Patrick J. Bednarski

Transferring the concept of multinuclearity to ruthenium complexes for improvement of anticancer activity.

Multinuclear platinum anticancer complexes are a proven option to overcome resistance of established anticancer compounds. Transferring this concept to ruthenium complexes led to the synthesis of dinuclear Ru(II)-arene compounds containing a bis(pyridinone)alkane ligand linker. A pronounced influence of the spacer length on the in vitro anticancer activity was found, which is correlated to the lipophilicity of the complexes. IC(50) values in the same dimension as for established platinum drugs were found in human tumor cell lines. No cross-resistance to oxoplatin, a cisplatin prodrug, was observed for the most active complex in three resistant cell lines; in fact, a 10-fold reversal of sensitivity in two of the oxoplatin-resistant lines was found. (Bio)analytical characterization of the representative examples showed that the ruthenium complexes hydrolyze rapidly, forming predominantly diaqua species that exhibit affinity toward transferrin and DNA, indicating that both proteins and nucleobases are potential targets.

Structure-activity relationships of targeted RuII(η6-p-cymene) anticancer complexes with flavonol-derived ligands.

RuII(arene) complexes have been shown to be promising anticancer agents, capable of overcoming major drawbacks of currently used chemotherapeutics. We have synthesized RuII(η6-arene) compounds carrying bioactive flavonol ligands with the aim to obtain multitargeted anticancer agents. To validate this concept, studies on the mode of action of the complexes were conducted which indicated that they form covalent bonds to DNA, have only minor impact on the cell cycle, but inhibit CDK2 and topoisomerase IIα in vitro. The cytotoxic activity was determined in human cancer cell lines, resulting in very low IC50 values as compared to other RuII(arene) complexes and showing a structure-activity relationship dependent on the substitution pattern of the flavonol ligand. Furthermore, the inhibition of cell growth correlates well with the topoisomerase inhibitory activity. Compared to the flavonol ligands, the RuII(η6-p-cymene) complexes are more potent antiproliferative agents, which can be explained by potential multitargeted properties.

Chiral platinum(II) metallointercalators with potent in vitro cytotoxic activity

Four platinum(II) metallointercalating complexes of 1,10‐phenanthroline (phen) with the chiral ancillary ligands trans‐R,R‐ and trans‐S,S‐1,2‐diaminocyclohexane (R,R‐ and S,S‐dach, respectively), and N,N′‐dimethyl‐R,R‐ and N,N′‐dimethyl‐S,S‐1,2‐diaminocyclohexane (Me2‐R,R‐dach and Me2‐S,S‐dach, respectively) have been synthesised and characterised. The crystal structure of [Pt(Me2‐S,S‐dach)(phen)](ClO4)2⋅1.5 H2O (C20H26Cl2N4O9.5Pt) has been determined; orthorhombic, space group P212121(No. 19), a=23.194(8), b=25.131(9), c=8.522(3) Å. In vitro cytotoxic assays (IC50) in the human bladder cancer cell line 5637 and in the murine leukemia L1210 cell line revealed that [Pt(S,S‐dach)(phen)](ClO4)2 (0.091 and 0.13 μM, respectively) and [Pt(R,R‐dach)(phen)](ClO4)2 (0.54 and 1.50 μM, respectively) were more cytotoxic than cisplatin (0.31 and 0.50 μM, respectively) and considerably more cytotoxic than their methylated counterparts, [Pt(Me2‐R,R‐dach)(phen)](ClO4)2 and [Pt(Me2‐S,S‐dach)(phen)](ClO4)2 (both>23 μM). Chiral discrimination for [Pt(S,S‐dach)(phen)](ClO4)2 over its R,R‐enantiomer was observed in all 13 cancer cell lines investigated. Moreover, [Pt(S,S‐dach)(phen)](ClO4)2 was more active than cisplatin in all cell lines tested and shows only partial cross‐resistance to cisplatin in two cisplatin resistant cell lines.

Trans,trans,trans-[PtIV(N3)2(OH)2(py)(NH3)]: A Light-Activated Antitumor Platinum Complex That Kills Human Cancer Cells by an Apoptosis-Independent Mechanism

Photoactivatable PtIV diazido complexes have unusual photobiologic properties. We show here that trans,trans,trans-[PtIV(N3)2(OH)2(py)(NH3)] complex 3 is a potent photoactivated cytotoxin toward human cancer cells in culture, with an average IC50 value in 13 cell lines of 55 ± 28 μmol/L after 30 minutes (0.12 mW/cm2) photoactivation with UVA, although visible light was also effective. Photoactivated complex 3 was noncross-resistant to cisplatin in 3 of 4 resistant cell lines. Cell swelling but very little blebbing was seen for HL60 cells treated with irradiated complex 3. Unlike cisplatin and etoposide, both of which cause apoptosis in HL60 cells, no apoptosis was observed for UVA-activated complex 3 by the Annexin V/propidium iodide flow cytotometry assay. Changes in the levels of the autophagic proteins LC3B-II and p62 in HL60 cells treated with UVA-activated complex 3 indicate autophagy is active during cell death. In a clonogenic assay with the SISO human cervix cancer cell line, 3 inhibited colony formation when activated by UVA irradiation. Antitumor activity of complex 3 in mice bearing xenografted OE19 esophageal carcinoma tumors was photoaugmented by visible light. Insights into the novel reaction pathways of complex 3 have been obtained from 14N{1H} nuclear magnetic resonance studies, which show that photoactivation pathways can involve release of free azide in buffered solution. Density functional theory (DFT) and time-dependent DFT calculations revealed the dissociative character of singlet and triplet excited states of complex 3, which gives rise to reactive, possibly cytotoxic azidyl radicals. Mol Cancer Ther; 11(9); 1894–904. ©2012 AACR.

Aroyl hydrazones of 2-phenylindole-3-carbaldehydes as novel antimitotic agents

Cell cycle arrest of malignant cells is an important option for cancer treatment. In this study, we modified the structure of antimitotic 2-phenylindole-3-carbaldehydes by condensation with hydrazides of various benzoic and pyridine carboxylic acids. The resulting hydrazones inhibited the growth of MDA-MB 231 and MCF-7 breast cancer cells with IC(50) values of 20-30 nM for the most potent derivatives. These 2-phenylindole derivatives also exerted an inhibitory effect on the growth of both proliferating and resting U-373 MG glioblastoma cells. Though the hydrazones exhibited similar structure-activity relationships as the aldehydes, they did not inhibit tubulin polymerization as the aldehydes but were capable of blocking the cell cycle in G(2)/M phase. The cell cycle arrest was accompanied by apoptosis as demonstrated by the activation of caspase-3. Since these 2-phenylindole-based hydrazones display no structural similarity with other antitumor drugs they are interesting candidates for further development.

Dancing of the Second Aromatic Residue around the 6,8-Diazabicyclo[3.2.2]nonane Framework: Influence on σ Receptor Affinity and Cytotoxicity

A series of 6,8-diazabicyclo[3.2.2]nonane derivatives bearing two aromatic moieties was prepared, the affinity toward sigma(1) and sigma(2) receptors was investigated, and the growth inhibition of six human tumor cell lines was determined. The enantiopure bicyclic ketones 5a ((+)-(1S,5S)-6-allyl-8-(4-methoxybenzyl)-6,8-diazabicyclo[3.2.2]nonane-2,7,9-trione) and 5b ((+)-(1S,5S)-6-allyl-8-(2,4-dimethoxybenzyl)-6,8-diazabicyclo[3.2.2]nonane-2,7,9-trione) as well as their enantiomers ent-5a and ent-5b served as chiral building blocks, which were derived from (S)- and (R)-glutamate, respectively. Structure-affinity relationships revealed that 11a (K(i) = 154 nM), ent-11a (K(i) = 91 nM), and ent-17a (K(i) = 104 nM) are the most potent sigma(1) ligands. High sigma(2) affinity was achieved with 17b (K(i) = 159 nM) and 8b (K(i) = 400 nM). The bicyclic sigma ligands showed a selective growth inhibition of the small cell lung cancer cell line A-427 with the benzyl ethers 11 and the benzylidene derivatives 17 being the most potent compounds. 11a has a cytotoxic potency (IC(50) = 0.92 muM), which exceeds the activity of cisplatin and interacts considerably with both sigma(1) and sigma(2) receptors.

Novel C,N-Cyclometalated Benzimidazole Ruthenium(II) and Iridium(III) Complexes as Antitumor and Antiangiogenic Agents: A Structure-Activity Relationship Study.

A series of novel C,N-cyclometalated benzimidazole ruthenium(II) and iridium(III) complexes of the types [(η(6)-p-cymene)RuCl(κ(2)-N,C-L)] and [(η(5)-C5Me5)IrCl(κ(2)-N,C-L)] (HL = methyl 1-butyl-2-arylbenzimidazolecarboxylate) with varying substituents (H, Me, F, CF3, MeO, NO2, and Ph) in the R4 position of the phenyl ring of 2-phenylbenzimidazole chelating ligand of the ruthenium (3a-g) and iridium complexes (4a-g) have been prepared. The cytotoxic activity of the new ruthenium(II) and iridium(III) compounds has been evaluated in a panel of cell lines (A2780, A2780cisR, A427, 5637, LCLC, SISO, and HT29) in order to investigate structure-activity relationships. Phenyl substitution at the R4 position shows increased potency in both Ru and Ir complexes (3g and 4g, respectively) as compared to their parent compounds (3a and 4a) in all cell lines. In general, ruthenium complexes are more active than the corresponding iridium complexes. The new ruthenium and iridium compounds increased caspase-3 activity in A2780 cells, as shown for 3a,d and 4a,d. Compound 4g is able to increase the production of ROS in A2780 cells. Furthermore, all the new compounds are able to overcome the cisplatin resistance in A2780cisR cells. In addition, some of the metal complexes effectively inhibit angiogenesis in the human umbilical vein endothelial cell line EA.hy926 at 0.5 μM, the ruthenium derivatives 3g (Ph) and 3d (CF3) being the best performers. QC calculations performed on some ruthenium model complexes showed only moderate or slight electron depletion at the phenyl ring of the C,N-cyclometalated ligand and the chlorine atom on increasing the electron withdrawing effect of the R substituent.

Indeno(1,2-b)indole derivatives as a novel class of potent human protein kinase CK2 inhibitors

Herein we describe the synthesis and properties of indeno[1,2-b]indole derivatives as a novel class of potent inhibitors of the human protein kinase CK2. A set of 19 compounds was obtained using a convenient and straightforward synthesis protocol. The compounds were tested for inhibition of human protein kinase CK2, which was recombinantly expressed in Escherichia coli. New inhibitors with IC(50) in the micro- and sub-micromolar range were identified. Compound 4b (5-isopropyl-7,8-dihydroindeno[1,2-b]indole-9,10(5H,6H)-dione) inhibited human CK2 with an IC(50) of 0.11 μM and did not significantly inhibit 22 other human protein kinases, suggesting selectivity towards CK2. ATP-competitive inhibition by compound 4b was shown and a K(i) of 0.06 μM was determined. Our findings indicate that indeno[1,2-b]indoles are a promising starting point for further development and optimization of human protein kinase CK2 inhibitors.

Synthesis and cytotoxic activity of 5,6-heteroaromatically annulated pyridine-2,4-diamines

A series of 5,6-heteroaromatically annulated pyridine-2,4-diamines have been synthesized and their in vitro cytotoxic activities evaluated against six human cancer cell lines. Benzo[g] annulated pyrido[2,3-b]indolediamines 7a-b and 8 showed relatively high cytotoxic activity as well as most of the diamines with pyrrolo[2,3-b]pyridine 17, thieno[2,3-b]pyridine and furo[2,3-b]pyridine 26-28, 1,8-naphthyridine 32 and 34 and benzo[h]quinoline 37 skeletons. Surprisingly, pyrido[2,3-b]indolediamines 13 and 14 without benzo[g] annulation were inactive. None of the new compounds were as potent as ellipticine, the reference compound.

Structure-activity relationships of novel heteroaryl-acrylonitriles as cytotoxic and antibacterial agents

Eighteen new 2,6-disubstituted acrylonitriles and two new (benzimidazol-1-yl)-acetamide derivatives were prepared and screened for antibacterial and cytotoxic activities on 12 human cancer cell lines. Based on the lead structure 2-(benzimidazol-2-yl)-3-(5-nitrothiophen-2-yl) acrylonitrile it was found that placement of methyl groups at the 5,6 positions of the benzimidazole ring lead to a 3-fold increase in overall cytotoxic activity. Replacing the nitrothiophene for pyridine reduced cytotoxic activity as did replacing the nitro group for a methoxy group. Cytotoxic activity was only slightly reduced when the benzimidazole ring was replaced by a imidazo[4,5-b]pyridine or a benzthiazole ring but replacement by benzoxazole led to a substantial decrease in activity. Moving the acrylonitrile group from position 2 to position 1 of the benzimidazole ring also resulted in moderately active compounds. (Benzimidazol-1-yl)acetamides showed only modest activity. The structure-activity relationships found in the cytotoxicity studies are mirrored in the results of the antibacterial experiments.