De novo pyrimidine nucleotide biosynthesis is activated in proliferating cancer cells in response to an increased demand for synthesis of DNA, RNA and phospholipids. The synthesis activates via oncogenic pathways, such as Myc, PI3K, PTEN and mTOR.
Dihydroorotate dehydrogenase (DHODH) locates on the surface of the inner mitochondrial membrane, which catalyzes the fourth enzymatic step, the ubiquinone-mediated oxidation of dihydroorotate to orotate in the de novo pyrimidine synthesis pathway.
GEMSTM technology phenotypic screening platform identifies PTC299 is an inhibitor of the translation of VEGFA mRNA.
In addition, the author performs extensive biochemical characterization of PTC299. Therefore, PTC299 interacts with and inhibits DHODH. DHODH is a rate limiting enzyme in the de novo biosynthesis of pyrimidine nucleotides.
PTC299 inhibits hypoxia-induced VEGFA protein production in HeLa cells. Meawhile, PTC299 has an EC50 of 1.64 ± 0.83 nM in a dose-dependent and stereo-selective manner. On the other hand, PTC299 dose-dependently inhibits VEGF 5’-UTR-mediated production of the VEGFA165-V5 protein. Futhermore, PTC299 decreases the levels of newly synthesized VEGFA protein. However, Total protein synthesis do not decrease. In a word, PTC299 results in the inhibition of VEGFA translation. The suppression of VEGFA mRNA translation requires the VEGFA 5’-UTR.
In vivo, PTC299 dose-dependently inhibits the growth of HT1080 fibrosarcoma in a mouse tumor xenograft model, without overt toxicity or significant body weight changes at any dose when compared to treatment with the vehicle alone. Meanwhile, PTC299 resulted in a dose-dependent reduction in the concentrations of intratumor and circulating plasma human VEGFA relative to those in control mice
Further study suggests that inhibition VEGFA translation and cell cycle arrest are two separate downstream effects of inhibiting de novo pyrimidine nucleotide synthesis. In fact, PTC299 interacts with and inhibits DHODH activity. Meanwhile, PTC299 demonstrates broad and potent inhibition of hematologic cancer cell proliferation.
In summary, PTC299 has greater potency, good oral bioavailability and lack of off-target kinase inhibition and myelosuppression. Thus, it may be useful for the targeted treatment of hematologic malignancies.