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Inhibition of spontaneous metastases formation by amifostine

Amifostine was investigated for its ability to inhibit spontaneous metastases formation using the well‐characterized murine sarcoma, Sa‐NH. Amifostine was administered intraperitoneally at a dose of 50 mg/kg every other day for 6 days to C3Hf/Kam mice until tumors reached an average size of 8–8.5 mm in diameter. Amifostine was again administered immediately after surgical removal of the tumor‐bearing limbs by amputation, and then once more 2 days later. Twenty‐one days later, animals were evaluated for the presence of spontaneously developed pulmonary metastases. Nontumor‐bearing control animals were sham treated using the same dosing and surgery schedules. Treatment with amifostine appeared to slightly delay tumor growth, that is, 13 vs. 12 days for tumors to reach an average diameter of 8 mm. Amifostine reduced both the incidence of pulmonary metastases formed in experimental animals from 77% to 57% (p < 0.05), and their average number per animal from 12.8 ± 5.4 (SEM) to 2.9 ± 1.1 (SEM). The effect of amifostine exposure on serum levels of the angiogenesis inhibitor angiostatin was also determined using Western blot analysis. Consistent with the antimetastatic effect, exposure of animals to 50 mg/kg of amifostine resulted in a 4‐fold enhanced serum level of angiostatin above control levels. This phenomenon occurred in tumor‐bearing and nontumor‐bearing animals. The effects of amifostine on matrix metalloproteinase (MMP) enzymatic activity was also determined using gelatin zymography. Conditioned growth medium collected from Sa‐NH cells grown to confluency was exposed to various concentrations of SH, i.e., 2‐[(aminopropyl)amino]ethane‐thiol (WR‐1065), the active thiol form of amifostine, for either 30 min or 18 hr. WR‐1065, as a function of increasing dose and time, inhibited the enzymatic activities of MMP‐2 and MMP‐9. At a concentration and time of exposure likely to be achieved in vivo, that is, 40 μM and 30 min, MMP‐2 and MMP‐9 activities were reduced to between 30% and 40% of control values. Consistent with these affects, WR‐1065 was also found to be effective in inhibiting the ability of Sa‐NH cells to migrate through Matrigel membranes. After an 18‐hr exposure under in vitro conditions, WR‐1065 at concentrations of 4, 40 and 400 μM, and 4 mM, inhibited Sa‐NH migration to 11%, 44%, 81% and 97% of control values, respectively. The abilities of amifostine and its active thiol WR‐1065 to stimulate angiostatin production in mice, and to inhibit the MMP enzymatic activities and invasion ability of Sa‐NH cells under in vitro conditions, are consistent with the observed antimetastatic effects exhibited against Sa‐NH tumors growing in vivo. © 2002 Wiley‐Liss, Inc.