Jitendra Kumar Saxena

Discovery of a New Class of Natural Product-Inspired Quinazolinone Hybrid as Potent Antileishmanial agents

The high potential of quinazolinone containing natural products and their derivatives in medicinal chemistry led us to discover four novel series of 53 compounds of quinazolinone based on the concept of molecular hybridization. Most of the synthesized analogues exhibited potent leishmanicidal activity against intracellular amastigotes (IC50 from 0.65 ± 0.2 to 7.76 ± 2.1 μM) as compared to miltefosine (IC50 = 8.4 ± 2.1 μM) and nontoxic toward the J-774A.1 cell line and Vero cells. Moreover, activation of Th1 type and suppression of Th2 type immune responses and induction in nitric oxide generation proved that 8a and 8g induce murine macrophages to prevent survival of parasites. Compounds 8a and 8g exhibited significant in vivo inhibition of parasite 73.15 ± 12.69% and 80.93 ± 10.50% against Leishmania donovani /hamster model. Our results indicate that compounds 8a, 8g, and 9f represent a new structural lead for this serious and neglected disease.

Synthesis of hybrid 4-anilinoquinoline triazines as potent antimalarial agents, their in silico modeling and bioevaluation as Plasmodium falciparumtransketolase and β-hematin inhibitors

Analogues of a novel class of hybrid 4-anilinoquinoline triazines have been synthesized with the aim of identifying the compounds with improved antimalarial activity preserving the potency of parent drug chloroquine (CQ). All the synthesized molecules were evaluated in vitro for their antimalarial activity against chloroquine-sensitive 3D7 and chloroquine-resistant K1 strains of P. falciparum. Molecules were also screened for their cytotoxicity towards VERO cell line. Sixteen compounds (17, 19, 26, 27, 29, 31, 32, 33, 35, 36, 37, 39, 40, 49, 50, and 52) exhibited excellent antimalarial activity with IC50 values ranging from 1.36–4.63 ng ml−1 and were also found to be nontoxic with good selectivity index. In silico activity prediction as well as enzyme inhibitory activity against P. falciparumtransketolase reveals that the molecules are also good inhibitors of the enzymeP. falciparumtransketolase. The compound 52 showed good in vivo activity by oral route and resulted in survival of 3 out of 5 mice till day 28.

Synthesis, structure-activity relationships, and biological studies of chromenochalcones as potential antileishmanial agents.

Antileishmanial activities of a library of synthetic chalcone analogues have been examined. Among them, five compounds (11, 14, 16, 17, 22, and 24) exhibited better activity than the marketed drug miltefosine in in vitro studies against the intracellular amastigotes form of Leishmania donovani. Three promising compounds, 16, 17, and 22, were tested in a L. donovani/hamster model. Oral administration of chalcone 16, at a concentration of 100 mg/kg of body weight per day for 5 consecutive days, resulted in >84% parasite inhibition at day 7 post-treatment and it retained the activity until day 28. The molecular and immunological studies revealed that compound 16 has a dual nature to act as a direct parasite killing agent and as a host immunostimulant. Pharmacokinetics and serum albumin binding studies also suggest that compound 16 has the potential to be a candidate for the treatment of the nonhealing form of leishmaniasis.

Synthesis and biological evaluation of a new class of 4-aminoquinoline-rhodanine hybrid as potent anti-infective agents.

Synthesis of novel 4-aminoquinoline-rhodanine hybrid using inexpensive starting materials via easy to operate methodology, and their biological activity is reported. All the compounds were screened for their in vitro antimalarial activity against chloroquine-resistant (K1) and chloroquine-sensitive (3D7) strains of Plasmodium falciparum, and their cytotoxicity toward VERO cell line. Compounds 9, 19, 21 and 23 exhibited excellent antimalarial activity with IC50 value ranging from 13.2 to 45.5 nM against chloroquine-resistant (K1) strain. Biochemical studies revealed that inhibition of hemozoin formation is the primary mechanism of action of these analogs for their antimalarial activity. Additionally, some derivatives (14, 18 and 26) of this series also exhibited the antimycobacterial activity against H37Rv strain of Mycobacterium tuberculosis with MIC value of 6.25 μM.

CONJUGATE ADDITION OF AMINES TO SUGAR DERIVED OLEFINIC ESTERS: SYNTHESIS OF GLYCOSYLATED AMINO ESTERS AS DNA TOPOISOMERASE-II INHIBITORS

Conjugate addition of amines to olefinic esters derived from sugars leading to formation of glycosylated amino esters in a stereoselective manner is described. Some of the synthesized compounds possess DNA topoisomerase-II enzyme inhibitory activities at low concentrations.

Litomosoides carinii: Biogenic amines in microfilariae and adults

Abstract The presence of biogenic amines has been shown in microfilariae and adults of Litomosoides carinii , the filarial parasite of the cotton rat, Sigmodon hispidus . The amine mosaic of microfilariae differed from that of the adults in that, while no dopamine could be detected in the former, the latter contained all the four amines studied in the present investigations. Also, the amine content of the microfilariae was markedly higher than that of the adult worms.

Molecular cloning and characterization of Plasmodium falciparum transketolase

The pentose phosphate pathway (PPP) is an important metabolic pathway for yielding reducing power in the form of NADPH and production of pentose sugar needed for nucleic acid synthesis. Transketolase, the key enzyme of non-oxidative arm of PPP, plays a vital role in the survival/replication of the malarial parasite. This enzyme in Plasmodium falciparum is a novel drug target as it has least homology with the human host. In the present study, the P. falciparum transketolase (PfTk) was expressed, localized and biochemically characterized. The recombinant PfTk harboring transketolase activity catalyzed the oxidation of donor substrates, fructose-6-phosphate (F6P) and hydroxypyruvate (HP), with K(m)(app) values of 2.25 and 4.78 mM, respectively. p-Hydroxyphenylpyruvate (HPP) was a potent inhibitor of PfTk, when hydroxypyruvate was used as a substrate, exhibiting a K(i) value of 305 microM. At the same time, noncompetitive inhibition was observed with F6P. The native PfTk is a hexamer with subunit molecular weight of 70kDa, which on treatment with low concentrations of guanidine hydrochloride (GdmCl) dissociated into functionally active dimers. This protein was localized in the cytosol and nucleus of the parasite as studied by confocal microscopy. A model structure of PfTk was constructed based on the crystal structure of the transketolases of Saccharomyces cerevisae, Leishmania mexicana and Escherichia coli to assess the structural homology. Consistent with the homology modeling predictions, CD analysis indicated that PfTk is composed of 39% alpha-helices and 26% beta-sheets. The availability of a structural model of PfTk and the observed differences in its kinetic properties compared to the host enzyme may facilitate designing of novel inhibitors of PfTk with potential anti-malarial activity.

Designing, synthesis of selective and high-affinity chalcone-benzothiazole hybrids as Brugia malayi thymidylate kinase inhibitors: In vitro validation and docking studies

In our continuing search for safe and efficacious antifilarials, a series of novel chalcone-benzothiazole hybrids have been synthesized and evaluated for their Brugia malayi thymidylate kinase (BmTMK) enzyme inhibition activity. Their selectivity towards BmTMK was studied and compared to the human TMK (HsTMK) by an in silico method. Out of seventeen derivatives, compounds 34 and 42 showed higher interactions with the BmTMK active site. MolDock docking model revealed the interactions of these two derivatives and the results corroborated well with their in vitro antifilarial activities. Our studies suggest that these hybrids are selective towards the BmTMK enzyme and may serve as potential therapeutic agents against filariasis.

Sensitization with anti-inflammatory BmAFI of Brugia malayi allows L3 development in the hostile peritoneal cavity of Mastomys coucha

Filarial parasites survive by inducing tolerance in host but the antigens and mechanisms involved are not clear. Recently we found that BmAFI, a Sephadex G-200 eluted fraction of Brugia malayi adult worm extract, stimulates IL-10 release from THP-1 cells. In the present study, we determined the SDS-PAGE profile of BmAFI and infective 3rd stage larva (L3), investigated the effect of pre-sensitization of host with BmAFI on the survival and development of L3 in the non-permissive peritoneal cavity (p.c.) of the permissive host Mastomys coucha and in the p.c. of non-permissive Swiss mice, and studied immunological correlates for the observed effects. The parasite development and burden in p.c., was determined in sensitized infected M. coucha and Swiss mice and the release of TGF-β, IL-4, IL-10, IL-13, IFN-γ and NO, cellular proliferative response to Con A and BmAFI and levels of IgG subclasses and IgE were determined in sensitized infected M. coucha. Cellular proliferative response to Con A and BmAFI, mRNA expression of GATA-3, CTLA-4 and T-bet were determined in sensitized Swiss mice. In addition, the parasitological parameter was also studied in BmAFI-sensitized M. coucha exposed to the infection by standard subcutaneous (s.c.) route to assess whether sensitization enhances the intensity of infection. BmAFI-sensitization permitted survival of L3 and their development to adult stage by day 60 p.i. in the p.c. of M. coucha; in non-sensitized animals L3 could molt to L4 only and no parasite could be recovered beyond day 30 p.i. In M. coucha that received infection by s.c. route, pre-sensitization with BmAFI enhanced the microfilaraemia and adult worm recovery. In sensitized Swiss mice L3 could successfully molt to L4 in p.c. with improved recovery of parasite. BmAFI sensitization upregulated TGF-β and IL-10 release, IgG1 and IgG2b levels, GATA-3 and CTLA-4 mRNA expression, suppressed the cellular proliferative response and downregulated Con A stimulated response, IgE, IL-13, IFN-γ and NO responses. Immunoblot analysis showed that the BmAFI antiserum also strongly reacts with some L3 molecules. The results show, for the first time, that sensitization with the anti-inflammatory BmAFI which shares some of its molecules with those in L3, facilitates parasite survival in the non-permissive p.c. of the permissive host M. coucha, render a non-permissive Swiss mouse partially permissive to infection and enhances parasite load in M. coucha receiving the infection through permissive s.c. route by evoking a modified Th2 type of response and anti-inflammatory milieu. In conclusion, the findings suggest that the anti-inflammatory BmAFI fraction facilitates survival of B. malayi infection even in non-permissive environment.

Hypolipidemic activity of Anthocephalus indicus (kadam) in hyperlipidemic rats

The hypolipidemic action of Anthocephalus indicus (family, Rubiaceae: Hindi name, Kadam) fruit extract has been studied in hyperlipidemic rats fed a triton- and cholesterol-rich high-fat diet. In triton WR-1339-induced hyperlipidemic rats, feeding with the fruit extract (500 mg/kg b.w.) exerted a lipid-lowering effect as assessed by reversal of plasma levels of total cholesterol, phospholipids, and triglyceride following reactivation of the post-heparin lipolytic activity. In another model, chronic feeding of this natural product (500 mg/kg, b.w.) to animals simultaneously fed a high-fat diet for 30 days caused lowering of lipid levels in plasma and liver accompanied with stimulation of hepatic lipolytic activity. The hypolipidemic activity of Anthocephalus indicus fruit extract iscompared with guggulipid, a known lipid-lowering drug, in both models.