T. Srinivasa Reddy

H2O-mediated isatin spiro-epoxide ring opening with NaCN: Synthesis of novel 3-tetrazolylmethyl-3-hydroxy-oxindole hybrids and their anticancer evaluation.

A simple method for isatin spiro-epoxide ring-opening by sodium cyanide in water to obtain a variety of isatin hydroxy nitriles has been developed. Further, these intermediates have been converted into new 3-tetrazolylmethyl-3-hydroxy-oxindole hybrids via azide-nitrile cycloaddition reaction in a sealed tube. These compounds were evaluated for their in vitro anticancer activity on five human cancer cell lines i.e. breast (BT549 and MDA MB-231), prostate (PC-3 and DU-145) and ovarian (PA-1). The compounds 6d and 6r showed potent anticancer activity against DU-145 cell line with IC50 values in the range of 7.01 ± 0.91 and 4.26 ± 0.09 μM respectively. The compounds 6d, 6g, 6q and 6r were also tested on human normal prostate epithelial (RWPE-1) cells and found to be safer with lesser cytotoxicity. The morphology and long term clonogenic survival of DU-145 cells were severely affected by compound 6r. Cell cycle analysis revealed that the compounds arrest the cells in G2/M phase. Acridine orange/ethidium bromide (AO/EB) staining, DAPI staining, annexin-V binding assay and DNA fragmentation analysis showed that cell proliferation was inhibited through induction of apoptosis. Moreover, one of the compounds 6r treatment led to collapse of the mitochondrial membrane potential (DΨm) and increased levels of reactive oxygen species (ROS) in DU-145 cells.

Synthesis and biological evaluation of podophyllotoxin congeners as tubulin polymerization inhibitors.

A series of new podophyllotoxin derivatives containing structural modifications at C-7, C-8, and C-9 were synthesized and evaluated for their cytotoxic activity against three human cancer cell lines. All the synthesized compounds showed significant growth inhibition with GI50 values in micromolar levels while some of the compounds were several times more potent against MCF-7 and HeLa cell lines than MIAPACA cell line. Three compounds (12a, 12d and 12e) emerged as potent compounds with broad spectrum of cytotoxic activity against all the tested cell lines with GI50 values in the range of 0.01-2.1 μM. These compounds induce microtubule depolymerization and arrests cells at the G2/M phase of the cell cycle. Moreover, compounds 12d and 12e disrupted microtubule network and accumulated tubulin in the soluble fraction in a similar manner to their parent podophyllotoxin scaffold. In addition, structure activity relationship studies within the series were also discussed. Molecular docking studies of these compounds into the colchicine-binding site of tubulin, revealed possible mode of inhibition by these compounds.

Spirooxindole-derived morpholine-fused-1,2,3-triazoles: Design, synthesis, cytotoxicity and apoptosis inducing studies

A series of new spirooxindole-derived morpholine-fused-1,2,3-triazole derivatives has been synthesized from isatin spiro-epoxides. The protocol involves regiospecific isatin-epoxide ring opening with azide nucleophile followed by sequential O-propargylation, and intramolecular 1,3-dipolar cycloaddition reaction. These compounds have been evaluated for their antiproliferative activity against selected human tumor cell lines of lung (A549), breast (MCF-7), cervical (HeLa), and prostate (DU-145). Among the tested compounds, 6i, 6n and 6p showed potent growth inhibition against A549 cell line with IC50 values in the range of 1.87-4.36 μM, which are comparable to reference standards doxorubicin and 5-flourouracil. The compounds 6i and 6p treated A549 cells displayed typical apoptotic morphological features such as cell shrinkage, nuclear condensation, fragmentation, and decreased migration potential. Flow-cytometry analysis revealed that the compounds arrested the cells in G2/M phase of cell cycle. Hoechst and acridine orange/ethidium bromide staining studies also showed that the cell proliferation was inhibited through induction of apoptosis. Moreover, the compounds treatment led to collapse of the mitochondrial membrane potential (DΨm) and increased levels of reactive oxygen species (ROS) were noted in A549 cells.

Synthesis and biological evaluation of 4-aza-2,3-dihydropyridophenanthrolines as tubulin polymerization inhibitors

A series of novel 4-aza-2,3-dihydropyridophenanthrolines 12(a-t) were synthesized by a one-step three component condensation of 1,10-phenanthroline amine, tetronic acid and various aromatic aldehydes. These were evaluated for their antiproliferative activity against three human cancer cell lines (MIAPACA, MCF-7 and HeLa) using SRB assay. Majority of the tested compounds exhibited significant anticancer activity on these cell lines and interestingly compounds 12h and 12i were more potent than etoposide and podophyllotoxin against all three tested cancer cell lines with GI50 values in the range of 0.01-0.5 μM. Furthermore, these compounds showed significant inhibition of tubulin polymerization which is comparable to that of podophyllotoxin and disrupted microtubule network by accumulating tubulin in the soluble fraction. The flow cytometry analysis confirmed that the synthesized compounds led to cell cycle arrest at the G2/M phase. Moreover, the structure activity relationship studies in this series are also discussed.

Synthesis of 2-aryl-1,2,4-oxadiazolo-benzimidazoles: Tubulin polymerization inhibitors and apoptosis inducing agents

A new series of 2-aryl 1,2,4-oxadiazolo-benzimidazole conjugates have been synthesized and evaluated for their antiproliferative activity in the sixty cancer cell line panel of the National Cancer Institute (NCI). Compounds 5l (NSC: 761109/1) and 5x (NSC: 761814/1) exhibited remarkable cytotoxic activity against most of the cancer cell lines in the one dose assay and were further screened at five dose concentrations (0.01, 0.1, 1, 10 and 100 μM) which showed GI50 values in the range of 0.79-28.2 μM. Flow cytometric data of these compounds showed increased cells in G2/M phase, which is suggestive of G2/M cell cycle arrest. Further, compounds 5l and 5x showed inhibition of tubulin polymerization and disruption of the formation of microtubules. These compounds induce apoptosis by DNA fragmentation and chromatin condensation as well as by mitochondrial membrane depolarization. In addition, structure activity relationship studies within the series are also discussed. Molecular docking studies of compounds 5l and 5x into the colchicine-binding site of the tubulin, revealed the possible mode of interaction by these compounds.

One-pot synthesis of podophyllotoxin–thiourea congeners by employing NH2SO3H/NaI: Anticancer activity, DNA topoisomerase-II inhibition, and apoptosis inducing agents

A facile one-pot method for the synthesis of novel podophyllotoxin-thiourea congeners has been developed by using NH2SO3H/NaI system. Interestingly, 4β-azido podophyllotoxin reduction with concomitant aryl isothiocyanates coupling under mild reaction conditions has been achieved. These compounds have been investigated for their in vitro cytotoxicity against A549, MDA MB-231, DU-145, LNCaP, and HGC-27 cancer cell lines. Some of the representative compounds have selectively exhibited cytotoxicity on DU-145 (human prostate cancer) cells and the most potent compound was 4a (IC50 of 0.50 ± 0.03 μM) with optimal safety therapeutic window (81.7 fold) on normal human prostate cell line (RWPE-1, IC50 of 40.85 ± 0.78). The flow-cytometric analysis of the compound 4a in prostate cancer cells indicated a strong G2/M-phase arrest and significant topoisomerase II inhibition activity. Furthermore, these compounds induce apoptosis as observed by Acridine Orange and Ethidium Bromide (AO/EB) staining and Annexin V binding assay. Molecular docking results of the title compounds with topoisomerase-IIα were presented as theoretical support for the experimental data.

Synthesis and biological evaluation of cis-restricted triazole/tetrazole mimics of combretastatin-benzothiazole hybrids as tubulin polymerization inhibitors and apoptosis inducers

A series of colchicine site binding tubulin inhibitors were synthesized by the modification of the combretastatin pharmacophore. The ring B was replaced by the pharmacologically relevant benzothiazole scaffolds, and the cis configuration of the olefinic bond was restricted by the incorporation of a triazole and tetrazole rings which is envisaged by the structural resemblance to a tubulin inhibitor like combretastatin (CA-4). These compounds were evaluated for their antiproliferative activity on selected cancer cell lines and an insight in the structure activity relationship was developed. The most potent compounds (9a and 9b) demonstrated an antiproliferative effect comparable to that of CA-4. Mitotic cell cycle arrest in G2/M phase revealed the disruption of microtubule dynamics that was confirmed by tubulin polymerization assays and immunocytochemistry studies at the cellular level. Western blot analysis revealed that these compounds accumulate more tubulin in the soluble fraction. The colchicine competitive binding assay and the molecular docking studies suggested that the binding of these mimics at the colchicine site of the tubulin is similar to that of CA-4. Moreover, the triggering of apoptotic cell death after mitotic arrest was investigated by studying their effect by Hoechst staining, Annexin-V-FITC assay, mitochondrial membrane potential, ROS generation and caspase-3 activation.

Cyclic RGDfK Peptide Functionalized Polymeric Nanocarriers for Targeting Gemcitabine to Ovarian Cancer Cells

Current cancer chemotherapies commonly suffer from nonspecificity, drug resistance, poor bioavailability, and narrow therapeutic indices. To achieve the optimum drug efficacy, we designed a polymeric drug delivery system for targeted intracellular delivery of a clinically approved, water-soluble anticancer drug, gemcitabine hydrochloride (GEM). We utilized the unique ability of a cyclic pentapeptide cRGDfK to specifically target αvβ3 integrin receptors that are overexpressed on SKOV-3 human ovarian cancer cells. This significantly increased the effective intracellular drug concentration even at low doses, thereby remarkably improving the chemotherapeutic potential of GEM. cRGDfK-conjugated, GEM-loaded nanoparticles reduced the nonspecific hemolytic cytotoxicity of the drug, simultaneously influencing intracellular processes such as mitochondrial membrane potential (DΨm), reactive oxygen species (ROS) levels, and apoptosis, thereby favorably influencing drug antiproliferative efficacy.

Anti-cancer gold(I) phosphine complexes: Cyclic trimers and tetramers containing the P-Au-P moiety

We report the application of cationic tri- and tetra-nuclear gold(I) phosphine complexes [Au3(μ-dppen)3]X3 and [Au4(μ-dppa)4]X4 (X=OTf, PF6) [OTf=trifluoromethanesulfonate, dppen=trans-1,2-bis(diphenylphosphino)ethene, dppa=bis(diphenylphosphino)acetylene] for cancer treatment. The results of cytotoxicity tests on four different cancer cells [prostate (DU145), cervical (HeLa), breast (MDAMB-231) and fibro sarcoma (HT1080)] indicate these complexes possess remarkable tumor cell growth inhibitory effects and high selectivity towards cancer cells. The anti-tumor mechanism of the tri- and tetra-nuclear gold(I) complexes has also been investigated.

Synthesis and biological evaluation of imidazopyridinyl-1,3,4-oxadiazole conjugates as apoptosis inducers and topoisomerase IIα inhibitors

A series of imidazopyridinyl-1,3,4-oxadiazole conjugates were synthesized and investigated for their cytotoxic activity and some compounds showed promising cytotoxic activity. Compound 8q (NSC: 763639) exhibited notable growth inhibition that satisfies threshold criteria at single dose (10μM) on all human cancer cell lines. This compound was further evaluated at five dose levels (0.01, 0.1, 1, 10 and 100μM) to obtain GI50 values ranging from 1.30 to 5.64μM. Flow cytometric analysis revealed that compound 8q arrests the A549 cells in sub G1 phase followed by induction of apoptosis which was further confirmed by Annexin-V-FITC, Hoechst nuclear staining, caspase 3 activation, measurement of mitochondrial membrane potential and ROS generation. Topo II mediated DNA relaxation assay results showed that conjugate 8q could significantly inhibit the activity of topo II. Moreover, molecular docking studies also indicated binding to the topoisomerase enzyme (PDBID 1ZXN).