Cell cycle synchronization of the mouse S-180 tumor following alternating period of hydroxyurea-blockade and release.

An attempt at synchronization was carried out by intravenous administration of hydroxyurea (HU) into mice bearing the S-180 solid tumor. Following HU blockade for 6.0 hrs equal to (Tc-Ts) period, 65% of all tumor cells were in S-phase. After 2 cycle blockade; HU blockade for 6 hrs, released for 7.5 hrs and reestablished for 6 hrs, 84% of tumor cells were gathered in S-phase with a sharp peak at G1-S junction. Appropriate cycles of HU infusion and release will synchronize significant increments of S-phase or mitotic cells in the S-180 tumor during predictable time intervals.