A series of pyrazolo[1,5-]pyrimidines substituted at C5 with 1-phenylprop-2-en-1-one () and 3-phenylprop-2-en-1-one () was synthesized and evaluated for antiproliferative activity. Among them, was found to be the most active compound against the MDA-MB-231 cell line with an IC of 2.6 μM . The antiproliferative activity of this series of compounds ranged from 2.6 to 34.9 μM against A549 (lung cancer), MDA-MB-231 (breast cancer) and DU-145 (prostate cancer) cell lines. FACS analysis revealed that these hybrids arrest the cell cycle at the subG1 phase. Western blot analysis and an immunofluorescence assay showed the inhibition of the EGFR and STAT3 axis, which plays an important role in cell survival and apoptosis. Western blot and RT-PCR analyses that displayed an increase in apoptotic proteins such as p53, p21 and Bax and a decrease in the anti-apoptotic proteins Bcl-2 and procaspase-9 confirmed the ability of these hybrids to trigger cell death by apoptosis. Molecular docking studies described the binding of these hybrids to the ATP binding site of EGFR.
A series of β-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 β-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 β-carboline-benzimidazole conjugates reveals that they possess drug-like properties.
A series of β-carboline hybrids bearing a substituted phenyl and a chalcone/(N-acetyl)-pyrazole moiety at the C1 and C3 positions, respectively, was designed, synthesized, and evaluated for anticancer activity. These new hybrid molecules showed significant cytotoxic activity, with IC50 values ranging from <2.0 μM to 80 μM, and the structure-activity relationships (SAR) associated with substitutions at positions 1 and 3 of these hybrids was clearly addressed. Further, induction of apoptosis was confirmed by Annexin V-FITC, Hoechst staining, and DNA fragmentation analysis. In addition, DNA photocleavage studies proved that two of the hybrids, (E)-1-(furan-2-yl)-3-(1-(4-(trifluoromethyl)phenyl)-9H-pyrido[3,4-b]indol-3-yl)prop-2-en-1-one (7 d) and 1-(3-(furan-2-yl)-5-(1-(4-(trifluoromethyl)phenyl)-9H-pyrido[3,4-b]indol-3-yl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone (8 d) could effectively cleave pBR322 plasmid DNA upon irradiation with UV light. Active hybrid 8 d inhibited DNA topoisomerase I activity efficiently and preserved DNA in the supercoiled form. To further corroborate the biological activities, as well as to understand the nature of the interaction of these hybrids with DNA, spectroscopic studies were also performed. Unlike simple β-carboline alkaloids, the binding mode of these new hybrid molecules with DNA was not similar, and both biophysical as well as molecular docking studies speculated a combilexin-type of interaction with DNA. Further, an in silico study of these β-carboline hybrids revealed their drug-like properties.
A series of 2-anilinopyridyl–triazole conjugates (6a–t) were prepared and evaluated for their cytotoxic activity against a panel of three human cancer cell lines. Among them compounds 6q, 6r and 6s showed significant cytotoxic activity with IC50 values ranging from 0.1 to 4.1 μM. Structure–activity relationships were elucidated with various substitutions on these conjugates. Flow cytometric analysis revealed that these compounds arrest the cell cycle at the G2/M phase and induce cell death by apoptosis. The tubulin polymerization assay and immunofluorescence analysis showed that these compounds (6q, 6r and 6s) effectively inhibited the microtubule assembly in human prostate cancer cells (DU-145). The docking studies showed that 6s interacts and binds efficiently with the tubulin protein at the colchicine binding site. This was further confirmed by the colchicine competitive binding assay. Moreover, compounds 6q, 6r and 6s possess anti-tubulin activity both in vitro and within cells as demonstrated by the ratio of soluble versus polymerized tubulin. Further the apoptotic effects of compounds were confirmed by Hoechst staining, caspase 3 activation, annexin-V FITC, mitochondrial membrane potential and DNA fragmentation analysis. Interestingly, these compounds did not affect the normal human embryonic kidney cells, HEK-293.
Apoptosis is a representative form of programmed cell death, which has been assumed to be critical for cancer prevention. Thus, any agent that can induce apoptosis may be useful for cancer treatment and apoptosis induction is arguably the most potent defense against cancer promotion. In our previous studies, 2-aryl benzimidazole conjugates were synthesized and evaluated for their antiproliferative activity and one of the new molecule (2f) was considered as a potential lead. This lead molecule showed significant antiproliferative activity against human breast cancer cell line, MCF-7. The results of the present study revealed that this compound arrested the cell cycle at G2/M phase. Topoisomerase II inhibition assay and Western blot analysis suggested that this compound effectively inhibits topoisomerase II activity which leads to apoptotic cell death. Apoptosis induction in MCF-7 cells was further confirmed by loss of mitochondrial membrane potential (∆Ψm), release of cytochrome c from mitochondria, an increase in the level of apoptosis inducing factor (AIF), generation of reactive oxygen species (ROS), up regulation of proapoptotic protein Bax and down regulation of anti apoptotic protein Bcl-2. Apoptosis assay using Annexin V-FITC assay also suggested that this compound induced cell death by apoptosis. However, compound 2f induced apoptosis could not be reversed by Z-VAD-FMK (a pan-caspase inhibitor) demonstrated that the 2f induced apoptosis was caspase independent. Further, 2f treatment did not activate caspase-7 and caspase-9 activity, suggesting that this compound induced apoptosis in breast cancer cells via a caspase independent pathway. Most importantly, this compound was less toxic towards non-tumorigenic breast epithelial cells, MCF-10A. Furthermore, docking studies also support the potentiality of this molecule to bind to the DNA topoisomerase II.
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