Researchers look to discover a CPS1 inhibitor with an eye on cancer – Without properly functioning carbamoyl-phosphate synthetase I (CPS1), large amounts of highly toxic ammonia is able to accumulate in the body contributing to neurological conditions.2 Increased levels of the enzyme have been found in some cancers including lung adenocarcinoma (LADC).1 When overexpressed, CPS1 can eliminate ammonia from quickly proliferating cancer cells to aid in the growth of the tumor. Moreover, the enzyme plays a role in pyrimidine synthesis which also assists in tumor growth.3
The mechanisms of this are not completely understood at this time; however, the heterodimeric carbamoyl phosphate synthase (CPSase) enzyme produces carbamoyl phosphate which is the starting material for both urea and pyrimidines. In addition to carbamoyl phosphate, ADP is a byproduct of the ATP dependant phosphorylation. An increase in CPS1 has been associated with a decreased survival probability and poorer prognosis in some cancer types.3
Due to research linking an abundance of CPS1 with cancer, Yao et al. set out to discover CPS1 inhibitors to treat cancer and gain more insight into the pathways involved.3 After first performing a high-throughput screening (HTS) followed by subsequent verification screenings, the scientists found a molecule to inhibit CPS1 without affecting the activity of carbamoyl phosphate synthetase II (CPS2). Both CPS1 and CPS2 enzymes have similar functions and are encoded by the same gene.3
Once the inhibitor, H3B-120, was discovered, additional assays were executed to further determine activity and functionality in relation to other proteins involved in pyrimidine synthesis. It’s not enough to discover a molecule to inhibit overexpressed CPS1 tumor cells, the inhibitor should not change the function of other proteins along the way.
Transcreener ADP CPS1 Inhibitor Assay
N-acetylglutamate (NAG) is a cofactor to CPS1 and without it, enzymatic activity is lower. The Transcreener® ADP² FP Assay was executed to examine the relationship between NAG and H3B-120. This assay has the ability to detect any enzyme that converts ATP to ADP.
Through various assay types, the researchers not only found a CPS1 inhibitor with the potential to treat specific cancers, but they were able to gain insight into how the inhibitor interacts within the pyrimidine synthesis pathway.
- Celiktas, M., Tanaka, I., Tripathi, S. C., Fahrmann, J. F., Aguilar-Bonavides, C., Villalobos, P., … Taguchi, A. (2017). Role of CPS1 in cell growth, metabolism, and prognosis in LKB1-inactivated lung adenocarcinoma. Journal of the National Cancer Institute, 109(3), 1–9. https://doi.org/10.1093/jnci/djw231
- Conditions, G. (n.d.). Genetics Home Reference CPS1 gene, 1–4. https://ghr.nlm.nih.gov/condition/carbamoyl-phosphate-synthetase-i-deficiency
- Yao, S., Nguyen, T.-V., Rolfe, A., Agrawal, A. A., Ke, J., Peng, S., … Bolduc, D. M. (2020). Small Molecule Inhibition of CPS1 Activity through an Allosteric Pocket. Cell Chemical Biology, 1–10. https://doi.org/10.1016/j.chembiol.2020.01.009