Human telomeres contain tandem repeats of the sequence TTAGGG, ending in single-stranded 3'-overhangs. Telomeric DNA protects the chromosomes from degradation and end-to-end fusion. In normal cells, the telomeres are shortened with each replication cycle, which eventually leads to natural cell aging (senescence). Unlike somatic cells, 80% of cancer tissues upregulate telomerase, the enzyme involved in maintaining the single-stranded overhang at a constant length. This process renders cancer cells immortal and is considered one of the major contributing factors to tumorigenesis. Hence, telomerase is deemed as a valuable target for anti-cancer treatment. The single-stranded overhang can fold into a unique DNA secondary structure called G-quadruplex under physiological conditions, with the four guanine bases linked via Hoogsteen hydrogen bonding. Telomerase is unable to process the folded form but requires a single DNA strand. Thus, molecules that induce and trap this non-processible conformation have the potential to disrupt limitless cell proliferation and act as inhibitors of cancer cell growth. The main goal of the current study was to develop platinum-intercalator conjugates which can stabilize the telomeric G-quadruplex by pi-stacking and covalently bind to it by platination. In a previous study our platinum-acidine agent, PT-ACRAMTU showed enhanced affinity for adenine bases in the loop regions of the telomeric G-quadruplex, which significantly differs from classical guanine-binding platinum drugs. To enhance the binding selectivity of our complex for quadruplex DNA, we replaced acridine in PT-ACRAMTU with a perylene ligand which complements the dimensions of a G-quartet. The "best fit" of the newly designed agent was established by molecular mechanics/molecular dynamics (MM/MD) simulations. In addition, we used circular dichroism (CD) spectropolarimetry, electrospray mass spectrometry (ESI-MS), and isothermal titration calorimetry to study the first (reversible) DNA binding of this compound. The results indicate that our platinum-perylene agent binds, with very high affinity, to G-quadruplex with a 2:1 stoichiometry, and stabilizes the DNA in its antiparallel conformation. We also found that the DNA and RNA forms of the telomeric sequence are recognized differently. Thus, platinum-perylenes may have applications in DNA-targeted chemotherapy.
2005-present: Doctor of Philosophy, Department of Chemistry, Wake Forest University, Winston Salem, NC
2000-2004: Bachelor of Science, Chemistry Department, Nankai University, Tianjin, P. R. China
POSITIONS AND HONORS
2008-present: Research Assistant, National Institute of Health
2007-2008: Teaching Assistant, Department of Chemistry, Wake Forest University, Winston-Salem, NC
2006-2007: Research Assistant, National Institutes of Health
2005-2006: Teaching Assistant, Department of Chemistry, Wake Forest University, Winston-Salem, NC
Zhidong Ma, Lu Rao & Ulrich Bierbach: Replacement of a Thiourea-S with an Amidine-NH Donor Group in a Platinum-Acridine Antitumor Compound Reduces the Metal�s Reactivity with Cysteine Sulfur. J. Med. Chem., 2009, 52 (10), 3424-3427
Lu Rao & Ulrich Bierbach: Kinetically Favored Platination of Adenine in the G-Rich Human Telomeric Repeat, J. Am. Chem. Soc., 2007, 129 (51), 15764-15765.
Lu Rao, Joshua D. Dworkin, William E. Nell & Ulrich Bierbach, Targeting Telomeric DNA with Platinum-Perylene Conjugates, 2009 14th International Conference on Biological Inorganic Chemistry (ICBIC), Nagoya, Japan, 2009 July 25-30
Lu Rao & Ulrich Bierbach, Spectroscopic and Molecular Mechanics/Dynamics Studies of a Platinum-based G-quadruplex-Specific Agent, 2008 60th Southeastern Regional American Chemical Society Meeting (SERMACS), Nashville, Tennessee, 2008 November 12-15
Lu Rao, Joshua D. Dworkin & Ulrich Bierbach, Design and Evaluation of Platinum Agents Targeted at Human Telomeric DNA, 2007 59th Southeastern Regional American Chemical Society Meeting (SERMACS), Greenville, South Carolina, 2007 October 24-27
Lu Rao & Ulrich Bierbach, Studies on Intercalator-Driven Platination of Adenine in Telomeric DNA, 2007 The 1st International Meeting on Quadruplex DNA, Louisville, Kentucky, 2007 April 21-24