There is provided use of a cyclic compound or a pharmaceutically active salt thereof in the manufacture of a medicament to prevent and/or inhibit and/or arrest cell cycling, wherein the cyclic compound comprises at least one ring, wherein Group I and Group II, independently of each other, are attached to a ring of the cyclic compound; wherein Group I is a hydrocarbyl or an oxyhydrocarbyl group; and wherein Group II is a group of the formula ##STR00001## X is P or S; when X is P, Y is .dbd.O or S, Z is --OH and R is hydrocarbyl or H; when X is S, Y is .dbd.O, Z is .dbd.O, and R is hydrocarbyl or N(R.sub.1)(R.sub.2), wherein each of R.sub.1 and R.sub.2 is independently selected from H or a hydrocarbyl group.