Butyrolactone I (Olomoucin) is an ATP-competitive inhibitor of CDK and cdc2 kinase family. Butyrolactone I shows antitumor effects in non-small cell lung, small cell lung, and prostate cancer cell lines.

Butyrolactone I (70 and 100 μM) increases the percentage of DU145 cells in the 4C phase of the cell cycle. Butyrolactone I increases the amount of cyclin B1 positive cells in the 4C phase on day 1 and returns to normal by day 3. Butyrolactone I inhibits Cdc2 of unsynchronized cultured prostate cancer cells and interrupts the cell cycle progression toward cell division. The Butyrolactone I inhibition of Cdc2 led to the accumulation of cells in the 4C phase without mitosis resulting in an accumulation of cyclin B1[3].