Topical Nitric oxide-releasing PDE5 inhibitor for wound healing indications.

[madman]

TOP-N53: A Clinical Drug Candidate for the Treatment of Non-healing Wounds

Reto Naef, Hermann Tenor, and Guido Koch





Abstract: Chronic non-healing wounds impose a huge burden on patients and health care providers. In spite of improvements in standards of care, there are no effective and safe treatments that promote new tissue formation and wound closure in ailments such as diabetic foot ulcer, pressure ulcer, venous leg ulcer, or digital ulcer in systemic sclerosis. Endothelial dysfunction, which associates with impaired endogenous nitric oxide formation is assumed to be the main disease mechanism in chronic, non-healing wounds in diabetic and elderly patients as well as in digital ulcers in systemic sclerosis. Topadur Pharma has invented small molecular weight nitric oxide-releasing PDE5 inhibitors, which by modulating a key enzyme system of intracellular signaling may address chronic non-healing wounds. The promising first drug candidate TOP-N53 is currently in early clinical development. Here we describe for the first time the design of TOP-N53 and the synthesis of the clinical GMP batch.




1. Chronic Non-healing Wounds with a High Medical Need

TOPADUR Pharma AG owns an R&D platform targeting several aging-related diseases, including new therapies for wound healing indications. In spite of the current standard of care, there remains a high medical need for effective drug treatment of chronic wounds such as diabetic foot ulcer, pressure ulcer, digital ulcers in systemic sclerosis, venous leg ulcers, dental wounds, or scars from surgery performed on elderly patients, where wound healing is delayed or fails.




2. Design of Dual Function NO-releasing PDE5 Inhibitors

When Topadur Pharma AG was founded in 2015, sGC and PDE5 were validated targets and several drugs were on the market and in development based on the NO/sGC/cGMP signaling cascade. cGMP elevating drugs impart vasodilatation but antifibrotic, anti-inflammatory, anti-proliferative, and anti-cancer effects have been described as well.[14]




3. Product/Service and Outlook

The medicinal chemistry project resulted in a remarkably potent and efficacious drug candidate which translated well into efficacy in preclinical wound healing models.[18] TOP-N53 is currently embarking on clinical development as a topical treatment for wound healing indications.

 

[Nelson Vergel]

I wonder what effect it has on erections.

 

[madman]

Fig. 1. Endothelial dysfunction and regulation of cGMP. In vascular smooth muscle cells intracellular cGMP is controlled by the balance between synthesis (for example by sGC) and degradation (for example by PDE5). Endothelial dysfunction can be attributed to impaired endogenous NO release from endothelial cells resulting in reduced sGC activation and less cGMP in vascular smooth muscle cells. Finally, impaired microcirculation may ensue. Consequently, the supply of oxygen and nutrients as well as waste elimination would be compromised that deteriorates tissue regeneration and delays wound healing.

 

[madman]

Fig. 2. TOP-N53, a highly potent NO-releasing PDE5 inhibitor elevates intracellular cGMP by a synergistic interaction between an enhanced cGMP synthesis secondary to stimulation of sGC by the released NO, and reduced cGMP degradation caused by inhibition of PDE5 by TOP-N53 and its active and more potent metabolite, TOP-52 in cells where sGC and PDE5 are expressed. Both NO and TOP-52 are products of the ‘bioactivation’ of TOP-N53.

 

[madman]

Fig. 3. Binding mode of PDE5 inhibitors to catalytic center in PDE5

 

[madman]

Fig. 4. Molecular structures of Sildenafil, TOP-N53, and TOP-52.

 

[madman]

Fig. 5. Docking of TOP-N53 into PDE5. a) without H2O solvate b) with H2O solvate in the protein.

 

[madman]

Table 1. Inhibition of human recombinant PDE5A1 by TOP-N53, TOP-52, and reference PDE5 inhibitors. IC50 (half-maximum inhibition) values were calculated from concentration-dependent inhibition curves recorded at 0.5 µM cGMP and shown as means from at least 3 independent experiments.

TOP-52, the active metabolite which is formed together with nitric oxide from TOP-N53 after intracellular bioactivation is a very potent PDE5 inhibitor (Table 1). The increased activity over TOP-N53 can be explained by the additional binding interaction with the polar residuesSer 661 and Gln 663 (Fig. 6). The intracellular release of locally active nitric oxide together with the very potent PDE5 inhibitor TOP-52 makes Topadur’s newly invented enzyme regulation system unique and led to unprecedented efficacy to elevate intracellular cGMP levels.



TOP-N53 was a potent inhibitor of PDE5 reflected by an IC50 of 1.18 nM. TOP-52, its main metabolite after the release of NO was revealed to be an even more potent inhibitor of PDE5 with an IC50 of 0.1 nM. In fact, compared with a range of marketed PDE5 inhibitors, TOP-52 was the most potent molecule (Table 1).



*In cellular assays, TOP-N53 was by far more effective than its corresponding PDE5 inhibitor TOP-52 or reference PDE5 inhibitors to increase cGMP as exemplified in washed human platelets (Fig. 7), likely reflecting the synergism inherent in TOP-N53 (Fig. 2).

 

[madman]

Fig. 6. Binding of TOP-N53 to PDE5.

Fig. 7. Effects of TOP-N53, TOP-52, and reference PDE5 inhibitors on cGMP in human platelets. Results are shown as means ± SEM from platelets of three donors. cGMP was measured after a 2 h incubation time and in presence of 1 µM riociguat and 100 nM BAY 60-7550, a PDE2 inhibitor.

 

[madman]

Scheme 1. GMP synthesis of TOP-N53