilutamide, and Enzalutamide, target the buried hydrophobic androgen binding pocket of this protein. However, effective resistance mechanisms against these therapeutics exist such as mutations occurring at the target site. To overcome these limitations, the surface pocket of the AR called binding function 3 (BF3) was characterized as an alternative target for small molecule therapeutics. A number of AR inhibitors directly targeting the BF3 were previously identified by us ( J. Med. Chem. 2011 . 54 , 8563 ). In the current study, based on the prior results, we have developed structure-activity relationships that allowed designing a series of 2-((2-phenoxyethyl)thio)-1H-benzimidazole and 2-((2-phenoxyethyl)thio)-1H-indole as lead BF3 inhibitors. Some of the developed BF3 ligands demonstrated significant antiandrogen potency against LNCaP and Enzalutamide-resistant prostate cancer cell lines.