We have already reported in Balb C mouse transplantable mammary
carcinoma, that
uroporphyrin I and III are superior as tumour localizers when compared to
hematoporphyrin derivative and a derivative thereof,
photofrin II. This study compares the binding of
porphyrins to
proteins which may be found in tumour cells or stroma to investigate whether there is a common binding determinant.
Coproporphyrin III and
deuteroporphyrin IX which are non-tumour localizing
porphyrins, were also part of the comparative study. The interaction of these
porphyrins with
acid soluble
collagen and
acid insoluble
collagen,
elastin, and
fibrin was evaluated, and the binding of uroporphyrin isomers I and III and
deuteroporphyrin IX to
gelatin and
fibrinogen, was also determined. The results suggest that
collagen, especially the
acid soluble form, and
gelatin preferentially bind the four
porphyrins which localize in mammary
carcinoma tissue. The well reported observations that malignant epithelial cells, including
breast cancer, produce
collagen and contain a rate-limiting
enzyme in
collagen biosynthesis would support the notion that de novo synthesis of this
protein may in part govern the tumour uptake and retention of
porphyrins.
Elastin,
fibrinogen and
fibrin showed non-discriminant binding to the
porphyrins under study.