Abstract: Myocardial ischemia followed by reperfusion (I/R) initiates a cascade of deleterious biochemical and structural changes, primarily driven by polymorphonuclear leukocyte (PMN) infiltration, superoxide radical release, and endothelial dysfunction. Gö 6983 is a fast-acting, lipid-soluble, broad-spectrum protein kinase C (PKC) inhibitor that has demonstrated significant cardioprotective effects in cardiovascular research. Unlike other bisindolylmaleimides, Gö 6983 effectively inhibits the atypical PKC zeta (ζ) isoform at nanomolar concentrations. By acting at the ATP binding site of PKC, Gö 6983 attenuates PMN-induced cardiac contractile dysfunction, reduces PMN adherence and transmigration, inhibits superoxide release, and augments endothelial-derived nitric oxide (NO) bioavailability. This literature review synthesizes the pharmacological activity, molecular mechanisms, structure-activity relationships, limitations, and future therapeutic perspectives of Gö 6983 in the context of cardiovascular disease and ischemia/reperfusion injury.
1. Introduction
The most effective means of limiting myocardial damage and restoring ventricular function after prolonged ischemia is through early reperfusion. However, the restoration of blood flow induces endothelial and myocyte injury, leading to cardiac arrhythmias and prolonged left ventricular dysfunction, a phenomenon known as ischemia/reperfusion (I/R) injury [1][2]. Reperfusion injury is characterized by a rapid decrease in endothelial nitric oxide (NO) release within minutes, upregulation of endothelial adhesion molecules, and the subsequent transmigration of polymorphonuclear leukocytes (PMNs) into the myocardium [1]. Activated PMNs release oxygen-derived free radicals and proteolytic enzymes, which are primary culprits in post-ischemic myocardial necrosis and contractile dysfunction [1].
Protein kinase C (PKC) is a critical mediator in the signal transduction cascades that govern PMN activation, superoxide release, and endothelial cell responses during I/R injury [2]. Gö 6983 is a potent, fast-acting bisindolylmaleimide analog and a broad-spectrum PKC inhibitor. It has garnered significant attention in cardiovascular research due to its unique ability to inhibit classical, novel, and atypical PKC isoforms—most notably PKC ζ—at nanomolar concentrations, offering profound cardioprotective effects against PMN-induced I/R injury [1][2].
2. Pharmacological Activity
Gö 6983 exerts robust cardioprotective effects in models of acute myocardial ischemia/reperfusion. In isolated rat heart models subjected to global ischemia followed by reperfusion with activated PMNs, Gö 6983 administration significantly restores cardiac contractile function. Specifically, treatment with 50 to 100 nM of Gö 6983 restores left ventricular developed pressure (LVDP) and the maximal rate of LVDP (+dP/dtmax) to near-baseline levels within the first 5 minutes of reperfusion [1][2]. Importantly, Gö 6983 exerts no direct inotropic effects on cardiac contractile function in non-ischemic sham hearts, indicating that its benefits are specifically linked to mitigating I/R-induced damage [1].
The cardioprotective efficacy of Gö 6983 is heavily associated with its anti-inflammatory and antioxidant actions. It significantly reduces PMN adherence to the vascular endothelium (by up to 61% at 100 nM) and limits PMN infiltration into post-reperfused cardiac tissue [1]. Furthermore, Gö 6983 concentration-dependently inhibits superoxide release from stimulated PMNs, achieving up to 90% inhibition at 100 nM [1]. Alongside reducing oxidative stress, Gö 6983 augments endothelial-derived NO release, which acts as a physiological inhibitor of leukocyte-endothelial cell interaction and promotes vasodilation, thereby improving tissue perfusion [2].
3. Molecular Mechanism of Action
Gö 6983 is a cell-permeable compound that enters cells via simple diffusion and exerts its inhibitory effect by binding to the highly conserved ATP binding site across various PKC isoforms [1][2]. It is a broad-spectrum inhibitor, effectively blocking classical (α, β, γ), novel (δ), and atypical (ζ) PKC isoforms [2].
In the context of I/R injury, the inhibition of PKC βII and PKC ζ is particularly critical. PKC βII is partially responsible for superoxide release, but the atypical PKC ζ isoform plays an indispensable role in regulating the NADPH oxidase enzyme complex (via phosphorylation of p47phox) and mediating PMN chemotaxis [1][2]. Additionally, PKC ζ stimulates the expression of intercellular adhesion molecule 1 (ICAM-1) on vascular endothelial cells in response to inflammatory cytokines. By inhibiting PKC ζ, Gö 6983 prevents the firm adhesion of PMNs to the endothelium and their subsequent transmigration [1][2].
Furthermore, PKC activation normally negatively regulates endothelial NO synthase (eNOS). By inhibiting PKC during early reperfusion, Gö 6983 preserves basal eNOS activity, leading to increased NO bioavailability. This NO quenches superoxide radicals (forming peroxynitrite) and further suppresses the upregulation of endothelial adhesion molecules like P-selectin [1][2]. Interestingly, while Gö 6983 is highly potent against most PKC isoforms, it is extremely ineffective at suppressing the kinase activity of PKC µ (IC50 = 20 µM), a property that has been used experimentally to differentiate PKC µ from other PKC isoenzymes [3].
4. Structure-Activity Relationship (SAR)
Gö 6983 (molecular weight 442.5) belongs to the bisindolylmaleimide class of PKC inhibitors, which are synthetic analogs of the natural fungal metabolite staurosporine [2]. Structurally, staurosporine possesses an intact central aromatic ring, whereas bisindolylmaleimides like Gö 6983 and Gö 6850 (bisindolylmaleimide I) feature an opened central aromatic ring [2][3]. This open ring structure renders Gö 6983 a very poor inhibitor of PKC µ, in stark contrast to closed-ring compounds like staurosporine and Gö 6976, which strongly inhibit PKC µ [3].
The most critical structural feature of Gö 6983 that distinguishes it from its prototype Gö 6850 is the presence of a methoxy (-OCH3) group substitution [2]. This specific methoxy group enables Gö 6983 to inhibit the atypical PKC ζ isoform at low nanomolar concentrations (IC50 = 60 nM). Other bisindolylmaleimides and staurosporine, which lack this methoxy group, require much higher micromolar concentrations to inhibit PKC ζ [2]. This unique structural attribute makes Gö 6983 exceptionally effective at attenuating the inflammatory events associated with I/R injury that are mediated by PKC ζ [1][2].
5. Current Limitations
Despite its potent cardioprotective effects, the therapeutic window of Gö 6983 requires careful consideration. Studies indicate a strict dose-dependency where optimal cardioprotection is observed at 50 to 100 nM. At a lower concentration of 25 nM, the compound only modestly inhibits superoxide release (29%) and fails to attenuate cardiac contractile dysfunction [1]. Conversely, at a higher concentration of 200 nM, Gö 6983 exhibits reduced cardioprotective efficacy despite inhibiting PMN superoxide release by 99% [1]. This paradoxical effect at high doses is attributed to a loss of PKC selectivity, which may lead to increased cytotoxicity, cell death in coronary endothelial cells and cardiac myocytes, and a subsequent increase in inflammatory cytokine release [1][2]. Therefore, precise dose titration is mandatory to ensure successful outcomes without inducing cellular toxicity [2]. Additionally, comprehensive in vivo pharmacokinetic profiles for Gö 6983 are currently limited compared to other clinical-stage bisindolylmaleimides like ruboxistaurin [2].
6. Future Perspectives
The broad-spectrum PKC inhibition profile of Gö 6983, particularly its potent activity against PKC ζ, positions it as a highly promising therapeutic agent for clinical scenarios involving exaggerated inflammatory responses and ischemia/reperfusion. A primary future application is its potential inclusion in preservation and perfusion solutions for donor organs in transplantation surgery, where it could mitigate vascular dysfunction and inflammation upon reperfusion [2].
Beyond myocardial applications, Gö 6983 holds significant promise in the treatment of cerebral ischemia (stroke). Since PKC isoforms (such as δ and ζ) are implicated in neurotoxicity, neutrophil migration into ischemic brain tissue, and NMDA-induced excitotoxic neuronal cell death, Gö 6983 could serve as a neuroprotective agent during cerebral reperfusion [2]. Furthermore, its ability to strongly inhibit superoxide anion release from leukocytes suggests potential utility in managing allergic conditions, such as asthma and rhinitis, where exaggerated immune responses drive tissue damage [2].
