Solid phase synthesis and biological activity of tuftsin conjugates.

New tuftsin/retro-tuftsin conjugates were designed and synthesized using a classical fluorenylmethoxycarbonyl (Fmoc) solid phase procedure. All the peptide conjugates were divided into three series: 1,4-dihydroxyanthraquinone (type A), 1-nitroacridine (type B), and 4-carboxyacridone (type C) derivatives. In type A conjugates, the N-terminal group of the peptide chain is directly connected to the anthraquinone ring at C1 (Scheme 1), whereas types B and C conjugates possess an amide bond formed between the carboxyl group of heterocyclic molecule and the N-termini of the tuftsin chain. The in vitro cytotoxic activity of the tuftsin conjugates and their precursors using two human tumor cell lines (lung adenocarcinoma (A549) and myeloblastic leukemia (HL-60)) was investigated. The analogues from groups A and C exhibited low cytotoxic activity, whereas several compounds of type B showed a potent and selective cytotoxic activity against tested tumor cell lines. None of the examined tuftsin conjugates demonstrated any significant effect on the catalytic activity of types I and II DNA topoisomerases.