Cu(II) adriamycin complexes. Identification and interaction with DNA

Abstract

Adriamycin (Adr) is an anthracycline antibiotic widely used in the treatment of various human cancers. Once in the cell, adriamycin localizes in the nucleus and is believed to act by inhibiting both DNA replication and RNA transcription [1]. Since metal t001 Stability Constants and Spectral Data of Complexes I and II. log β Spectral data I 16.7 Ab λ(nm) 304 400 512 ϵ 8300 2400 6700 CDλ(nm) 230 260 300 350 380 430 490 540 Δϵ −26.5 −8.8 −18 +4 +5.5 +1.7 t 6 ̄ +8.5 II 12.2 Abλ(nm) 316 420 540 ϵ 9400 3000sh 6000 CDλ(nm) 260 305 570 605 Δϵ +16.4 +2 +4.5 +6.2 ions are present in all biological processes involving the nucleic acid and since DNA seems to be the target for adriamycin action, the occurrence of metal-adriamycin complexes inside the cell may play a crucial role in chemotherapeutic action. Several recent observations have focussed attention on the interaction of adriamycin and Cu(II) in the absence and in the presence of DNA [2–5]. In this communication we report the results of a detailed potentiometric and spectroscopic investigation which was undertaken to characterize accurately Cu(II)adriamycin complexes, their stability constants and their effect on DNA. The addition of Cu(II) to Adr at 1:1 molar ratio yields a first complex (I) at pH 5.8 and a second one (II) at pH 7.2. Using the results of potentiometric titrations these complexes can be formulated as Cu(AdH) 2(I) and Cu(Ad)(II). AdH and Ad stand for Adr in which the 1,4-dihydroxianthraquinone moiety is half deprotonated and fully deprotonated respectively. Absorption, CD data and the stability constants of both complexes are reported in Table I. The visible CD spectrum of complex I is of the couplet type indicating stacking of Adr due to the presence of Cu(II). Resonance Raman spectroscopy measurements indicate that coordination takes place through quinone and phenolate oxygens as shown by the shifting of the corresponding CO stretching Raman bands (carbonyl and phenolic). When DNA is added to Adr at pH 7.4 (HEPES 0.05 M) precipitation of a DNA·Adr complex occurs, with a molar ratio of one nucleotide per Adr, if the Adr concentration is higher than 100 μM. When DNA is added to complexes I or II a Cu·Adr·ADN species precipitates. In this case, however, an Adr concentration lower than 20 μM has to be reached to prevent precipitation.