Sub-micromolar Cytotoxicity Research Articles

Derivatization of Abietane Acids by Peptide-like Substituents Leads to Submicromolar Cytotoxicity at NCI-60 Panel.

Natural compounds, including diterpenoids, play a critical role in various biological processes and are recognized as valuable components in cancer treatment. Isocyanides multicomponent reactions (IsMCRs) are one of the effective methods to obtain adducts at the carboxyl group with a peptide-like substituent. In this study, dehydroabietic acid and levopimaric acid diene adducts as the starting scaffolds were modified by the multicomponent Passerini (P-3CR) and Ugi (U-4CR) reactions to afford α-acyloxycarboxamides and α-acylaminocarboxamides. A group of twenty novel diterpene hybrids was subjected to NCI in vitro assessment, and a consistent structure-activity relationship was established. Eleven of the synthesized derivatives inhibited the growth of cancer cells of 4 to 39 cell lines in one dose assay, and the most active were derivatives 3d, 9d, and 10d holding a fragment of 1a,4a-dehydroquinopimaric acid. They were selected for a five-dose analysis and demonstrated a significant antiproliferative effect towards human cancer cell lines. The outstanding cytotoxic activity was observed for the P-3CR product 3d with growth inhibitory at submicromolar and micromolar concentrations (GI50 = 0.42-3 μM) against the most sensitive cell lines. The U-4CR products 9d and 10d showed selective activity against all leukemia cell lines with GI50 in the range of 1-17 µM and selectivity indexes of 5.49 and 4.72, respectively. Matrix COMPARE analysis using the GI50 vector showed a moderate positive correlation of compound 3d with standard anticancer agents that can influence kinase receptors and epidermal growth factor receptors (EGFRs). The ADMET analysis acknowledges the favorable prognosis using compounds as potential anticancer agents. The obtained results indicate that these new hybrids could be useful for the further development of anticancer drugs, and 1a,4a-dehydroquinopimaric acid derivatives could be recommended for in-depth studies and the synthesis of new antitumor analogs on their basis.

A bis-quinoline ruthenium(II) arene complex with submicromolar cytotoxicity in castration-resistant prostate cancer cells.

A new Ru(II) arene chlorido organometallic complex [(η6-p-cymene)(L)RuCl]PF6 (named as pCYRuL) using 2-bis(quinolin-2-ylmethylene) hydrazine (L) was developed that exhibits potent anticancer activity against castration-resistant prostate cancer (CRPC) (IC50 = 0.71 μM), and it is 45 times more effective than the standard drug cisplatin (IC50 = 31.3 μM) in a castration-resistant human prostatic adenocarcinoma cell line (PC-3) but non-toxic in normal human kidney cells (HK2) as well as normal breast cells (MCF10A) and found that pCYRuL exerted anticancer activity via apoptosis induction and cell cycle arrest in the G2/M phase of PC-3 cells.

Probing tricarbocyanine dyes for targeted delivery of anthracyclines

Along with bright fluorescence in the near-IR range, heptamethine carbocyanine dyes possess affinity to cancer cells. Thus, these dyes could be utilized as fluorescent labels and vectors for drug delivery as covalent conjugates with cytotoxic compounds. To test the properties, structure–activity relationship, and scope of such conjugates, we synthesized drug-dye dyads of tricarbocyanine dyes with anthracycline drug daunorubicin. We used hydrophilic zwitterionic and hydrophobic positively charged benzoindoline-benzothiazole-based heptamethine dyes as terminal alkyne derivatives and N-acylated or oxime-linked daunorubicin as azido-derivatives. These two alkynes and two azides were coupled to each other by Cu-catalyzed Huisgen–Meldal–Sharpless cycloaddition (click reaction) to afford four conjugates. Molecules based on hydrophobic dyes possess submicromolar cytotoxicity to HCT116 cells. Cytotoxicity, cell penetration, intracellular distribution, apoptosis induction and the effect of antioxidants on toxicity were evaluated. The results show that the structure of the cyanine–anthracycline conjugate (hydrophilicity/hydrophobicity, charge, linker, attachment site) is important for its biological activity, thus, expansion of the chemical space of such conjugates could provide new molecular research tools for diagnostics and therapy.

Methoxy and bromo scans on N-(5-methoxyphenyl) methoxybenzenesulphonamides reveal potent cytotoxic compounds, especially against the human breast adenocarcinoma MCF7 cell line

Thirty seven N-(5-methoxyphenyl)-4-methoxybenzenesulphonamide with methoxy or/and bromo substitutions (series 1-4) and with different substituents on the sulphonamide nitrogen have been synthesised. 21 showed sub-micromolar cytotoxicity against HeLa and HT-29 human tumour cell lines, and were particularly effective against MCF7. The most potent series has 2,5-dimethoxyanilines, especially the 4-brominated compounds 23–25. The active compounds inhibit microtubular protein polymerisation at micromolar concentrations, thus pointing at tubulin as the target. Co-treatment with the MDR inhibitor verapamil suggests that they are not MDR substrates. Compound 25 showed nanomolar antiproliferative potency. It severely disrupts the microtubule network in cells and arrests cells at the G2/M cell-cycle phase, thus confirming tubulin targeting. 25 triggered apoptotic cell death, and induced autophagy. Docking studies suggest binding in a distinct way to the colchicine site. These compounds are promising new antitumor agents acting on tubulin.

Photochemical and Photobiological Properties of Pyridyl-pyrazol(in)e-Based Ruthenium(II) Complexes with Sub-micromolar Cytotoxicity for Phototherapy.

The discovery of new light-triggered prodrugs based on ruthenium (II) complexes is a promising approach for photoactivated chemotherapy (PACT). The light-mediated activation of “strained” Ru(II) polypyridyl complexes resulted in ligand release and produced a ligand-deficient metal center capable of forming covalent adducts with biomolecules such as DNA. Based on the strategy of exploiting structural distortion to activate photochemistry, biologically active small molecules were coordinated to a Ru(II) scaffold to create light-triggered dual-action agents. Thirteen new Ru(II) complexes with pyridyl-pyrazol(in)e ligands were synthesized, and their photochemical reactivity and anticancer properties were investigated. Isomeric bidentate ligands were investigated, where “regular” ligands (where the coordinated nitrogens in the heterocycles are linked by C–C atoms) were compared to “inverse” isomers (where the coordinated nitrogens in the heterocycles are linked by C–N atoms). Coordination of the regular 3-(pyrid-2-yl)-pyrazol(in)es to a Ru(II) bis-dimethylphenanthroline scaffold yielded photoresponsive compounds with promising photochemical and biological properties, in contrast to the inverse 1-(pyrid-2-yl)-pyrazolines. The introduction of a phenyl ring to the 1N-pyrazoline cycle increased the distortion in complexes and improved ligand release upon light irradiation (470 nm) up to 5-fold in aqueous media. Compounds 1–8, containing pyridyl-pyrazol(in)e ligands, were at least 20–80-fold more potent than the parent pyridyl-pyrazol(in)es, and exhibited biological activity in the dark, with half-maximal inhibitory concentration (IC50) values ranging from 0.2 to 7.6 μM in the HL60 cell line, with complete growth inhibition upon light irradiation. The diversification of coligands and introduction of a carboxylic acid into the Ru(II) complex resulted in compounds 9–12, with up to 146-fold improved phototoxicity indices compared with complexes 1–8.

Proapoptotic Activity of Achillea membranacea Essential Oil and Its Major Constituent 1,8-Cineole against A2780 Ovarian Cancer Cells.

Among the hundreds of reported Achillea species, A. membranacea (Labill.) DC. is one of the six that grow in Jordan. Many species of this genus are used in folk medicine to treat a variety of ailments and several biological and pharmacological activities have been ascribed to their essential oil (EO). For this study, the EO obtained from a specimen of A. membranacea grown in Jordan was analyzed by GC-MS. Ninety-six compounds were detected, of which oxygenated monoterpenes was the predominant class (47.9%), followed by non-terpene derivatives (27.9%), while sesquiterpenes represented 14.2% of the total composition. The most abundant compound in the EO was 1,8-cineole (21.7%). The cytotoxic activity of the EO was evaluated against three cancer cell lines (MCF7, A2780 and HT29), and one normal fibroblast cell line (MRC5) by MTT assay. Significant growth inhibition was observed in EO-exposed A2780 and HT29 cells (IC50 = 12.99 and 14.02 μg/mL, respectively), while MCF7 and MRC5 were less susceptible. The EO induced apoptosis and increased the preG1 events in A2780 cells. 1,8-Cineole, the major constituent of the EO, exhibited submicromolar cytotoxicity against A2780 cells, and was 42 times more selective against MRC5 cells. Its cytotoxicity against A2780 cells was comparable with that of doxorubicin, but 1,8-cineole was more selective for MRC5 normal cells. Interestingly, 1,8-cineole enhanced apoptosis in A2780, and caused a remarkable dose-dependent increase in preG1 events. Thus, 1,8-cineole has demonstrated promising cytotoxic and proapoptotic properties.

Synthesis and biological evaluation of structurally diverse α-conformationally restricted chalcones and related analogues.

Numerous members of the combretastatin and chalcone families of natural products function as inhibitors of tubulin polymerization through a binding interaction at the colchicine site on β-tubulin. These molecular scaffolds inspired the development of many structurally modified derivatives and analogues as promising anticancer agents. A productive design blueprint that involved molecular hybridization of the pharmacophore moieties of combretastatin A-4 (CA4) and the chalcones led to the discovery of two promising lead molecules referred to as KGP413 and SD400. The corresponding water-soluble phosphate prodrug salts of KGP413 and SD400 selectively damaged tumor-associated vasculature, thus highlighting the potential development of these molecules as vascular disrupting agents (VDAs). These previous studies prompted our current investigation of conformationally restricted chalcones. Herein, we report the synthesis of cyclic chalcones and related analogues that incorporate structural motifs of CA4, and evaluation of their cytotoxicity against human cancer cell lines [NCI-H460 (lung), DU-145 (prostate), and SK-OV-3 (ovarian)]. While these molecules proved inactive as inhibitors of tubulin polymerization (IC50 > 20 μM), eight molecules demonstrated good antiproliferative activity (GI50 < 20 μM) against all three cancer cell lines, and compounds 2j and 2l demonstrated sub-micromolar cytotoxicity. To the best of our knowledge these molecules represent the most potent (based on GI50) cyclic chalcones known to date, and are promising lead molecules for continued investigation.

Synthesis, conformational preferences, and biological activity of conformational analogues of the microtubule-stabilizing agents, (-)-zampanolide and (-)-dactylolide.

Zampanolide and dactylolide are microtubule-stabilizing polyketides possessing potent cytotoxicity towards a variety of cancer cell lines. Using our understanding of the conformational preferences of the macrolide core in both natural products, we hypothesized that analogues lacking the C17-methyl group would maintain the necessary conformation for bioactivity while reducing the number of synthetic manipulations necessary for their synthesis. Analogues 3, 4 and 5 were prepared via total synthesis, and their conformational preferences were determined through computational and high-field NMR studies. While no observable activities were present in dactylolide analogues 3 and 4, zampanolide analogue 5 exhibited sub-micromolar cytotoxicity. Herein, we describe these efforts towards understanding the structure- and conformation-activity relationships of dactylolide and zampanolide.

Seaweed Secondary Metabolites In Vitro and In Vivo Anticancer Activity.

Isolation, finding or discovery of novel anticancer agents is very important for cancer treatment, and seaweeds are one of the largest producers of chemically active metabolites with valuable cytotoxic properties, and therefore can be used as new chemotherapeutic agents or source of inspiration to develop new ones. Identification of the more potent and selective anticancer components isolated from brown, green and red seaweeds, as well as studies of their mode of action is very attractive and constitute a small but relevant progress for pharmacological applications. Several researchers have carried out in vitro and in vivo studies in various cell lines and have disclosed the active metabolites among the terpenoids, including carotenoids, polyphenols and alkaloids that can be found in seaweeds. In this review the type of metabolites and their cytotoxic or antiproliferative effects will be discussed additionally their mode of action, structure-activity relationship and selectivity will also be revealed. The diterpene dictyolactone, the sterol cholest-5-en-3β,7α-diol and the halogenated monoterpene halomon are among the reported compounds, the ones that present sub-micromolar cytotoxicity. Additionally, one dimeric sesquiterpene of the cyclolaurane-type, three bromophenols and one halogenated monoterpene should be emphasized because they exhibit half maximal inhibitory concentration (IC50) values between 1–5 µM against several cell lines.

Macrophilone A: Structure Elucidation, Total Synthesis, and Functional Evaluation of a Biologically Active Iminoquinone from the Marine Hydroid Macrorhynchia philippina.

A previously uncharacterized pyrroloiminoquinone natural product, macrophilone A, was isolated from the stinging hydroid Macrorhynchia philippina. The structure was assigned utilizing long-range NMR couplings and DFT calculations and proved by a concise, five-step total synthesis. Macrophilone A and a synthetic analogue displayed potent biological activity, including increased intracellular reactive oxygen species levels and submicromolar cytotoxicity toward lung adenocarcinoma cells.

Ulapualides C-E Isolated from a Hawaiian Hexabranchus sanguineus Egg Mass.

Three new ulapualides (3-5) were isolated from egg masses of the nudibranch Hexabranchus sanguineus. The structures of 3-5 were deduced by analyses of physical and spectroscopic data in comparisons with ulapualides A (1) and B (2). Ulapualide C demonstrated submicromolar cytotoxicity against select NCI cell lines (768-0, DU-145, MDA-MB-231, and A549) with the most potent activity against MDA-MB-231 cells (IC50 0.58 μM). Ulapualides A (1) and B (2) were 2- to 4-fold more potent than 3.

Tumor-selective Cytotoxicity of a Novel Pentadiene Analogue on Human Leukemia/lymphoma Cells

A novel series of structurally divergent 1,5-diaryl-3-oxo-1,4-pentadiene analogues 1-10 displayed marked cytotoxic potencies towards a number of human leukemia/lymphoma cells. To identify novel selective cytotoxic compounds that induce apoptosis. The Differential Nuclear Staining (DNS) screening protocol was utilized to measure the cytotoxicity of all experimental dienones on several cancerous cells. Additionally, the selective cytotoxicity index was calculated by comparing the dienone's cytotoxicity between leukemia/lymphoma cells vs. non-cancerous cells. Furthermore, to discern whether a selected dienone induced cell death via apoptosis or necrosis on T-lymphocyte leukemia cells, diverse approaches were utilized to detect individual biochemical facets of apoptosis. The dienones were tested for their anti-neoplastic efficiency on human leukemia/lymphoma-derived cell lines. Special emphasis was applied on dienone 1, on the basis of its sub-micromolar cytotoxicity (CC50=0.43+0.02 μM) and high selective cytotoxicity index (11.1) exerted on T-leukemia cells. In general, dienone 1 showed the most potent cytotoxic properties as compared to other dienones and a related reference cytotoxin curcumin as well as the EF-24 curcumin analogue. Dienone 1 caused cell death by apoptosis in Jurkat cells as evidenced by inducing phosphatidylserine externalization, mitochondrial depolarization and caspase-3/7. These effects were mainly attributed to the induction of apoptotic pathways. The novel dienone 1 was found to exhibit potent anti-leukemia activity by inducing programmed cell death/apoptosis. Consequently, dionone 1 should be developed further to examine its potential efficacy to combat malignancies in a pre-clinical animal model.

Transition‐Metal‐Free Synthesis of Polysubstituted Cyclopropane Derivatives from N‐Tosylhydrazones and their Cytotoxic Activities

AbstractWe describe a general method for metal‐free cyclopropanation of different electron‐deficient olefins with N‐tosylhydrazones as a source of diazo compounds. This method works with N‐tosylhydrazones derived from acetophenones or benzophenones. This reaction is carried out in the presence of LiOtBu as a base to generate diazo species in situ. This method is compatible with various electron‐donating or electron‐withdrawing substituents and allows us to obtain a large library of functionalized tetrasubstituted cyclopropanes. Furthermore, we have used this method to synthesize isocombretastatine A4 analogues, which have submicromolar cytotoxicity against HCT‐116 cell lines.

One-pot synthesis of cinnamylideneacetophenones and their in vitro cytotoxicity in breast cancer cells

A series of cinnamylideneacetophenones were synthesized via a modified Claisen–Schmidt condensation reaction and evaluated for cytotoxicity against breast cancer cells using the Alamar Blue™ assay. Derivatives 17 and 18 bearing a 2-nitro group on the B ring, exhibited sub-micromolar cytotoxicity in MCF-7 cells (IC50=71 and 1.9nM), respectively. Derivative 17 also displayed sub-micromolar (IC50=780nM) cytotoxicity in MDA-MB-468 cells. Additionally, 17 and 18 displayed significantly less cytotoxicity than the chemotherapeutic doxorubicin in non-tumorigenic MCF-10A cells. This study provides evidence supporting the continued development of nitro-substituted cinnamylideneacetophenones as small molecules to treat breast cancer.

Synthesis and topoisomerase I inhibitory activity of a novel diazaindeno[2,1-b]phenanthrene analogue of Lamellarin D

A novel 5-oxa-6a,8-diazaindeno[2,1-b]phenanthren-7-one scaffold was designed and synthesized as an active analogue of the cytotoxic marine alkaloid Lamellarin D. The design was based on molecular modeling of the site of interaction of Lamellarin D with DNA–topoisomerase I cleavable complex, whereas the synthesis capitalized on a simple Friedel–Crafts cyclization of indole to a β-carbolinone nucleus. The product exhibited topoisomerase I poisoning activity and submicromolar cytotoxicity on human non-small cell lung cancer H460 cell line.

Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents

Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. Combilexin molecules, which combine DNA minor groove binding and intercalating functionalities, have the potential for increased DNA binding affinity and increased selectivity due to their dual mode of DNA binding. This study describes the synthesis of DNA minor groove binder netropsin analogs containing either one or two N-methylpyrrole carboxamide groups linked to DNA-intercalating anthrapyrazoles. Those hybrid molecules which had both two N-methylpyrrole groups and terminal (dimethylamino)alkyl side chains displayed submicromolar cytotoxicity towards K562 human leukemia cells. The combilexins were also evaluated for DNA binding by measuring the increase in DNA melting temperature, for DNA topoisomerase IIalpha-mediated double strand cleavage of DNA, for inhibition of DNA topoisomerase IIalpha decatenation activity, and for inhibition of DNA topoisomerase I relaxation of DNA. Several of the compounds stabilized the DNA-topoisomerase IIalpha covalent complex indicating that they acted as topoisomerase IIalpha poisons. Some of the combilexins had higher affinity for DNA than their parent anthrapyrazoles. In conclusion, a novel group of compounds combining DNA intercalating anthrapyrazole groups and minor groove binding netropsin analogs have been designed, synthesized and biologically evaluated as possible novel anticancer agents.

Abstract 3509: Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents

Abstract Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. Combilexin molecules, which combine DNA minor groove binder and intercalator functionalities, have the potential for increased DNA binding affinity and increased cytotoxicity due to their dual mode of DNA binding. In this study DNA minor groove binder netropsin analogs containing either a mono-N-methylpyrrole carboxamide or two units of N-methylpyrrole carboxamide linked to DNA intercalating anthrapyrazoles were synthesized. Two of the hybrid molecules which possessed bis-methylpyrrole moities and amine head groups displayed submicromolar cytotoxicity towards K562 human leukemia cells. The synthesized hybrids were also evaluated for DNA binding by measuring the increase in DNA melting temperature, for DNA topoisomerase IIα-mediated double strand cleavage of DNA, for inhibition of DNA topoisomerase IIα decatenation activity, and for inhibition DNA topoisomerase I relaxation of DNA. Several of the compounds stabilized the DNA-topoisomerase IIα covalent complex, indicating that they acted as topoisomerase IIα poisons. The results indicate that the hybrid agents have higher affinity for DNA than the parent compounds. In conclusion, a novel group of compounds combining DNA intercalating anthrapyrazoles and minor groove binding netropsin analogs have been designed, synthesized and biologically evaluated as possible novel anticancer agents. Support: CIHR, a Canada Research Chair in Drug Development, National Institutes of Health grant CA090787 to J.C.Y., the Dishman Foundation at Southwestern University and the Robert A. Welsh Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3509.

X-ray structural analysis, antioxidant and cytotoxic activity of newly synthesized salicylic acid derivatives

New salicylic (2-hydroxybenzoic) acid derivatives 1–6 were prepared by conventional heating or microwave irradiation of a mixture consisting of methyl salicylate and the corresponding amino alcohol (2,2′-dihydroxydiethylamine, 2,2′,2″-trihydroxytriethylamine or N-phenyl-2,2′-dihydroxydiethylamine) and metallic sodium as catalyst. For compounds 1, 3, and 5 X-ray structure analysis was performed, as well as molecular mechanics calculations (MMC), to define their conformation in terms of their energy minima. Comparison of crystal and MMC structures for these three compounds (1, 3, and 5) revealed that the intramolecular hydrogen bonds play an important role, stabilizing conformation of the most part of the molecule. The antioxidant activity and cytotoxicity of the synthesized derivatives were evaluated in a series of in vitro tests. The newly synthesized compounds exhibited strong activity against hydroxyl radical, as well as promising lipid peroxidation inhibition. The study showed that the electronic effects of the groups at the N atom are responsible for neutralization of the OH radical, i.e., antioxidant activity. Compounds 1–3 exhibited sub-micromolar cytotoxicity against HeLa S3, whereas compounds 1, 3 and 5 efficiently inhibited the growth of PC3 cells.

An asymmetric C8/C8′-tripyrrole-linked sequence-selective pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimer DNA interstrand cross-linking agent spanning 11 DNA base pairs

A novel sequence-selective extended PBD dimer 4 has been synthesized that binds with high affinity to an interstrand cross-linking site spanning 11 DNA base pairs. Despite its molecular weight (984.07) and length, the molecule has significant DNA interstrand cross-linking potency (approximately 100-fold greater than the clinically used agent melphalan) and sub-micromolar cytotoxicity in a number of tumour cell lines, suggesting that it readily penetrates cellular and nuclear membranes to reach its DNA target.

Synthesis, Antitumor Activity, and Mechanism of Action of Benzo[a]pyrano[3,2-h]acridin-7-one Analogues of Acronycine

Twenty-two derivatives belonging to the cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[a]pyrano[3,2-h]acridin-7-one series were synthesized in nine steps starting from 3,5-dimethoxyacetanilide (5) and 2-methoxy-1-naphthalenecarboxylic acid (7). Most of them exhibited submicromolar cytotoxicity when tested against murine leukemia (L1210) and human epidermoid carcinoma (KB-3-1) cell lines. The cytotoxic activity correlated strongly with the ability of the compounds to form covalent adducts with purified DNA. Among the most active compounds, 25, with IC50 values of 0.7 and 0.15 microM against L1210 and KB-3-1, respectively, was selected for evaluation in vivo against Colon 38 adenocarcinoma implanted in mice. This compound was active at 3 mg/kg i.v. (day 12 and 24) with 3/7 tumor free mice by day 80.