Scientific Objectives and Rationale: Since the discovery of topoisomerases in 1971 and subsequent development as "druggable" cancer targets, the role of these enzymes and repertoire of biological functions has expanded. In particular, Topoisomerase II (TopoII) enzymes have been shown to play a key role in gene expression implicated in promoting the metastatic phenotype; thus, TopoII drugs may be a relevant treatment against metastatic cancer. Nevertheless, the current TopoII drugs have not been successful in the treatment of metastatic cancer, which we propose is due to the mode by which these drugs inhibit TopoII. Most of the current TopoII drugs were discovered when solid tumors were modeled as a homogeneous population of uncontrolled proliferating cells. The therapeutic model during this era was that tumor cells were more susceptible to cytotoxic agents than healthy cells because of dependence on cell proliferation. Thus, old TopoII drugs were developed because of their ability to form stable complexes with DNA, producing DNA lesions and subsequent cell death. Healthy cells are also susceptible to these drugs, resulting in adverse side effects, including hair loss, sickness, and even secondary tumor formation.

We now know that tumors are comprised of heterogeneous populations of cells with different phenotypes including metastatic cells. Metastatic cells are not dependent on proliferation, and inherent to this phenotype is resistance to cell death and increased invasive potential. We propose that TopoII changes roles from a master regulator of cell proliferation to master regulator of the metastatic phenotype. We hypothesize that in metastatic tumors TopoII is in complex with various proteins, which act in concert to promote metastasis by promoting metastatic gene expression. As a result of these protein complexes, binding sites that accommodate cytotoxic TopoII drugs are hindered or altered, leading to drug resistance. An Achilles heel to this mechanism of drug resistance is that adenine triphosphate (ATP: used by enzymes to change shape or do work) is required to bind TopoII to form protein complexes. Therefore, TopoII-ATP-binding sites conserved and unobstructed by such complexes.

We identified a natural product from a marine sponge that reverts metastatic colon cancer to a benign state, by blocking TopoII dependent metastatic gene expression and metastatic potential. This natural product is an ATP-competitive inhibitor of TopII and is active in a number of drug resistance cancer models. We have designed and synthesized derivatives and show they are active inhibitors. These compounds do not cause DNA lesions; thus, we anticipate few adverse side effects. The proposed research will focus on further developing this novel class of compounds as anti-metastatic agents for the treatment of metastatic breast and colon cancers.

The PI and Career Development: I have dedicated my career to discovering novel therapies for the treatment of cancer. I received my Ph.D. in medicinal chemistry from Arizona State University for discovering and developing novel antitumor agents from nature. As a postdoctoral fellow, I received a National Institutes of Health (NIH) career award to conduct multidisciplinary cancer research at the University of Utah. As a result, my research program is highly multidisciplinary, encompasing chemistry, cancer biology, and an understanding of the clinical treatment of cancer. My unique skills are ideal for the proposed career development and to be a Principal Investigator in the field of colon cancer research. My lab has attracted external funding to discover and develop therapies for the treatment of human disease, notably from the NIH National Eye Institute targeting diabetic eye disease. Funding from the Department of Defense will ensure my continued development and success as a cancer researcher, where I hope to be dedicating my life to eradicate cancer and its debilitating effects.

Research Applicability, Outcomes and Military Relevance: Colorectal cancer (CRC) incidence in the U.S. Military ranks third highest overall and is compounded when veterans and family members are factored in. Hence, there is considerable risk of CRC for active military, veterans, and family members. We show TopoII is a required component of a protein complex known as TCF, shown to regulate metastatic gene expression. TCF is notorious in promoting CRC, including 80% of sporadic CRC and familial adenomatous polyposis. We have characterized TopoII as an Achilles heel to this gene expression. Novel therapies that specifically block TCF have the potential to block or suppress the malignant phenotype, preventing metastasis and tumor recurrence, and may also sensitize CRC to chemotherapy. The proposed research will be the stepping-stone of developing such anti-metastatic agents and will facilitate the translation to patient care within 10 years. However, the discoveries from the proposed research will transform the way scientists discover and develop future cancer drugs and can be used to re-purpose existing cancer drugs deemed safe to be more effective. Finally, our proposed studies to eradicate colorectal cancer can be translated for the treatment of various types of cancer.