Disclosed is a compound represented by the Structural Formula (I): ##STR00001## Y is a covalent bond, a phenylene group or a substituted or unsubstituted straight chained hydrocarbyl group. In addition, Y, taken together with both >C=Z groups to which it is bonded, is a substituted or unsubstituted aromatic group. Preferably, Y is a covalent bond or --C(R.sub.7R.sub.8)--. R.sub.1 and R.sub.2 are independently an aryl group or a substituted aryl group, R.sub.3 and R.sub.4 are independently --H, an aliphatic group, a substituted aliphatic group, an aryl group or a substituted aryl group. R.sub.5-R.sub.6 are independently --H, an aliphatic group, a substituted aliphatic group, an aryl group or a substituted aryl group. R.sub.7 and R.sub.8 are each independently --H, an aliphatic or substituted aliphatic group, or R.sub.7 is --H and R.sub.8 is a substituted or unsubstituted aryl group, or, R.sub.7 and R.sub.8, taken together, are a C2-C6 substituted or unsubstituted alkylene group. Z is .dbd.O or .dbd.S. Also disclosed are pharmaceutical compositions comprising the compound of the present invention and a pharmaceutically acceptable carrier or diluent. Also disclosed is a method of treating a subject with cancer by administering to the subject a compound of Structural Formula (I) in combination with Paclitaxel or an analog of Paclitaxel.