Summary
Thrombin stimulates proliferation, invasion and metastasis by cleaving protease-activated
receptor 1 (PAR1) on human prostate cancer cells. Current direct thrombin inhibitors
pose risks for bleeding in the cancer patients. We have developed an oral reversible
direct thrombin inhibitor called FM19. FM19 inhibits thrombin-induced calcium mobilisation
of PC3 cells with an IC50 of 15 μM with a 95% confidence interval of 7.3–31.6 μM. Thrombin stimulation increases
PC3 cell invasion threefold from 27.1 ± 11.4 to 66 ± 11.6. FM19 or bivalirudin reduces
cell invasion at ≥0.1 μM (p≤0.02). After inoculation with PC3 cells, nude mice were
treated with oral FM19 at 3 mg/ml in the drinking water. The treated mice did not
have long bleeding times and only a 1.4-fold increase in their thrombin clotting time.
However, with treatment, the mice have a reduced rate of tumour growth 0.26 ± 0.17
fold change/day vs. 0.55 ± 0.35 for untreated (p = 0.038), reduced fold change in
tumour size 5.3 ± 0.47 to 8.9 ± 1.8 (untreated) (p=0.048), and reduced overall tumour
weight 0.5 ± 0.31 g vs. 0.82 ± 0.32 g (untreated) (p=0.04). On microscopic examination,
FM19 treatment reduces the number of large vessels in the tumours from 4.6 ± 2.1 per
high-powered field in untreated samples to 1.4 ± 1.4 in treated samples (p≤0.04).
These studies show FM19 reduces prostate tumour growth in vivo at a concentration
below that needed for anticoagulation. These data suggest novel opportunities for
oral direct thrombin inhibitors in cancer therapy.
Keywords
Prostate cancer - oral direct thrombin inhibitor - anticoagulation - cancer treatment