Synthesis and biological evaluation of substituted 4-(thiophen-2-ylmethyl)-2H-phthalazin-1-ones as potent PARP-1 inhibitors

Optimization of the Urea Linker of Triazolopyridazine MMV665917 Results in a New Anticryptosporidial Lead with Improved Potency and Predicted hERG Safety Margin

Cryptosporidiosis is caused by infection of the small intestine by Cryptosporidium parasites, resulting in severe diarrhea, dehydration, malabsorption, and potentially death. The only FDA-approved therapeutic is only partially effective in young children and ineffective for immunocompromised patients. Triazolopyridazine MMV665917 is a previously reported anti-Cryptosporidium screening hit with in vivo efficacy but suffers from modest inhibition of the hERG ion channel, which could portend cardiotoxicity. Herein, we describe our initial development of structure-activity relationships of this novel lead series with a particular focus on optimization of the piperazine-urea linker. We have discovered that piperazine-acetamide is a superior linker resulting in identification of SLU-2633, which has an EC₅₀ of 0.17 μM, an improved projected margin versus hERG, prolonged pharmacokinetic exposure in small intestine, and oral efficacy in vivo with minimal systemic exposure. SLU-2633 represents a significant advancement toward the identification of a new effective and safe treatment for cryptosporidiosis.

Novel Pyran-Linked Phthalazinone-Pyrazole Hybrids: Synthesis, Cytotoxicity Evaluation, Molecular Modeling, and Descriptor Studies

A series of novel pyran-linked phthalazinone-pyrazole hybrids were designed and synthesized by a facile one-pot three-component reaction employing substituted phthalazinone, 1H-pyrazole-5-carbaldehyde, and active methylene compounds. Optimization studies led to the identification of L-proline and ethanol as efficient catalyst and solvent, respectively. This was followed by evaluation of anticancer activity against solid tumor cell lines of lung and cervical carcinoma that displayed IC₅₀ values in the range of 9.8–41.6 µM. Molecular modeling studies were performed, and crucial interactions with the target protein were identified. The drug likeliness nature of the compounds and molecular descriptors such as molecular flexibility, complexity, and shape index were also calculated to understand the potential of the synthesized molecules to act as lead-like molecule upon further detailed biological investigations as well as 3D-QSAR studies.

Phthalazinone Scaffold: Emerging Tool in the Development of Target Based Novel Anticancer Agents

Phthalazinones are important nitrogen-rich heterocyclic compounds which have been a topic of considerable medicinal interest because of their diversified pharmacological activities. This versatile scaffold forms a common structural feature for many bioactive compounds, which leads to the design and development of novel anticancer drugs with fruitful results. The current review article discusses the progressive development of novel phthalazinone analogues that are targets for various receptors such as PARP, EGFR, VEGFR-2, Aurora kinase, Proteasome, Hedgehog pathway, DNA topoisomerase and P-glycoprotein. It describes mechanistic insights into the anticancer properties of phthalazinone derivatives and also highlights various simple and economical techniques for the synthesis of phthalazinones.

Discovery of 2,4-diaminopyrimidine derivatives targeting p21-activated kinase 4: Biological evaluation and docking studies

In this study, novel 2,4-diaminopyrimidine derivatives targeting p21-activated kinase 4 (PAK4) were discovered and evaluated for their biological activity against PAK4. Among the derivatives studied, promising compounds A2, B6, and B8 displayed the highest inhibitory activities against PAK4 (IC₅₀  = 18.4, 5.9, and 20.4 nM, respectively). From the cellular assay, compound B6 exhibited the highest potency with an IC₅₀ value of 2.533 μM against A549 cells. Some compounds were selected for computational ADME (absorption, distribution, metabolism, and elimination) properties and molecular docking studies against PAK4. The detailed structure-activity relationship based on the biochemical activities and molecular docking studies were explored. According to the docking studies, compound B6 had the lowest docking score (docking energy: -7.593 kcal/mol). The molecular docking simulation indicated the binding mode between compound B6 and PAK4. All these results suggest compound B6 as a useful candidate for the development of a PAK4 inhibitor.

Discovery, Optimization, and Characterization of ML417: A Novel and Highly Selective D3 Dopamine Receptor Agonist

To identify novel D₃ dopamine receptor (D3R) agonists, we conducted a high-throughput screen using a β-arrestin recruitment assay. Counterscreening of the hit compounds provided an assessment of their selectivity, efficacy, and potency. The most promising scaffold was optimized through medicinal chemistry resulting in enhanced potency and selectivity. The optimized compound, ML417 (20), potently promotes D3R-mediated β-arrestin translocation, G protein activation, and ERK1/2 phosphorylation (pERK) while lacking activity at other dopamine receptors. Screening of ML417 against multiple G protein-coupled receptors revealed exceptional global selectivity. Molecular modeling suggests that ML417 interacts with the D3R in a unique manner, possibly explaining its remarkable selectivity. ML417 was also found to protect against neurodegeneration of dopaminergic neurons derived from iPSCs. Together with promising pharmacokinetics and toxicology profiles, these results suggest that ML417 is a novel and uniquely selective D3R agonist that may serve as both a research tool and a therapeutic lead for the treatment of neuropsychiatric disorders.

Synthesis, preliminarily biological evaluation and molecular docking study of new Olaparib analogues as multifunctional PARP-1 and cholinesterase inhibitors

A series of new Olaparib derivatives was designed and synthesized, and their inhibitory activities against poly (ADP-ribose) polymerases-1 (PARP-1) enzyme and cancer cell line MDA-MB-436 in vitro were evaluated. The results showed that compound 5l exhibited the most potent inhibitory effects on PARP-1 enzyme (16.10 ± 1.25 nM) and MDA-MB-436 cancer cell (11.62 ± 2.15 μM), which was close to that of Olaparib. As a PARP-1 inhibitor had been reported to be viable to neuroprotection, in order to search for new multitarget-directed ligands (MTDLs) for the treatment of Alzheimer’s disease (AD), the inhibitory activities of the synthesized compounds against the enzymes AChE (from electric eel) and BChE (from equine serum) were also tested. Compound 5l displayed moderate BChE inhibitory activity (9.16 ± 0.91 μM) which was stronger than neostigmine (12.01 ± 0.45 μM) and exhibited selectivity for BChE over AChE to some degree. Molecular docking studies indicated that 5l could bind simultaneously to the catalytic active of PARP-1, but it could not interact well with huBChE. For pursuit of PARP-1 and BChE dual-targeted inhibitors against AD, small and flexible non-polar groups introduced to the compound seemed to be conducive to improving its inhibitory potency on huBChE, while keeping phthalazine-1-one moiety unchanged which was mainly responsible for PARP-1 inhibitory activity. Our research gave a clue to search for new agents based on AChE and PARP-1 dual-inhibited activities to treat Alzheimer’s disease.

The crystal structure of phthalazin-1(2H)-one, C8H6N2O1

C8H6N2O1, monoclinic, P21/c (no. 14), a = 8.6277(17) Å, b = 13.134(3) Å, c = 13.062(5) Å, β = 110.54(3)°, V = 1386.0(7) Å3, Z = 8, R gt(F) = 0.0512, wR ref(F 2) = 0.1581, T = 293(2) K.

PARP inhibitors as antitumor agents: a patent update (2013-2015)

INTRODUCTION

PARP inhibitors have been extensively explored as antitumor agents and have shown potent efficacy both in vitro and in vivo. They can be used in monotherapy under the synthetic lethality concept or in combination with radiotherapy or chemotherapy, inducing a synergistic effect. Areas covered: This review covers relevant efforts in the development of PARP inhibitors with a particular focus on recently patented PARP inhibitors, combination therapy involving PARP inhibitors, tumor responsiveness to PARP inhibitors as detailed in reports made from 2013 - 2015, and PARP drugs in clinical trials and other novel inhibitors that emerged in 2013 - 2015. Expert opinion: Clinical studies and applications of PARP inhibitors as antitumor agents have gained considerable recognition in the last few years. In addition to FDA-approved olaparib, an increasing number of new inhibitors have been designed and synthesized, some of which are under preclinical or clinical evaluation. Novel inhibitors are still required, especially new scaffold compounds or drugs with improved properties, such as higher selectivity, higher potency and lower toxicity. The development of combination therapies involving PARP inhibitors and the exploration of biomarkers to predict outcomes with PARP inhibitors would expand the applications of these inhibitors, allowing more patients to benefit from this promising class of drugs in the future.

An Update on Poly(ADP-ribose)polymerase-1 (PARP-1) Inhibitors: Opportunities and Challenges in Cancer Therapy

Poly(ADP-ribose)polymerase-1 (PARP-1) is a critical DNA repair enzyme in the base excision repair pathway. Inhibitors of this enzyme comprise a new type of anticancer drug that selectively kills cancer cells by targeting homologous recombination repair defects. Since 2010, important advances have been achieved in PARP-1 inhibitors. Specifically, the approval of olaparib in 2014 for the treatment of ovarian cancer with BRCA mutations validated PARP-1 as an anticancer target and established its clinical importance in cancer therapy. Here, we provide an update on PARP-1 inhibitors, focusing on breakthroughs in their clinical applications and investigations into relevant mechanisms of action, biomarkers, and drug resistance. We also provide an update on the design strategies and the structural types of PARP-1 inhibitors. Opportunities and challenges in PARP-1 inhibitors for cancer therapy will be discussed based on the above advances.

Design, Synthesis, and Biological Evaluation of Novel PARP-1 Inhibitors Based on a 1H-Thieno[3,4-d] Imidazole-4-Carboxamide Scaffold

A series of poly(ADP-ribose)polymerase (PARP)-1 inhibitors containing a novel scaffold, the 1H-thieno[3,4-d]imidazole-4-carboxamide moiety, was designed and synthesized. These efforts provided some compounds with relatively good PARP-1 inhibitory activity, and among them, 16l was the most potent one. Cellular evaluations indicated that the anti-proliferative activities of 16g, 16i, 16j and 16l against BRCA-deficient cell lines were similar to that of olaparib, while the cytotoxicities of 16j and 16l toward human normal cells were lower. In addition, ADMET prediction results indicated that these compounds might possess more favorable toxicity and pharmacokinetic properties. This study provides a basis for our further investigation.

Exploration of 6,7-dimethoxyquinazoline derivatives as dual acting α1- and AT1-receptor antagonists: synthesis, evaluation, pharmacophore & 3D-QSAR modeling and receptor docking studies

The 6,7-dimethoxyquinazoline scaffold was further explored to provide dual acting α₁- and AT₁-receptor antagonists by synthesizing a series of derivatives and biologically evaluating the newly synthesized compounds.

N-Heterocyclic Carbene-Catalyzed δ-Carbon LUMO Activation of Unsaturated Aldehydes

An N-heterocyclic carbene (NHC) catalyzed domino reaction triggered by a δ-LUMO activation of α,β-γ,δ-diunsaturated enal has been developed for the formal [4 + 2] construction of multisubstituted arenes and 3-ylidenephthalide. These two products, formed in a highly chemo- and regioselective manner, were obtained via different catalytic pathways due to a simple change of the substrate. The activation of the remote δ-carbon of unsaturated aldehydes expands the synthetic potentials of NHC organocatalysis.