Extending apo-sGC to haem-sensing proteins and a landscape of haem mimetic pharmacophores with broad applications

Haem, a fundamental prosthetic group, mediates oxygen transport and metabolism in proteins while exerting signalling functions in haemolytic disorders through its pro-oxidant, pro-inflammatory, and cytotoxic effects when unbound. In addition to its established functions, haem plays a crucial role in regulating haem-responsive proteins such as apo-soluble guanylate cyclase (apo-sGC) and the REV-ERB nuclear receptors, both of which are targets for clinical drug development. Through a comprehensive series of in vitro assays involving apo-sGC, REV-ERB, and four other haem-sensing proteins—Slo1/BK potassium channel, cystathionin-β-synthase, Gis1 transcription factor, and hNaV1.5 sodium channel—we discovered unexpected interactions between apo-sGC activators, traditionally developed for cardiovascular and pulmonary conditions, and REV-ERB, along with most of the tested haem-responsive proteins. Heme concentration dynamics were unaffected. Conversely, REV-ERB ligands, designed initially to address sleep disorders and metabolic syndromes, influenced apo-sGC activity. This investigation significantly broadens our understanding of the pharmacological implications of haem and haem mimetics, highlighting the importance of integrating haem-sensing protein assays into the pharmacological profiling of a class of haem mimetic pharmacophores such as apo-sGC activators and REV-ERB modulators to mitigate potential off-target effects and adverse reactions.