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The mode of action of antitumour anthraquinone derivatives (i.e. mitoxantrone) is not clearly established yet. It includes, among others, intercalation and binding to DNA, bioreduction and aerobic redox cycling. A series of anthraquinone derivatives, with potentially bioreducible groups sited in the side chain, have been synthesized and biologically evaluated. Their redox and cytotoxic activities were screened. Derivatives which bear a 2-(dimethylamino)ethylamino substituent, known to confer high DNA affinity, demonstrated cytotoxicity but not redox activity (beside the anthraquinone reduction). Conversely, derivatives which showed redox activity were not cytotoxic toward the P388 cell line. The results suggest that bioreduction is not the main mode of action in the cytotoxicity of anthraquinones.

Summary A series of complexes PtAm2L [where Am2 = (NH3)2, ethylenediamine(en), 1,2-diaminocyclohexane (DACH) or (NH3)(c-C6H11NH2) and where L is a bidentate 1,1-dicarboxylate ligand tethered to 1-aminoanthraquinone by various spacers] was prepared and screened in vitro against P388 leukemia cells. The free ligands displayed moderate activity and the corresponding platinum complexes were tenfold more active. The nature of the linker chain does not seem to affect the potency of the complexes. The potency depends on the nature of the inert amine ligand [NH3 > DACH > en]. The low aqueous solubility of these complexes prevented any in vivo studies and the preparation of water soluble analogs is currently under way.

A new series of complexes of the type [PtAm2LCl]+ (where Am = NH3 or Am2 = ethylenediamine and L is a monodentate AQ-Y-(CH2)n-NH2, AQ = anthraquinone, Y = NH, O) was prepared and screened in vitro against P388 leukemia. These complexes displayed higher activities than the corresponding neutral PtAm2L2 1:2 Pt:anthraquinone complexes but lower than the neutral diaminedichloro 1:1 complexes. The [Pt(en)LCl]+ complexes were significantly less active than the cis- and trans-[Pt(NH3)2LCl]+ complexes. The cis and trans isomers displayed similar activities. The complexes bearing the shorter linker chains were more active than those with longer chains. In vivo toxicity studies indicate that they are significantly less toxic than cis-DDP.

Anthraquinones, monosubstituted by aminoalkylamino side chains at positions 1, 2 or disubstituted at positions 1, 5 or 1, 8 were prepared. Their in vitro cytotoxic activity ( ED 50 ) was evaluated using: 1) P388 murine leukemia cells and 2) a subline of these cells resistant to doxorubicin (P388/ADR). The results of the structure—activity relationship analysis indicated that monosubstitution in position 1 or 2 showed a decrease of the activity when compared to adryamicin. Disubstitution in positions 1, 5 by N,N -dimethyl ethylenediamine side chain led to optimal activity, whereas the presence of cyclic dialkylamino substituents in the same positions resulted in a corresponding decrease in the anti-tumor activity. Disubstitution in positions 1,8 did not show any improvement in the cytotoxic activity.

The effects of cis -diamminedichloroplatinum(II) ( cis -DDP) and a new analog ( cis -DANAP) derived from aminoalkylaminoanthraquinones (RNH(CH 2 ) 3 NH 2 ) 2 PtCl 2 , R = anthraquinone on the oligonucleotide poly(dG)·poly(dC) were studied by electron microscopy. It was observed that with cis -DANAP, the extent of small fragments increased with the increase of the drug/nucleotide molar ratio (Rb) . This effect was not observed with cis -DDP and with the parent aminoalkylaminoanthraquinone free base. The effect was not time dependent and could be observed only at Rb > 0.4. Explanation for this phenomenon was given on the basis of monoadduct formation between the platinum and purine/pyrimidine bases which leads to strand degradation. A salt effect on the length of poly(dG)·poly(dC) is also present.