Inactivation of Non-canonical Cyclic Nucleotides: Hydrolysis and Transport

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

cCMP and cUMP phosphodiesterases in viral infections

In bacteria, cCMP and cUMP have a key role in defense against infection with bacterial viruses. Bacteriophages encode phosphodiesterases (PDEs; 'nucleases'; Apyc1), which cleave cCMP/cUMP, counteracting this defense. We propose that PDEs are of broader biological relevance, including cCMP/cUMP-cleaving PDEs of eukaryotic viruses, which may constitute new drug targets.

Alteration of the soluble guanylate cyclase system in coronary arteries of high cholesterol diet-fed rabbits

This study aimed to investigate how atherosclerosis affects the soluble guanylate cyclase (sGC) system in coronary arteries. Rabbits were fed a normal diet for 12 weeks (N group) or a diet containing high cholesterol (1%) for 4 weeks (S-HC group) and 12 weeks (L-HC group). Cholesterol deposition in the intima of coronary arteries was observed in the S-HC group, but the formation of an atherosclerotic plaque was not observed. In contrast, a major plaque developed in the L-HC group. The relaxant response of isolated coronary arteries to sodium nitroprusside (SNP, nitric oxide donor) was not different between the N and S-HC groups, whereas the response in the L-HC group was markedly attenuated. The relaxation induced by BAY 60-2770 (sGC activator) tended to be augmented in the S-HC group, but it was significantly impaired in the L-HC group compared to that in the N group. sGC β1 immunostaining was equally detected in the medial layer of the arteries among the N, S-HC, and L-HC groups. In addition, a strong staining was observed in the plaque region of the L-HC group. cGMP levels in the arteries stimulated with SNP were identical in the N and S-HC groups and slightly lower in the L-HC group than the other groups. BAY 60-2770-stimulated cGMP formation tended to be increased in the S-HC and L-HC groups. These findings suggest that the sGC system was not normal in atherosclerotic coronary arteries. The redox state of sGC and the distribution pattern are likely to change with the progression of atherosclerosis.

cGMP: a unique 2nd messenger molecule - recent developments in cGMP research and development

Cyclic guanosine monophosphate (cGMP) is a unique second messenger molecule formed in different cell types and tissues. cGMP targets a variety of downstream effector molecules and, thus, elicits a very broad variety of cellular effects. Its production is triggered by stimulation of either soluble guanylyl cyclase (sGC) or particulate guanylyl cyclase (pGC); both enzymes exist in different isoforms. cGMP-induced effects are regulated by endogenous receptor ligands such as nitric oxide (NO) and natriuretic peptides (NPs). Depending on the distribution of sGC and pGC and the formation of ligands, this pathway regulates not only the cardiovascular system but also the kidney, lung, liver, and brain function; in addition, the cGMP pathway is involved in the pathogenesis of fibrosis, inflammation, or neurodegeneration and may also play a role in infectious diseases such as malaria. Moreover, new pharmacological approaches are being developed which target sGC- and pGC-dependent pathways for the treatment of various diseases. Therefore, it is of key interest to understand this pathway from scratch, beginning with the molecular basis of cGMP generation, the structure and function of both guanylyl cyclases and cGMP downstream targets; research efforts also focus on the subsequent signaling cascades, their potential crosstalk, and also the translational and, ultimately, the clinical implications of cGMP modulation. This review tries to summarize the contributions to the "9th International cGMP Conference on cGMP Generators, Effectors and Therapeutic Implications" held in Mainz in 2019. Presented data will be discussed and extended also in light of recent landmark findings and ongoing activities in the field of preclinical and clinical cGMP research.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.