Iron complexes of the cardioprotective agent dexrazoxane (ICRF-187) and its desmethyl derivative, ICRF-154: solid state structure, solution thermodynamics, and DNA cleavage activity

doi:10.1016/S0162-0134(00)00013-1

Journal of Inorganic Biochemistry

Volume 78, Issue 3, 29 February 2000, Pages 209-216

https://doi.org/10.1016/S0162-0134(00)00013-1 Get rights and content

Abstract

This study investigates the solution thermodynamics of the iron complexes of dexrazoxane (ICRF-187, (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane), [Fe(ADR-925)]^+/0, and its desmethyl derivative ICRF-154, [Fe(ICRF-247)H₂O]^+/0. The solid state structure of [Fe(ICRF-247)H₂O]⁺ is also reported. [Fe(ICRF-247)H₂O]Br·0.5NaBr·H₂O crystallizes in the P42₁2 space group with Z=4, a=14.9851(8), b=14.9851(8), c=8.0825(9) Å and R=0.03(2) for 1839 reflections and exhibits a pentagonal bipyramidal geometry with a labile water molecule occupying the seventh coordination site. Potentiometric titrations (FeL=8.5 mM, 0.1 M NaNO₃, 25 °C) reveal stable monomeric complexes (log K_f=18.2±0.1, [Fe(ADR-925)]⁺, and 17.4±0.1, [Fe(ICRF-247)H₂O]⁺) exist in solution at relatively low pH. Upon addition of base, the iron-bound water is deprotonated; the pK_a values for [Fe(ICRF-247)H₂O]⁺ and [Fe(ADR-925)]⁺ are 5.63±0.07 and 5.84±0.07, respectively. At higher pH both complexes undergo μ-oxo dimerization characterized by log K_d values of 2.68±0.07 for [Fe(ICRF-247)H₂O]⁺ and 2.23±0.07 for [Fe(ADR-925)]⁺. In the presence of an oxidant and reductant, both [Fe(ICRF-247)H₂O]⁺ and [Fe(ADR-925)]⁺ produce hydroxyl radicals that cleave pBR322 plasmid DNA at pH 7 in a metal complex concentration-dependent manner. At low metal complex concentrations (∼10⁻⁵ M) where the monomeric form predominates, cleavage by both FeICRF complexes is efficient while at higher concentrations (∼5×10⁻⁴ M) DNA cleavage is hindered. This change in reactivity is in part accounted for by dimer formation.

Introduction

The bisdioxopiperazine dexrazoxane (Zinecard^®, ICRF-187, Ia) is used to effectively reduce the cardiomyopathic side effects of the antitumor antibiotic, doxorubicin (DOX) in chemotherapy [1], [2]. By first hydrolyzing to either its one-ring intermediate or its fully open diacid/diamide form (ADR-925, IIa), this ICRF drug chelates and removes iron ions from membrane-bound FeDOX [3], [4], a complex capable of catalyzing the production of reactive hydroxyl radicals (OH) that cause lipid peroxidation and other biomolecular damage [5], [6], [7]. Notably, [Fe(ADR-925)]⁺ also produces OH in the presence of an oxidant and a reductant [8], [9], [10], [11]. The charged nature of this FeICRF complex, however, is thought to lessen its affinity for the cell membrane; the redox active iron is effectively removed and oxidative damage to the heart muscle is reduced [9], [10], [11].

Although dexrazoxane affords protection to the lipid-based cell membrane, Thomas et al. have shown that catalytic hydroxyl radical production by FeICRF complexes can result in protein oxidative damage [12]. Malisza and Hasinoff also concluded that [Fe(ADR-925)]⁺ may target other cellular sites [11]. These reports prompted our lab to investigate FeICRF oxidative reactivity in the presence of DNA [13]. Our study showed that [Fe(ADR-925)]⁺ and its desmethyl derivative [Fe(ICRF-247)H₂O]⁺ (ICRF-247, IIb, referred to as edta-bisamide²⁻ in Refs. [13], [14], the hydrolysis product of ICRF-154, Ib) in the presence of molecular oxygen and ascorbic acid produce OH that cleave pBR322 plasmid. A comparative metal complex concentration study involving these FeICRF complexes and [Fe(edta)H₂O]⁻ (edta⁴⁻=ethylenediaminetetraacetate) revealed metal complex-dependent differences in the cleavage patterns. [Fe(edta)H₂O]⁻ and to a lesser extent [Fe(ADR-925)]⁺ caused increased cleavage with increasing concentration while [Fe(ICRF-247)H₂O]⁺ reactivity was inhibited at higher concentrations. Spectrophotometric base titrations indicated that [Fe(ICRF-247)H₂O]⁺ and [Fe(ADR-925)]⁺ form μ-oxo iron dimers at a relatively low pH (pH∼5.5 and pH∼6, respectively). This is similar to [Fe(edta)H₂O]⁻, which also forms this dimer but at high pH (∼9)[15], [16]. Assuming a structure and Fenton-like reactivity similar to [Fe(edta)H₂O]⁻ [17], [18], [19], [20], [21], FeICRF dimerization would effectively block the seventh, labile iron coordination site (normally occupied by H₂O) required for OH production, offering a partial explanation for the reactivity differences observed for these complexes at pH 7.

To probe this hypothesis more fully, this study examines the solid state and solution structures of FeICRF complexes, reporting for the first time the crystal structure of an Fe(III)ICRF complex, [Fe(ICRF-247)H₂O]⁺. Thermodynamic formation, water hydrolysis, and dimerization constants for both [Fe(ICRF-247)H₂O]⁺ and [Fe(ADR-925)]⁺ have been determined. An extension of the FeICRF concentration dependence on DNA cleavage described by Magliery et al. [13] is also reported and the results discussed in light of the solution properties of FeICRF complexes.

Section snippets

Materials

All chemicals used in this study were of highest available purity. ADR-925 was generously provided by Dr Anthony Imondi of Pharmacia/Upjohn (currently of Battelle, Columbus, OH). Barnstead Nanopure (18 MΩ cm) water was used throughout. All glassware was acid-washed with concentrated H₂SO₄, and plastic ware with 3 M HCl, or purchased metal-free.

[Fe(ICRF-247)H₂O]Br·0.5NaBr·H₂O ([Fe(ICRF-247)H₂O]⁺)

ICRF-247 was prepared from ethylenediaminetetraacetic dianhydride (Aldrich) and 30% (aq) NH₄OH as described in the literature [14]. Saturated NaHCO_3(aq)

Molecular crystal structure of [Fe(ICRF-247)H₂O]⁺

Fenton-like chemistry involving iron(III)edta chelates is well studied [5], [6], [7], [18], [19], [20], [21]. Facile, catalytic OH production is thought to involve an inner-sphere electron transfer between the metal ion, oxidant and reductant (Eq. (1)). Key to this chemistry is the labile water molecule, which occupies the seventh coordination site of [Fe(edta)H₂O]⁻.

(1)

Fig. 1 shows the solid state structure of [Fe(ICRF-247)H₂O]⁺ and Table 3 presents selected bond distances and angles for both

Conclusions

Iron(III) chelation by hydrolyzed dexrazoxane (ADR-925) is thought to be the primary mechanism by which dexrazoxane ameliorates cardiac toxicity during doxorubicin chemotherapy. [Fe(ADR-925)]⁺ and its desmethyl derivative, [Fe(ICRF-247)H₂O]⁺, however, also exhibit favorable redox activity that can lead to catalytic OH production and biopolymer damage. The reports by Thomas et al. [12] and Magliery et al. [13], as well as the work presented here, raise the question as to whether or not FeICRF

Supplementary material

Tables of structure factors (S1), anisotropic parameters (S2), H-atom coordinates (S3), and complete geometry (S4-S7) are available as supplementary material from the authors.

Acknowledgements

The authors gratefully acknowledge the Research Corporation Award CC3833 (R.A.M.), HHMI Award 71196-504202 Teacher Summer Research Fellowship (P.A.), and Kenyon College Science Scholar Research Funds (N.K.D., L.K.V.) for generous monetary support of this work. Thanks are also expressed to Dr Anthony Imondi (Battelle, Columbus, OH) for samples of ADR-925, to Dr R.J. Motekaitis (Texas A&M University, College Station, TX) for help with stability constant determination, and to Ken Eward (BioGrafx,

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ADR-925 may be chelating iron and preventing iron-dependent doxorubicin-induced oxidative damage to cardiac myocytes. This metabolite binds Fe2 + and Fe3 + with formation constants of 1010 M− 1 and 1018.2 M− 1 [44], respectively, which is several orders of magnitude weaker than that for binding to EDTA, but it is still a very strong iron chelator. ADR-925 or the one-ring open intermediates can either quickly (t1/2 ~ 1 and 6 min, respectively) remove Fe3 + from Fe3 +–anthracycline complexes or bind free iron in the cell [45,47].
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Despite incomplete understanding to its mechanism of action, dexrazoxane (DEX) is still the only clearly effective cardioprotectant against chronic anthracycline (ANT) cardiotoxicity. However, its clinical use is currently restricted to patients exceeding significant ANT cumulative dose (300 mg/m²), although each ANT cycle may induce certain potentially irreversible myocardial damage. Therefore, the aim of this study was to compare early and delayed DEX intervention against chronic ANT cardiotoxicity and study the molecular events involved. The cardiotoxicity was induced in rabbits with daunorubicin (DAU; 3 mg/kg/week for 10 weeks); DEX (60 mg/kg) was administered either before the 1st or 7th DAU dose (i.e. after ≈300 mg/m² cumulative dose). While both DEX administration schedules prevented DAU-induced premature deaths and severe congestive heart failure, only the early intervention completely prevented the left ventricular dysfunction, myocardial morphological changes and mitochondrial damage. Further molecular analyses did not support the assumption that DEX cardioprotection is based and directly proportional to protection from DAU-induced oxidative damage and/or deletions in mtDNA. Nevertheless, DAU induced significant up-regulation of heme oxygenase 1 pathway while heme synthesis was inversely regulated and both changes were schedule-of-administration preventable by DEX. Early and delayed DEX interventions also differed in ability to prevent DAU-induced down-regulation of expression of mitochondrial proteins encoded by both nuclear and mitochondrial genome. Hence, the present functional, morphological as well as the molecular data highlights the enormous cardioprotective effects of DEX and provides novel insights into the molecular events involved. Furthermore, the data suggests that currently recommended delayed intervention may not be able to take advantage of the full cardioprotective potential of the drug.
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Iron complexes of the cardioprotective agent dexrazoxane (ICRF-187) and its desmethyl derivative, ICRF-154: solid state structure, solution thermodynamics, and DNA cleavage activity

Abstract

Introduction

Section snippets

Materials

[Fe(ICRF-247)H2O]Br·0.5NaBr·H2O ([Fe(ICRF-247)H2O]+)

Molecular crystal structure of [Fe(ICRF-247)H2O]+

Conclusions

Supplementary material

Acknowledgements

J. Inorg. Biochem.

Biochem. Pharm.

Arch. Biochem. Biophys.

J. Biol. Chem.

Inorg. Chim. Acta

Inorg. Chim. Acta

Inorg. Chim. Acta

Curr. Med. Chem.

Contrib. Oncol.

Agents Actions

ACS Symp. Ser.

Free Radical Res.

Redox Rep.

Free Radical Res.

Met.-Based Drugs

Acta Crystallogr., Sect. C

[Fe(ICRF-247)H₂O]Br·0.5NaBr·H₂O ([Fe(ICRF-247)H₂O]⁺)

Molecular crystal structure of [Fe(ICRF-247)H₂O]⁺