Figure 1.

Chemical structure of DOX, MTX and PIX. DOX is composed by a tetracyclic quinone-hydroquinone chromophore, a carbonyl-containing side chain, and an aminosugar (daunosamine). MTX is a three-ring quinone-hydroquinone anthracenedione; its side chains lack carbonyl groups and MTX also lacks daunosamine. PIX differs from MTX in its lack of the hydroquinone, insertion of a nitrogen heteroatom in the same ring (black arrow), and substitution of (ethylamino)-diethylamino for (hydroxyethylamino)-ethylamino side chains (grey circles).