Ecological Importance of Viral Lysis as a Loss Factor of Phytoplankton in the Amundsen Sea.

Whether phytoplankton mortality is caused by grazing or viral lysis has important implications for phytoplankton dynamics and biogeochemical cycling. The ecological relevance of viral lysis for Antarctic phytoplankton is still under-studied. The Amundsen Sea is highly productive in spring and summer, especially in the Amundsen Sea Polynya (ASP), and very sensitive to global warming-induced ice-melt. This study reports on the importance of the viral lysis, compared to grazing, of pico- and nanophytoplankton, using the modified dilution method (based on apparent growth rates) in combination with flow cytometry and size fractionation. Considerable viral lysis was shown for all phytoplankton populations, independent of sampling location and cell size. In contrast, the average grazing rate was 116% higher for the larger nanophytoplankton, and grazing was also higher in the ASP (0.45 d-1 vs. 0.30 d-1 outside). Despite average specific viral lysis rates being lower than grazing rates (0.17 d-1 vs. 0.29 d-1), the average amount of phytoplankton carbon lost was similar (0.6 µg C L-1 d-1 each). The viral lysis of the larger-sized phytoplankton populations (including diatoms) and the high lysis rates of the abundant P. antarctica contributed substantially to the carbon lost. Our results demonstrate that viral lysis is a principal loss factor to consider for Southern Ocean phytoplankton communities and ecosystem production.

Design and Discovery of N-(3-(2-(2-Hydroxyethoxy)-6-morpholinopyridin-4-yl)-4-methylphenyl)-2-(trifluoromethyl)isonicotinamide, a Selective, Efficacious, and Well-Tolerated RAF Inhibitor Targeting RAS Mutant Cancers: The Path to the Clinic.

Direct pharmacological inhibition of RAS has remained elusive, and efforts to target CRAF have been challenging due to the complex nature of RAF signaling, downstream of activated RAS, and the poor overall kinase selectivity of putative RAF inhibitors. Herein, we describe 15 (LXH254, Aversa, R.; et al. Int. Patent WO2014151616A1, 2014), a selective B/C RAF inhibitor, which was developed by focusing on drug-like properties and selectivity. Our previous tool compound, 3 (RAF709; Nishiguchi, G. A.; et al. J. Med. Chem. 2017, 60, 4969), was potent, selective, efficacious, and well tolerated in preclinical models, but the high human intrinsic clearance precluded further development and prompted further investigation of close analogues. A structure-based approach led to a pyridine series with an alcohol side chain that could interact with the DFG loop and significantly improved cell potency. Further mitigation of human intrinsic clearance and time-dependent inhibition led to the discovery of 15. Due to its excellent properties, it was progressed through toxicology studies and is being tested in phase 1 clinical trials.

Improved human bioavailability of vemurafenib, a practically insoluble drug, using an amorphous polymer-stabilized solid dispersion prepared by a solvent-controlled coprecipitation process.

The present work deals with improving the solubility of vemurafenib, a practically insoluble drug, by converting it into an amorphous-solid dispersion using a solvent-controlled precipitation process. The dispersion containing vemurafenib and hypromellose acetate succinate (HPMCAS), an enteric polymer, is termed microprecipitated bulk powder (MBP), in which the drug is uniformly dispersed within the polymeric substrate. HPMCAS was found to be the most suitable polymer for vemurafenib MBP, among a series of enteric polymers based on superior physical stability and drug-release characteristics of the MBP. The MBP provided a greater rate and extent of dissolution than crystalline drug, reaching an apparent drug concentration of 28-35 µg/mL, almost 30-fold higher than solubility of crystalline drug at 1 µg/mL. The supersaturation was also maintained for more than 4 h. Upon exposure to high temperature and humidity, the MBP was destabilized, resulting in crystallization and lower dissolution rate. The control of moisture and temperature is essential to maintain the stability of the MBP. In a relative human bioavailability study, vemurafenib MBP provided a four- to fivefold increase in exposure compared with crystalline drug. Improving solubility with an amorphous-solid dispersion is a viable strategy for the development of practically insoluble compounds.

Development of novel microprecipitated bulk powder (MBP) technology for manufacturing stable amorphous formulations of poorly soluble drugs.

A novel method was developed to manufacture amorphous formulations of poorly soluble compounds that cannot be processed with existing methods such as spray drying and melt extrusion. The manufacturing process and the characterization of the resulting amorphous dispersion are presented via examples of two research compounds. The novel process is utilized N,N-dimethylacetamide (DMA) to dissolve the drug and the selected ionic polymer. This solution is then co-precipitated into aqueous medium. The solvent is extracted out by washing and the co-precipitated material is isolated by filtration followed by drying. The dried material is referred to as microprecipitated bulk powder (MBP). The amorphous form prepared using this method not only provides excellent in vitro and in vivo performance but also showed excellent stability. The stabilization of amorphous dispersion is attributed to the high T(g), ionic nature of the polymer that help to stabilize the amorphous form by possible ionic interactions, and/or due to the insolubility of polymer in water. In addition to being an alternate technology for amorphous formulation of difficult compounds, MBP technology provides advantages with respect to stability, density and downstream processing.

Impact of polymers on dissolution performance of an amorphous gelleable drug from surface-coated beads.

A non-ionic amorphous active API ((RR)-3((1R)-3-oxocyclopentyl)-2-[3-chloro-4-methyl sulfonyl]phenyl-N-pyrozin-2ylpropanamide) with a glass transition temperature of 60 degrees C and aqueous solubility of 0.8 mg/mL was layered on the cellulose beads by the help of an anionic (Eudragit L100) and a non-ionic (polyvinylpyrrolidone) PVP K30 polymer respectively. An "immediate" and complete release of API from the anionic (Eudragit L100), and "sustained" but incomplete release from the hygroscopic non-ionic polymer coatings were observed. The effect of the PVP K30, and delivery patterns were investigated. Water uptake of the polymers and flow properties of API upon exposure to humidity as well as moisture sorption of beadlets were determined. Drug-polymer interactions and coating morphologies that were examined via near infrared imaging (NIR), microscopy and FTIR, enlightened any possible drug-polymer interaction. From the anionic polymer coating 93.5% API was dissolved in 50 min whereas the non-ionic polymer coating released 60% drug within 5 h. There were no API-polymer interactions as demonstrated by FTIR, implying that, this factor did not play any role in the differences observed in the release profiles. However, gelling, clumping and agglomeration was observed on the surface of the particles coated with PVP which resulted in slow and incomplete release of the drug. The anionic polymer protected API, by preventing its gelling and clumping in situ while the non-ionic polymer promoted gelling. Because API gels at a critical moisture level and at an associated critical time interval, any delivery system that can protect the drug from reaching to the critical moisture level can control API release. The drug was released via surface erosion from the Eudragit L100 coating, whereas PVP K30, the non-ionic polymer, released API via diffusion process. The results indicate that polymer properties can play a critical role in the release mechanism and kinetics of gelleable drugs. The anionic polymers may protect drugs of similar nature from gelling when exposed to the dissolution media. An understanding of mechanisms involved in drug-polymer interactions will be useful to screen the polymers that are useful in engineering suitable delivery systems for such drugs.