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Modulation of Prostaglandin Biosynthesis in Hypoxic Murine Mammary Adenocarcinoma Cells by Misonidazole¹

Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana 70112

Resistance of hypoxic cells to radiation and chemotherapy remains a major limitation to effective therapy of solid tumors. Misonidazole, a 2-nitroimidazole analogue, has been studied extensively as a radiosensitizer of hypoxic cells and has been shown to undergo bioreductive metabolism to exert preferential cytotoxicity against hypoxic cells. We have investigated the effects of misonidazole on the biosynthesis of prostaglandins (PGs) in a murine mammary adenocarcinoma cell line (No. 4526) under aerobic and hypoxic conditions in attempts to exploit modulation of PG levels under hypoxia as a means of improving therapeutic approaches for the treatment of solid tumors. We report a time-dependent inhibition of PG biosynthesis by the suspended cells under hypoxia induced by flushing sealed vials with N₂ (1.5 liters/min). After 30 min of hypoxia, PG formation was inhibited by 50%. Indomethacin was able to further inhibit the PG formation in a concentration-dependent manner under hypoxia. Misonidazole, however, selectively increased the PGE₂ biosynthesis under hypoxia by 49% at 100 µM. This increase was concentration dependent over the range of 25 to 100 µM and was blocked by indomethacin (0.1 µM). Imidazole, the heterocyclic moiety in misonidazole without the nitro function, had no effect on PG biosynthesis at these concentrations. These data suggest that arachidonic acid metabolism is sensitive to the differential oxygen levels which exist within solid tumors and that PG levels may be modulated by electron-affinic agents in hypoxic tumor cells.

¹ Supported in part by USPHS Grant CA 21050 awarded by the National Cancer Institute, Department of Health and Human Services.

² Portions of these investigations were submitted as a dissertation in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

³ To whom requests for reprints should be addressed.

Received 8/22/88. Revised 4/ 6/89. Accepted 4/14/89.