The serum protein binding of pharmacologically active gallium(III) compounds assessed by hyphenated CE‐MS techniques

Abstract

Transition metal-based drugs exhibit high affinity to the soft donors of human serum proteins, especially of the high-abundance protein HSA and of transferrin (Tf), whereas Ga(III) salts are known to bind to Tf and other iron-containing metalloproteins, thereby interfering with the iron metabolism. Herein, the utilization of CE-MS methods for studying the binding behavior of a therapeutic gallium nitrate formulation and the anticancer drug candidate Tris(8-oxyquinolinato)gallium(III) to Tf and HSA under simulated physiological conditions is described. Both the Ga(III) salt and the complex were found to bind to Tf exclusively in the presence of carbonate, however, at different kinetics and to a different extent. Fe(III) induces the release of the Ga ions due to the higher affinity constant and also prevents the Ga(III) species from accessing the iron-binding pockets of Tf. In contrast, only low affinity to HSA was observed and even when present at ca. 20-fold excess, the majority of the Ga was attached to Tf.

Comparative solution equilibrium studies of anticancer gallium(III) complexes of 8-hydroxyquinoline and hydroxy(thio)pyrone ligands

“…Binding of Ga(III) to the iron site of the R2 subunit of this enzyme results in the destabilization of the tyrosyl radical essential for enzymatic activity [9]. Ga(III) is able to bind to the iron sites of transferrin, which promotes the cellular absorption of Ga(III) [10], in particular in proliferating cancer cells with strong iron demand and overexpressed transferrin receptors, although cellular gallium uptake may also occur by a transferrin-independent pathway [5,9].…”

Metallomics related to gallium compounds: biochemical and xenobiochemical aspects

“…Although its affinity is reduced compared to that of Fe 3+ , when in excess, Ga 3+ replace Fe 2+ from this protein [41]. Nevertheless, using gel electrophoresis autoradiography experiments with 67 Ga and 59 Fe, it was shown that the two ions in fact entail slightly different pathways of entry and efflux into cells. Additionally, and perhaps not unexpectedly due to its increased solubility, Ga, unlike Fe 3+ , is not sequestered inside cells by ferritin [42].…”

“…This method efficiently provides valuable information about binding parameters, including changes in the content of gallium-protein adducts and equilibrium binding constants [58]. Other studies used CE-MS to evaluate the binding of gallium nitrate and gallium quinolate to transferrin and human serum albumin [59]. Having similar coordination geometries and strong affinity for groups that contain oxygen, Ga 3+ is used as a substitute for Fe 3+ in some applications regarding iron-binding proteins and binding of phosphopeptides.…”

“…In vitro studies also revealed that 67 Ga may be transferred from transferrin to the iron-storage protein ferritin [109] A comparative study regarding transferrin complexes with 59 Fe, 111 In and 69 Ga was performed on Wistar rats. The aim was to find a good macromolecular tracer for the evaluation of vascular permeability in tumours and other body tissues.…”

Rákellenes gallium- és platinafém komplexek oldatkémiája, kölcsönhatásuk vérszérum-fehérjékkel és DNS-sel

“…Ugyanakkor az ezt jóval meghaladó in vivo mérhető maximális szérumkoncentrációk arra utalnak, hogy a véráramban nagyobb részt fehérjékhez kötődik [67]. CE-MS vizsgálatok szerint a fémion szinte kizárólag Tf-hez kötődött, míg a HSA szerepe igen mérsékelt volt [72]. Másrészről röntgenabszorpciós spektroszkópiás mérések szerint a fémion körüli koordinációs szféra nem változott sem Tf, sem HSA jelenlétében, ami a nem koordinatív, másodlagos kötésmódok lehetőségét veti fel [73].…”