Nishant Jain

Design, Synthesis, and Structure–Activity Correlations of Novel Dibenzo[b,d]furan, Dibenzo[b,d]thiophene, and N-Methylcarbazole Clubbed 1,2,3-Triazoles as Potent Inhibitors of Mycobacterium tuberculosis

A molecular hybridization approach is an emerging structural modification tool to design new molecules with improved pharmacophoric properties. In this study, 1,2,3-triazole-based Mycobacterium tuberculosis inhibitors and synthetic and natural product-based tricyclic (carbazole, dibenzo[b,d]furan, and dibenzo[b,d]thiophene) antimycobacterial agents were integrated in one molecular platform to prepare various novel clubbed 1,2,3-triazole hybrids using click chemistry. Structure-activity correlations and in vitro activity against M. tuberculosis strain H37Rv of new analogues revealed the order: dibenzo[b,d]thiophene > dibenzo[b,d]furan > 9-methyl-9H-carbazole series. Two of the most potent M. tuberculosis inhibitors 13h and 13q with MIC = 0.78 μg/mL (∼1.9 μM) displayed a low cytotoxicity and high selectivity index (50-255) against four different human cancer cell lines. These results together provided the potential importance of molecular hybridization and the development of triazole clubbed dibenzo[b,d]thiophene-based lead candidates to treat mycobacterial infections.

Design and Synthesis of Resveratrol-Based Nitrovinylstilbenes as Antimitotic Agents

A new series of resveratrol analogues was designed, synthesized, and demonstrated to be tubulin polymerization inhibitors. Most of these compounds exhibited antiproliferative activity and inhibited in vitro tubulin polymerization effectively at concentrations of 4.4-68.1 and 17-62 μM, respectively. Flow cytometry studies showed that compounds 7c, 7e, and 7g arrested cells in the G2/M phase of the cell cycle. Immunocytochemistry revealed loss of intact microtubule structure in cells treated with 7c and 7e. Docking of compounds 7c and 7e with tubulin suggested that the A-ring of the compounds occupies the colchicine binding site of tubulin, which coordinates with Cys241, Leu242, Ala250, Val318, Val328, and I378, and that the nitrovinyl side chain forms two hydrogen bonds with the main loop of the β-chain at Asn249 and Ala250.

Synthesis of a new 4-aza-2,3-didehydropodophyllotoxin analogues as potent cytotoxic and antimitotic agents.

A series of novel conjugates of 4-aza-2,3-didehydropodophyllotoxins (11a-w) were synthesized by a straightforward one-step multicomponent synthesis that demonstrated cytotoxicity against five human cancer cell lines (breast, oral, colon, lung and ovarian). All the twenty three compounds (11a-w) have been examined for the inhibition of tubulin polymerization. Among these compounds, 11a, 11k and 11p exhibited inhibition of polymerization tubulin comparable to podophyllotoxin apart from disruption of microtubule organization within the cells. Flow cytometric analysis showed that these compounds (11a, 11k and 11p) arrested the cell cycle in the G2/M phase of cell cycle leading to caspase-3 dependent apoptotic cell death.

Design and synthesis of pyrazole-oxindole conjugates targeting tubulin polymerization as new anticancer agents.

A series of twenty one compounds with pyrazole and oxindole conjugates were synthesized by Knoevenagel condensation and investigated for their antiproliferative activity on different human cancer cell lines. The conjugates are comprised of a four ring scaffold; the structural isomers 12b and 12c possess chloro-substitution in the D ring. Among the congeners 12b, 12c, and 12d manifested significant cytotoxicity and inhibited tubulin assembly. Treatments with 12b, 12c and 12d resulted in accumulation of cells in G2/M phase, disruption of microtubule network, and increase in cyclin B1 protein. Zebrafish screening revealed that 12b, and 12d caused developmental defects. Docking analysis demonstrated that the congeners occupy the colchicine binding pocket of tubulin.

Synthesis, anticancer activity and photophysical properties of novel substituted 2-oxo-2H-chromenylpyrazolecarboxylates.

2-Oxo-2H-chromenylpyrazolecarboxylates (8a-h and 12a-zb) have been synthesized by [3 + 2] cycloaddition of 2H-chromenophenylhydrazones (7a-h and 11a-w) with diethyl/dimethylbut-2-ynedioates. Phenylchromeno[4,3-c]pyrazol-4(1H)-ones (13i-n) were prepared from corresponding phenylhydrazones (7a-h) with catalytic amount of piperidine in presence of pyridine as a solvent at 100 °C. All the synthesized compounds (8a-h, 12a-zb and 13a-n) were screened for anticancer activity against three human cancer cell lines such as prostate (DU-145), lung adenocarcinoma (A549), and cervical (HeLa) by standard MTT assay method. Further, photophysical properties (UV and fluorescence) for these compounds were discussed.

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.

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 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 and evaluation of benzosuberone embedded with 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole moieties as new potential anti proliferative agents.

As an aspect of our ongoing research in search of new anti proliferative agents, a series of novel analogs of benzosuberone embedded with 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole moieties were synthesized in excellent yields (82-93%). All the newly synthesized compounds were characterized by (1)H NMR, (13)C NMR, ESI/LC-MS, HRMS and evaluated for their in vitro anti proliferative activity against four human cancer cell lines (cervical, breast, pancreatic and alveolar). Among the synthesized compounds, 4b, 6a, 7d and 7l showed potent anti proliferative activity with GI50 values range of 0.079-0.957μM against four human cancer cell lines. However, it was revealed that the compound 7d have shown very close GI50 value 0.079μM as compared with positive control of colchicine against cervical cancer cell line.

Regulation of PSMB5 Protein and β Subunits of Mammalian Proteasome by Constitutively Activated Signal Transducer and Activator of Transcription 3 (STAT3): POTENTIAL ROLE IN BORTEZOMIB-MEDIATED ANTICANCER THERAPY*

Background: Malignancies are frequently associated with altered abundance of proteasome and elevated proteasome activity. Results: EGF-induced PSMB5 expression requires STAT3 activation. Conclusion: The catalytic subunits and activities of the mammalian proteasome are regulated by STAT3. Significance: Proteasome function is regulated by oncogenic signaling. The ubiquitin-proteasome system facilitates the degradation of ubiquitin-tagged proteins and performs a regulatory role in cells. Elevated proteasome activity and subunit expression are found in several cancers. However, the inherent molecular mechanisms responsible for increased proteasome function in cancers remain unclear despite the well investigated and defined role of the mammalian proteasome. This study was initiated to elucidate the mechanisms involved in the regulation of β subunits of the mammalian proteasome. Suppression of STAT3 tyrosine phosphorylation coordinately decreased the mRNA and protein levels of the β subunits of the 20 S core complex in DU145 cells. Notably, PSMB5, a molecular target of bortezomib, was shown to be a target of STAT3. Knockdown of STAT3 decreased PSMB5 protein. Inhibition of phospho-STAT3 substantially reduced PSMB5 protein levels in cells expressing constitutively active-STAT3. Accumulation of activated STAT3 resulted in the induction of PSMB5 promoter and protein levels. In addition, a direct correlation was observed between the endogenous levels of PSMB5 and constitutively active STAT3. PSMB5 and STAT3 protein levels remained unaltered following the inhibition of proteasome activity. The EGF-induced concerted increase of β subunits was blocked by inhibition of the EGF receptor or STAT3 but not by the PI3K/AKT or MEK/ERK pathways. Decreased proteasome activities were due to reduced protein levels of catalytic subunits of the proteasome in STAT3-inhibited cells. Combined treatments with bortezomib and inhibitor of STAT3 abrogated proteasome activity and enhanced cellular apoptosis. Overall, we demonstrate that aberrant activation of STAT3 regulates the expression of β subunits, in particular PSMB5, and the catalytic activity of the proteasome.