HIV/AIDS continues to be a menace to public health. Several drugs currently on the market have successfully improved the ability to manage the viral burden in infected patients. However, new drugs are needed to combat the rapid emergence of mutated forms of the virus that are resistant to existing therapies. Currently, approved drugs target three of the four major enzyme activities encoded by the virus that are critical to the HIV life cycle. Although a number of inhibitors of HIV RNase H activity have been reported, few inhibit by directly engaging the RNase H active site. Here, we describe structures of naphthyridinone-containing inhibitors bound to the RNase H active site. This class of compounds binds to the active site via two metal ions that are coordinated by catalytic site residues, D443, E478, D498, and D549. The directionality of the naphthyridinone pharmacophore is restricted by the ordering of D549 and H539 in the RNase H domain. In addition, one of the naphthyridinone-based compounds was found to bind at a second site close to the polymerase active site and non-nucleoside/nucleotide inhibitor sites in a metal-independent manner. Further characterization, using fluorescence-based thermal denaturation and a crystal structure of the isolated RNase H domain reveals that this compound can also bind the RNase H site and retains the metal-dependent binding mode of this class of molecules. These structures provide a means for structurally guided design of novel RNase H inhibitors.

Chikungunya virus-like particles (VLPs) have potential to be used as a prophylactic vaccine based on testing in multiple animal models and are currently being evaluated for human use in a Phase I clinical trial. The current method for producing these enveloped alphavirus VLPs by transient gene expression in mammalian cells presents challenges for scalable and robust industrial manufacturing, so the insect cell baculovirus expression vector system was evaluated as an alternative expression technology. Subsequent to recombinant baculovirus infection of Sf21 cells in standard culture media (pH 6.2–6.4), properly processed Chikungunya structural proteins were detected and assembled capsids were observed. However, an increase in culture pH to 6.6–6.8 was necessary to produce detectable concentrations of assembled VLPs. Since this elevated production pH exceeds the optimum for growth medium stability and Sf21 culture, medium modifications were made and a novel insect cell variant (SfBasic) was derived by exposure of Sf21 to elevated culture pH for a prolonged period of time. The high-pH adapted SfBasic insect cell line described herein is capable of maintaining normal cell growth into the typical mammalian cell culture pH range of 7.0–7.2 and produces 11-fold higher Chikungunya VLP yields relative to the parental Sf21 cell line. After scale-up into stirred tank bioreactors, SfBasic derived VLPs were chromatographically purified and shown to be similar in size and structure to a VLP standard derived from transient gene expression in HEK293 cells. Total serum anti-Chikungunya IgG and neutralizing titers from guinea pigs vaccinated with SfBasic derived VLPs or HEK293 derived VLPs were not significantly different with respect to production method, suggesting that this adapted insect cell line and production process could be useful for manufacturing Chikungunya VLPs for use as a vaccine. The adaptation of Sf21 to produce high levels of recombinant protein and VLPs in an elevated pH range may also have applications for other pH-sensitive protein or VLP targets.

A comprehensive study of the base hydrolysis of all phosphodiester bond-containing capsular polysaccharides of the 23-valent pneumococcal vaccine is described here. Capsular polysaccharides from serotypes 6B, 10A, 17F, 19A, 19F, and 20 contain a phosphodiester bond that connects the repeating units in these polysaccharides (also referred to as backbone phosphodiester bonds), and polysaccharides from serotypes 11A, 15B, 18C, and 23F contain a phosphodiester bond that links a side chain to their repeating units. Molecular weight measurements of the polysaccharides, using high performance size exclusion chromatography with tandem multiangle laser light scattering and refractive index detection, was used to evaluate the kinetics of hydrolysis. The measurement of molecular weight provides a high degree of sensitivity in the case of small extents of reaction, thus allowing reliable measurements of the kinetics over short times. Pseudo-first-order rate constants for these polysaccharides were estimated using a simple model that accounts for the polydispersity of the starting sample. It was found that the relative order of backbone phosphodiester bond instability due to base hydrolysis was 19A > 10A > 19F > 6B > 17F, 20. Degradation of side-chain phosphodiester bonds was not observed, although the high degree of sensitivity in measurements is lost in this case, due to the low contribution of the side chains to the total polysaccharide molecular weight. In comparison with literature data on pneumococcal polysaccharide 6A, 19A was found to be the more labile, and hence appears to be the most labile pneumococcal polysaccharide studied to date. The rate of hydrolysis increased at higher pH and in the presence of divalent cation, but the extent was lower than expected based on similar data on RNA. Finally, the differences in the phosphodiester bond stabilities were analyzed by considering stereochemical factors in these polysaccharides. These results also provide a framework for evaluation of molecular integrity of phosphodiester-bond-containing polysaccharides in different solution conditions.

Live virus vaccines are a critical component of worldwide vaccination strategy for reducing disease burden but often require complex biological production processes that are sensitive to many different factors, both known and often unknown. Prior application of high‐throughput process development (HTPD) approaches to these processes has been hampered by a complex design space, low‐throughput analytics, and challenges inherent in biosafety level 2 containment and asepsis in laboratory automation. In 2013, we initiated a project with HighRes Biosolutions to design and install an integrated high‐throughput screening platform to enable HTPD for biosafety level 2 upstream process development studies. The system incorporates the necessary tools for performing cell and virus culture studies in microplates, as well as advanced analytical capabilities necessary for assessment of cell phenotype, product quality, and antigen yield. To date, we have applied this system to screen optimal media formulations and viral production conditions in support of two viral vaccine programs, with phenotypic assays performed as an integrated part of the workflow. This case study illustrates the power of HTPD in addressing large‐scale biological screening challenges by narrowing a vast design space and identifying parameter interactions in live virus production processes.

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