Compounds of formula (I) and salts and physiologically functional derivatives thereof, wherein R.sup.2 is attached at the 4- or 5-position of the thiazole ring and is hydrogen, alkyl, halogen, cyano, alkoxy, haloalkoxy, or alkylamino; X independently represents a divalent linkage group selected from S, O, NR.sup.4, SO, or SO.sub.2; R.sup.4 is hydrogen, alkyl, cycloalkyl, cycloalkylalkyl, or heterocyclyl; R.sup.1 is attached at the 4- or 5-position of the thiazole ring and independently represents a group of formula (II): wherein the dotted line represents a single or double bond; * indicates the point of attachment to the thiazole ring; and n is 1, 2, or 3. Also disclosed are pharmaceutical compositions comprising the above compounds and method of treatments for cancer and other diseases.