Dengue is a mosquito-borne viral disease with a global prevalence. It is caused by four closely-related dengue viruses (DENVs 1–4). A dengue vaccine that can protect against all four viruses is an unmet public health need. Live attenuated vaccine development efforts have encountered unexpected interactions between the vaccine viruses, raising safety concerns. This has emphasized the need to explore non-replicating dengue vaccine options. Virus-like particles (VLPs) which can elicit robust immunity in the absence of infection offer potential promise for the development of non-replicating dengue vaccine alternatives. We have used the methylotrophic yeast Pichia pastoris to develop DENV envelope (E) protein-based VLPs. We designed a synthetic codon-optimized gene, encoding the N-terminal 395 amino acid residues of the DENV-2 E protein. It also included 5’ pre-membrane-derived signal peptide-encoding sequences to ensure proper translational processing, and 3’ 6× His tag-encoding sequences to facilitate purification of the expressed protein. This gene was integrated into the genome of P. pastoris host and expressed under the alcohol oxidase 1 promoter by methanol induction. Recombinant DENV-2 protein, which was present in the insoluble membrane fraction, was extracted and purified using Ni2+-affinity chromatography under denaturing conditions. Amino terminal sequencing and detection of glycosylation indicated that DENV-2 E had undergone proper post-translational processing. Electron microscopy revealed the presence of discrete VLPs in the purified protein preparation after dialysis. The E protein present in these VLPs was recognized by two different conformation-sensitive monoclonal antibodies. Low doses of DENV-2 E VLPs formulated in alum were immunogenic in inbred and outbred mice eliciting virus neutralizing titers >1∶1200 in flow cytometry based assays and protected AG129 mice against lethal challenge (p<0.05). The formation of immunogenic DENV-2 E VLPs in the absence of pre-membrane protein highlights the potential of P. pastoris in developing non-replicating, safe, efficacious and affordable dengue vaccine.

BackgroundDengue, a mosquito-borne viral disease, poses a significant global public health risk. In tropical countries such as India where periodic dengue outbreaks can be correlated to the high prevalence of the mosquito vector, circulation of all four dengue viruses (DENVs) and the high population density, a drug for dengue is being increasingly recognized as an unmet public health need.Methodology/Principal findingsUsing the knowledge of traditional Indian medicine, Ayurveda, we developed a systematic bioassay-guided screening approach to explore the indigenous herbal bio-resource to identify plants with pan-DENV inhibitory activity. Our results show that the alcoholic extract of Cissampelos pariera Linn (Cipa extract) was a potent inhibitor of all four DENVs in cell-based assays, assessed in terms of viral NS1 antigen secretion using ELISA, as well as viral replication, based on plaque assays. Virus yield reduction assays showed that Cipa extract could decrease viral titers by an order of magnitude. The extract conferred statistically significant protection against DENV infection using the AG129 mouse model. A preliminary evaluation of the clinical relevance of Cipa extract showed that it had no adverse effects on platelet counts and RBC viability. In addition to inherent antipyretic activity in Wistar rats, it possessed the ability to down-regulate the production of TNF-α, a cytokine implicated in severe dengue disease. Importantly, it showed no evidence of toxicity in Wistar rats, when administered at doses as high as 2g/Kg body weight for up to 1 week.Conclusions/SignificanceOur findings above, taken in the context of the human safety of Cipa, based on its use in Indian traditional medicine, warrant further work to explore Cipa as a source for the development of an inexpensive herbal formulation for dengue therapy. This may be of practical relevance to a dengue-endemic resource-poor country such as India.

Dengue is a serious public health concern worldwide, with ∼3 billion people at risk of contracting dengue virus (DENV) infections, with some suffering severe consequences of disease and leading to death. Currently, there is no broad use vaccine or drug available for the prevention or treatment of dengue, which leaves only anti-mosquito strategies to combat the dengue menace. The present study is an extension of our earlier study aimed at determining the in vitro and in vivo protective effects of a plant-derived phytopharmaceutical drug for the treatment of dengue. In our previous report, we had identified a methanolic extract of aerial parts of Cissampelos pareira to exhibit in vitro and in vivo anti-dengue activity against all the four DENV serotypes. The dried aerial parts of C. pareira supplied by local vendors were often found to be mixed with aerial parts of another plant of the same Menispermaceae family, Cocculus hirsutus, which shares common homology with C. pareira. In the current study, we have found C. hirsutus to have more potent anti-dengue activity as compared with C. pareira. The stem part of C. hirsutus was found to be more potent (∼25 times) than the aerial part (stem and leaf) irrespective of the extraction solvent used, viz., denatured spirit, hydro-alcohol (50:50), and aqueous. Moreover, the anti-dengue activity of stem extract in all the solvents was comparable. Hence, an aqueous extract of the stem of C. hirsutus (AQCH) was selected due to greater regulatory compliance. Five chemical markers, viz., Sinococuline, 20-Hydroxyecdysone, Makisterone-A, Magnoflorine, and Coniferyl alcohol, were identified in fingerprinting analysis. In a test of primary dengue infection in the AG129 mice model, AQCH extract at 25 mg/kg body weight exhibited protection when administered four and three times a day. The AQCH was also protective in the secondary DENV-infected AG129 mice model at 25 mg/kg/dose when administered four and three times a day. Additionally, the AQCH extract reduced serum viremia and small intestinal pathologies, viz., viral load, pro-inflammatory cytokines, and vascular leakage. Based on these findings, we have undertaken the potential preclinical development of C. hirsutus-based phytopharmaceutical, which could be studied further for its clinical development for treating dengue.

Oxazolidinones are a new class of totally synthetic antibacterial agents with wide spectrum of activity against a variety of clinically significant susceptible and resistant bacteria. These compounds have been shown to inhibit translation at the initiation phase of protein synthesis. DuP-721, the first oxazolidinone showed good activity against M. tuberculosis when given orally or parenterally to experimental animals but was not developed further due to lethal toxicity in animal models. Later two oxazolidinones, PNU-100480 and Linezolid, demonstrated promising antimycobacterial activities in the murine model. While Linezolid has been approved for clinical use, PNU-100480 was not been developed further. DA-7867 showed good in vitro and better in vivo efficacy than Linezolid but was poorly tolerated in rat toxicology studies. The antimycobacterial activity of AZD-2563 has not been explored. RBx 7644 had modest antimycobacterial activity while RBx 8700 has potent antibacterial and concentration dependent activity against all slow growing mycobacteria. It demonstrated better activity than RBx 7644 against MDR strains of M. tuberculosis along with intracellular activity. Toxicity, especially myelosuppression, has been an important limiting factor for development of an oxazolidinones. The GM-CSF assay has helped in selecting molecules with less myleosuppressive potential. We report, a review on the promising antituberculosis activities of the class oxazolidinones.

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