Synthesis of 1,4-Thiazepane-Based Curcuminoids with Promising Anticancer Activity

Curcumin, the main component of turmeric (Curcuma longa) is known to display an interesting bioactivity profile, including pronounced anticancer properties. However, its low bioavailability, metabolic instability and nonspecific activity are concerns that have to be addressed before curcuminoids can be considered for therapeutic applications. Within that framework, intensive research has been carried out in the last decades to develop new curcumin derivatives, generally centered on standard modifications of the sp² curcumin framework, with the aim to augment its bioavailability while maintaining or improving its anticancer properties. To find potential hit molecules by moving away from the classical flat curcumin framework, we investigated an unexplored modification to produce novel, out-of-plane 1,4-thiazepane-based curcuminoids and assessed the impact of this modification on the biological activity. In this way, 21 new, structurally diverse thiazepane scaffolds (4-aryl-1-(7-aryl-1,4-thiazepan-5-ylidene)but-3-en-2-ones) were synthesized, as well as some biologically interesting unexpected reaction products (such as 5-aryl-6-arylmethylene-3-ethoxycyclohex-2-en-1-ones and 4-acetyl-5-aryl-2-(3-arylacryloyl)-3-methylcyclohex-2-en-1-ones). All these analogues were subsequently tested on their antioxidant capacity, their cytotoxicity properties and their ROS (reactive oxygen species) production. Many compounds demonstrated interesting activities, with ten curcuminoids, whereof eight 1,4-thiazepane-based, showing better antiproliferative properties compared to their mother compounds, as well as an increased ROS production. This unprecedented 3D curcumin modification has thus delivered promising new hit compounds with good activity profiles eligible for further exploration.     

Synthesis and Biological Investigation of Bile Acid-Paclitaxel Hybrids

Chenodeoxycholic acid and ursodeoxycholic acid (CDCA and UDCA, respectively) have been conjugated with paclitaxel (PTX) anticancer drugs through a high-yield condensation reaction. Bile acid-PTX hybrids (BA-PTX) have been investigated for their pro-apoptotic activity towards a selection of cancer cell lines as well as healthy fibroblast cells. Chenodeoxycholic-PTX hybrid (CDC-PTX) displayed cytotoxicity and cytoselectivity similar to PTX, whereas ursodeoxycholic-PTX hybrid (UDC-PTX) displayed some anticancer activity only towards HCT116 colon carcinoma cells. Pacific Blue (PB) conjugated derivatives of CDC-PTX and UDC-PTX (CDC-PTX-PB and UDC-PTX-PB, respectively) were also prepared via a multistep synthesis for evaluating their ability to enter tumor cells. CDC-PTX-PB and UDC-PTX-PB flow cytometry clearly showed that both CDCA and UDCA conjugation to PTX improved its incoming into HCT116 cells, allowing the derivatives to enter the cells up to 99.9%, respect to 35% in the case of PTX. Mean fluorescence intensity analysis of cell populations treated with CDC-PTX-PB and UDC-PTX-PB also suggested that CDC-PTX-PB could have a greater ability to pass the plasmatic membrane than UDC-PTX-PB. Both hybrids showed significant lower toxicity with respect to PTX on the NIH-3T3 cell line.     

A Highly Luminescent Tetrahydrocurcumin IrIII Complex with Remarkable Photoactivated Anticancer Activity

Curcumin has chemopreventative properties against a variety of tumours, but has poor bioavailability. Here, two new bis-cyclometallated iridium(III) complexes have been prepared, featuring the natural product curcumin (CUR) or its reduced form, tetrahydrocurcumin (THC), as bidentate, anionic O O-binding ligands. The iridium THC complex is highly luminescent in deoxygenated solution and efficiently generates singlet oxygen under aerated conditions, whereas in the CUR analogue, other non-radiative decay pathways are competitive. The complexes are rapidly taken up by a variety of human tumour cell lines from solutions of micromolar concentration. They show negligible cytotoxicity in the absence of irradiation. When briefly irradiated with visible light, Ir-THC becomes highly phototoxic, inducing rapid apoptosis within 2 h. The results show the high potential of such complexes as sensitizers in photodynamic therapy (PDT).     

Mechanism‐Guided Design and Synthesis of a Mitochondria‐Targeting Artemisinin Analogue with Enhanced Anticancer Activity

Understanding the mechanism of action (MOA) of bioactive natural products will guide endeavor to improve their cellular activities. Artemisinin and its derivatives inhibit cancer cell proliferation, yet with much lower efficiencies than their roles in killing malaria parasites. To improve their efficacies on cancer cells, we studied the MOA of artemisinin using chemical proteomics and found that free heme could directly activate artemisinin. We then designed and synthesized a derivative, ART‐TPP, which is capable of targeting the drug to mitochondria where free heme is synthesized. Remarkably, ART‐TPP exerted more potent inhibition than its parent compound to cancer cells. A clickable probe ART‐TPP‐Alk was also employed to confirm that the attachment of the TPP group could label more mitochondrial proteins than that for the ART derivative without TPP (AP1). This work shows the importance of MOA study, which enables us to optimize the design of natural drug analogues to improve their biological activities.     

Fluorinated Analogues of Lepidilines A and C: Synthesis and Screening of Their Anticancer and Antiviral Activity

Starting with fluorinated benzylamines, a series of 2-unsubstituted imidazole N-oxides was prepared and subsequently deoxygenated in order to prepare the corresponding imidazoles. The latter were treated with benzyl halides yielding imidazolium salts, which are considered fluorinated analogues of naturally occurring imidazolium alkaloids known as lepidilines A and C. A second series of oxa-lepidiline analogues was obtained by O-benzylation of the initially synthetized imidazole N-oxides. Both series of imidazolium salts were tested as anticancer and antiviral agents. The obtained results demonstrated that the introduction of a fluorine atom, fluoroalkyl or fluoroalkoxy substituents (F, CF₃ or OCF₃) amplifies cytotoxic properties, whereas the cytotoxicity of some fluorinated lepidilines is promising in the context of drug discovery. All studied compounds revealed a lack of antiviral activity against the investigated viruses in the nontoxic concentrations.     

Potent Anticancer Activity and Possible Low Toxicity of Platinum(II) Complexes with Functionalized 1,1‐Cyclobutanedicarboxylate as a Leaving Ligand

Two platinum(II) complexes, DN603 and DN604, were designed and prepared by using 3‐oxocyclobutane‐1,1‐dicarboxylate as a ligand. The compounds were prepared according to the concept that incorporation of a functionalized moiety in the leaving ligand that did not affect its coordination bonding to the metal atom would play a key role in the anticancer activity of the resulting platinum complex. The newly prepared compounds were found to show potent in vitro anticancer activity comparable to cisplatin and oxaliplatin; especially DN604, which exhibited low acute toxicity similar to carboplatin, and presented acceptable solubility and stability in water. Chemical and biological results indicated that the functionalized moiety, uncoordinated, led to potent anticancer activity and low apparent toxicity of the platinum complexes by affecting the kinetic properties of the compounds.     

Synthesis and Biological Evaluation of Flavonoid-Cinnamic Acid Amide Hybrids with Distinct Activity against Neurodegeneration in Vitro and in Vivo

Flavonoids are polyphenolic natural products and have shown significant potential as disease-modifying agents against neurodegenerative disorders like Alzheimer's disease (AD), with activities even in vivo. Hybridization of the natural products taxifolin and silibinin with cinnamic acid led to an overadditive effect of these compounds in several phenotypic screening assays related to neurodegeneration and AD. Therefore, we have exchanged the flavonoid part of the hybrids with different flavonoids, which show higher efficacy than taxifolin or silibinin, to improve the activity of the respective hybrids. Chemical connection between the flavonoid and cinnamic acid was realized by an amide instead of a labile ester bond to improve stability towards hydrolysis. To investigate the influence of a double bond at the C-ring of the flavonoid, the dehydro analogues of the respective hybrids were also synthesized. All compounds obtained show neuroprotection against oxytosis, ferroptosis and ATP-depletion, respectively, in the murine hippocampal cell line HT22. Interestingly, the taxifolin and the quercetin derivatives are the most active compounds, whereby the quercetin derivate shows even more pronounced activity than the taxifolin one in all assays applied. As aimed for, no hydrolysis product was found in cellular uptake experiments after 4 h whereas different metabolites were detected. Furthermore, the quercetin-cinnamic acid amide showed pronounced activity in an in vivo AD mouse model at a remarkably low dose of 0.3 mg/kg.     

In Vitro Anticancer Activity of Methanolic Extract of Justicia adhatoda Leaves with Special Emphasis on Human Breast Cancer Cell Line

Natural products are being targeted as alternative anticancer agents due to their non-toxic and safe nature. The present study was conducted to explore the in vitro anticancer potential of Justicia adhatoda (J. adhatoda) leaf extract. The methanolic leaf extract was prepared, and the phytochemicals and antioxidant potential were determined by LCMS analysis and DPPH radical scavenging assay, respectively. A docking study performed with five major alkaloidal phytoconstituents showed that they had a good binding affinity towards the active site of NF-κB. Cell viability assay was carried out in five different cell lines, and the extract exhibited the highest cytotoxicity in MCF-7, a breast cancer cell line. Extract-treated cells showed a significant increase in nitric oxide and reactive oxygen species production. Cell cycle analysis showed an arrest in cell growth at the Sub-G0 phase. The extract successfully inhibited cell migration and colony formation and altered mitochondrial membrane potential. The activities of superoxide dismutase and glutathione were also found to decrease in a dose-dependent manner. The percentage of apoptotic cells was found to increase in a dose-dependent manner in MCF-7 cells. The expressions of caspase-3, Bax, and cleaved-PARP were increased in extract-treated cells. An increase in the expression of NF-κB was found in the cytoplasm in extract-treated cells. J. adhatoda leaf extract showed a potential anticancer effect in MCF-7 cells.     

Maltol‐Derived Ruthenium–Cymene Complexes with Tumor Inhibiting Properties: The Impact of Ligand–Metal Bond Stability on Anticancer Activity In Vitro

Organometallic ruthenium–arene compounds bearing a maltol ligand have been shown to be nearly inactive in in vitro anticancer assays, presumably due to the formation of dimeric Ru^II species in aqueous solutions. In an attempt to stabilize such complexes, [Ru(η⁶‐p‐cymene)(XY)Cl] (XY=pyrones or thiopyrones) complexes with different substitution pattern of the (thio)pyrone ligands have been synthesized, their structures characterized spectroscopically, and their aquation behavior investigated as well as their tumor‐inhibiting potency. The aquation behavior of pyrone systems with electron‐donating substituents and of thiopyrone complexes was found to be significantly different from that of the maltol‐type complex reported previously. However, the formation of the dimer can be excluded as the primary reason for the inactivity of the complex because some of the stable compounds are not active in cancer cell lines either. In contrast, studies of their reactivity towards amino acids demonstrate different reactivities of the pyrone and thiopyrone complexes, and the higher stability of the latter probably renders them active against human tumor cells.     

Lung Cancer: EGFR Inhibitors with Low Nanomolar Activity against a Therapy‐Resistant L858R/T790M/C797S Mutant

The treatment of non‐small‐cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) inhibitors is made challenging by acquired resistance caused by somatic mutations. Third‐generation EGFR inhibitors have been designed to overcome resistance through covalent binding to the Cys 797 residue of the enzyme, and these inhibitors are effective against most clinically relevant EGFR mutants. However, the high dependence of these recent EGFR inhibitors on this particular interaction means that additional mutation of Cys 797 results in poor inhibitory activity, which leads to tumor relapse in initially responding patients. A new generation of irreversible and reversible mutant EGFR inhibitors was developed with strong noncovalent binding properties, and these compounds show high inhibitory activities against the cysteine‐mutated L858R/T790M/C797S EGFR.     

Epothilone Analogues with Benzimidazole and Quinoline Side Chains: Chemical Synthesis,Antiproliferative Activity,and Interactions with Tubulin

A series of epothilone B and D analogues bearing isomeric quinoline or functionalized benzimidazole side chains has been prepared by chemical synthesis in a highly convergent manner. All analogues have been found to interact with the tubulin/microtubule system and to inhibit human cancer cell proliferation in vitro, albeit with different potencies (IC₅₀ values between 1 and 150 nM ). The affinity of quinoline‐based epothilone B and D analogues for stabilized microtubules clearly depends on the position of the N‐atom in the quinoline system, while the induction of tubulin polymerization in vitro appears to be less sensitive to N‐positioning. The potent inhibition of human cancer cell growth by epothilone analogues bearing functionalized benzimidazole side chains suggests that these systems might be conjugated with tumor‐targeting moieties to form tumor‐targeted prodrugs.     

Design,Synthesis, and Biological Evaluation of Novel Dihydropyridine and Pyridine Analogs as Potent Human Tissue Nonspecific Alkaline Phosphatase Inhibitors with Anticancer Activity: ROS and DNA Damage-Induced Apoptosis

Small molecules with nitrogen-containing scaffolds have gained much attention due to their biological importance in the development of new anticancer agents. The present paper reports the synthesis of a library of new dihydropyridine and pyridine analogs with diverse pharmacophores. All compounds were tested against the human tissue nonspecific alkaline phosphatase (h-TNAP) enzyme. Most of the compounds showed excellent enzyme inhibition against h-TNAP, having IC₅₀ values ranging from 0.49 ± 0.025 to 8.8 ± 0.53 µM, which is multi-fold higher than that of the standard inhibitor (levamisole = 22.65 ± 1.60 µM) of the h-TNAP enzyme. Furthermore, an MTT assay was carried out to evaluate cytotoxicity against the HeLa and MCF-7 cancer cell lines. Among the analogs, the most potent dihydropyridine-based compound 4d was selected to investigate pro-apoptotic behavior. The further analysis demonstrated that compound 4d played a significant role in inducing apoptosis through multiple mechanisms, including overproduction of reactive oxygen species, mitochondrial dysfunction, DNA damaging, and arrest of the cell cycle at the G1 phase by inhibiting CDK4/6. The apoptosis-inducing effect of compound 4d was studied through staining agents, microscopic, and flow cytometry techniques. Detailed structure–activity relationship (SAR) and molecular docking studies were carried out to identify the core structural features responsible for inhibiting the enzymatic activity of the h-TNAP enzyme. Moreover, fluorescence emission studies corroborated the binding interaction of compound 4d with DNA through a fluorescence titration experiment.