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. XVIII. Synthesis, physico-chemical properties; genetic, virological, and biochemical studies of fluorescent dimeric bisbenzimidazoles DBPA(n)

A set of AT-specific fluorescent dimeric bisbenzimidazoles DBPA(n) with linkers of different lengths bound to DNA in the minor groove were synthesized and their genetic, virological, and biochemical studies were performed. The DBPA(n) were shown to be effective inhibitors of the histon-like protein H-NS, a regulator of the DNA transcription factor, as well as of the Aliivibrio logei Quorum Sensing regulatory system in E. coli cells. Their antiviral activity was tested in model cell lines infected with herpes simplex virus type I. Also, it was found that DBPA(n) could inhibit catalytic activities of HIV-1 integrase at low micromolar concentrations. All of the dimeric bisbenzimidazoles DBPA(n) manifested fluorescent properties, were well soluble in water, nontoxic up to concentrations of 200 µM, and could penetrate into nuclei followed by binding to DNA.

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.

Hyperexpression of Integrin α5β1 Promotes Resistance of MCF-7 Human Breast Carcinoma Cells to Doxorubicin via ERK Protein Kinase Down-regulation

In MCF-7 human breast carcinoma cells, α5β1 integrin hyperexpression, which was accomplished by transduction of a full-length α5 integrin cDNA, increased by about 50-70% the number of cells, survived during 48-72 h cell treatment with doxorubicin. Up-regulation of α5β1 reduced the level of the apoptogenic p53 protein and p21 cell cycle inhibitor, but enhanced the activity of Akt and mTOR protein kinases. In addition to these findings, we observed a significant decrease in the activity of both isoforms of phosphokinase Erk1/2, which is known to play a key role in cell viability pathways, including pathways alleviating stress damages caused by distinct antitumor drugs. Diminished Erk activity accompanying the rise of drug resistance can be explained by an "atypical" function of this kinase, which, in the cells studied, promotes an enhanced rather than reduced sensitivity to doxorubicin. To verify this suggestion, the effect of a specific Erk inhibitor, PD98059, on the resistance to doxorubicin of control and α5 cDNA-transduced MCF-7 cells was investigated. The data showed that suppression of Erk activity increased the resistance of control cells (transduced with an "empty" vector) to a level higher than that demonstrated by the α5 cDNA-transduced cells. The highest level of resistance was observed in α5β1-trancduced cells treated with PD98059. Akt and mTOR kinase inhibitors had little if any effect on doxorubicin resistance of α5 cDNA-transduced MCF-7 cells. The data show for the first time that integrin α5β1 can stimulate drug resistance of tumor cells through a mechanism based on the inhibition of protein kinase Erk. From a more general view, the results of this investigation suggest that signal protein kinases can perform in tumor cells "non-canonical" functions, opposite to those, which are the basis for using kinase inhibitors in targeted cancer therapy. It follows that if a protein kinase is supposed to be used as a target for such therapy, it is important to explore its features in the particular tumor prior to the onset of treatment.

Implication of α2β1 integrin in anoikis of MCF-7 human breast carcinoma cells

Silencing of α2β1 integrin expression significantly promoted anchorage-dependent apoptosis (anoikis) and drastically reduced clonal activity of MCF-7 human breast carcinoma cells. Depletion of α2β1 enhanced the production of apoptotic protein p53 and of inhibitor of cyclin-dependent protein kinases, p27, while downregulating antiapoptotic protein Bcl-2 and multifunctional protein cMyc. Blocking the expression of α2β1 had no effect on activity of protein kinase Akt, but it sharply increased the kinase activity of Erk1/2. Pharmacological inhibition of Erk1/2 had a minor effect on anoikis of control cells, while it reduced anoikis of cells with downregulated α2β1 to the level of control cells. The data show for the first time that integrin α2β1 is implicated in the protection of tumor cells from anoikis through a mechanism based on the inhibition of protein kinase Erk.

DNA specific fluorescent symmetric dimeric bisbenzimidazoles DBP(n): the synthesis, spectral properties, and biological activity

A series of new fluorescent symmetric dimeric bisbenzimidazoles DBP(n) bearing bisbenzimidazole fragments joined by oligomethylene linkers with a central 1,4-piperazine residue were synthesized. The complex formation of DBP(n) in the DNA minor groove was demonstrated. The DBP(n) at micromolar concentrations inhibit in vitro eukaryotic DNA topoisomerase I and prokaryotic DNA methyltransferase (MTase) M.SssI. The DBP(n) were soluble well in aqueous solutions and could penetrate cell and nuclear membranes and stain DNA in live cells. The DBP(n) displayed a moderate effect on the reactivation of gene expression.

Naphthoindole-based analogues of tryptophan and tryptamine: synthesis and cytotoxic properties

The efficacy of anthracycline based anticancer drugs is limited by pleiotropic drug resistance of tumor cells. Aiming at the design of anthracyclinone congeners capable of circumventing drug resistance, we synthesized naphthoindole containing derivatives of tryptophan and tryptamine. In doing so we adapted the traditional, gramine based approach for tryptophan and tryptamine synthesis. The most potent new compound, 3-(2-aminoethyl)-4,11-dihydroxynaphtho[2,3-f]indole-5,10-dione (16), was equally cytotoxic (IC(50) within low micromolar concentrations) for human K562 leukemia and HCT116 colon carcinoma cell lines and their isogenic sublines with genetically defined determinants of altered drug response, that is, the expression of the multidrug transporter P-glycoprotein and loss of pro-apoptotic p53. Each of these mechanisms conferred resistance to the reference drug adriamycin. In contrast, naphthotryptamine 16, although less potent than adriamycin, was equally toxic for wild type cell lines and drug resistant counterparts. Moreover, at 3-5 microM 16 inhibited topoisomerase I in vitro. Thus, our novel naphthoindole based derivative of tryptamine gained new activities important for anticancer therapy, namely, suppression of topoisomerase I and the ability to overcome resistance mediated by P-glycoprotein expression and p53 dysfunction.

Synthesis and structure–activity relationship studies of 4,11-diaminonaphtho[2,3-f]indole-5,10-diones

We describe the synthesis of derivatives of 4,11-diaminonaphtho[2,3-f]indole-5,10-dione and their cytotoxicity for human tumor cells that express major determinants of altered anticancer drug response, the efflux pump P-glycoprotein, and non-functional p53. Nucleophilic substitution of methoxy groups in 4,11-dimethoxynaphtho[2,3-f]indole-5,10-dione with various ethylenediamines yielded the derivatives of 4,11-diaminonaphtho[2,3-f]indole-5,10-dione, the indole containing analogues of the antitumor agent ametantrone. The cytotoxicity of novel compounds for multidrug resistant, P-glycoprotein-expressing tumor cells is highly dependent on the N-substituent at the terminal amino group of the ethylenediamine moiety. Whereas p53 null colon carcinoma cells were less sensitive to the reference drug doxorubicin than their counterparts with wild type p53, the majority of novel naphthoindole derivatives were equally potent for both cell lines, regardless of the p53 status.