A spectroscopic study of the reaction of NAMI, a novel ruthenium(III)anti‐neoplastic complex, with bovine serum albumin

Abstract

The reaction of Na [transRuCl 4 Me 2 SO(Im)] (NAMI; where Im is imidazole), a novel anti-neoplastic ruthenium(III) complex, with BSA, was studied in detail by various physico-chemical techniques. It is shown that NAMI, following chloride hydrolysis, binds bovine serum albumin tightly; spectrophotometric and atomic absorption data point out that up to five ruthenium ions are bound per albumin molecule when BSA is incubated for 24 h with an eightfold excess of NAMI. CD and electronic absorption results show that the various ruthenium centers bound to albumin exhibit well distinct spectroscopic features. The first ruthenium equivalent produces a characteristic positive CD band at 415 nm whereas the following NAMI equivalents produce less specific and less marked spectral effects. At high NAMI/BSA molar ratios a broad negative CD band develops at 590 nm. Evidence is provided that the bound ruthenium centers remain in the oxidation state +3. By analogy with the case of transferrins it is proposed that the BSA-bound ruthenium ions are ligated to surface histidines of the protein; results from chemical modification experiments with diethylpyrocarbonate seem to favor this view. Spectral patterns similar to those shown by NAMI are observed when BSA is reacted with two strictly related ruthenium(III) complexes Na[transRuCl 4 (Me 2 SO) 2 ] and H(Im)[transRuCl 4 (Im) 2 ] (ICR), implying a similar mechanism of interaction in all cases. It is suggested that the described NAMI-BSA adducts may form in vivo and may be relevant for the biological properties of this complex; alternatively NAMI/BSA adducts may be tested as specific carriers of the ruthenium complex to cancer cells. Implications of these findings for the mechanism of action of NAMI and of related ruthenium(III) complexes are discussed. The imidazolium salt of NAMI, NAMI-A, which has improved characteristics of stability in the solid state compared to NAMI, is currently being tested in clinical phase I studies as an antimetastatic drug [5]. The complex is pseudooctahedral with four equatorial chloride ligands, and DMSO and imidazole as axial ligands (Scheme 1) [6]. The behavior of NAMI under physiological conditions was previously studied in detail; notably the complex slowly looses its chloride ligands and transforms into the corresponding, more reactive, aquatedspecies [4,7,8]. The hydrolysis process can be easily monitored spectrophotometrically [4]. Apparently, the loss of two coordinated chlorides is the prerequisite for any further reactivity [7]. The resulting bis-aquaspecies may bind various biomolecular targets and is very likely responsible for the biological effects of NAMI. Yet, the final targets and the mechanisms through which NAMI and its parent ruthenium(III) complexes exert their anti-tumor effects are largely unknown, and controversial opinions still exist on this issue [3,5].Within this frame it is of interest to consider the interactions of NAMI with plasma proteins, and in particular with serum albumin (by far the most abundant protein in the pl...

Tumor apoptosis induced by ruthenium(II)‐ketoconazole is enhanced in nonsusceptible carcinoma by monoclonal antibody to EGF receptor

“…Although Ru(III)-based NAMI-A shows promising results in animal models and is currently in early clinical trials, 15,17,33 it does not have a single target since it interacts with DNA, 39 collagen 40 and major plasma proteins like serum albumin. 41 This is in great contrast with C225, a chimeric antihuman EGF-R MAb that specifically blocks ligand binding and functional activation of this receptor. 24,37,42 However, repeated exposure of some tumors to C225 can lead to acquisition of resistance to this treatment.…”

“…24,37,42 However, repeated exposure of some tumors to C225 can lead to acquisition of resistance to this treatment. 24,41 To widen the scope of Ru(III)-based NAMI-like drugs, our study was devoted to an Ru(II)-based complex, which demonstrated a significant antitumor effect irrespective of p53 status against cell monolayers, unlike cisplatin. 9,10 However, we discovered that A431 spheroids, which overexpress EGF-R, 24 like many human carcinomas, 37 are not susceptible to either C225 or RuCl 2 (KTZ) 2 but to the joint use of both agents.…”

Interactions of arene ruthenium metallaprisms with human proteins

“…14,[16][17][18] By analogy with platinum complexes, it was originally assumed that DNA binding was the main reason for the anticancer activity of ruthenium complexes. 16,[19][20][21] While the ability of ruthenium complexes to bind to DNA has been demonstrated, [22][23][24][25] in particular for arene ruthenium ethylenediamine complexes, 26,27 it was also observed that DNA binding of ruthenium was weaker and different from that observed for platinum complexes. 22 Recent examples of rationally designed metal complexes that inhibit enzymatic activities involved in cancer proliferation were investigated, 28,29 including ruthenium half-sandwich complexes that bind to specific enzymes.…”

Anti-tubercular Activity of Ruthenium (II) Complexes with Polypyridines

“…A number of such selected metal based compounds contain metal-oxygen (M-O) hemilabile bonds e.g., (M-OvM-OH 2 ) [13,14,22] or (M-SOMe 2 ) [16] which have shown interesting and potential anti-tumor or antibacterial activity (Figure 1). …”

“…12.5 mg/ mL [15]. Na[trans-RuCl 4 (Me 2 SO)(Im)] (Im ¼ imidazole), a ruthenium(III) complex shows encouraging antitumour and anti-metastatic properties [16].…”