Angiostatin generating capacity and anti-tumour effects of D-penicillamine and plasminogen activators.
BACKGROUND
Upregulation of endogenous angiostatin levels may constitute a novel anti-angiogenic, and therefore anti-tumor therapy. In vitro, angiostatin generation is a two-step process, starting with the conversion of plasminogen to plasmin by plasminogen activators (PAs). Next, plasmin excises angiostatin from other plasmin molecules, a process requiring a donor of a free sulfhydryl group. In previous studies, it has been demonstrated that administration of PA in combination with the free sulfhydryl donor (FSD) agents captopril or N-acetyl cysteine, resulted in angiostatin generation, and anti-angiogenic and anti-tumour activity in murine models.


METHODS
In this study we have investigated the angiostatin generating capacities of several FSDs. D-penicillamine proved to be most efficient in supporting the conversion of plasminogen to angiostatin in vitro. Next, from the optimal concentrations of tPA and D-penicillamine in vitro, equivalent dosages were administered to healthy Balb/c mice to explore upregulation of circulating angiostatin levels. Finally, anti-tumor effects of treatment with tPA and D-penicillamine were determined in a human melanoma xenograft model.


RESULTS
Surprisingly, we found that despite the superior angiostatin generating capacity of D-penicillamine in vitro, both in vivo angiostatin generation and anti-tumour effects of tPA/D-penicillamine treatment were impaired compared to our previous studies with tPA and captopril.


CONCLUSIONS
Our results indicate that selecting the most appropriate free sulfhydryl donor for anti-angiogenic therapy in a (pre)clinical setting should be performed by in vivo rather than by in vitro studies. We conclude that D-penicillamine is not suitable for this type of therapy.
de Groot-Besseling
Renate R J
RR
Department of Pathology, University Medical Centre Nijmegen, P,O, Box 9101, 6500 HB Nijmegen, The Netherlands. renatedegroot@gmail.com
Ruers
Theo J M
TJ
Lamers-Elemans
Iris L
IL
Maass
Cathy N
CN
de Waal
Robert M W
RM
Westphal
Johan R
JR
D043168:Angiostatins / Q000096:biosynthesis* / Q000097:blood; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008545:Melanoma / Q000098:blood supply; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D010396:Penicillamine / Q000008:administration & dosage / Q000494:pharmacology*; D010960:Plasminogen Activators / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
D043168:Angiostatins; D010960:Plasminogen Activators; D010396:Penicillamine