A series of 3-substituted spiro[(dihydropyrazine-2,5-dione)-6,3'-(2',3'-dihydrothieno[2,3-b]naphtho-4',9'-dione)] derivatives were prepared using an easy synthetic route via condensation of the 3-amino-3-(ethoxycarbonyl)-2,3-dihydrothieno[2,3-b]naphtho-4,9-dione system and
amino acids followed by intramolecular lactamization.
Amino acids containing alkyl and aryl, linear and cyclic, polar and apolar, and basic and
acid residues were incorporated. Evaluation of these analogues against the MCF-7 human
breast carcinoma and SW 620 human colon
carcinoma cell lines revealed, for the 3S,3'R isomers derived from Pro (7a), Cys (11a), and Met (12a) and the 3R,3'S isomer derived from D-Pro (7c), a cytotoxic potency comparable to or greater than that of
doxorubicin. Some of these selected analogues were potent
cytotoxic agents in several other sensible and resistant human solid tumor cell lines and may be able to circumvent the multiple-drug-resistance mechanism. In particular, only a partial cross-resistance to the compounds 7, 11, and 12 was observed in selected
tumor cell sublines known to be resistant to
doxorubicin (MCF-7/Dx and A2780/Dx), whereas a very low level of cross-resistance to compounds 7 and 11 was found in a
tumor cell subline selected for resistance to
cisplatin (A2780/DDP). In addition, the
topoisomerase II inhibition activity and
DNA-binding properties were investigated.