The major focus of the lab is to study the structure function and drug design of the cancer target ribonucleotide reductase (RR). RR is involved in the rate determining step of dNTP synthesis. Due to the essential role played by RR in cell proliferation it is a major cancer target. Frontline chemotherapies such as gemcitabine, fludarabine and cladribine target RR. Gemcitabine is used against pancreatic cancer but as it is a DNA chain terminator it suffers from major side effects. Our lab is developing a new class of RR inhibitors that have improved therapeutic indices over gemcitabine (1-3). We use structure-based in silico drug discovery methods in combination with medicinal chemistry for lead discovery and optimization. The knowledge of the structure function of RR aids with drug design. RR is a multi-subunit enzyme consisting of RR 1 that contains two allosteric sites and the catalytic site that associates with RR 2 the small subunit containing an essential free radical for catalysis. RR has exquisite specificity where it selects for substrates based on the specific nucleotides bound at the allosteric site. Our lab helped unravel the molecular basis for how RR achieves its specificity (4). The allosteric activator ATP and the allosteric inhibitor dATP bind at a distal allosteric site causing the elevation and inhibition of the enzyme’s activity, respectively (4). ATP and dATP binding at the allosteric site cause RR 1 to form hexamers and our lab was the first to structurally visualize RR 1 hexamers (4). The inactive holo-complex is when the ATP induces alpha 6 beta 2 complex which was first structurally visualized using electron microscopy by our lab.
We use in silico drug discovery tools used in the RR project against other cancer and non-cancer targets in the lab. For a sample look at reference 5. Additionally, we study enzyme mechanisms at the proton level using neutron diffraction. X-rays are unable to observe protons but neutrons being a nuclear particle is ideal for visualizing hydrogen atoms. 50% of the protein’s work is conducted by hydrogen which is the missing element in all x-ray structures. Our lab has demonstrated the use of neutron diffraction in elucidating catalytic mechanisms using the cancer target dihydrofolate reductase (DHF are) (6). The lab uses neutron diffraction as a structural enzymatic tool.
PI: Chris Dealwis, Ph.D.