The invention relates to the new, asymmetrically substituted derivatives of 2,7-dihydro-3H-dibenzo[de,h]cinnoline-3,7-dione and their use as cytostatics exhibiting activity against tumor cells, especially against cells with multidrug resistance (MDR). In particular, the invention concerns derivatives of 2,7-dihydro-3H-dibenzo[de,h]cinnoline-3,7-dione represented by the general formula (I).