Unsymmetrical Pd(II) Pincer Complexes with Benzothiazole and Thiocarbamate Flanking Units: Expedient Solvent-Free Synthesis and Anticancer Potential.

Driven by the growing threat of cancer, many research efforts are directed at developing new chemotherapeutic agents, where the central role is played by transition metal complexes. The proper ligand design serves as a key factor to unlock the anticancer potential of a particular metal center. Following a recent trend, we have prepared unsymmetrical pincer ligands that combine benzothiazole and thiocarbamate donor groups. These compounds are shown to readily undergo direct cyclopalladation, affording the target S,C,N-type Pd(II) pincer complexes both in solution and in the absence of a solvent. The solid-phase strategy provided the complexes in an efficient and ecologically friendly manner. The resulting palladacycles are fully characterized using nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy and, in one case, by single-crystal X-ray diffraction (XRD). The solvent-free reactions are additionally analyzed by powder XRD. The pincer complexes exhibit remarkable cytotoxicity against several solid and blood cancer cell lines, including human colorectal carcinoma (HCT116), breast cancer (MCF7), prostate adenocarcinoma (PC3), chronic myelogenous leukemia (K562), multiple plasmacytoma (AMO1), and acute lymphoblastic leukemia (H9), with the dimethylamino-substituted derivative being particularly effective. The latter also induced an appreciable level of apoptosis in both parental and doxorubicin-resistant cells K562 and K562/iS9, vindicating the high anticancer potential of this type of palladacycles.

(Aminoalkyl)diphenylphosphine sulfides: synthesis and application as building blocks in the design of multidentate ligands for cytotoxic Pd(II) complexes.

Amino-functionalized phosphoryl compounds are among the most useful molecular scaffolds in medicinal chemistry, while the potential of their thiophosphorylated analogs, especially those having an alkylamino moiety, is still uncovered. This is mainly due to the lack of convenient synthetic routes to these organophosphorus derivatives. To address this issue, we have suggested the facile approaches to α-(aminomethyl)- and substituted/unsubstituted α-(aminobenzyl)diphenylphosphine sulfides based on either the sequential transformations of (hydroxymethyl)diphenylphosphine sulfide, with the Staudinger reaction of an azide derivative as the key stage, or the addition of Ph2P(S)H to hydrobenzamides followed by the acid hydrolysis. The compounds obtained were reacted with picolinyl chloride to yield functionalized amides which readily underwent direct cyclopalladation, resulting in new representatives of non-classical N-metalated Pd(II) pincer complexes. The latter exhibit promising cytotoxic activity against several human cancer cell lines and apoptosis inducing ability along with the remarkable cytotoxic effects on doxorubicin-resistant cell sublines.

High and Low Levels of ABCB1 Expression Are Associated with Two Distinct Gene Signatures in Lung Tissue of Pulmonary TB Patients with High Inflammation Activity.

P-glycoprotein (encoded by the ABCB1 gene) has a dual role in regulating inflammation and reducing chemotherapy efficacy in various diseases, but there are few studies focused on pulmonary TB patients. In this study, our objective was to identify a list of genes that correlate with high and low levels of ABCB1 gene expression in the lungs of pulmonary TB patients with different activity of chronic granulomatous inflammation. We compared gene expression in two groups of samples (with moderate and high activity of tuberculomas) to identify their characteristic gene signatures. Gene expression levels were determined using quantitative PCR in samples of perifocal area of granulomas, which were obtained from 65 patients after surgical intervention. Subsequently, two distinct gene signatures associated with high inflammation activity were identified. The first signature demonstrated increased expression of HIF1a, TGM2, IL6, SOCS3, and STAT3, which correlated with high ABCB1 expression. The second signature was characterized by high expression of TNFa and CD163 and low expression of ABCB1. These results provide insight into various inflammatory mechanisms and association with P-gp gene expression in lung tissue of pulmonary TB patients and will be useful in the development of a host-directed therapy approach to improving the effectiveness of anti-TB treatment.

Modulation of the Cytotoxic Properties of Pd(II) Complexes Based on Functionalized Carboxamides Featuring Labile Phosphoryl Coordination Sites.

Platinum-based drugs are commonly recognized as a keystone in modern cancer chemotherapy. However, intrinsic and acquired resistance as well as serious side effects often caused by the traditional Pt(II) anticancer agents prompt a continuous search for more selective and efficient alternatives. Today, significant attention is paid to the compounds of other transition metals, in particular those of palladium. Recently, our research group has suggested functionalized carboxamides as a useful platform for the creation of cytotoxic Pd(II) pincer complexes. In this work, a robust picolinyl- or quinoline-carboxamide core was combined with a phosphoryl ancillary donor group to achieve hemilabile coordination capable of providing the required level of thermodynamic stability and kinetic lability of the ensuing Pd(II) complexes. Several cyclopalladated derivatives featuring either a bi- or tridentate pincer-type coordination mode of the deprotonated phosphoryl-functionalized amides were selectively synthesized and fully characterized using IR and NMR spectroscopy as well as X-ray crystallography. The preliminary evaluation of the anticancer potential of the resulting palladocycles revealed a strong dependence of their cytotoxic properties on the binding mode of the deprotonated amide ligands and demonstrated certain advantages of the pincer-type ligation.

Pincer-dipeptide and pseudodipeptide conjugates: Synthesis and bioactivity studies.

Following a recent trend on the application of different pincer scaffolds for the development of new metal-based antitumor agents, in this work, dipeptides and dipeptide surrogates based on picolinyl- and 4-chloropicolinylamides with S-donor amino acid residues (cysteine, homocysteine, or methionine) bearing glycinate, alaninate, or phosphonate moieties either at the C-terminus or in the S-donor side arm have been designed as nonclassical pincer ligands with central amide units and shown to smoothly undergo site-selective direct cyclopalladation under mild conditions, affording the target Pd(II) pincer complexes in good to high yields. The realization of S,N,N-coordination through the sulfur atom of the thioether group and nitrogen atoms of the pyridine and deprotonated amide units was unambiguously confirmed using different NMR techniques (1H, 13C, 31P, and 2D NMR methods, including 1H15N HMBC) and IR spectroscopy; the structure of one representative was elucidated by X-ray crystallography. The resulting pincer-(pseudo)dipeptide conjugates were screened for cytotoxicity against several cancer cell lines and noncancerous human embryonic kidney cells and at least some of them provided an appreciable level of activity comparable to that of cisplatin. The S-modified homocysteine-based derivatives exhibited also significant antiproliferative effects against doxorubicin-resistant transformed breast cells HBL100/Dox, implying the possibility of overcoming drug resistance. The complexes can induced apoptosis but did not affect mitochondria. The comparative DNA/protein binding studies of one of the most active pincer-(pseudo)dipeptide conjugates with the monoamino acid-based prototype revealed certain advantages of the former and gave further insights into the potential of this type of palladium-based antitumor agents.

Mechanochemistry for the synthesis of non-classical N-metalated palladium(II) pincer complexes.

The peculiarities of cyclopalladation of a series of non-classical pincer-type ligands based on monothiooxalyl amides bearing ancillary N- or S-donor groups in the amide units have been scrutinized both under conditions of conventional solution-based synthesis and in the absence of a solvent according to a solid-phase methodology including mechanochemical activation. Grinding the functionalized monothiooxamides with PdCl2(NCPh)2 in a mortar or vibration ball mill is shown to serve as an efficient and green alternative to the synthesis of these complex metal-organic systems in solution that can offer such advantages as the absence of any auxiliary and significant rate and yield enhancement, especially for the challenging ligands. The realization of S,N,N- or S,N,S-monoanionic tridentate coordination in the resulting pincer complexes has been confirmed by multinuclear NMR (including 2D NMR) and IR spectroscopy and, in some cases, X-ray diffraction. The course and outcome of the solid-phase reactions have been studied by a combination of different spectroscopic methods as well as SEM/EDS analysis. The preliminary evaluation of cytotoxic activity against several human cancer cell lines has revealed the high potency of some of the cyclopalladated derivatives obtained, rendering further development of solvent-free synthetic routes to this type of complexes very urgent.

Triterpenoids with modified A-ring as modulators of P-gp-dependent drug-resistance in cancer cells.

Semi-synthetic A-cycle modified triterpenic derivatives with A-cycle condensed with a heterocyclic fragment (compound 1) and fragmented A-ring (compound 2) were tested for cytotoxicity against several tumor cell cultures and doxorubicin (Dox)-resistant cell lines. The equal cytotoxicity of the tested compounds to the parental tumor cell lines (HBL-100, K562) and their resistant subclones (HBL-100/Dox, K562/i-S9) was revealed. The overexpression of ABCB1 (MDR1) gene and P-glycoprotein (P-gp) was confirmed for both resistant subclones of tumor cells. Compounds 1 and 2 were shown to inhibit the ABC-transporter gene expression (MDR1, MRP, MVP, and BCRP) and the transport of well-known P-gp substrate Rhodamine 123 from resistant cells. The docking of triterpenoids 1 and 2 into the drug binding site of P-gp revealed a similarity between the conformation of the tested triterpenoids and that of classical inhibitor verapamil, thus assuming these compounds to be more likely the inhibitors than the substrates of P-gp. Any tested triterpenic derivatives, when combined at non-toxic concentrations with doxorubicin, improved cytotoxic effect of the therapeutic drug against resistant subclones of tumor cells.

Palladium(II) Pincer Complexes of Functionalized Amides with S-Modified Cysteine and Homocysteine Residues: Cytotoxic Activity and Different Aspects of Their Biological Effect on Living Cells.

In the search for potential new metal-based antitumor agents, two series of nonclassical palladium(II) pincer complexes based on functionalized amides with S-modified cysteine and homocysteine residues have been prepared and fully characterized by 1D and 2D NMR (1H, 13C, COSY, HMQC or HSQC, 1H-13C, and 1H-15N HMBC) and IR spectroscopy and, in some cases, X-ray diffraction. Most of the resulting complexes exhibit a high level of cytotoxic activity against several human cancer cell lines, including colon (HCT116), breast (MCF7), and prostate (PC3) cancers. Some of the compounds under consideration are also efficient in both native and doxorubicin-resistant transformed breast cells HBL100, suggesting the prospects for the creation of therapeutic agents based on the related compounds that would be able to overcome drug resistance. An analysis of different aspects of their biological effects on living cells has revealed a remarkable ability of the S-modified derivatives to induce cell apoptosis and efficient cellular uptake of their fluorescein-conjugated counterpart, confirming the high anticancer potential of Pd(II) pincer complexes derived from functionalized amides with S-donor amino acid pendant arms.

DNA sequence-specific ligands. XVII. Synthesis, spectral properties, virological and biochemical studies of fluorescent dimeric bisbenzimidazoles DBA(n).

A series of DNA minor groove binding fluorescent dimeric bisbenzimidazoles DBA(n) bearing linkers of various length were synthesized and their biochemical and antiviral activities were evaluated. Their antiviral activity was assessed in model cell systems infected with human herpes simplex virus (HSV-1) and cytomegalovirus (CMV). Compounds DBA(1) and DBA(7) demonstrated in vitro inhibitory properties towards HSV-1, and DBA(7) completely blocked the viral infection. Compound DBA(11) displayed the in vitro therapeutic activity towards both HSV-1 and CMV. All of the DBA(n) could fluoresce, were well soluble in water, not cytotoxic to a concentration of 240 µM, penetrated well into cell nuclei by binding to DNA and could inhibit topo-I at low micromolecular concentrations.

Highly Cytotoxic Palladium(II) Pincer Complexes Based on Picolinylamides Functionalized with Amino Acids Bearing Ancillary S-Donor Groups.

The reactions of picolinyl and 4-chloropicolinyl chlorides with methyl esters of S-methyl-l-cysteine, l- and d-methionine, and l-histidine afforded a series of functionalized carboxamides, which readily formed pincer-type complexes upon interaction with PdCl2(NCPh)2 in solution under mild conditions. The direct cyclopalladation of the ligands derived was also accomplished in the solid phase, in particular, mechanochemically, although it was complicated by the partial deactivation of the starting amides. The resulting complexes with 5,5- and 5,6-membered fused metallocycles were fully characterized by IR and NMR spectroscopy, including variable-temperature and 2D-NMR studies. In the case of some cysteine- and methionine-based derivatives, the realization of κ3-N,N,S-coordination was supported by X-ray diffraction. The cytotoxic effects of these complexes were examined on HCT116, MCF7, and PC3 human cancer cell lines as well as HEK293 as a representative of normal cells. The comparative studies allowed us to determine that the presence of the sulfide ancillary donor group is crucial for cytotoxic activity of this type of Pd(II) complexes. The main structure-activity relationships and the most promising palladocycles were outlined. The additional studies by gel electrophoresis revealed that 4-chloropicolinyl derivatives, despite the nature of an amino acid, can bind with DNA and inhibit topoisomerase I activity.

Methylenebisphosphonates with dienone pharmacophore: synthesis, structure, antitumor and fluorescent properties.

The synthesis and the antitumor activity and fluorescent properties screening of novel bisphosphonate conjugates with cytotoxic 3,5-bis((hetero)arylidene)-4-piperidone residues were performed. The facile and rapid synthetic route was based on the aza-Michael addition of NH-3,5-bis((hetero)arylidene)-4-piperidones to tetraethyl ethylidenebisphosphonate. The synthesized compounds displayed high inhibitory properties towards Caov3, A549, PC3, and KB 3-1 human carcinoma cell lines. Among those, compounds bearing 4-cyano-phenyl and 3-pyridinyl substituents were revealed as the most active drug candidates with IC(50) values in the range of 0.5-2.5 µM. Methylenebisphosphonate with 4-Me(2) N-C(6) H(4) groups in the piperidone framework possessing fluorescence properties may be of interest for visualization of BPs skeletal distribution and cellular uptake in bones and other tissues.

Structure-cytotoxicity relationship in a series of N-phosphorus substituted E,E-3,5-bis(3-pyridinylmethylene)- and E,E-3,5-bis(4-pyridinylmethylene)piperid-4-ones.

In order to give further insight on the influence of the aromatic ring nature and the presence of the phosphorus substituent at the piperidone nitrogen atom of E,E-3,5-bis((hetero)arylidene)piperid-4-ones on their antitumor properties, a series of phosphorus substituted E,E-3,5-bis(pyridinylmethylene)piperid-4-ones bearing either 3-pyridine or 4-pyridine rings was obtained. Novel NH-3,5-bis(pyridinylmethylene)piperid-4-ones 1a,b were converted into the corresponding N-phosphorylated derivatives 3a-c, 4a-c differing in the substitution at the phosphorus atom (amidophosphates and amidophosphonates), via direct phosphorylation while N-(ω-phosphorylalkyl)-substituted compounds 8a-c were obtained via aldol-crotonic condensation of preformed N-phosphorylalkyl substituted piperidones with the corresponding pyridinecarboxaldehyde. The cytotoxicity screen has revealed that phosphorylated compounds based on E,E-3,5-bis(4-pyridinylmethylene)piperid-4-one framework displayed higher inhibitory properties toward Caov3, A549, KB 3-1 and KB 8-5 human carcinoma cell lines comparing with their analogues with 3-pyridine rings. Introduction of the phosphorus moiety substantially increased the antitumor properties in the case of E,E-3,5-bis(3-pyridinylmethylene)piperid-4-ones derivatives but this influence less pronounced for more active analogues bearing 4-pyridinyl rings. Most of the compounds tested are potent against multi-drug resistant cell line KB 8-5 affording some guidelines for the search of perspective drug-candidates among phosphorus substituted E,E-3,5-bis((hetero)arylidene)piperid-4-ones.

Synthesis, characterization and structure-activity relationship of novel N-phosphorylated E,E-3,5-bis(thienylidene)piperid-4-ones.

In order to design the agents with improved antitumor activity of 3,5-bis(thienylidene)piperid-4-one type, E,E-N-phosphoryl-3,5-bis(thienylidene)piperid-4-ones 6a-c and E,E-N-omega-phosphorylalkyl-3,5-bis-(thienylidene)piperid-4-ones 7a-c were obtained via the direct phosphorylation of the parent NH-3,5-bis(thienylidene)piperid-4-one and by condensation of preformed N-phosphorylalkyl substituted piperidones with thiophene 2-carbaldehyde, respectively. The structures of the compounds were elucidated by (1)H, (31)P, (13)C NMR along with a single crystal X-ray diffraction analysis. Under the action of visible light thermodynamically more stable E,E-isomers slowly undergo photochemical conversion in CDCl(3) solution to the corresponding E,Z-isomers and E,Z-N-methyl-3,5-bis(thienylidene)piperid-4-one 5 was isolated in individual state. The importance of phosphorylation for cytotoxic properties of 3,5-bis(thienylidene)piperid-4-ones towards human carcinoma cell lines Caov3, Scov3, and A549 and influence of olefin configuration on antitumor activity were demonstrated.

Design, cytotoxic and fluorescent properties of novel N-phosphorylalkyl substituted E,E-3,5-bis(arylidene)piperid-4-ones.

A series of E,E-N-phosphorylalkylene-3,5-bis(arylidene)piperid-4-ones 7a-k was prepared via the condensation of aromatic aldehydes with omega-aminophosphonates 5a-c and 6a,b bearing piperidone or a protected piperidone moiety, respectively. The synthetic routes to the starting aminophosphonates 5a-c and 6a,b varied depending on the number of methylene groups in the alkylene chain and comprised the Kabachnik-Fields reaction (n=1), the aza-Michael reaction (n=2) or alkylation of 4-piperidone hydrochloride with diethyl omega-bromoalkylphosphonates under phase transfer catalysis conditions (n=3,4). Phosphoryl substituted 3,5-bis(arylidene)piperid-4-ones 7b,c,e,f,h,i,k bearing both nitro groups and fluorine atoms in the para-position of the arene rings possess cytotoxicity toward human carcinoma cell lines CaOv3, Scov3, PC3 and A549 in the low micromolar range while their analogues having para-dimethylamino groups had IC(50) values greater than 50 microM. In contrast, only Me(2)N-substituted phosphonates 7g,j (n=3 and 4) and the salts of Me(2)N-substituted phosphonic acids 10c,f (n=2 and 3) display fluorescence.