Baljinder Singh

The hydroalcoholic extract of Cassia alata (Linn.) leaves and its major compound rhein exhibits antiallergic activity via mast cell stabilization and lipoxygenase inhibition.

ETHNOPHARMACOLOGICAL RELEVANCE Leaves of Cassia alata (family: Caesalpiniaceae) are ethnomedically claimed as anti-asthmatic. In the current study we aimed to investigate the anti-allergic activities of hydro-methanolic extract of Cassia alata (Linn.) and its constituents rhein and kaempferol on triple antigen/sheep serum-induced mast-cell degranulation in rats. MATERIALS AND METHODS Antiallergic activity of hydroalcoholic extract of Cassia alata along with its two components rhein and kaempferol was evaluated using in vivo mast cell stabilization assay. Inhibitory effect on lipoxygenase (LOX) enzyme was also evaluated in vitro. Further chemical standardization of Cassia alata extract was done using rhein and kaempferol by HPTLC-densitometric method. RESULTS The hydroalcoholic extract of Cassia alata significantly inhibited mast cell degranulation at 200mg/kg dose. Both chemical constituents rhein and kaempferol also showed potent (>76%) inhibition of mast-cell degranulation at 5mg/kg. Extract and rhein inhibited LOX enzyme with IC(50) values of 90.2 and 3.9μg/mL, respectively, whereas kaempferol was inactive. CONCLUSION Our results suggest that Cassia alata exhibit anti-allergic activity through mast cell stabilization and LOX inhibition. Thus, Cassia alata or its active constituents could be potential alternative treatment for allergic diseases.

Total synthesis and anti-cholinesterase activity of marine-derived bis-indole alkaloid fascaplysin

A short and efficient two-step total synthesis of marine-derived bis-indole alkaloid fascaplysin starting from commercially available tryptamine in 68% overall yield is reported. A key step involved in the present strategy is tandem dehydrative condensation between ortho-halo substituted glyoxal with tryptamine followed by dehydrogenation. Fascaplysin inhibited acetylcholinesterase (AChE) in non-competitive manner with IC50 and ki values of 1.49 and 2.28 μM respectively and with 60-fold selectivity for AChE versus butyrylcholinesterase. Molecular docking studies revealed that fascaplysin accommodates within a peripheral anionic site and inner linings of the AChE active site gorge.

Synthesis and anti-proliferative activities of new derivatives of embelin.

Embelin (1), a benzoquinone isolated from Embelia ribes is known to possess variety of biological activities. Despite of several promising biological activities, preclinical efforts on embelin were hampered because of its poor aqueous solubility. In order to address the solubility issue, herein, we have synthesized a series of Mannich products of embelin by treating it with various secondary amines. The synthesized compounds were screened for antiproliferative and antimicrobial activities. In cytotoxicity screening, the benzyl-piperidine linked derivative 8m was found to possess better antiproliferative activity compared to parent natural product embelin against a panel of cell lines including HCT-116, MCF-7, MIAPaCa-2 and PC-3 with IC50 values of 30, 41, 34 and 36 μM, respectively. The mechanistic study of compound 8m revealed that it exhibits cytotoxicity via induction of apoptosis and mitochondrial membrane potential loss. Further, the compounds were tested for antimicrobial activity where dimethylamino- 8a and piperidine linked derivative 8b displayed antibacterial activity against Staphylococcus aureus with MIC values of 8 and 16 μg/mL, respectively. Mannich derivatives did now show improved aqueous solubility, however their hydrochloride salts 8a·HCl, 8b·HCl and 8m·HCl showed significantly improved aqueous solubility without affecting biological activities of parent Mannich derivatives.

Osthol and curcumin as inhibitors of human Pgp and multidrug efflux pumps of Staphylococcus aureus: reversing the resistance against frontline antibacterial drugs

The in-house IIIM natural product repository of 302 small molecules was screened for their ability to inhibit P-glycoprotein (Pgp) in Pgp-overexpressing human adenocarcinoma LS-180 cells. The screening has identified 13 natural products displaying significant Pgp-inhibition activity, which include praeruptorin B, curcumin, imperatorin, osthol, 5,7-diacetoxy-8-(3-methyl-2-butenyl)-coumarin, 5,7-dihydroxy-8-(3-methyl-2-butenyl) coumarin, pongamol, phellopterin, tangeretin, 3-(2-methyl but-3-en-2-yl) xanthyletin, 7-demethyl osthol, allorottlerin and tetrahydroangeolide. These natural products were then screened for their effects on bacterial efflux pump inhibition activity against NorA (Staphylococcus aureus), MdeA (S. aureus Mupr-1), TetK (S. aureus SA-K2192), and MsrA (S. aureus SA-K2191) efflux pumps. Curcumin and osthol showed significant inhibition of the S. aureus NorA efflux pump with 8- and 4-fold reductions in the MIC of ciprofloxacin at 25 μM. The molecular docking studies of curcumin and osthol with the human Pgp and S. aureus NorA efflux pump identified plausible binding modes and binding sites for these natural products.

A novel microtubule depolymerizing colchicine analogue triggers apoptosis and autophagy in HCT-116 colon cancer cells.

Colchicine is a tubulin‐binding natural product isolated from Colchicum autumnale. Here we report the in vitro anticancer activity of C‐ring modified semi‐synthetic derivative of colchicine; N‐[(7S)‐1,2,3‐trimethoxy‐9‐oxo‐10‐(4‐phenyl‐piperidin‐1‐yl)‐5,6,7,9 tetrahydrobenzo[a]heptalen‐7‐yl]acetamide (4h) on colon cancer HCT‐116 cell line. The compound 4h was screened for anti‐proliferative activity against different human cancer cell lines and was found to exhibit higher cytotoxicity against colon cancer cell lines HCT‐116 and Colo‐205 with IC50 of 1 and 0.8 μM respectively. Cytotoxicity of the compound to the normal fR2 breast epithelial cells and normal HEK293 human embryonic kidney cells was evaluated in concentration and time‐dependent manner to estimate its selectivity for cancer cells which showed much better selectivity than that of colchicine. Compound 4h induced cell death in HCT‐116 cells by activating apoptosis and autophagy pathways. Autophagy inhibitor 3‐MA blocked the production of LC3‐II and reduced the cytotoxicity in response to 4h, but did not affect apoptosis, suggesting thereby that these two were independent events. Reactive oxygen species scavenger ascorbic acid pretreatment not only decreased the reactive oxygen species level but also reversed 4h induced cytotoxicity. Treatment with compound 4h depolymerized microtubules and the majority of cells arrested at the G2/M transition. Together, these data suggest that 4h has better selectivity and is a microtubule depolymerizer, which activates dual cell‐death machineries, and thus, it could be a potential novel therapeutic agent in cancer therapy. Copyright

Modulation of k-Ras Signaling by Natural Products

Ras proteins regulate diverse cellular pathways that are important in the growth and spread of malignancies, including cell proliferation, cell cycle regulation, cell survival, angiogenesis and cell migration. These proteins lack the conventional transmembrane or hydrophobic domain typical of membrane associated proteins. Being small and hydrophilic in nature, these proteins undergo four-stage post-translational lipid modifications viz. prenylation, AAX proteolysis, carboxymethylation and palmitoylation for membrane localization which is important for their function. Therefore, enzymes involved in these modifications viz. farnesyl transferase (FTase), geranylgeranyl transferase-I (GGTase-I), geranylgeranyl transferase-II (GGTase-II), Ras converting enzyme-1 (Rce-1) and isoprenyl cysteine methyl transferase (ICMT) are emerging as potential therapeutic targets for the discovery of newer anticancer therapeutics. Several natural products have shown modulation of these post-translational enzymes. In the present review, natural products isolated from terrestrial as well as marine sources showing ability to modulate these k-Ras post-translational targets and their promise as potential anticancer agents have been discussed. A total of 157 natural products with 141 corresponding references have been covered.

A novel colchicine-based microtubule inhibitor exhibits potent antitumor activity by inducing mitochondrial mediated apoptosis in MIA PaCa-2 pancreatic cancer cells.

Colchicine, an antimitotic alkaloid isolated from Colchicum autumnale, is a classical drug for treatment of gout and familial Mediterranean fever. It causes antiproliferative effects through the inhibition of microtubule formation, which leads to mitotic arrest and cell death by apoptosis. Here, we report that a novel colchicine analog, 4o (N-[(7S)-1,2,3-trimethoxy-9-oxo-10-[3-(trifluoromethyl)-4-chlorophenylamino]-5,6,7,9-tetrahydrobenzo[a]heptalen-7-yl]acetamide), which exhibited potent anticancer activities both in vitro and in vivo. In this study, 4o with excellent pharmacokinetic profile and no P-gp induction liability displayed strong inhibition of proliferation against various human cancer cell lines. However, pancreatic cancer cell line MIA PaCa-2 was found to be more sensitive towards 4o and showed strong inhibition in concentration and time-dependent manner. By increasing intracellular reactive oxygen species (ROS) levels, 4o induced endoplasmic reticular stress and mitochondrial dysfunction in MIA PaCa-2 cells. Blockage of ROS production reversed 4o-induced endoplasmic reticulum (ER) stress, calcium release, and cell death. More importantly, it revealed that increased ROS generation might be an effective strategy in treating human pancreatic cancer. Further 4o treatment induced mitotic arrest, altered the expression of cell cycle-associated proteins, and disrupted the microtubules in MIA PaCa-2 cells. 4o treatment caused loss of mitochondrial membrane potential, cytochrome c release, upregulation of Bax, downregulation of Bcl-2, and cleavage of caspase-3, thereby showing activation of mitochondrial mediated apoptosis. The in vivo anticancer activity of the compound was studied using sarcoma-180 (ascitic) and leukemia (P388 lymphocytic and L1210 lymphoid) models in mice and showed promising antitumor activity with the least toxicity unlike colchicine. Such studies have hitherto not been reported. Taken together, these findings highlighted that 4o, a potent derivative of colchicine, causes tumor regression with reduced toxicity and provides a novel anticancer candidate for the therapeutic use.

QSAR and pharmacophore modeling of N-acetyl-2-aminobenzothiazole class of phosphoinositide-3-kinase-α inhibitors

The mTOR-mediated PI3K/AKT/mTOR signal transduction pathway plays a key role in a broad spectrum of cancers. In the present article, QSAR and pharmacophore studies were carried out using a series of 61 benzothiazole class of PI3Kα inhibitors to characterize molecular features and structural requirements crucial for biological interaction. QSAR study performed using TSAR 3.3 by multiple regression analysis and partial least square methods identified inertia moment-1-size, kier chiv5 (path) index, and number of H-bond donors as important descriptors responsible for PI3Kα inhibitory activity. Further analysis of pharmacophore model by means of Phase module of Schrodinger revealed that two hydrogen-bond acceptors, one hydrogen-bond donors, and two hydrophobic aromatic rings as crucial molecular features that predict binding affinity for high-affinity ligands to the PI3Kα enzyme. These observations provide important insights to the key structural requirements of these molecules for potent PI3Kα inhibition. Excellent statistical results of developed models strongly suggest that these models are reasonable for the prediction of the activity of new inhibitors and in future drug design.

KF/alumina catalyzed regioselective benzylation and benzoylation using solvent-free grind-stone chemistry

Potassium fluoride-impregnated on alumina catalyzes solvent-free regioselective O-benzylation, benzoylation and cinnamylation of phenols. Reaction proceeds simply by triturating together equivalent amounts of phenol and corresponding halide in the presence of 5 mol% of KF/alumina for 5–20 min with a mortar and pestle, without need for any additive such as phase-transfer catalyst or solvent. Key features of the protocol include its efficiency also for solid–solid precursors and regioselectivity for phenolic hydroxyls versus alcoholic hydroxyls. Utility of the protocol for N- and S-benzylation has also been explored. Products were obtained in excellent yields and the catalyst can be easily recycled several times without significant loss of activity.

Anti-inflammatory and immunomodulatory flavones from Actinocarya tibetica Benth.

Herein, we report the isolation and immunomodulatory activity of 11 phytoconstituents, viz. 7 flavonoids, 3 pentacyclic triterpenes and 1 phytosterol of an unexplored plant Actinocarya tibetica Benth. Three flavones, 5-methoxy-6,7-methylenedioxyflavone (6), mosloflavone (7) and negletein (8), showed promising anti-inflammatory activity via inhibition of TNF-α and IL-1β with IC50 values of 0.22, 0.71, 16.4 μM and 10.8, 7.8, 6.4 μM, respectively. These flavones also showed dose-dependent inhibition of TNF-α, IL-1β and iNOS levels in the supernatant of mouse macrophage cell line J774A. Molecular modelling studies revealed orientation and interactions of flavones 6–8 in the active site of TNF-α. These flavones can be used as a starting point to discover lead structures for treatment of inflammatory and immunomodulatory diseases.