An imidazothiazole compound having the formula (A):
wherein R1 is a phenyl or napthyl which may have a substituent, R2 is an acyl, and the two bonds at dotted line portions may or may not exist simultaneously, or a pharmacologically acceptable salt thereof and an agent for overcoming resistance to an anti-neoplastic agent or an enhancer for the effect of an anti-neoplastic agent comprising said compound or a pharmacologically acceptable salt thereof as an active ingredient.
An imidazothiazole compound having the formula (A): ##STR1## wherein R.sub.1 is a phenyl or napthyl which may have a substituent, R.sub.2 is an acyl, and the two bonds at dotted line portions may or may not exist simultaneously, or a pharmacologically acceptable salt thereof and an agent for overcoming resistance to an anti-neoplastic agent or an enhancer for the effect of an anti-neoplastic agent comprising said compound or a pharmacologically acceptable salt thereof as an active ingredient.