department of pharmacology

Tessianna Misko

Research Abstract

Ribonucleotide reductase (RNR) is a multi-subunit enzyme that catalyzes the rate-limiting step of de novo DNA synthesis. Tight control of dNTP pools is vital for both the cell survival and proliferation. Human ribonucleotide reductase (hRNR) controls the cellular dNTP pool due to the critical role it plays in de novo dNTP synthesis and is a well established cancer target. Drugs such as Gemcitabine, Fludarabine, Cladarabine, Clofrabine and Hydroxyurea target hRNR. Most of these drugs that target RNR are the nucleoside based antimetabolites class of drugs and unfortunately most nucleoside analogs cause severe side-effects as they suffer from the lack of specificity and the poor conversion of the prodrug to the drug by the cellular kinases. There are several advantages of targeting allosteric modulator binding sites in drug discovery over orthosteric sites where endogenous ligands bind. For human RNR, there is tight regulation that occurs both at the transcriptional and at the allosteric levels depending on the growth cycle of the cell (S, G0 and G2M phases). During the S-phase of the cell cycle, RNR is regulated allosterically. The allosteric regulation involves two allosteric sites called the activity site (A-site) and the specificity site (S-site), which regulates activity at the catalytic site (C-site) of the enzyme. Developing allosteric modulator that targets hRNR is an attractive alternative where drugs will be specific to a single target leading to reduced side-effects. Using a druggable site that our lab recently discovered (M site), work is being done to target and inhibit this site which modulates the RNR activity. Through the use of x-ray crystallography, biochemical assays and cancer cell culture work, we hope to develop a drug to target RNR for the use in cancer therapy.