The binding of tumor localizing porphyrins to a fibrin matrix and their effects following photoirradiation.

The binding of two tumor localizing porphyrins, meso-tetra (4-carboxyphenyl) porphine (TCPP) and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) to fibrin clots was determined in vitro. Both TCPP and TPPS4 were found to bind extensively, although weakly, to fibrin. No appreciable binding by Hematoporphyrin IX to the fibrin matrix was detectable. Similar results were obtained whether the clot was non-crosslinked or crosslinked with factor XIII. Photoirradiation of a porphyrin-impregnated non-crosslinked clot rendered it urea insoluble. Electrophoretic analysis indicated that the alpha chain of the fibrinogen molecule was most affected by photoirradiation. This was manifested as a loss of the alpha chain intensity and a concomitant increase of high molecular weight components, suggesting the formation of crosslinks. No substantial differences were noted in susceptibility to plasmin lysis between photoirradiated and non-irradiated clots. Photoirradiated clots were, however, significantly more resistant to lysis induced by the plasminogen activators urokinase and streptokinase, suggesting that inactivation of plasminogen within the clot matrix had occurred during photoirradiation. The relevance of porphyrin binding to fibrin with regard to tumor localization and destruction is also discussed.