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.