Experimental treatment of Staphylococcus aureus bovine intramammary infection using a guanine riboswitch ligand analog.

Staphylococcus aureus is a leading cause of intramammary infections (IMI). We recently demonstrated that Staph. aureus strains express the gene guaA during bovine IMI. This gene codes for a guanosine monophosphate synthetase and its expression is regulated by a guanine riboswitch. The guanine analog 2,5,6-triaminopyrimidine-4-one (PC1) is a ligand of the guanine riboswitch. Interactions between PC1 and its target result in inhibition of guanosine monophosphate synthesis and subsequent death of the bacterium. The present study describes the investigational use of PC1 for therapy of Staph. aureus IMI in lactating cows. The in vitro minimal inhibitory concentration of PC1 ranged from 0.5 to 4 µg/mL for a variety of Staph. aureus and Staphylococcus epidermidis strains and required a reducing agent for stability and full potency. A safety assessment study was performed, whereby the healthy quarters of 4 cows were infused with increasing doses of PC1 (0, 150, 250, and 500 mg). Over the 44 h following infusions, no obvious adverse effect was observed. Ten Holstein multiparous cows in mid lactation were then experimentally infused into 3 of the quarters with approximately 50 cfu of Staph. aureus strain SHY97-3906 and infection was allowed to progress for 2 wk before starting PC1 treatment. Bacterial counts reached then about 10(3) to 10(4) cfu/mL of milk. Infected quarters were treated with 1 of 3 doses of PC1 (0, 250, or 500 mg) after each morning and evening milking for 7d (i.e., 14 intramammary infusions of PC1). During the treatment period, milk from PC1-treated quarters showed a significant reduction in bacterial concentrations. However, this reduction of Staph. aureus count in milk was not maintained during the 4 wk following the end of the treatment and only 15% of the PC1-treated quarters underwent bacteriological cure. The somatic cell count and the quarter milk production were not affected by treatments. Although bacterial clearance was not achieved following treatment with PC1, these results demonstrate that the Staph. aureus guanine riboswitch represents a relevant and promising drug target for a novel class of antibiotics for the animal food industry.

Cross-linked high amylose starch derivatives as matrices for controlled release of high drug loadings.

Selection of hydrogels as excipients in controlled drug release systems depends on the characteristics of the gel and of the drug. Three types of derivatives were synthesized from cross-linked high amylose starch (HASCL-6) by substitution of hydroxylic groups with cationic (carboxymethyl: CM), anionic (aminoethyl: AE) and acetate (Ac) groups. These new polymeric excipients are able to control the release over 20 h from monolithic tablets loaded with 20 to 60% drug. Three drugs were used as model tracer: acetaminophen (uncharged), acetylsalicylic acid (having an acidic group) and metformin (having a basic group). It was found that the release of ionic drugs from CM-HASCL-6 and AE-HASCL-6 matrices can be partially controlled by ionic interaction between pendant groups of polymer and drugs. The substitution degree of HASCL-6 derivatives can also be varied to modulate the drug's release time. These derivatives represent a novel generation of pharmaceutical excipients, recommended for high loading dosage formulations.