Fluoroquinolone Amorphous Polymeric Salts and Dispersions for Veterinary Uses.

Enrofloxacin (ENRO) is a poorly soluble drug used in veterinary medicine. It differs from the more widely used fluoroquinolone ciprofloxacin (CIP) by the presence of an ethyl substituent on its piperazine amino group. While a number of recent studies have examined amorphous composite formulations of CIP, little research has been conducted with ENRO in this area. Therefore, the main purpose of this work was to produce amorphous solid dispersions (ASDs) of ENRO. The solid-state properties of these samples were investigated and compared to those of the equivalent CIP ASDs, and their water uptake behavior, solubility, dissolution, and antibacterial activity were assessed. Like CIP, X-ray amorphous solid dispersions were obtained when ENRO was ball milled with acidic polymers, whereas the use of neutral polymers resulted in semi-crystalline products. Proton transfer from the carboxylic acids of the polymers to the tertiary amine of ENRO's piperazine group appears to occur in the ASDs, resulting in an ionic bond between the two components. Therefore, these ASDs can be referred to as amorphous polymeric salts (APSs). The glass transition temperatures of the APSs were significantly higher than that of ENRO, and they were also resistant to crystallization when exposed to high humidity levels. Greater concentrations were achieved with the APSs than the pure drug during solubility and dissolution studies, and this enhancement was sustained for the duration of the experiments. In addition, the antimicrobial activity of ENRO was not affected by APS formation, while the minimum inhibitory concentrations and minimum bactericidal concentrations obtained with the APS containing hydroxypropyl methylcellulose acetate succinate grade MG (HPMCAS-MG) were significantly lower than those of the pure drug. Therefore, APS formation is one method of improving the pharmaceutical properties of this drug.

Polymer/Amorphous Salt Solid Dispersions of Ciprofloxacin.

PURPOSE: To improve the pharmaceutical properties of amorphous ciprofloxacin (CIP) succinate salts via formulation as polymer/amorphous salt solid dispersions (ASSDs). METHODS: ASSDs consisting of an amorphous CIP/succinic acid 1:1 or 2:1 salt dispersed in PVP or Soluplus were produced by spray drying and ball milling. The solid state characteristics, miscibility, stability, solubility and passive transmembrane permeability of the ASSDs were then examined. RESULTS: The ASSDs had higher glass transition and crystallization temperatures than the corresponding amorphous succinate salts, and were also more stable during long-term stability studies. The results of inverse gas chromatography and thermal analysis indicated that the salts and polymers form a miscible mixture. The solubility of the pure drug in water and biorelevant media was significantly increased by all of the formulations. The permeability of the ASSDs did not differ significantly from that of the amorphous CIP succinate salts, however all samples were less permeable than the pure crystalline drug. CONCLUSIONS: The formulation of amorphous CIP succinate salts as ASSDs with polymer improved their long-term stability, but did not significantly affect their solubility or permeability.

Preparation and characterization of amorphous ciprofloxacin-amino acid salts.

The amorphization of the poorly soluble drug ciprofloxacin (CIP) may be facilitated by the use of a suitable stabilizer. In this study seven amino acids, with various side chain properties, were evaluated in this regard. Solid dispersions were prepared by ball milling 1:1 molar ratios of CIP with the amino acids, and their solid-state and pharmaceutical properties were then examined. Fully X-ray amorphous solid dispersions were obtained with aspartic acid, glutamic acid, cysteine and arginine. In each case, evidence of salt formation between the drug and amino acids was found via Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance. In contrast, semi-crystalline solid dispersions were obtained with serine, alanine and glycine. The glass transition temperatures of the amorphous salts were significantly higher than those of the starting materials, and they remained fully X-ray amorphous during long-term stability studies. Significant improvements in the solubility of CIP were also observed with the amorphous salts in water and simulated biological fluids, over and above that of the corresponding physical mixtures. In permeability studies on the other hand, the amorphous aspartate and glutamate salts were found to be less permeable than the pure drug, whereas formulation as an amorphous salt containing cysteine or arginine increased the permeability of CIP. Therefore, while amorphous salt formation with amino acids appears to be a suitable means of improving the thermal stability and solubility of CIP, in some cases this is associated with a decrease in permeability.

Amorphous Polymeric Drug Salts as Ionic Solid Dispersion Forms of Ciprofloxacin.

Ciprofloxacin (CIP) is a poorly soluble drug that also displays poor permeability. Attempts to improve the solubility of this drug to date have largely focused on the formation of crystalline salts and metal complexes. The aim of this study was to prepare amorphous solid dispersions (ASDs) by ball milling CIP with various polymers. Following examination of their solid state characteristics and physical stability, the solubility advantage of these ASDs was studied, and their permeability was investigated via parallel artificial membrane permeability assay (PAMPA). Finally, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ASDs were compared to those of CIP. It was discovered that acidic polymers, such as Eudragit L100, Eudragit L100-55, Carbopol, and HPMCAS, were necessary for the amorphization of CIP. In each case, the positively charged secondary amine of CIP was found to interact with carboxylate groups in the polymers, forming amorphous polymeric drug salts. Although the ASDs began to crystallize within days under accelerated stability conditions, they remained fully X-ray amorphous following exposure to 90% RH at 25 °C, and demonstrated higher than predicted glass transition temperatures. The solubility of CIP in water and simulated intestinal fluid was also increased by all of the ASDs studied. Unlike a number of other solubility enhancing formulations, the ASDs did not decrease the permeability of the drug. Similarly, no decrease in antibiotic efficacy was observed, and significant improvements in the MIC and MBC of CIP were obtained with ASDs containing HPMCAS-LG and HPMCAS-MG. Therefore, ASDs may be a viable alternative for formulating CIP with improved solubility, bioavailability, and antimicrobial activity.

In vivo modulation of hypoxia-inducible signaling by topographical helix mimetics.

Development of small-molecule inhibitors of protein-protein interactions is a fundamental challenge at the interface of chemistry and cancer biology. Successful methods for design of protein-protein interaction inhibitors include computational and experimental high-throughput and fragment-based screening strategies to locate small-molecule fragments that bind protein surfaces. An alternative rational design approach seeks to mimic the orientation and disposition of critical binding residues at protein interfaces. We describe the design, synthesis, biochemical, and in vivo evaluation of a small-molecule scaffold that captures the topography of α-helices. We designed mimics of a key α-helical domain at the interface of hypoxia-inducible factor 1α and p300 to develop inhibitors of hypoxia-inducible signaling. The hypoxia-inducible factor/p300 interaction regulates the transcription of key genes, whose expression contributes to angiogenesis, metastasis, and altered energy metabolism in cancer. The designed compounds target the desired protein with high affinity and in a predetermined manner, with the optimal ligand providing effective reduction of tumor burden in experimental animal models.

Protein domain mimetics as in vivo modulators of hypoxia-inducible factor signaling.

Selective blockade of gene expression by designed small molecules is a fundamental challenge at the interface of chemistry, biology, and medicine. Transcription factors have been among the most elusive targets in genetics and drug discovery, but the fields of chemical biology and genetics have evolved to a point where this task can be addressed. Herein we report the design, synthesis, and in vivo efficacy evaluation of a protein domain mimetic targeting the interaction of the p300/CBP coactivator with the transcription factor hypoxia-inducible factor-1α. Our results indicate that disrupting this interaction results in a rapid down-regulation of hypoxia-inducible genes critical for cancer progression. The observed effects were compound-specific and dose-dependent. Gene expression profiling with oligonucleotide microarrays revealed effective inhibition of hypoxia-inducible genes with relatively minimal perturbation of nontargeted signaling pathways. We observed remarkable efficacy of the compound HBS 1 in suppressing tumor growth in the fully established murine xenograft models of renal cell carcinoma of the clear cell type. Our results suggest that rationally designed synthetic mimics of protein subdomains that target the transcription factor-coactivator interfaces represent a unique approach for in vivo modulation of oncogenic signaling and arresting tumor growth.