Platinum(IV) Prodrugs Incorporating an Indole-Based Derivative, 5-Benzyloxyindole-3-Acetic Acid in the Axial Position Exhibit Prominent Anticancer Activity.

Kinetically inert platinum(IV) complexes are a chemical strategy to overcome the impediments of standard platinum(II) antineoplastic drugs like cisplatin, oxaliplatin and carboplatin. In this study, we reported the syntheses and structural characterisation of three platinum(IV) complexes that incorporate 5-benzyloxyindole-3-acetic acid, a bioactive ligand that integrates an indole pharmacophore. The purity and chemical structures of the resultant complexes, P-5B3A, 5-5B3A and 56-5B3A were confirmed via spectroscopic means. The complexes were evaluated for anticancer activity against multiple human cell lines. All complexes proved to be considerably more active than cisplatin, oxaliplatin and carboplatin in most cell lines tested. Remarkably, 56-5B3A demonstrated the greatest anticancer activity, displaying GI50 values between 1.2 and 150 nM. Enhanced production of reactive oxygen species paired with the decline in mitochondrial activity as well as inhibition of histone deacetylase were also demonstrated by the complexes in HT29 colon cells.

Synthesis and Characterisation of Platinum(II) Diaminocyclohexane Complexes with Pyridine Derivatives as Anticancer Agents.

Cisplatin-type covalent chemotherapeutics are a cornerstone of modern medicinal oncology. However, these drugs remain encumbered with dose-limiting side effects and are susceptible to innate and acquired resistance. The bulk of platinum anticancer research has focused on Cisplatin and its derivatives. Here, we take inspiration from the design of platinum complexes and ligands used successfully with other metals to create six novel complexes. Herein, the synthesis, characterization, DNA binding affinities, and lipophilicity of a series of non-traditional organometallic Pt(II)-complexes are described. These complexes have a basic [Pt(PL)(AL)]Cl2 molecular formula which incorporates either 2-pyrrolidin-2-ylpyridine, 2-(1H-Imidazol-2-yl)pyridine, or 2-(2-pyridyl)benzimidazole as the PL; the AL is resolved diaminocyclohexane. Precursor [Pt(PL)(Cl)2] complexes were also characterized for comparison. While the cytotoxicity and DNA binding properties of the three precursors were unexceptional, the corresponding [Pt(PL)(AL)]2+ complexes were promising; they exhibited different DNA binding interactions compared with Cisplatin but with similar, if not slightly better, cytotoxicity results. Complexes with 2-pyrrolidin-2-ylpyridine or 2-(2-pyridyl)benzimidazole ligands had similar DNA binding properties to those with 2-(1H-Imidazol-2-yl)pyridine ligands but were not as cytotoxic to all cell lines. The variation in activity between cell lines was remarkable and resulted in significant selectivity indices in MCF10A and MCF-7 breast cancer cell lines, compared with previously described similar Pt(II) complexes such as 56MESS.

Versatile Platinum(IV) Prodrugs of Naproxen and Acemetacin as Chemo-Anti-Inflammatory Agents.

Developing new and versatile platinum(IV) complexes that incorporate bioactive moieties is a rapidly evolving research strategy for cancer drug discovery. In this study, six platinum(IV) complexes (1-6) that are mono-substituted in the axial position with a non-steroidal anti-inflammatory molecule, naproxen or acemetacin, were synthesised. A combination of spectroscopic and spectrometric techniques confirmed the composition and homogeneity of 1-6. The antitumour potential of the resultant complexes was assessed on multiple cell lines and proved to be significantly improved compared with cisplatin, oxaliplatin and carboplatin. The platinum(IV) derivatives conjugated with acemetacin (5 and 6) were determined to be the most biologically potent, demonstrating GI50 values ranging between 0.22 and 250 nM. Remarkably, in the Du145 prostate cell line, 6 elicited a GI50 value of 0.22 nM, which is 5450-fold more potent than cisplatin. A progressive decrease in reactive oxygen species and mitochondrial activity was observed for 1-6 in the HT29 colon cell line, up to 72 h. The inhibition of the cyclooxygenase-2 enzyme was also demonstrated by the complexes, confirming that these platinum(IV) complexes may reduce COX-2-dependent inflammation and cancer cell resistance to chemotherapy.

Synthesis and Characterisation of Fluorescent Novel Pt(II) Cyclometallated Complexes with Anticancer Activity.

Cancer poses a significant threat to global health and new treatments are required to improve the prognosis for patients. Previously, unconventional platinum complexes designed to incorporate polypyridyl ligands paired with diaminocyclohexane have demonstrated anticancer activity in KRAS mutated cells, previously thought to be undruggable and have cytotoxicity values up to 100 times better than cisplatin. In this work, these complexes were used as inspiration to design six novel cyclometallated examples, whose fluorescence could be exploited to better understand the mechanism of action of these kinds of platinum drugs. The cytotoxicity results revealed that these cyclometallated complexes (CMCs) have significantly different activity compared to the complexes that inspired them; they are as cytotoxic as cisplatin and have much higher selectivity indices in breast cancer cell lines (MCF10A/MCF-7). Complexes 1b, 2a, and 3b all had very high selectivity indexes compared to previous Pt(II) complexes. This prompted further investigation into their DNA binding properties, which revealed that they had good affinity to ctDNA, especially CMCs 1a and 3b. Their inherent fluorescence was successfully utilised in the calculation of their DNA binding affinity and could be useful in future work.

Potent Platinum(IV) Prodrugs That Incorporate a Biotin Moiety to Selectively Target Cancer Cells.

Four platinum(IV) prodrugs incorporating a biotin moiety to selectively target cancer cells were synthesised, characterised, and their biological activity assessed. All complexes exhibited exceptional in vitro cytotoxicity against a panel of cancer cell lines, with [Pt(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO3)2, (2) exhibiting the lowest GI50 of 4 nM in the prostate Du145 cancer cell line. Each complex displayed significantly enhanced activity compared to cisplatin, with 2 being 1000-fold more active in the HT29 colon cancer cell line. Against the MCF-7 breast cancer cell line, in which high levels of biotin receptors are expressed, 2, [Pt(4,7-dimethoxy-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO3)2, (3), and [Pt(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)(biotin)(hydroxido)](NO3)2, (4) exhibited enhanced activity compared to their platinum(II) cores, with 4 being 6-fold more active than its platinum(II) precursor. Furthermore, 3 exhibited 3-fold greater selectivity towards MCF-7 breast cancer cells compared to MCF10A breast healthy cells, and this was further confirmed by platinum uptake studies, which showed 3 to have almost 3-fold greater uptake in MCF-7 cells, compared to MCF10A cells. The results show that lipophilicity and selectivity both contributed to the cellular uptake of 1-4; however, this was not always translated to the observed cytotoxicity.

Novel Platinum(II) and Platinum(IV) Antitumor Agents that Exhibit Potent Cytotoxicity and Selectivity.

A novel platinum(II) complex 47OMESS(II) and its platinum(IV) derivative 47OMESS(IV) were synthesized and characterized. Cytotoxicity studies against mesenchymal cells (MCs) and lung (A549), breast (MDA-MB-231), and melanoma (A375) cancer cells demonstrated 7-20-fold superior activity for both complexes relative to cisplatin. Remarkably, 47OMESS(IV) demonstrated 17-22-fold greater selectivity toward the cancerous cells compared to the non-cancerous MCs. Western blot analysis on A549 cells showed the involvement of the intrinsic apoptotic pathway. Cellular fractionation and uptake experiments in A549 cells using ICP-mass spectrometry (MS) indicated that 47OMESS(II) and 47OMESS(IV) cross the cellular membrane predominantly via active transport mechanisms. The significant improvement in selectivity that is exhibited by 47OMESS(IV) is reported for the first time for this class of complexes.

Bioactive Platinum(IV) Complexes Incorporating Halogenated Phenylacetates.

A new series of cytotoxic platinum(IV) complexes (1-8) incorporating halogenated phenylacetic acid derivatives (4-chlorophenylacetic acid, 4-fluorophenylacetic acid, 4-bromophenylacetic acid and 4-iodophenylacetic acid) were synthesised and characterised using spectroscopic and spectrometric techniques. Complexes 1-8 were assessed on a panel of cell lines including HT29 colon, U87 glioblastoma, MCF-7 breast, A2780 ovarian, H460 lung, A431 skin, Du145 prostate, BE2-C neuroblastoma, SJ-G2 glioblastoma, MIA pancreas, the ADDP-resistant ovarian variant, and the non-tumour-derived MCF10A breast line. The in vitro cytotoxicity results confirmed the superior biological activity of the studied complexes, especially those containing 4-fluorophenylacetic acid and 4-bromophenylacetic acid ligands, namely 4 and 6, eliciting an average GI50 value of 20 nM over the range of cell lines tested. In the Du145 prostate cell line, 4 exhibited the highest degree of potency amongst the derivatives, displaying a GI50 value of 0.7 nM, which makes it 1700-fold more potent than cisplatin (1200 nM) and nearly 7-fold more potent than our lead complex, 56MESS (4.6 nM) in this cell line. Notably, in the ADDP-resistant ovarian variant cell line, 4 (6 nM) was found to be almost 4700-fold more potent than cisplatin. Reduction reaction experiments were also undertaken, along with studies aimed at determining the complexes' solubility, stability, lipophilicity, and reactive oxygen species production.

Novel Planar Pt(II) Cyclometallated Cytotoxic Complexes with G-Quadruplex Stabilisation and Luminescent Properties.

Herein is described the development of a series of novel quadruplex DNA (QDNA)-stabilising cyclometallated square-planar metal complexes (CMCs). Melting experiments using quadruplex DNA (QDNA) demonstrated that interactions with the complexes increased the melting temperature by up to 19 °C. This QDNA stabilisation was determined in two of the major G-quadruplex structures formed in the human c-MYC promoter gene (c-MYC) and a human telomeric repeat sequence (H-Telo). The CMCs were found to stabilise H-telo more strongly than c-MYC, and the CMCs with the highest cytotoxic effect had a low-moderate correlation between H-telo binding capacity and cytotoxicity (R2 values up to 10 times those of c-MYC). The melting experiments further revealed that the stabilisation effect was altered depending on whether the CMC was introduced before or after the formation of QDNA. All CMCs' GI50 values were comparable or better than cisplatin in human cancer cell lines HT29, U87, MCF-7, H460, A431, Du145, BE2-C, SJ-G2, MIA, and ADDP. Complexes 6, 7, and 9 were significantly more cytotoxic than cisplatin in all cell lines tested and had good to moderate selectivity indices, 1.7-4.5 in MCF10A/MCF-7. The emission quantum yields were determined to be relatively high (up to 0.064), and emission occurred outside cellular autofluorescence, meaning CMC fluorescence is ideal for in vitro analyses.

Potent Chlorambucil-Platinum(IV) Prodrugs.

The DNA-alkylating derivative chlorambucil was coordinated in the axial position to atypical cytotoxic, heterocyclic, and non-DNA coordinating platinum(IV) complexes of type, [PtIV(HL)(AL)(OH)2](NO3)2 (where HL is 1,10-phenanthroline, 5-methyl-1,10-phenanthroline or 5,6-dimethyl-1,10-phenanthroline, AL is 1S,2S-diaminocyclohexane). The resultant platinum(IV)-chlorambucil prodrugs, PCLB, 5CLB, and 56CLB, were characterized using high-performance liquid chromatography, nuclear magnetic resonance, ultraviolet-visible, circular dichroism spectroscopy, and electrospray ionization mass spectrometry. The prodrugs displayed remarkable antitumor potential across multiple human cancer cell lines compared to chlorambucil, cisplatin, oxaliplatin, and carboplatin, as well as their platinum(II) precursors, PHENSS, 5MESS, and 56MESS. Notably, 56CLB was exceptionally potent in HT29 colon, Du145 prostate, MCF10A breast, MIA pancreas, H460 lung, A2780, and ADDP ovarian cell lines, with GI50 values ranging between 2.7 and 21 nM. Moreover, significant production of reactive oxygen species was detected in HT29 cells after treatment with PCLB, 5CLB, and 56CLB up to 72 h compared to chlorambucil and the platinum(II) and (IV) precursors.

Cyclooxygenase-Inhibiting Platinum(IV) Prodrugs with Potent Anticancer Activity.

Platinum(IV) prodrugs of the [Pt(PL)(AL)(COXi)(OH)]2+ type scaffold (where PL is 1,10-phenanthroline or 5,6-dimethyl-1,10-phenanthroline, AL is 1S,2S-diaminocyclohexane, and COXi is a COX inhibitor, either indomethacin or aspirin) were synthesised and characterised, and their biological activity was explored. MTT assays showed that these complexes exhibit outstanding activity against a range of cancer cell lines, and nanomolar activities were observed. The most potent complex, 4, exhibited a GI50 of 3 nM in the Du145 prostate cancer cell line and was observed to display a 1614-fold increased activity against the HT29 colon cancer cell line relative to cisplatin. ICP-MS studies showed a linear correlation between increased cellular accumulation of the complexes and increased cytotoxicity, while an enzyme immunoassay showed that 1 and 2 inhibited COX-2 at 14 and 1.4 µM, respectively, which is comparable to the inhibition exhibited by indomethacin. These results suggest that while the cytotoxicity of prodrugs 1-4 was influenced by cellular uptake, it was not entirely dependent on either COX inhibition or lipophilicity.

Synthesis, characterisation and biological activity of the ruthenium(II) complexes of the N4-tetradentate (N4-TL), 1,6-di(2'-pyridyl)-2,5-dibenzyl-2,5-diazahexane (picenBz2).

A series of complexes of the type rac-cis-ß-[Ru(N4-TL)(N2-bidentates)]2+ (where N4-TL = 1,6-di(2'-pyridyl)-2,5-dibenzyl-2,5-diazahexane (picenBz2, N4-TL-2) and N2-bidentates = 1,10-phenanthroline (phen, Ru-2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, Ru-3), 7,8-dimethyl-dipyrido[3,2-a:2',3'-c] phenazine (dppzMe2,Ru-4), 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBz, Ru-5), 2-(p-tolyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBzMe, Ru-6), 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phenpyrBzNO2,Ru-7), were synthesised and characterised and X-ray crystallography of Ru-5 obtained. The in vitro cytotoxicity assays revealed that Ru-6 was 5, 2 and 19-fold more potent than oxaliplatin, cisplatin, and carboplatin, respectively displaying an average GI50 value of ≈ 0.76 µM against a panel of 11 cancer cell lines.

Pyrimidyn-Based Dynamin Inhibitors as Novel Cytotoxic Agents.

Five focused libraries of pyrimidine-based dynamin GTPase inhibitors, in total 69 compounds were synthesised, and their dynamin inhibition and broad-spectrum cytotoxicity examined. Dynamin plays a crucial role in mitosis, and as such inhibition of dynamin was expected to broadly correlate with the observed cytotoxicity. The pyrimidines synthesised ranged from mono-substituted to trisubstituted. The highest levels of dynamin inhibition were noted with di- and tri- substituted pyrimidines, especially those with pendent amino alkyl chains. Short chains and simple heterocyclic rings reduced dynamin activity. There were three levels of dynamin activity noted: 1-10, 10-25 and 25-60 µM. Screening of these compounds in a panel of cancer cell lines: SW480 (colon), HT29 (colon), SMA (spontaneous murine astrocytoma), MCF-7 (breast), BE2-C (glioblastoma), SJ-G2 (neuroblastoma), MIA (pancreas), A2780 (ovarian), A431 (skin), H460 (lung), U87 (glioblastoma) and DU145 (prostate) cell lines reveal a good correlation between the observed dynamin inhibition and the observed cytotoxicity. The most active analogues (31 a,b) developed returned average GI50 values of 1.0 and 0.78 µM across the twelve cell lines examined. These active analogues were: N2 -(3-dimethylaminopropyl)-N4 -dodecyl-6-methylpyrimidine-2,4-diamine (31 a) and N4 -(3-dimethylaminopropyl)-N2 -dodecyl-6-methylpyrimidine-2,4-diamine (31 b).

Amino alcohol acrylonitriles as broad spectrum and tumour selective cytotoxic agents.

We have identified specific dichlorophenylacrylonitriles as lead compounds in the development of novel anticancer compounds, notably, (Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide (1) and ANI-7 (2). Herein we specifically probe the SAR associated with the terminal aromatic ring and associated cytoxicity in a broad range of human cancer cell lines. Synthesis of three focused libraries revealed a poor tolerance for electron withdrawing and donating moieties (Library A). A clear preference for hydrophobic substituents on a terminal piperazine moiety (Library B) with good levels of broad spectrum cytotoxicity, e.g. 13a (GI50 2.5-6.0 µM), as did the introduction of a methylene spacer with 13i (4-CH3PhCH2; GI50 1.5-4.5 µM). Removal of the aromatic moiety and installation of simple hydrophobic groups (Library C), in particular an adamantyl moiety, afforded highly active broad spectrum cytotoxic agents with GI50 values ranging from 1.7 µM (14k; 1-adamantyl) to 5.6 µM (14i; pyrrolidine). Within these libraries we note lung cancer selectivity, relative to normal cells, of 13h (fluoro substituted acrylonitrile, GI50 1.6 µM, 9.3-fold selective); the colorectal selectivity of 14h (methylpiperidine analogue, GI50 0.36 µM, 6.9-fold selective) and the breast cancer selectivity of 13f (nitrile substituted acrylonitrile, GI50 2.3-6.0 µM, up to 20-fold selective). The latter was confirmed as a novel AhR ligand and a CYP1A1 activating compound, that likely induces cell death following bioactivation; a phenomenon previously described in breast cancer cell populations.

Modelling and Phenotypic Screening of NAP-6 and 10-Cl-BBQ, AhR Ligands Displaying Selective Breast Cancer Cytotoxicity in Vitro.

To exploit the interaction of the aryl hydrocarbon receptor (AhR) pathway in developing breast-cancer-specific cytotoxic compounds, we examined the breast cancer selectivity and the docking pose of the AhR ligands (Z)-2-(2-aminophenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NAP-6; 5) and 10-chloro-7H-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (10-Cl-BBQ; 6). While the breast cancer selectivity of 5 in vitro is known, we discuss the SAR around this lead and, by using phenotypic cell-line screening and the MTT assay, show for the first time that 6 also presents with breast cancer selectivity, notably in the triple-negative (TN) receptor breast cancer cell line MDA-MB-468, the ER+ breast cancer cell lines T47D, ZR-75-1 and the HER2+ breast cancer cell line SKBR3 (GI50 values of 0.098, 0.97, 0.13 and 0.21 µM, respectively). Indeed, 6 is 55 times more potent in MDA-MB-468 cells than normal MCF10A breast cells (GI50 of 0.098 vs 5.4 µM) and more than 130 times more potent than in cell lines derived from pancreas, brain and prostate (GI50 of 0.098 vs 10-13 µM). Molecular docking poses of 5 and 6 together with analogue synthesis and phenotypic screening show the importance of the naphthalene moiety, and an ortho-disposed substituent on the N-phenyl moiety for biological activity.

Amino Alcohol Acrylonitriles as Activators of the Aryl Hydrocarbon Receptor Pathway: An Unexpected MTT Phenotypic Screening Outcome.

Lead (Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide, 1 showed MCF-7 GI50 =30 nM and 400-fold selective c.f. MCF10A (normal breast tissue). Acetamide moiety modification (13 a-g) to introduce additional hydrophobicity was favoured with MCF-7 breast cancer cell activity enhanced at 1.3 nM. Other analogues were potent against the HT29 colon cancer cell line at 23 nM. Textbook SAR data was observed in the MCF-7 cell line, in an MTT assay, via the ortho (17 a), meta (17 b) and para (13 f). The amino alcohol -OH moiety was pivotal, but no stereochemical preference noted. But, these data did not fit our homology modelling expectations. Aberrant MTT ((3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) screening results and metabolic interference confirmed by sulforhodamine B (SRB) screening. Interfering analogues resulted in 120 and 80-fold CYP1A1 and CYP1A2 amplification, with no upregulation of SULT1A1. This is consistent with activation of the AhR pathway. Piperidine per-deuteration reduced metabolic inactivation. 3-OH / 4-OH piperidine analogues showed differential MTT and SRB activity supporting MTT assay metabolic inactivation. Data supports piperidine 3-OH, but not the 4-OH, as a CYP substrate. This family of ß-amino alcohol substituted 3,4-dichlorophenylacetonitriles show broad activity modulated via the AhR pathway. By SRB analysis the most potent analogue was 23 b, (Z)-3-(4-(3-(4-phenylpiperidin-1-yl)-2-hydroxypropoxy)phenyl)-2-(3,4-dichlorophenyl)-acrylonitrile.

A simplified method to calculate telomere length from Southern blot images of terminal restriction fragment lengths.

Southern blotting of DNA terminal restriction fragment lengths is the gold standard for measuring mean telomere length. Analysis of the final image is a crucial step in this process, however, current techniques are cumbersome and prone to error. Here we present a simple and accurate method for analyzing telomere smears. Basic 2D gel imaging software was used to automatically subtract background, generate standard curves and calculate net intensity and MW at each position (i) along the telomere smear. Our method required no statistical software or major data manipulation and correctly classified >80% of 18 samples as having short, medium or long telomeres compared with 33-72% using other methods.

Synthesis, characterisation and influence of lipophilicity on cellular accumulation and cytotoxicity of unconventional platinum(iv) prodrugs as potent anticancer agents.

Lipophilic platinum(iv) complexes were synthesised of the type [Pt(HL)(AL)(OH)(R)]2+ and [Pt(HL)(AL)(R)2]2+ (HL = 5,6-dimethyl-1,10-phenanthroline or 1,10-phenanthroline; AL = 1S,2S-diaminocyclohexane and R = increasingly lipophilic carboxylate axial ligands (C10-18)) from hydrophilic platinum(ii) precursors that exhibit exceptional anticancer activity. The increased overall lipophilicity of the complexes suggested the formation of spontaneously self-assembled structures in an aqueous environment. The anti-proliferative properties were assessed against one non-cancerous and a panel of cancerous cell lines. Nanomolar levels of activity were observed against several cell lines, with the lowest GI50 of 3.4 nm against the Du145 prostate cancer cell line and over 1100-fold greater activity than cisplatin against HT29 colon carcinoma. RP-HPLC was utilised to establish the relative lipophilicities of each complex. While there seemed to be an increase in cellular accumulation for the lipophilic derivatives in some instances, ICP-MS studies showed no clear correlation between increasing lipophilicity, cellular accumulation and cytotoxicity.

Synthesis, characterisation and potent cytotoxicity of unconventional platinum(iv) complexes with modified lipophilicity.

Novel platinum(iv) complexes were synthesised to examine the facile modulation of the lipophilicity of the complex by incorporating axial ligands of increasing length, ranging from 2-6 carbons. RP-HPLC was used to establish the lipophilicity of each complex. The in vitro cytotoxicities of all complexes were determined against a panel of malignant cell lines and a non-cancerous cell line. While there was no clear correlation between lipophilicity and cytotoxicity, all complexes demonstrated nanomolar activity against all cell lines. The most potent complexes exhibited 850-fold greater activity than cisplatin against HT29 colon carcinoma with GI50 values of 13 nM.

Synthesis and Cytotoxicity of Octahydroepoxyisoindole-7-carboxylic Acids and Norcantharidin-Amide Hybrids as Norcantharidin Analogues.

Octahydroepoxyisoindole analogues of norcantharidin were accessed through a Diels-Alder reaction of an amine-substituted furan with maleic anhydride and subsequent reduction of the bicyclo[2.2.1]heptene olefin. Despite retention of the carboxylate and the ether bridgehead known to impart cytotoxic activity to norcantharidin, none of these analogues displayed notable cytotoxicity against the 11 cell lines examined: HT29 (colon), MCF-7 (breast), A2780 (ovarian), H460 (lung), A431 (skin), Du145 (prostate), BE2-C (neuroblastoma), SJ-G2 and U87 (glioblastoma), MIA (pancreatic), and SMA (spontaneous murine astrocytoma). The incorporation of an amino-substituted system post-synthesis of norcantharidin afforded facile access to 14 acid/amide-substituted norcantharidin analogues. Of these, only four displayed sufficient activity at the initial 25 µm compound screening dose to warrant full evaluation of growth inhibition. Common to these analogues was the presence of a 4-biphenyl moiety, and in particular 3-(2-(furan-2-ylmethyl)-3-(4-biphenylamino)-3-oxopropylcarbamoyl)-7-oxabicyclo[2.2.1]heptane-2-carboxylic acid (13 c) and 3-(2-(pyrrole-2-ylmethyl)-3-(4-biphenylamino)-3-oxopropylcarbamoyl)-7-oxabicyclo[2.2.1]heptane-2-carboxylic acid (24) displayed high levels of cytotoxicity, returning GI50 values of 15 nm (HT29) to 2.9 µm (U87) and 17 nm (SMA) to 2.8 µm (U87), respectively. These are the most cytotoxic norcantharidin analogues reported to date.

Dichlorophenylacrylonitriles as AhR Ligands That Display Selective Breast Cancer Cytotoxicity in vitro.

Knoevenagel condensation of 3,4-dichloro- and 2,6-dichlorophenylacetonitriles gave a library of dichlorophenylacrylonitriles. Our leads (Z)-2-(3,4-dichlorophenyl)-3-(1H-pyrrol-2-yl)acrylonitrile (5) and (Z)-2-(3,4-dichlorophenyl)-3-(4-nitrophenyl)acrylonitrile (6) displayed 0.56±0.03 and 0.127±0.04 µm growth inhibition (GI50 ) and 260-fold selectivity for the MCF-7 breast cancer cell line. A 2,6-dichlorophenyl moiety saw a 10-fold decrease in potency; additional nitrogen moieties (-NO2 ) enhanced activity (Z)-2-(2,6-dichloro-3-nitrophenyl)-3-(2-nitrophenyl)acrylonitrile (26) and (Z)-2-(2,6-dichloro-3-nitrophenyl)-3-(3-nitrophenyl)acrylonitrile (27), with the corresponding -NH2 analogues (Z)-2-(3-amino-2,6-dichlorophenyl)-3-(2-aminophenyl)acrylonitrile (29) and (Z)-2-(3-amino-2,6-dichlorophenyl)-3-(3-aminophenyl)acrylonitrile (30) being more potent. Despite this, both 29 (2.8±0.03 µm) and 30 (2.8±0.03 µm) were found to be 10-fold less cytotoxic than 6. A bromine moiety effected a 3-fold enhancement in solubility with (Z)-3-(5-bromo-1H-pyrrol-2-yl)-2-(3,4-dichlorophenyl)acrylonitrile 18 relative to 5 at 211 µg mL-1 . Modeling-guided synthesis saw the introduction of 4-aminophenyl substituents (Z)-3-(4-aminophenyl)-2-(3,4-dichlorophenyl)acrylonitrile (35) and (Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide (38), with respective GI50 values of 0.030±0.014 and 0.034±0.01 µm. Other analogues such as 35 and 36 were found to have sub-micromolar potency against our panel of cancer cell lines (HT29, colon; U87 and SJ-G2, glioblastoma; A2780, ovarian; H460, lung; A431, skin; Du145, prostate; BE2-C, neuroblastoma; MIA, pancreas; and SMA, murine glioblastoma), except compound 38 against the U87 cell line. A more extensive evaluation of 38 ((Z)-N-(4-(2-cyano-2-(3,4-dichlorophenyl)vinyl)phenyl)acetamide) in a panel of drug-resistant breast carcinoma cell lines showed 10-206 nm potency against MDAMB468, T47D, ZR-75-1, SKBR3, and BT474. Molecular Operating Environment docking scores showed a good correlation between predicted binding efficiencies and observed MCF-7 cytotoxicity. This supports the use of this model in the development of breast-cancer-specific drugs.