Development of the S-303 Pathogen Inactivation Technology for Red Blood Cell Concentrates

Abstract

Pathogen inactivation systems are in use in many European countries as routine procedures. However, a pathogen inactivation system for erythrocytes is currently not available. Although significant improvements have been made to decrease the incidence of transfusion-transmitted infections, risks remain for infectious disease agents specific to red blood cell concentrates, such as parasitic infections resulting in babesiosis and malaria. The pathogen inactivation system for erythrocytes utilizes S-303 and glutathione for the treatment of red blood cell concentrates. Preclinical studies to assess the pathogen inactivation efficacy and toxicology as well as preliminary clinical studies have been completed. Preclinical studies have shown log reduction for leukocytes, several viruses and bacteria in excess of 4 to 6 logs. Preclinical toxicology studies were conducted to enable the initiation of two phase III clinical studies in the USA for support of acute and chronic anemia. A second-generation system was developed after observation of an unexpected immune response in two chronic anemia patients. Preclinical pathogen inactivation studies, serological evaluations and a clinical study to evaluate survival of S-303-treated erythrocytes have been completed to support advanced development of the S-303 pathogen inactivation system. A functional system for the inactivation of red blood cell concentrates has been completed and is reaching clinical application.

Fig. 1

Absorption spectra of oxygenated and de-oxygenated hemoglobin. Absorption of UV light by hemoglobin requires high energy, long exposures or thin path lengths for sufficient compound activation (psoralens, methylene blue or riboflavin) for effective pathogen inactivation. S-303 is active at neutral pH and does not require activation via an external energy source.

Fig. 2

The chemical structure of the S-303 molecule and mechanism of action. S-303 is a nucleic acid-targeted alkylator with three components: i) an acridine anchor that intercalates non-covalently into nucleic acids, ii) a bis-alkylator effector group that reacts with nucleophiles such as DNA and RNA bases, and iii) a small flexible carbon linker containing a labile ester bond that hydrolyzes at neutral pH to yield the non-reactive, negatively charged breakdown product, S-300.

Fig. 3

Degradation of S-303 molecule in RBCs. The degradation kinetics of S-303 in RBCs (SAG-M RBC + treatment solution) were measured by an HPLC method for concentrations greater than 1 μmol/l and an LC/MS/MS method for lower concentrations. The limit of quantitation for the LC/MS/MS assay is 0.75 nmol/l. The residual levels of S-303 are shown without the volume exchange step. The level of S-303 after the pathogen inactivation process is below the limit of quantitation.

Fig. 4

Description of the S-303 treatment process for RBCs. The RBC unit is transferred to the mixing container of the processing set which contains an aqueous treatment solution. The GSH and S-303 are reconstituted and then sterilely transferred to the mixing container of the processing set resulting in a final concentration of 0.2 mmol/1 S-303 and 20 mmol/1 GSH. Following addition and mixing with GSH and S-303, the treated RBC unit is transferred to the Incubation container. The RBC unit is incubated at room temperature (20–25 °C) for up to 18 h. At the end of the incubation period the RBC unit is centrifuged, the supernatant expressed and the RBC unit transferred to a storage container with SAG-M.