Summary
Platelets are known to play a role in blood borne metastasis. Previous experimental
studies have suggested that platelet GpIIb/IIIa may be a therapeutic target. However,
the need for intravenous administration limits the potential application of current
GpIIb/IIIa inhibitors to cancer therapy. The aim of the present study was to assess
the efficacy of a novel, non-peptide oral GpIIb/IIIa antagonist (XV454) on tumor cell-induced
platelet aggregation in vivo and on experimental metastasis. A Lewis lung carcinoma (LL2) mouse model of experimental
metastasis was used in this study. XV454 (100 μg) was administered intravenously (via
tail vein) or orally (gavages) to 20 g mice. To determine the effect of XV454 on platelet
aggregation, blood samples were collected by cardiac puncture 10 minutes after intravenous
and 1-24 hrs after oral XV454, and platelet function was assessed by aggregometry,
thrombelastography and the Platelet Function Analyzer (PFA100®). The effect of XV454 on tumor cell-induced thrombocytopenia was determined 10 minutes
after intravenous and 3 hrs after oral XV454 administration. Tumor cells (2 x 106) were injected intravenously and 15 minutes after cell injection, platelet count
was measured and compared to baseline (pre-injection) counts. To assess the effect
on metastasis, XV454 was administered intravenous or orally 10 minutes and 3 hrs before
tumor cell injection, respectively. Eighteen days later, surface lung tumor nodules
were counted and the total lung tumor burden assessed. In a fourth group, in addition
to the initial oral dose (before tumor cell injection), oral XV454 was given daily
for the first week and three times in the second week. Administration of XV454 (5
mg/kg) completely inhibited platelet aggregation and this effect persisted for at
least 24 hrs after oral delivery. Both intravenous and oral XV454 significantly inhibited
tumor cell-induced thrombocytopenia (P<0.01), the number of surface lung tumor nodules
(80-85%; P<0.001) and total tumor burden (83% for intravenous group; 50% oral [single
treatment] group; 91% oral [multiple treatment] group, P<0.001). Overall, these data
provide further evidence for the effect of oral and intravenous GpIIb/IIIa antagonism
on tumor cell-platelet interaction and metastasis.
Keywords
Platelet GpIIb/IIIa antagonists - platelet-tumor interaction - metastasis - thrombosis
- cancer