Therapeutic approaches designed to target connexins and pannexins involved in disease were an integral part of this workshop. These consisted of approaches to target specific functional aspects of these channels. Luc Leybaert (Gent University, Belgium) presented connexin hemichannel targeting peptides as tools to protect against cell injury and cell death. He stated that while GJC has major physiological roles, connexin hemichannels are thought to have mostly detrimental effects. As a result, there is a strong need for specific hemichannel blockers that do not affect GJC. He demonstrated that peptides like L2 and Gap19 (Fig.
2) specifically block Cx43-based hemichannels without affecting GJC. Their effect is based on blocking the interaction between the cytoplasmic loop and the C-terminal tail of Cx43. Recent work with the hemichannel blocking peptide RRNYRRNY, the design of which is based on the pharmacophore for CL to CT binding, has the advantage to counteract gap junction channel closure [
18,
28]. He also found that this peptide blocks mitochondrial Cx43 hemichannels and mitochondrial calcium ion uptake, thereby protecting against cell death. Finally, he proposed that connexin channels could be targeted at three levels: the gap junction channels, the hemichannels in the plasma membrane and the mitochondrial hemichannels.
As an critical innovative aspect of this meeting, Pharma and Biotech companies, having a common interest in connexins as potential therapeutical targets, revealed their targeting strategies. Gautam Ghatnekar (FirstString Research, USA) gave an overview of their focus on scar prevention, inflammation reduction, wound healing, and complex tissue regeneration. He claimed that Cx43 is a novel therapeutic target with the potential to manipulate the body’s injury response. With this objective FirstString has implemented a 25aa peptide (αCT1) with a compact 2-domain design based on linkage of an antennapedia internalization domain to the C-terminal PDZ binding domain of Cx43 (CT9 in Fig.
2), originally reported by Gourdie and colleagues [
29]. When applied on cutaneous wounds, αCT1 restores GJC that is lost in injured tissues and reduces excessive inflammatory responses characterizing chronic wounds [
30]. This reestablishes a normal wound repair cascade, accelerates re-epithelialization, and prevents excessive fibrosis. αCT1’s design enables translocation within cells and inhibition of the interaction between Cx43 and zonula occludens-1 (ZO-1). Such inhibition leads to phosphorylation of Ser368 on Cx43, and cellular redistribution of Cx43. The result is a transition of cell-surface Cx43 from hemichannels to gap junction channels, enhancing the stability of gap junction channel aggregates, reducing hemichannel activity and tempering inflammatory responses. FirstString Research is currently advancing a topical αCT1 formulation (Granexin
®) through pivotal human clinical trials for acute and chronic cutaneous wounds. Three phase 2 (n = 276) clinical trials validate the clinical potential of Granexin
® in accelerating the closure of refractory diabetic foot ulcers [
31] and venous leg ulcers [
32], and in the mitigation of acute surgical incision scars. Results of clinical trials support the tolerability and clinically significant efficacy of αCT1 in the treatment of acute and chronic wounds. Its beneficial effects in cutaneous wound healing translate easily to the treatment of other injury pathologies similarly defined within the context of connexin signaling. Mathieu Charvériat (Theranexus, France) presented data on astroglial connexins and modafinil efficacy. Modafinil is a standard of care used in narcolepsy, a rare disease characterized by excessive daytime sleepiness, and it modulates astroglial GJC [
33]. He presented findings in mice on the impact of GJC on the effects of modafinil using flecainide, an anti-arrhythmic registered drug repurposed as an astroglial GJC inhibitor [
34]. Indeed, modafinil enhances astrocyte GJC and he demonstrated that this modafinil-induced effect on GJC was prevented by co-administration with flecainide. He also established that flecainide enhanced the wake-promoting and pro-cognitive effects of modafinil; in addition modafinil/flecainide treatment resulted in a decrease in the number of narcoleptic episodes. This study indicates that flecainide improves the pharmacological profile of modafinil, likely through the normalization of GJC in astroglial networks, opening new perspectives in the management of narcolepsy. In fact, Theranexus recently been announced the results of a proof of concept clinical trial in excessive daytime sleepiness (EDS) induced by sleep deprivation in healthy volunteers. THN102 (combination of modafinil and flecainide, repurposed at low dose as a glial connexin modulator) has a beneficial effect on vigilance and cognition throughout the sleep deprivation when compared to the standard of care modafinil. Finally, Rie Hansen and Anneline Nansen (Zealand Pharma A/S, Smedeland, Denmark) spoke about this biotech company’s leading scientific expertise in turning peptides into medicines with several libraries of gap junction modulating compounds. These include a library of 200 Cx43 CT interacting compounds from 40 mer peptides to modified tripeptides, a library of 20 Cx37 CT-interacting peptides, a library related to danegaptide/rotigaptide (zealandpharma.com) that contains 500 compounds, including hexapeptides, cyclic peptides, modified dipeptides and small molecules, a library containing of 150 modified Gap-peptides, GJC/pannexin1 inhibitors against Cx43, 40, 36, 32, 31.1, 26 and pannexin1, and many more. Zealand is willing to share the compounds for scientific investigation under a material transfer agreement. Within the gap junction field Zealand is running a project focused on accelerated dermal wound healing by specific Cx43 inhibition. Furthermore, Zealand has very recently conducted a phase 2 study focused to treat reperfusion injury after acute myocardial infarction, with danegaptide, a modulator of Cx43. Unfortunately, this study did not meet its primary endpoint. Another company, CoDa Therapeutics Inc., was, unfortunately, unable to participate in the meeting. CoDa has three connexin channel modulators in clinical development, in the first instance for chronic skin wounds and ocular disease. These are an antisense oligodeoxynucleotide (Nexagon
®) which transiently downregulates Cx43 protein expression, an extracellular acting Cx43 peptidomimetic that can be delivered locally or systemically (Peptagon™) (Peptide 5 in Fig.
2) and a small molecule for systemic or oral delivery (HCB1019) [
35]. The latter two are specifically used to target hemichannels. Nexagon
® and HCB1019 are Phase III ready. CoDa has focused significant activity on the connexin hemichannel and has demonstrated efficacy in a number of skin, eye and central nervous system injury and disease animal models where hemichannel block, or transient down regulation of Cx43, reduces oedema, inflammation, vascular leak and lesion spread [
36]. In human eye burns for example, reduced inflammation and recovery of vascular integrity following down regulation of Cx43, leads to epithelial recovery and healing [
37].