Inhibition of murine tumor growth and prostaglandin synthesis by indomethacin.

Inhibition of the growth of a transplantable methylcholanthrene-induced tumor was achieved in mice by administering indomethacin or aspirin in the drinking water, these drugs having in common the ability to inhibit prostaglandin synthesis. Indomethacin was able to reduce the levels of prostaglandin E (PGE) in the tumor tissue. When tumors from these animals were cultured in vitro, the culture supernatant fluid from drug-treated animals showed lower levels of PGE released into the media, but after several days in culture, tumor cells from indomethacin-treated animals fully recovered their ability to produce PGE. The relative size of tumors in untreated animals was directly related to the amount of PGE activity present in these tumors.