Inactivation of photosensitizing merocyanine dyes by plasma, serum and serum components.

Merocyanine dyes with an oxygen in the electron donor heterocycle were rapidly degraded by plasma, serum and serum components. Replacement of the oxygen by a sulfur or selenium atom rendered the dyes refractory to degradation. The degradation of labile merocyanine dyes was temperature dependent and oxygen independent. The plasma component that was responsible for the degradation of merocyanine dyes was sensitive to heat and detergent, suggesting an enzymatic process. The identification of the structural requirements for sensitivity/resistance to degradation provides the experimenter with a simple means to manipulate the stability of merocyanines in high serum or plasma environments and may expand the clinical utility of merocyanine photosensitizers beyond their traditional role in the extracorporeal purging of bone marrow grafts.