A universal GMP assay to aid in PDE research and potential COVID-19 disruption. – Phosphodiesterase enzymes (PDEs) modulate pathways throughout the body. Since unregulated PDEs contribute to disease in many cases, it makes sense therapies that inhibit these enzymes have the potential to treat several different ailments. These include cardiovascular and respiratory issues, diabetes, fibrotic disorders, and peripheral nerve damage. At the regulation level, the PDE enzymes degrade second messengers such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP).¹
These second messengers trigger many cell signaling functions within the human body. Respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma combined affect at least 300 million people worldwide. There is an increasing need for therapeutic agents to treat illnesses that attack the respiratory tract. The obstruction to the airway in COPD is not fully reversible, while it can be in asthma patients. Some COPD patients are given a variety of therapeutic agents combined with roflumilast, a PDE 4 inhibitor to minimize the symptoms.²
Many researchers focus on the ubiquitous cAMP and cGMP second messengers when finding ways to eliminate or decrease symptoms of respiratory diseases. These molecules play essential roles in regulating cellular functions in the lung, including but not limited to the airway smooth muscle (ASM) tone, cell proliferation, differentiation, apoptosis, migration, secretion of inflammatory mediators, deposition of extracellular matrix, and the maintenance of the endothelial and epithelial barrier. A GMP assay is one such tool to aid in this research.
PDE Inhibitors and COVID-19
Just as there are several subtypes of PDEs, there is an assortment of PDE specific and non-selective inhibitors currently being used to treat a variety of different illnesses. Even though there are inhibitors already on the market treating disease, there’s room for discovery, especially as new conditions like COVID-19 emerge.
In fact, Giorgi et al. have suggested the use of PDE4 and PDE5 inhibitors to curb COVID-19 symptoms as they have had success in COPD and high altitude pulmonary edema (HAPE) patients – respiratory diseases with similar pathology to COVID-19. PDE5 is found in airways and vascular smooth muscle and has been shown to regulate via the cGMP-PKG signaling pathway. Inhibitors increase cGMP levels with anti-inflammatory effects and reduce pulmonary hypertension, both of which are issues found in COVID-19 patients.³
As PDEs are critical elements within the cGMP cascade, it’s no surprise that many scientists are working to understand the basic science and move closer to drug discoveries. These are breakthroughs that will assist with the current pandemic and have lasting impacts on many diseases.
GMP Assay for Measuring PDE Activity
Researchers have already started discovering PDE inhibitors to combat a plethora of illnesses, including respiratory disease; however, there is much to learn and even more potential for drug discovery. The Transcreener® AMP2/GMP2 Assay can detect PDE activity through direct detection of GMP (or AMP). A PDE enzyme converts a precursor cGMP to the product GMP, which displaces a fluorescent tracer from a highly selective antibody. The result is a change in fluorescence, which can be read as an FI, FP, or TR-FRET readout. This robust measurement of PDE activity can be used to discover new inhibitors via HTS and lead discovery campaigns, thus helping many patients suffering from respiratory issues and a range of other illnesses.
1. Wikipedia contributors. (2020, December 27). Phosphodiesterase inhibitor. In Wikipedia, The Free Encyclopedia. Retrieved 10:55, January 6, 2021, from https://en.wikipedia.org/w/index.php?title=Phosphodiesterase_inhibitor&oldid=996511629
2. Zuo, H., Cattani-Cavalieri, I., Musheshe, N., Nikolaev, V. O., & Schmidt, M. (2019). Phosphodiesterases as therapeutic targets for respiratory diseases. Pharmacology and Therapeutics, 197, 225–242. https://doi.org/10.1016/j.pharmthera.2019.02.002
3. Giorgi, M., Cardarelli, S., Ragusa, F., Saliola, M., Biagioni, S., Poiana, G., … Massimi, M. (2020). Phosphodiesterase inhibitors: Could they be beneficial for the treatment of COVID-19? International Journal of Molecular Sciences, 21(15), 1–11. https://doi.org/10.3390/ijms21155338