Radezolid

Radezolid Description:
MIC90: Radezolid was approximately four-times more potent than linezolid against MRSA, with MIC90 of 0.5 mg/l and 2.0 mg/l, respectively [1].
Radezolid is an investigational oxazolidinone with excellent in vitro and in vivo activity against a variety of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Effcacy has been attributed to the finding that radezolid accumulates in vitro in macrophages, polymorphonuclear leukocytes (PMNs), epithelial and endothelial cells.
In vitro: A study found that radezolid accumulated to similar levels (~10-fold) in all cell types (human keratinocytes, endothelial cells, bronchial epithelial cells, osteoblasts, macrophages, and rat embryo fibroblasts). At equivalent weight concentrations, radezolid proved consistently 10-fold more potent than linezolid in all these models, irrespective of the bacterial species and resistance phenotype or of the cell type infected. These data suggest the potential interest of radezolid for recurrent or persistent infections where intracellular foci play a determinant role [2].
In vivo: When administered at 50 mg/kg, radezolid and linezolid showed comparable reductions in bacterial burden 24 hours after inoculation. Area under the curve (AUC) analysis of tissue concentrations demonstrated that radezolid accumulated 2.4-fold in infected thighs when compared to non-infected thigh tissue (table). Linezolid showed no accumulation in infected thighs [3].
Clinical trial: Radezolid (INN, codenamed RX-1741) is developed by Rib-X Pharmaceuticals, Inc. for the treatment of serious multi-drug–resistant infections. Radezolid has completed two phase-II clinical trials. One of these clinical trials was for uncomplicated skin and skin-structure infections (uSSSI) and the other clinical trial was for community acquired pneumonia (CAP) (http://en.wikipedia.org/wiki/Radezolid)..
Reference:
[1] Laura Lawrence, Paul Danese, Joe DeVito, Francois Franceschi, and Joyce Sutcliffe. In Vitro Activities of the Rx-01 Oxazolidinones against Hospital and Community Pathogens. Antimicrob Agents Chemother. 2008; 52(5): 1653–1662.
[2] Lemaire S, Kosowska-Shick K, Appelbaum PC, Verween G, Tulkens PM, Van Bambeke F. Cellular pharmacodynamics of the novel biaryloxazolidinone radezolid: studies with infected phagocytic and nonphagocytic cells, using Staphylococcus aureus, Staphylococcus epidermidis, Listeria monocytogenes, and Legionella pneumophila. Antimicrob Agents Chemother. 2010;54(6):2549-59.
[3] Burak E, Bortolon E, Molstad D, Jing H and Wu Y. Radezolid, a novel oxazolidinone, accumulates in infected thigh tissue. Post A1-1938. 49th ICAAC San Francisco, CA, USA September 12-15, 2009

Cellular pharmacodynamics of the novel biaryloxazolidinone radezolid: studies with infected phagocytic and nonphagocytic cells, using Staphylococcus aureus, Staphylococcus epidermidis, Listeria monocytogenes, and Legionella pneumophila.[Pubmed:20385852]

Antimicrob Agents Chemother. 2010 Jun;54(6):2549-59.

Radezolid is a novel biaryloxazolidinone in clinical development which shows improved activity, including against linezolid-resistant strains. In a companion paper (29), we showed that Radezolid accumulates about 11-fold in phagocytic cells, with approximately 60% of the drug localized in the cytosol and approximately 40% in the lysosomes of the cells. The present study examines its activity against (i) bacteria infecting human THP-1 macrophages and located in different subcellular compartments (Listeria monocytogenes, cytosol; Legionella pneumophila, vacuoles; Staphylococcus aureus and Staphylococcus epidermidis, mainly phagolysosomal), (ii) strains of S. aureus with clinically relevant mechanisms of resistance, and (iii) isogenic linezolid-susceptible and -resistant S. aureus strains infecting a series of phagocytic and nonphagocytic cells. Radezolid accumulated to similar levels ( approximately 10-fold) in all cell types (human keratinocytes, endothelial cells, bronchial epithelial cells, osteoblasts, macrophages, and rat embryo fibroblasts). At equivalent weight concentrations, Radezolid proved consistently 10-fold more potent than linezolid in all these models, irrespective of the bacterial species and resistance phenotype or of the cell type infected. This results from its higher intrinsic activity and higher cellular accumulation. Time kill curves showed that Radezolid's activity was more rapid than that of linezolid both in broth and in infected macrophages. These data suggest the potential interest of Radezolid for recurrent or persistent infections where intracellular foci play a determinant role.

Enantioselective recognition of radezolid by cyclodextrin modified capillary electrokinetic chromatography and electronic circular dichroism.[Pubmed:28279932]

J Pharm Biomed Anal. 2017 May 30;139:98-108.

A method for the enantioseparation of Radezolid (RAD), an analogue of a truly new class of antibacterial agents, oxazolidinones, was developed based on capillary electrokinetic chromatography using a cyclodextrin as a chiral pseudophase (CD-cEKC). The mechanism of RAD separation, together with its precursor, were investigated to directly define the relationship between the oxazolidinone structure and the complexation process. During the development of the method, anionic single isomer cyclodextrins were tested. They were ranked in order from hydrophilic to hydrophobic as follows: heptakis-(2,3-dihydroxy-6-sulfo)-beta-cyclodextrin (HS-beta-CD), heptakis-(2,3-diacetyl-6-sulfo)-beta-cyclodextrin (HDAS-beta-CD) and heptakis-(2,3-dimethyl-6-sulfo)-beta-cyclodextrin (HDMS-beta-CD). Experiments were performed at pH values of 2.5, 6.6, 8.2 and 9.6. The cyclodextrins that had an acetyl or methyl group at the C2 and C3 positions, referred to as HDAS-beta-CD and HDMS-beta-CD, respectively, exhibited partial and baseline separation of enantiomers in a low pH buffer. However, higher temperatures were required for HDAS-beta-CD and acetonitrile addition was required for HDMS-beta-CD. During the experiments, different organic solvents, varying in their amphiprotic or aprotic nature, were tested. The best results for the separation of enantiomers using the CD-cEKC method were obtained with 40mM HDMS-beta-CD dissolved in a 50mM phosphate buffer (pH 2.5) with the addition of acetonitrile (65:35, v/v) at 27 degrees C, reversed polarity and a voltage equal to 28kV. The apparent binding constants for each enantiomer to HDAS-beta-CD or HDMS-beta-CD were calculated. Finally, the stereochemistry of (S) and (R)-RAD and the behaviour of selected complex formations were established using electronic circular dichroism.

Cellular pharmacokinetics of the novel biaryloxazolidinone radezolid in phagocytic cells: studies with macrophages and polymorphonuclear neutrophils.[Pubmed:20385873]

Antimicrob Agents Chemother. 2010 Jun;54(6):2540-8.

Radezolid (RX-1741) is the first biaryloxazolidinone in clinical development. It shows improved activity, including against linezolid-resistant strains. Radezolid differs from linezolid by the presence of a biaryl spacer and of a heteroaryl side chain, which increases the ionization and hydrophilicity of the molecule at physiological pH and confers to it a dibasic character. The aim of this study was to determine the accumulation and subcellular distribution of Radezolid in phagocytic cells and to decipher the underlying mechanisms. In THP-1 human macrophages, J774 mouse macrophages, and human polymorphonuclear neutrophils, Radezolid accumulated rapidly and reversibly (half-lives of approximately 6 min and 9 min for uptake and efflux, respectively) to reach, at equilibrium, a cellular concentration 11-fold higher than the extracellular one. This process was concentration and energy independent but pH dependent (accumulation was reduced to 20 to 30% of control values for cells in medium at a pH of <6 or in the presence of monensin, which collapses pH gradients between the extracellular and intracellular compartments). The accumulation at equilibrium was not affected by efflux pump inhibitors (verapamil and gemfibrozil) and was markedly reduced at 4 degrees C but was further increased in medium with low serum content. Subcellular fractionation studies demonstrated a dual subcellular distribution for Radezolid, with approximately 60% of the drug colocalizing to the cytosol and approximately 40% to the lysosomes, with no specific association with mitochondria. These observations are compatible with a mechanism of transmembrane diffusion of the free fraction and partial segregation of Radezolid in lysosomes by proton trapping, as previously described for macrolides.