Design, synthesis and biological evaluation of new ß-carboline-bisindole compounds as DNA binding, photocleavage agents and topoisomerase I inhibitors.

A series of new ß-carboline-bisindole compounds were designed, synthesized and evaluated for their antiproliferative activity against human cancer cell lines, such as A549 (lung cancer), DU-145 (prostate cancer), HeLa (cervical cancer) and MCF-7 (breast cancer). All the compounds exhibited considerable antiproliferative activity. Among them, compounds 7g and 7r exhibited significant antiproliferative activity against DU-145 cells with IC50 values 1.86 and 1.80 µM respectively. Further, these compounds effectively inhibit DNA topoisomerase I activity and can also cleave the pBR322 plasmid upon irradiation with UV light. In addition, Annexin V-FITC assay suggested that these compounds induced apoptosis in DU- 145 cell line (prostate cancer). To know the binding mode of these compounds with DNA, spectroscopic studies were also carried out. These new compounds were showing a unique mode of binding with DNA, both biophysical studies such as UV-Visible, fluorescence, circular dichroism and molecular docking studies revealed that the ß-carboline-bisindole compounds exhibit combilexin type of interaction with DNA.

Synthesis and biological evaluation of imidazo[2,1-b][1,3,4]thiadiazole-linked oxindoles as potent tubulin polymerization inhibitors.

A series of imidazo[2,1-b][1,3,4]thiadiazole-linked oxindoles composed of an A, B, C and D ring system were synthesized and investigated for anti-proliferative activity in various human cancer cell lines; test compounds were variously substituted at rings C and D. Among them, compounds 7 ((E)-5-fluoro-3-((6-p-tolyl-2-(3,4,5-trimethoxyphenyl)-imidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylene)indolin-2-one), 11 ((E)-3-((6-p-tolyl-2-(3,4,5-trimethoxyphenyl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylene)indolin-2-one), and 15 ((E)-6-chloro-3-((6-phenyl-2-(3,4,5-trimethoxyphenyl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylene)indolin-2-one) exhibited potent anti-proliferative activity. Treatment with these three compounds resulted in accumulation of cells in G2 /M phase, inhibition of tubulin assembly, and increased cyclin-B1 protein levels. Compound 7 displayed potent cytotoxicity, with an IC50 range of 1.1-1.6 µM, and inhibited tubulin polymerization with an IC50 value (0.15 µM) lower than that of combretastatin A-4 (1.16 µM). Docking studies reveal that compounds 7 and 11 bind with αAsn101, ßThr179, and ßCys241 in the colchicine binding site of tubulin.

Synthesis of ß-carboline-benzimidazole conjugates using lanthanum nitrate as a catalyst and their biological evaluation.

A series of ß-carboline-benzimidazole conjugates bearing a substituted benzimidazole and an aryl ring at C3 and C1 respectively were designed and synthesized. The key step of their preparation was determined to involve condensation of substituted o-phenylenediamines with 1-(substituted phenyl)-9H-pyrido[3,4-b]indole-3-carbaldehyde using La(NO3)3·6H2O as a catalyst and their cytotoxic potential was evaluated. Conjugates 5a, 5d, 5h and 5r showed enhanced cytotoxic activity (GI50 values range from 0.3 to 7.1 µM in most of the human cancer cell lines) in comparison to some of the previously reported ß-carboline derivatives. To substantiate the cytotoxic activity and to understand the nature of interaction of these conjugates with DNA, spectroscopy, DNA photocleavage and DNA topoisomerase I inhibition (topo-I) studies were performed. These conjugates (5a, 5d and 5r) effectively cleave pBR322 plasmid DNA in the presence of UV light. In addition, the effect of these conjugates on DNA Topo I inhibition was studied. The mode of binding of these new conjugates with DNA was also examined by using both biophysical as well as molecular docking studies, which supported their multiple modes of interaction with DNA. Moreover, an in silico study of these ß-carboline-benzimidazole conjugates reveals that they possess drug-like properties.