FACTORS AFFECTING VIRUS PHOTOINACTIVATION BY A SERIES OF PHENOTHIAZINE DYES

A series of four phenothiazine dyes, including methylene blue (MB), we re previously tested for their ability to photoinactivate viruses in r ed cell suspensions. One of the dyes, methyl-3-dimethylamino-7-dimethy laminophenotiazine (1,9-dimethylmethylene blue), exhibited good intrac ellular and extracellular virucidal activity for several RNA and DNA v iruses under conditions that minimally affected red cell properties. I n order to understand why the virucidal specificity of 1,9-dimethylmet hylene blue was greater than other phenothiazines tested, the physical and chemical properties of the dye were compared to three other close ly related analogues (MB, imethyl-3-diethylamino-7-dibutylaminophenoth iazine [compound 4-140], methyl-3-dimethylamino-7-diethylaminophenothi azine [compound 6-136]). All compounds required light and oxygen for v irucidal activity and had relatively high singlet oxygen yields (>0.5) , but 1,9-dimethylmethylene blue had a singlet oxygen yield approximat ely 50% greater than that of MB. In addition, the hydrophobicity/hydop hilicity of the compounds varied, with the partition coefficients (2-o ctanol:water) ranging from 0.11 for MB to 3560 for compound 4-140. The dyes had the following affinities for DNA:1,9-dimethylmethylene blue > compound 6-136 > MB approximate to compound 4-140. This order was si milar to the order of activities for photoinactivation of the nonenvel oped bacteriophage, R17, by the four compounds. Results with the most hydrophobic compound, 4-140, contrasted with those obtained with 1,9-d imethylmethylene blue. Compound 4-140 had a high affinity for protein and a low affinity for DNA. Although compound 4-140 and light inactiva ted the nonenveloped bacteriophage R17 poorly, the dye readily photoin activated enveloped viruses in buffer. However, unlike results with 1, 9-dlimethylmethylene blue, viral inactivation of enveloped viruses by compound 4-140 was completely inhibited by the presence of red cells a nd plasma. Thus, the high affinity of 1,9-dimethylmethylene blue for D NA and the dye's efficient singlet oxygen yield suggest viral nucleic acid as a potential target, which could explain the photosensitizer's ability to Inactivate viruses without adversely affecting anucleate re d cells.