Ribonucleotide metabolism and DNA synthesis machinery

The ribonucleotide metabolism and DNA synthesis machinery is a complex network of enzymes and pathways responsible for the production and regulation of nucleotide pools required for genomic integrity. This system encompasses the de novo synthesis of purines and pyrimidines, the salvage pathways, and the critical conversion of ribonucleotides to deoxyribonucleotides by ribonucleotide reductase (RNR) (NCBI, 2023). These processes are essential for DNA replication during the S-phase of the cell cycle and for DNA repair mechanisms following damage (UniProt, 2024). In disease states, particularly cancer and viral infections, this machinery is often upregulated to meet the high demand for DNA precursors needed for rapid cellular or viral proliferation (StatPearls, 2024). Consequently, it has been a cornerstone of chemotherapy for decades, with drugs designed to deplete nucleotide pools or incorporate 'fraudulent' nucleotides into DNA, thereby inducing apoptosis (PubMed, 2021). However, the lack of absolute specificity for diseased cells leads to significant side effects in healthy, rapidly dividing tissues such as the bone marrow and intestinal epithelium (NIH, 2023).

Other names

Nucleotide metabolismDNA replication machineryDe novo nucleotide synthesis pathwayNucleotide biosynthesis and DNA repair machinery

Drugs targeting this machinery primarily act as antimetabolites that interfere with the production of deoxyribonucleotides or act as fraudulent bases. For example, antifolates inhibit dihydrofolate reductase (DHFR), depleting the folate pool necessary for purine and thymidylate synthesis (PubChem, 2024). Fluoropyrimidines inhibit thymidylate synthase (TS), blocking the de novo synthesis of dTMP (StatPearls, 2024). Other agents, like hydroxyurea and gemcitabine, inhibit ribonucleotide reductase (RNR), the rate-limiting enzyme for dNTP production (NCBI, 2023). Additionally, nucleoside analogs are phosphorylated into active forms that compete with natural dNTPs for incorporation into DNA by DNA polymerases, leading to chain termination or defective DNA repair (PubMed, 2021).