The thiolprotease
bromelain, isolated from pine apple stem, was suggested for use in adjuvant
tumor therapy. This study examined the in vitro effects of crude
bromelain,
bromelain F9 and
papain on B16F10 mouse
melanoma cell lung colonization, in vitro cell proliferation, invasion through
matrigel and CD44 expression. In vitro treatment of the
melanoma cells with
bromelain F9 and
papain before i.v. injection into mice prevented lung colonization. The lung weight at day 20 was significantly reduced from 5.1% (untreated cells) to 1.6% (
bromelain F9 treated cells).
Papain was as effective as
bromelain F9. However, there was no difference in the lung weight between
bromelain F9 treated and the untreated group at day 27.
Protease removal and further incubation of the B16F10 cells retained their capacity to induce lung
tumor metastases. The
proteases inhibited growth of the
melanoma cells in a dose dependent manner. Crude
bromelain was most active with a half maximal value of 7.5 mu g/ml. However, the antiproliferative effects did not correlate with the proteolytic activity. In a
matrigel invasion assay, the
proteases reduced the invasive capacity of the
melanoma cells maximally by about 30%. Using flow cytometry, the
proteases were found to reduce the CD44 density, present on the
melanoma cells, to a different degree: crude
bromelain was more active than
bromelain F9 and
papain, which had higher proteolytic activity. Crude
bromelain was most active in abolishing the CD44 re-expression after
protease treatment.