CRYSTAL-STRUCTURES OF 4 MORPHOLINO-DOXORUBICIN ANTICANCER DRUGS COMPLEXED WITH D(CGTACG) AND D(CGATCG) - IMPLICATIONS IN DRUG-DNA CROSS-LINK

Among the new generations of anthracycline drugs, morpholino-doxorubicin (MDox) and its derivative have unusually potent activity when compared with the parent doxorubicin. 3 ''-Cyano-morpholino-doxorubicin (CN-MDox)has been suggested to form a covalent crosslink to DNA, although the exact mode of interactions remains unclear. To establish the structural basis of this crosslink, we carried out X-ray diffraction analyses of the complexes between four different morpholino-doxorubicins (i.e., MDox, CN-MDox, (R)- and (S)-2 ''-methoxymorpholino-Dox (MMDox)) and two DNA hexamers CGTACG and CGATCG. Their crystal data are similar to other Dau/Doxcomplexes with spacegroup P4(1)2(1)2,a=b similar to 28 Angstrom,c similar to 53 Angstrom The refined structures at similar to 1.8 Angstrom resolution revealed that two drug molecules bind to the duplex with the aglycons intercalated between the CpG steps with their N-3'-morpholino-daunosamines in the minor groove. The morpholino moiety is flexible and may adopt different conformations dependent on the sequence context. The O-1' atoms of the two morpholino groups in the drug-DNA complexes are in van der Waals contact. The structural results suggest possible crosslinking mechanism of CN-MDox. It is worth pointing out that by linking two piperazinyl- or piperidinyl-doxorubicins at the 1 '' positions a new type of bis-doxorubicin derivatives maybe synthesized which may bind to a hexanucleotide sequence with some specificity.