Vangala Santhosh Reddy

Synthesis of arylpyrazole linked benzimidazole conjugates as potential microtubule disruptors.

In an attempt to develop potent and selective anticancer agents, a series of twenty arylpyrazole linked benzimidazole conjugates (10a-t) were designed and synthesized as microtubule destabilizing agents. The joining of arylpyrazole to the benzimidazole moiety resulted in a four ring (A, B, C and D) molecular scaffold that comprises of polar heterocyclic rings in the middle associated with rotatable single bonds and substituted aryl rings placed in the opposite directions. These conjugates were evaluated for their ability to inhibit the growth of sixty cancer cell line panel of the NCI. Among these some conjugates like 10a, 10b, 10d, 10e, 10p and 10r exhibited significant growth inhibitory activity against most of the cell lines ranging from 0.3 to 13μM. Interestingly, the conjugate 10b with methoxy group on D-ring expressed appreciable cytotoxic potential. A549 cells treated with some of the potent conjugates like 10a, 10b and 10d arrested cells at G2/M phase apart from activating cyclin-B1 protein levels and disrupting microtubule network. Moreover, these conjugates effectively inhibited tubulin polymerization with IC50 values of 1.3-3.8μM. Whereas, the caspase assay revealed that they activate the casepase-3 leading to apoptosis. Particularly 10b having methoxy substituent induced activity almost 3 folds higher than CA-4. Furthermore, a competitive colchicine binding assay and molecular modeling analysis suggests that these conjugates bind to the tubulin successfully at the colchicine binding site. These investigations reveal that such conjugates having pyrazole and benzimidazole moieties have the potential in the development of newer chemotherapeutic agents.

Synthesis of imidazo[2,1-b][1,3,4]thiadiazole–chalcones as apoptosis inducing anticancer agents

A series of new imidazo[2,1-b][1,3,4]thiadiazole–chalcones were synthesized by Claisen–Schmidt condensation and evaluated for their cytotoxic activity against various human cancer cell lines. These compounds showed moderate to appreciable antiproliferative activities. Interestingly, compounds like 11a and 11b exhibited significant cytotoxic activity with IC50 values ranging from 0.65 to 2.25 μM in certain cancer cell lines. The structure–activity relationship (SAR) studies reveal that 3,4,5-trimethoxy group containing compounds showed superior cytotoxic activity against selected cancer cell lines compared to other chalcones. These compounds showed G0/G1 phase arrest, apart from activation of caspase-3 and 8 in DU-145 cells. The growth inhibitory effect of these compounds was associated with a decrease in cell cycle regulatory protein cyclin D1 and increase in cyclin dependent kinase inhibitors like Cip1/p21 and Kip1/p27.

Design, synthesis and biological evaluation of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as potential anticancer agents

A series of imidazopyridine/imidazopyrimidine-benzimidazole conjugates (11a–t) were synthesized and evaluated for their antiproliferative activity. All of these conjugates showed moderate to improved cytotoxic activity against the human cervical (Hela), lung (A549), prostate (DU-145) and melanoma (B-16) cancer cell lines. Among them, conjugates 11i and 11p showed significant antiproliferative activity against lung cancer cell line A549 with IC50 values 1.48 and 1.92 μM, respectively. Flow cytometric analysis revealed that these conjugates induced cell cycle arrest at G2/M phase in the A549 cell line leading to caspase-3-dependent apoptotic cell death. The tubulin polymerization assay (IC50 of 11i is 2.06 μM and 11p is 2.26 μM) and immuofluorescence analysis displayed that these conjugates effectively inhibit microtubule assembly at both the molecular and cellular levels in A549 cells. Further, Hoechst staining, caspase-3 activation assay, DNA fragmentation analysis and Annexin V-FITC assay also suggested that these compounds induced cell death by apoptosis. Furthermore, molecular docking studies indicated that these conjugates efficiently interact and bind with tubulin protein. Overall, the present study demonstrates that the synthesis of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as promising tubulin inhibitors with G2/M phasecell cycle arrest and apoptotic-inducing ability.

Design and Synthesis of Aminostilbene–Arylpropenones as Tubulin Polymerization Inhibitors

A series of aminostilbene—arylpropenones were designed and synthesized by Michael addition and were investigated for their cytotoxic activity against various human cancer cell lines. Some of the investigated compounds exhibited significant antiproliferative activity against a panel of 60 human cancer cell lines of the US National Cancer Institute, with 50 % growth inhibition (GI50) values in the range from <0.01 to 19.9 μM. One of the compounds showed a broad spectrum of antiproliferative efficacy on most of the cell lines, with a GI50 value of <0.01 μM. All of the synthesized compounds displayed cytotoxicity against A549 (non‐small‐cell lung cancer), HeLa (cervical carcinoma), MCF‐7 (breast cancer), and HCT116 (colon carcinoma) with 50 % inhibitory concentration (IC50) values ranging from 0.011 to 8.56 μM. A cell cycle assay revealed that these compounds arrested the G2/M phase of the cell cycle. Two compounds exhibited strong inhibitory effects on tubulin assembly with IC50 values of 0.71 and 0.79 μM. Moreover, dot‐blot analysis of cyclin B1 demonstrated that some of the congeners strongly induced cyclin B1 protein levels. Molecular docking studies indicated that these compounds occupy the colchicine binding site of tubulin.

Interaction of Pyrrolobenzodiazepine (PBD) Ligands with Parallel Intermolecular G-Quadruplex Complex Using Spectroscopy and ESI-MS

Studies on ligand interaction with quadruplex DNA, and their role in stabilizing the complex at concentration prevailing under physiological condition, has attained high interest. Electrospray ionization mass spectrometry (ESI-MS) and spectroscopic studies in solution were used to evaluate the interaction of PBD and TMPyP4 ligands, stoichiometry and selectivity to G-quadruplex DNA. Two synthetic ligands from PBD family, namely pyrene-linked pyrrolo[2,1-c][1,4]benzodiazepine hybrid (PBD1), mixed imine-amide pyrrolobenzodiazepine dimer (PBD2) and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) were studied. G-rich single-stranded oligonucleotide d(5′GGGGTTGGGG3′) designated as d(T2G8), from the telomeric region of Tetrahymena Glaucoma, was considered for the interaction with ligands. ESI-MS and spectroscopic methods viz., circular dichroism (CD), UV-Visible, and fluorescence were employed to investigate the G-quadruplex structures formed by d(T2G8) sequence and its interaction with PBD and TMPyP4 ligands. From ESI-MS spectra, it is evident that the majority of quadruplexes exist as d(T2G8)2 and d(T2G8)4 forms possessing two to ten cations in the centre, thereby stabilizing the complex. CD band of PBD1 and PBD2 showed hypo and hyperchromicity, on interaction with quadruplex DNA, indicating unfolding and stabilization of quadruplex DNA complex, respectively. UV-Visible and fluorescence experiments suggest that PBD1 bind externally where as PBD2 intercalate moderately and bind externally to G-quadruplex DNA. Further, melting experiments using SYBR Green indicate that PBD1 unfolds and PBD2 stabilizes the G-quadruplex complex. ITC experiments using d(T2G8) quadruplex with PBD ligands reveal that PBD1 and PBD2 prefer external/loop binding and external/intercalative binding to quadruplex DNA, respectively. From experimental results it is clear that the interaction of PBD2 and TMPyP4 impart higher stability to the quadruplex complex.

Design, synthesis of phenstatin/isocombretastatin-oxindole conjugates as antimitotic agents.

A series of phenstatin/isocombretastatin-oxindole conjugates was synthesized and tested for their cytotoxic activity against five human cancer cells such as prostate (DU-145), lung (A549), colon (HT-29), breast (MCF-7), liver (HepG2) cancer cells with IC50 values ranging from 0.049 to 38.90 μM. Amongst them, two conjugates (5c and 5d) showed broad spectrum of antiproliferative efficacy on lung cancer cells with an IC50 value of 79 nM and 93 nM, respectively, whereas on colon cancer cells with an IC50 values 45 nM and 49 nM, respectively. In addition, cell cycle assay revealed that these conjugates (5c and 5d) arrest at the G2/M phase and leads to apoptotic cell death which was confirmed by Annexin V-FITC and mitochondrial membrane depolarization. Further, the tubulin polymerization assay analysis results suggest that these conjugates particularly 5c and 5d exhibit significant inhibitory effect on the tubulin assembly with an IC50 value of 1.23 μM and 1.01 μM, respectively. Molecular docking studies indicated that these compounds (5c and 5d) occupy the colchicine binding site of the tubulin.

Synthesis of 2-anilinopyridine–arylpropenone conjugates as tubulin inhibitors and apoptotic inducers

A series of new (Z)-3-(arylamino)-1-(2-(arylamino)pyridin-3-yl)prop-2-en-1-one conjugates 9a–p were synthesized and evaluated for their cytotoxic activity against some human cancer cell lines. Some of the treated compounds like 9a, 9g and 9j showed significant activity with IC50 values ranging from 0.51 to 1.29 μM. Flow cytometry results revealed that for A549 cells these compounds caused accumulation of cells in the G2/M phase. Interestingly, compound 9a demonstrated a considerable inhibitory effect on tubulin polymerization and showed significant inhibition of tubulin polymerization with an IC50 value of 1.34 μM, whereas nocodazole showed antitubulin activity with an IC50 value 2.64 μM. Further, Hoechst staining and activation of caspase-3 suggested that these conjugates induced cell death by apoptosis. Fluorescence based competitive colchicine binding assay and docking studies suggest that these conjugates 9a and 9g bind to the tubulin perfectly at the colchicine binding site.

Synthesis of benzopyran linked pyrrolo[2,1-c][1,4]benzodiazepines as DNA-binding and potential anticancer agents.

A series of twelve benzopyran linked pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) have been synthesized. They exhibit significant DNA-binding activity and excellent cytotoxic activity against various human cancer cell lines.