The University of Mississippi School of Pharmacy

“THE BIOLOGICAL-CHEMICAL INTERFACE: ANTI-CANCER DRUG DISCOVERY PROJECTS at OLEMISS”

Dr. Nagle’s research focuses on the discovery of new drugs. His program combines natural products chemistry with cutting edge molecular mechanism-targeted bioassay techniques. Dr. Nagle explores the biomedical potential of natural products as new sources of drug leads for the treatment of cancer. He and Dr. Yu-Dong Zhou (Department of Pharmacognosy) have developed new molecular-based bioassays to investigate natural products for their potential to supplement existing chemotherapeutic agents by acting as promoters of tumor differentiation and cell death. Dr. Nagle’s research examines new methods to rapidly detect the presence of potentially useful anticancer agents that target specific biochemical mechanisms involved in the development and spread of tumors.

Dramatic progress during the past two decades has led to the identification of many genes involved in tumorigenesis and cancer progression, the molecular mechanisms underlying how these genes function, as well as the biochemical/physiological conditions required for tumor growth and metastatic spread. These have revolutionized antitumor drug discovery from traditional cytotoxic methods to more mechanism-based molecular-targeted approaches. Specifically, our research is now aimed at the discovery of new non-cytotoxic molecular-targeted antitumor agents.

Insufficient vascularization produces poorly oxygenated hypoxic regions within rapidly growing solid tumor masses. Alterations in the expression of specific genes in hypoxic tumor cells can promote the survival and metastatic spread of solid tumors. The transcription factor hypoxia-inducible factor-1 (HIF-1) is recognized as the primary mediator of the transcriptional response to cellular hypoxia. HIF-1 regulates the expression of over 100 genes involved in cellular adaptation and survival under hypoxic stress. In cancer patients, HIF-1 activation is directly correlated with advanced disease stages and resistance to conventional therapeutic options. HIF-1 has become an important molecular target for the discovery of new anticancer agents.

HIF-1 is a heterodimer of the bHLH-PAS proteins HIF-1a and HIF-1b (a.k.a. ARNT). Under normoxic conditions, HIF-1a protein is degraded rapidly and is stabilized under hypoxic conditions. Meanwhile, HIF-1b protein is constitutively expressed. Upon hypoxic induction and activation, HIF-1 binds to the hypoxia response element (HRE) present in the promoters of target genes and activates transcription. Figure 1 summarizes the classical oxygen-dependent post-translational regulation of HIF-1protein.

Natural Products have recently become an important source of small molecule chemical entities that regulate various tumor-related molecular targets. Examples of natural products and natural product-derived compounds that have been found to inhibit HIF-1 signaling are illustrated in Figure 2.

Figure 2. Natural Products Regulate HIF-1 Expression and Transcriptional Activation under Hypoxic and Normoxic Conditions.

Dr. Nagle and Dr. Zhou have developed high-throughput bioassays for inhibitors of hypoxia-induced gene expression, in order to discover novel natural products that selectively target hypoxic tumor cells within the solid tumor mass and at poorly vascularized metastatic sites. This project uses a luciferase reporter gene under the control of the hypoxia response element recognized by HIF-1. Over 22,600 crude extracts from plants, marine invertebrates, algae, and microorganisms have been evaluated in the primary T47D human breast tumor cell-based reporter assay for activities that inhibit HIF-1 activation. These samples include 10,560 lipid extracts of marine invertebrates/algae and 7,656 lipid extracts of terrestrial plants from the NCI Open Repository, 3,170 crude extracts of terrestrial plants from the University of Mississippi - National Center for Natural Products Research (NCNPR) Repository, and over 2,000 extracts from the collective repositories of UM researchers Marc Slattery and Dale G. Nagle.

This unique HIF-1 inhibitor discovery effort that combines the chemical diversity offered by natural products with effective bioassays has resulted in the identification of some of the most potent HIF-1 inhibitors known (Figure 3). These include the marine sponge metabolites 7-hydroxyneolamellarin A, furospongolide, latrunculin A, algal compound laurenditerpenol, and plant secondary metabolites manassantin A, manassantin B, manassantin B1, 4-O-demethylmanassantin B, 4´-O-methylsaucerneol, emetine, klugine, 4’-methylalpinumisoflavone, and the cardiac glycosides ouabain and proscillaridin A. Not only are these natural products potent inhibitors of HIF-1 activation in tumor cells, many of these agents appear to function through mechanisms that have not yet been recognized to regulate HIF-1 activity.

Figure 3: Examples of Natural Product-Based Inhibitors of HIF-1 Signaling Identified by Nagle/Zhou Group.

Rather than focus on conventional pharmacognosy, phytochemistry, or traditional natural product chemistry, students in Dr. Nagle’s and Dr. Zhou’s research groups specialize in molecular-targeted drug discovery and in vitro molecular pharmacology of purified natural products from terrestrial and marine sources. Graduate training includes the development of cell-based bioassay systems for drug discovery, and the application of an array of methods in molecular and cell biology for characterizing the pharmacological properties of antitumor natural products. Special requirements for graduate students in Dr. Nagle’s and Dr. Zhou’s research groups include a degree in biochemistry, molecular biology, cell biology, or related biological sciences. Students with a background in chemistry will only be accepted, if the student also has significant biological training. Only highly self-motivated individuals will be considered.