Repositioning HIV-1 Integrase Inhibitors for Cancer Therapeutics: 1,6-Naphthyridine-7-carboxamide as a Promising Scaffold with Drug-like Properties

Anticancer Drug Discovery By Structure-Based Repositioning Approach

Despite the tremendous progress that has occurred in recent years in cell biology and oncology, in chemical, physical and computer sciences, the disease cancer has continued as the major cause of death globally. Research organizations, academic institutions and pharmaceutical companies invest huge amounts of money in the discovery and development of new anticancer drugs. Though much effort is continuing and whatever available approaches are being attempted, the success of bringing one effective drug into the market has been uncertain. To overcome problems associated with drug discovery, several approaches are being attempted. One such approach has been the use of known, approved and marketed drugs to screen these for new indications, which have gained considerable interest. This approach is known in different terms as "drug repositioning or drug repurposing." Drug repositioning refers to the structure modification of the active molecule by synthesis, in vitro/ in vivo screening and in silico computational applications where macromolecular structure-based drug design (SBDD) is employed. In this perspective, we aimed to focus on the application of repositioning or repurposing of essential drug moieties present in drugs that are already used for the treatment of some diseases such as diabetes, human immunodeficiency virus (HIV) infection and inflammation as anticancer agents. This review thus covers the available literature where molecular modeling of drugs/enzyme inhibitors through SBDD is reported for antidiabetics, anti-HIV and inflammatory diseases, which are structurally modified and screened for anticancer activity using respective cell lines.

Diversity-Oriented Synthesis of Benzo[f][1,4]oxazepine-, 2H-Chromene-, and 1,2-Dihydroquinoline-Fused Polycyclic Nitrogen Heterocycles under Microwave-Assisted Conditions

An efficient, diversity-oriented synthesis of oxazepino[5,4-b]quinazolin-9-ones, 6H-chromeno[4,3-b]quinolines, and dibenzo[b,h][1,6]naphthyridines was established involving a substrate-based approach under microwave-assisted and conventional heating conditions in high yields (up to 88%). The CuBr₂-catalyzed, chemoselective cascade annulation of O-propargylated 2-hydroxybenzaldehydes and 2-aminobenzamides delivered oxazepino[5,4-b]quinazolin-9-ones involving a 6-exo-trig cyclization-air oxidation-1,3-proton shift-7-exo-dig cyclization sequence. This one-pot process showed excellent atom economy (-H₂O) and constructed two new heterocyclic rings (six- and seven-membered) and three new C-N bonds in a single synthetic operation. On the other side of diversification, the reaction between O/N-propargylated 2-hydroxy/aminobenzaldehydes and 2-aminobenzyl alcohols delivered 6H-chromeno[4,3-b]quinolines and dibenzo[b,h][1,6]naphthyridines involving sequential imine formation-[4 + 2] hetero-Diels-Alder reaction-aromatization steps. The influence of microwave assistance was superior to conventional heating, where the reactions were clean, rapid, and completed in 15 min, and the conventional heating required a longer reaction time at a relatively elevated temperature.

1,6-Naphthyridin-7(6H)-ones: synthesis and optical properties

Efficient synthesis of original 1,6-naphthyridin-7(6H)-ones and their optical properties are described. Their powerful fluorescence properties including dual fluorescence, solvatochromism, acidochromism, large Stokes shifts and high quantum yields, suitable for biological applications or as luminescent devices in materials science, are evidenced.

Microwave-assisted one-pot two-step imine formation-hetero-Diels-Alder-detosylation/aromatization sequence: direct access to dibenzo[b,h][1,6]naphthyridines

A microwave-assisted, copper-catalyzed, one-pot, two-step reaction is established to access functionalized [1,6]naphthyridines in high yields (up to 96%) starting from 2-(N-propargylamino)benzaldehydes and arylamines. This rapid and operationally simple sequential reaction allowed the construction of two new heterocyclic rings and three new (2 C-C and 1 C-N) bonds in a single synthetic operation. This reaction tolerated various electron-donating and electron-withdrawing substituents well and delivered the desired products in a shorter reaction time under microwave irradiation. This reaction proceeds through a sequential imine formation, intramolecular [4 + 2] hetero-Diels-Alder reaction, and air oxidation, followed by detosylation-aromatization steps.

Repurposing non-oncology small-molecule drugs to improve cancer therapy: Current situation and future directions

Drug repurposing or repositioning has been well-known to refer to the therapeutic applications of a drug for another indication other than it was originally approved for. Repurposing non-oncology small-molecule drugs has been increasingly becoming an attractive approach to improve cancer therapy, with potentially lower overall costs and shorter timelines. Several non-oncology drugs approved by FDA have been recently reported to treat different types of human cancers, with the aid of some new emerging technologies, such as omics sequencing and artificial intelligence to overcome the bottleneck of drug repurposing. Therefore, in this review, we focus on summarizing the therapeutic potential of non-oncology drugs, including cardiovascular drugs, microbiological drugs, small-molecule antibiotics, anti-viral drugs, anti-inflammatory drugs, anti-neurodegenerative drugs, antipsychotic drugs, antidepressants, and other drugs in human cancers. We also discuss their novel potential targets and relevant signaling pathways of these old non-oncology drugs in cancer therapies. Taken together, these inspiring findings will shed new light on repurposing more non-oncology small-molecule drugs with their intricate molecular mechanisms for future cancer drug discovery.

Synthesis and Anticancer Properties of Functionalized 1,6-Naphthyridines

The burgeoning interest in synthesis and biological applications of 1,6-naphthyridines reflects the importance of 1,6-naphthyridines in the synthetic as well as medicinal chemistry fields. Specially, 1,6-naphthyridines are pharmacologically active, with variety of applications such as anticancer, anti-human immunodeficiency virus (HIV), anti-microbial, analgesic, anti-inflammatory and anti-oxidant activities. Although collective recent synthetic developments have paved a path to a wide range of functionalized 1,6-naphthyridines, a complete correlation of synthesis with biological activity remains elusive. The current review focuses on recent synthetic developments from the last decade and a thorough study of the anticancer activity of 1,6-naphthyridines on different cancer cell lines. Anticancer activity has been correlated to 1,6-naphthyridines using the literature on the structure-activity relationship (SAR) along with molecular modeling studies. Exceptionally, at the end of this review, the utility of 1,6-naphthyridines displaying activities other than anticancer has also been included as a glimmering extension.

Kinetic resolution of azaflavanones via a RuPHOX-Ru catalyzed asymmetric hydrogenation

The kinetic resolution of azaflavanones has been established via RuPHOX-Ru catalyzed asymmetric hydrogenation, providing chiral azaflavanones and azaflavanols in high yields with up to >20 : 1 dr and 99.7% ee.

Grignard Reagent Utilization Enables a Practical and Scalable Construction of 3-Substituted 5-Chloro-1,6-naphthyridin-4-one Derivatives

A robust, practical, and scalable approach for the construction of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 via the addition of Grignard reagents to 4-amino-2-chloronicotinonitrile (15) was developed. Starting with various Grignard reagents, a wide range of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 were conveniently synthesized in moderate-to-good yields through addition–acidolysis–cyclocondensation. In addition, the robustness and applicability of this synthetic route was proven on a 100 g scale, which would enable convenient sample preparation in the preclinical development of 1,6-naphthyridin-4-one-based MET-targeting antitumor drug candidates.

Efficient Arylation of 2,7-Naphthyridin-1(2H)-one with Diaryliodonium Salts and Discovery of a New Selective MET/AXL Kinase Inhibitor

New 8-chloro-2-phenyl-2,7-naphthyridin-1(2H)-one building blocks bearing diverse substitutes on the 2-phenyl group were synthesized via an efficient diaryliodonium salt-based N-arylation strategy with the advantage of mild conditions, short reaction times, and high yields. A small combinatorial library of 8-amino substituted 2-phenyl-2,7-naphthyridin-1(2H)-one was further conveniently constructed based on the above chlorinated naphthyridinones and substituted aniline. Preliminary biochemical screening resulted in the discovery of the new 2,7-naphthyridone-based MET/AXL kinase inhibitors. More importantly, 17c (IC_50,MET of 13.8 nM) or 17e (IC_50,AXl of 17.2 nM) and 17i (IC_50,AXl of 31.8 nM) can efficient selectively inhibit MET or AXL kinase, respectively, while commercial cabozantinib showed no selectivity. The further exploration of the 8-substituted 2-phenyl-2,7-naphthyridin-1(2H)-one combinatorial library would significantly accelerate the discovery of more potent and selective inhibitors against diverse kinases.

Identification and Optimization of a Series of 8-Hydroxy Naphthyridines with Potent In Vitro Antileishmanial Activity: Initial SAR and Assessment of In Vivo Activity

Visceral leishmaniasis (VL) is a parasitic infection that results in approximately 26 000–65 000 deaths annually. The available treatments are hampered by issues such as toxicity, variable efficacy, and unsuitable dosing options. The need for new treatments is urgent and led to a collaboration between the Drugs for Neglected Diseases initiative (DNDi), GlaxoSmithKline (GSK), and the University of Dundee. An 8-hydroxynaphthyridine was identified as a start point, and an early compound demonstrated weak efficacy in a mouse model of VL but was hampered by glucuronidation. Efforts to address this led to the development of compounds with improved in vitro profiles, but these were poorly tolerated in vivo. Investigation of the mode of action (MoA) demonstrated that activity was driven by sequestration of divalent metal cations, a mechanism which was likely to drive the poor tolerability. This highlights the importance of investigating MoA and pharmacokinetics at an early stage for phenotypically active series.

Overview of Recent Strategic Advances in Medicinal Chemistry

Introducing novel strategies, concepts, and technologies that speed up drug discovery and the drug development cycle is of great importance both in the highly competitive pharmaceutical industry as well as in academia. This Perspective aims to present a "big-picture" overview of recent strategic innovations in medicinal chemistry and drug discovery.

Synthesis and photocytotoxic activity of [1,2,3]triazolo[4,5-h][1,6]naphthyridines and [1,3]oxazolo[5,4-h][1,6]naphthyridines

[1,2,3]Triazolo[4,5-h][1,6]naphthyridines and [1,3]oxazolo[5,4-h][1,6]naphthyridines were synthesized with the aim to investigate their photocytotoxic activity. Upon irradiation, oxazolo-naphtapyridines induced light-dependent cell death at nanomolar/low micromolar concentrations (EC₅₀ 0.01-6.59 μM). The most photocytotoxic derivative showed very high selectivity and photocytotoxicity indexes (SI = 72-86, PTI>5000), along with a triplet excited state with exceptionally long lifetime (18.0 μs) and high molar absorptivity (29781 ± 180 M^-1cm^-1 at λ_max 315 nm). The light-induced production of ROS promptly induced an unquenchable apoptotic process selectively in tumor cells, with mitochondrial and lysosomal involvement. Altogether, these results demonstrate that the most active compound acts as a promising singlet oxygen sensitizer for biological applications.

Palladium meets copper: one-pot tandem synthesis of pyrido fused heterocycles via Sonogashira conjoined electrophilic cyclization

An efficient step-economical tandem approach for the direct synthesis of pyrido fused indole, quinoline, benzofuran and benzothiophene derivatives using a bimetallic Pd/Cu catalytic system has been described. The three component reaction of o-halo aldehydes, alkynes and tert-butylamine leads to the synthesis of biologically active polyheterocycles. The present strategy involves the dual role of tert-butylamine and copper(i) in Sonogashira coupling followed by electrophilic cyclization through imine formation. The chemistry has been validated by X-ray crystallographic studies.

Multi Component Reactions under Increased Pressure: On the Mechanism of Formation of Pyridazino[5,4,3-de][1,6]naphthyridine Derivatives by the Reaction of Malononitrile, Aldehydes and 2-Oxoglyoxalarylhydrazones in Q-Tubes

Efficient synthesis of phenanthridin-6(5H)-one derivatives 12a–n in a four-component reaction of aldehyde hydrazone, aromatic aldehydes and malononitrile in Q-Tubes is reported. The results showed that the methodology has the advantage of being a one-pot synthesis of tricyclic systems in good yields. Potential routes leading to formation of compounds 12 are discussed. The structures of the synthesized compounds could be unequivocally established via X-ray crystal structure determination and spectroscopic methods.

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6] naphthyridines and 4-fluoroisoquinolines via iminofluorination of alkynes with Selectfluor

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6]naphthyridines is described from o-alkynylquinolinyl aldehydes through imines.

Characterization of the C-Terminal Nuclease Domain of Herpes Simplex Virus pUL15 as a Target of Nucleotidyltransferase Inhibitors

The natural product α-hydroxytropolones manicol and β-thujaplicinol inhibit replication of herpes simplex viruses 1 and 2 (HSV-1 and HSV-2, respectively) at nontoxic concentrations. Because these were originally developed as divalent metal-sequestering inhibitors of the ribonuclease H activity of HIV-1 reverse transcriptase, α-hydroxytropolones likely target related HSV proteins of the nucleotidyltransferase (NTase) superfamily, which share an "RNase H-like" fold. One potential candidate is pUL15, a component of the viral terminase molecular motor complex, whose C-terminal nuclease domain, pUL15C, has recently been crystallized. Crystallography also provided a working model for DNA occupancy of the nuclease active site, suggesting potential protein-nucleic acid contacts over a region of ∼ 14 bp. In this work, we extend crystallographic analysis by examining pUL15C-mediated hydrolysis of short, closely related DNA duplexes. In addition to defining a minimal substrate length, this strategy facilitated construction of a dual-probe fluorescence assay for rapid kinetic analysis of wild-type and mutant nucleases. On the basis of its proposed role in binding the phosphate backbone, studies with pUL15C variant Lys700Ala showed that this mutation affected neither binding of duplex DNA nor binding of small molecule to the active site but caused a 17-fold reduction in the turnover rate (kcat), possibly by slowing conversion of the enzyme-substrate complex to the enzyme-product complex and/or inhibiting dissociation from the hydrolysis product. Finally, with a view of pUL15-associated nuclease activity as an antiviral target, the dual-probe fluorescence assay, in combination with differential scanning fluorimetry, was used to demonstrate inhibition by several classes of small molecules that target divalent metal at the active site.

Pharmacokinetics and antitumor efficacy of DSPE-PEG2000 polymeric liposomes loaded with quercetin and temozolomide: Analysis of their effectiveness in enhancing the chemosensitization of drug-resistant glioma cells

In the present study, a new type of DSPE-PEG2000 polymeric liposome for the brain-targeted delivery of poorly water-soluble anticancer drugs was successfully prepared and characterized. The nanoparticles were formed by the self-assembly of an amphiphilic polymer consisting of hydrophilic 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE‑PEG2000). These nanoliposomes served as a safe delivery platform for the simultaneous delivery of quercetin (QUE) and temozolomide (TMZ) to rat brains. The 2-in-1 PEG2000‑DSPE nanoliposomes containing QUE and TMZ (QUE/TMZ-NLs) were rapidly taken up by the U87 glioma cells in vitro, whereas at the same concentrations, the amounts of the free drugs taken up were minimal. The QUE/TMZ-NLs showed an enhanced potency in the U87 cells and the TMZ-resistant U87 cells (U87/TR cells), possibly due to the high intracellular drug concentration and the subsequent drug release. In vivo biodistribution experiments revealed a significant accumulation of QUE/TMZ-NLs in the brain, with significantly increased plasma concentrations of QUE and TMZ, as well as delayed clearance in our rat model of glioma. The results were not so significant for the QUE-loaded nanoliposomes (QUE-NLs) and free TMZ. The findings of our study establish the DSPE‑PEG2000 polymeric liposome as a novel and effective nanocarrier for enhancing drug delivery to brain tumors.

Ligand-free palladium-catalyzed facile construction of tetra cyclic dibenzo[b,h][1,6]naphthyridine derivatives: domino sequence of intramolecular C–H bond arylation and oxidation reactions

A ligand-free Pd-catalyzed approach has been developed for the synthesis of dibenzo-fused naphthyridines.

Dual inhibition of survivin and MAOA synergistically impairs growth of PTEN-negative prostate cancer

Background:

Survivin and monoamine oxidase A (MAOA) levels are elevated in prostate cancer (PCa) compared to normal prostate glands. However, the relationship between survivin and MAOA in PCa is unclear.

Methods:

We examined MAOA expression in the prostate lobes of a conditional PTEN-deficient mouse model mirroring human PCa, with or without survivin knockout. We also silenced one gene at a time and examined the expression of the other. We further evaluated the combination of MAOA inhibitors and survivin suppressants on the growth, viability, migration and invasion of PCa cells.

Results:

Survivin and MAOA levels are both increased in clinical PCa tissues and significantly associated with patients' survival. Survivin depletion delayed MAOA increase during PCa progression, and silencing MAOA decreased survivin expression. The combination of MAOA inhibitors and the survivin suppressants (YM155 and SC144) showed significant synergy on the inhibition of PCa cell growth, migration and invasion with concomitant decrease in survivin and MMP-9 levels.

Conclusions:

There is a positive feedback loop between survivin and MAOA expression in PCa. Considering that survivin suppressants and MAOA inhibitors are currently available in clinical trials and clinical use, their synergistic effects in PCa support a rapid translation of this combination to clinical practice.

A Sc(OTf)3-catalyzed cascade reaction of o-aminoacetophenone with methanamine: construction of dibenzo[b,h][1,6]naphthyridine derivatives

An unexpected Sc(OTf)3-catalyzed and air-mediated cascade reaction of o-aminoacetophenones with methanamines was discovered as an efficient synthetic approach to a novel class of fluorescent fused-four-ring dibenzo[b,h][1,6]naphthyridine derivatives. Two possible mechanisms of the reaction were proposed. The photophysical properties of the dibenzo[b,h][1,6]naphthyridine were initially considered.

Synthesis and evaluation of 3-salicyloylpyridine derivatives as cytotoxic mitochondrial apoptosis inducers

A series of novel 3-salicyloylpyridines (4a-h) were synthesized with good yield by modified Knoevenagel-Stobbel method; o-allylation with allyl bromide lead to formation of compounds (5a-h). The synthesized compounds were characterized by spectroscopic techniques and evaluated for cytotoxic activity against human cancer cell lines. Compounds bearing hydroxyl group displayed high cytotoxicity (4a-h) as compared to o-allylated molecules (5a-h). The most active compound 4b was selected for further investigation to look for mechanism of cell death in prostate cancer (PC-3) cells. The apoptotic bodies induced by 4b in PC-3 cells were scanned by confocal microscopy and confirmed by scanning electron microscopy (SEM). Further results obtained from spectrofluorimetric determination of mitochondrial membrane potential (ΔΨm) and intracellular reactive oxygen species (ROS) in treated PC-3 cells revealed that mitochondria dependent apoptosis was involved in the cell death.