Dimeric Bis-Benzimidazole-Pyrroles DB2Py(n) - AT-Site-Specific Ligands: Synthesis, Physicochemical Analysis, and Biological Activity.

Its broad spectrum of biological activity makes benzimidazole a fundamental pharmacophore in pharmaceutics. The paper describes newly synthesized AT-specific fluorescent bis-benzimidazole molecules DB2Py(n) that contain a pyrrolcarboxamide fragment of the antibiotic drug netropsin. Physico-chemical methods using absorption, fluorescence, and circular dichroism spectra have shown the ability of bis-benzimidazole- pyrroles to form complexes with DNA. The new DB2Py(n) series have turned out to be more toxic to human tumor lines and less vulnerable to non-tumor cell lines. Bis-benzimidazole-pyrroles penetrated the cell nucleus, affected the cell-cycle synthesis (S) phase, and inhibited eukaryotic topoisomerase I in a cellfree model at low concentrations. A real-time tumor cell proliferation test confirmed the molecule's enhanced toxic properties upon dimerization. Preliminary cytotoxicity data for the bis-benzimidazole-pyrroles tested in a cell model with a MDR phenotype showed that monomeric compounds can overcome MDR, while dimerization weakens this ability to its intermediate values as compared to doxorubicin. In this respect, the newly synthesized cytotoxic structures seem promising for further, in-depth study of their properties and action mechanism in relation to human tumor cells, as well as for designing new AT-specific ligands.

Hyperexpression of Integrin α5ß1 Promotes Resistance of MCF-7 Human Breast Carcinoma Cells to Doxorubicin via ERK Protein Kinase Down-regulation.

In MCF-7 human breast carcinoma cells, α5ß1 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 α5ß1 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 α5ß1-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 α5ß1 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 α2ß1 integrin in anoikis of MCF-7 human breast carcinoma cells.

Silencing of α2ß1 integrin expression significantly promoted anchorage-dependent apoptosis (anoikis) and drastically reduced clonal activity of MCF-7 human breast carcinoma cells. Depletion of α2ß1 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 α2ß1 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 α2ß1 to the level of control cells. The data show for the first time that integrin α2ß1 is implicated in the protection of tumor cells from anoikis through a mechanism based on the inhibition of protein kinase Erk.

Naphtho[2,3-f]indole-5,10-dione aminoalkyl derivatives: a new class of topoisomerase I inhibitors.

Naphtho[2,3-f]indole-5,10-dione aminoalkyl derivatives in cytotoxic concentrations inhibit topoisomerase I, which is an important factor of antitumor activity of compounds of this chemical class. The degree of topoisomerase I inhibition with naphtho[2,3-f]indole-5,10-dione derivatives depends on the structure and position of active (aminoalkyl) groups. The mechanism of topoisomerase I inhibition with aminoalkylnaph-tho[2,3-f]indole-5,10-diones differs from specific blocking of the catalytic activity of the enzyme and depends on interactions of these compounds with DNA.