The cardioprotective effect of dexrazoxane (Cardioxane) is consistent with sequestration of poly(ADP-ribose) by self-assembly and not depletion of topoisomerase 2B

Abstract

Following systematic scrutiny of the evidence in support of the hypothesis that the cardioprotective mechanism of action of dexrazoxane is mediated by a 'depletion' or 'downregulation' of Top2β protein levels in heart tissue, the author concludes that this hypothesis is untenable. In seeking to understand how dexrazoxane protects the heart, the outcomes of a customised association rule learning algorithm incorporating the use of antecedent surrogate variables (CEME, 2017 McCormack Pharma) reveal a previously unknown relationship between dexrazoxane and poly(ADP-ribose) (PAR) polymer. The author shows how this previously unknown relationship explains both acute and long-term cardioprotection in patients receiving anthracyclines. In addition, as a direct inhibitor of PAR dexrazoxane has access to the epigenome and this offers a new insight into protection by dexrazoxane against doxorubicin-induced late-onset damage [McCormack K, manuscript in preparation]. Notably, through this review article, the author illustrates the practical application of probing natural language text using an association rule learning algorithm for the discovery of new and interesting associations that, otherwise, would remain lost. Historically, the use of CEME enabled the first report of the capacity of a small molecule to catalyse the hybrid self-assembly of a nucleic acid biopolymer via canonical and non-canonical, non-covalent interactions analogous to Watson Crick and Hoogsteen base pairing, respectively.

Keywords: Watson Crick; anthracyclines; cardioprotection; dexrazoxane; epigenome; poly(ADP-ribose); topoisomerase 2β.

Figure 1.. Each dioxopiperazine moiety of dexrazoxane contains a thymine face and cyanuric acid has three thymine faces.

Figure 2.. Correlation between Top2β expression and the percentage of apoptotic cells in peripheral blood leucocytes of 22 healthy volunteers following 24 hours ex vivo incubation with 1-μM doxorubicin. Data adapted from Kersting et al [57].

Figure 3.. Effect of the proteasome inhibitors, bortezomib and carfilzomib on the dexrazoxane-induced decrease in Top2β levels in neonatal rat cardiomyocytes. Myocytes were treated with bortezomib (1 μM) or carfilzomib (2 μM) for 30 minutes in growth medium prior to a 6-hour treatment with dexrazoxane (100 μM), lysed and subject to sodium dodecyl sulphate polyacrylamide gel electrophoresis and western blotting. Images reproduced from Hasinoff et al [61] with permission (Springer; Copyright Clearance Licence: 4165441151593).

Figure 4.. PAR is a polymer of ADP-ribose monomers.

Figure 5.. Lack of identity of dexrazoxane with a contemporary pharmacophore of PARP1.

Figure 6.. Dexrazoxane catalyses the formation of a hybrid self-assembled supramolecular structure between adjacent strands of PAR. This assembly depicts an antiparallel orientation of canonical Watson–Crick base pairing of dexrazoxane with adenine bases.

Figure 7.. Canonical Watson–Crick adenine-thymine base pairing of double-stranded DNA.

Figure 8.. The dexrazoxane-catalysed supramolecular structure with PAR (top diagram) is characterised by two in-series hydrogen bonded base pairs at the level of each stack; this structural feature is reminiscent of the synthetic fibre, nylon 66 in which hydrogen bonds between adjacent polymer chains result in considerable tensile strength.

Figure 9.. Tautomeric stabilisation of the dexrazoxane-adenine interaction.

Figure 10.. Cyanuric acid (red)-catalysed self-assembly of a poly(A) triplex. Adapted from Avakyan et al [102].

Figure 11.. The three thymine faces of cyanuric acid (red) self-assemble with melamine-containing polyacrylate polymer strands. The hydrogen-bonding pattern shown is adapted from Zhou and Bong [105].

Figure 12.. Poly(A) is closely related to PAR [poly(ADP-ribose)].

Figure 13.. Cyanuric acid monomer(s) self-assembles with three poly(A) strands; canonical Watson–Crick base pairing is shown in (A) and a hexameric rosette structure formed by both canonical and non-canonical Hoogsteen base pairing is shown in B. Adapted from Avakyan et al [102] and Berger and Gazit [108]. (B) adapted with permission (Springer; Copyright Clearance Licence: 4165441151593).

Figure 14.. Dexrazoxane may also self-assembly with PAR through a combination of both canonical and non-canonical Hoogsteen base pairing to bring together a PAR triplex; the adenine moieties of PAR are shown in black. Furthermore, the contribution from both types of base pairing may lead to the formation of assemblies beyond a triplex.

Figure 15.. The anthracycline-compromised cardiomyocyte represents a deep compartment for the accumulation of dexrazoxane. Uncharged dexrazoxane transits the lipid membrane of the cardiomyocyte and encounters PARP-elaborated PAR within the intracellular compartment.

Figure 16.. Dexrazoxane prevents AIF release from isolated mitochondria. Track 1 = Control; track 2 = 100 nM PAR and 100 nM dexrazoxane; track 3 = 100 nM PAR and 50 nM dexrazoxane; track 4 = 100 nM PAR and 10 nM dexrazoxane. PAR and dexrazoxane were incubated together for 10 minutes before adding to the mitochondrial suspension (western blots reproduced from the study final report).