Cancer has been thought of as a mostly genetic phenomenon, however recent research into epigenetic causes of cancer emphasizes that these causes of cancer are also important. RIZ1 is a tumor suppressor which is silenced in many human leukemias, such as human Acute Myeloid Leukemia and Chronic Myelogenous Leukemia. It was the goal of this thesis to re-express RIZ1 using three epigenetic drugs: decitabine, a DNA methylation inhibitor, Trichostatin A, a histone deacetylase inhibitor and chaetocin, an inhibitor of SUV39h1. Cells were treated with these drugs and analyzed for toxicity, methylation status, and RIZ1 expression levels. The synergy between the drugs was also determined. It was found that cells treated with decitabine and chaetocin had an induction of RIZ1 expression. Chaetocin induced RIZ1 expression without affecting the methylation status of the cell. Also, cells which were treated with decitabine paired with either Trichostatin A or chaetocin showed the highest amount of RIZ1 expression. Cells treated with all three drugs together had a higher amount of RIZ1 expression than cells treated with either drug alone, however had less expression than cells which had been treated with decitabine paired with either Trichostatin A or chaetocin. Using these data a model was developed in which H3K9 methylation is the dominant epigenetic event in transcriptional silencing.

Cancer has been thought of as a mostly genetic phenomenon, however recent research into epigenetic causes of cancer emphasizes that these causes of cancer are also important. RIZ1 is a tumor suppressor which is silenced in many human leukemias, such as human Acute Myeloid Leukemia and Chronic Myelogenous Leukemia. It was the goal of this thesis to re-express RIZ1 using three epigenetic drugs: decitabine, a DNA methylation inhibitor, Trichostatin A, a histone deacetylase inhibitor and chaetocin, an inhibitor of SUV39h1. Cells were treated with these drugs and analyzed for toxicity, methylation status, and RIZ1 expression levels. The synergy between the drugs was also determined. It was found that cells treated with decitabine and chaetocin had an induction of RIZ1 expression. Chaetocin induced RIZ1 expression without affecting the methylation status of the cell. Also, cells which were treated with decitabine paired with either Trichostatin A or chaetocin showed the highest amount of RIZ1 expression. Cells treated with all three drugs together had a higher amount of RIZ1 expression than cells treated with either drug alone, however had less expression than cells which had been treated with decitabine paired with either Trichostatin A or chaetocin. Using these data a model was developed in which H3K9 methylation is the dominant epigenetic event in transcriptional silencing.

Chronic myelogenous leukemia is a myeloproliferative hematopoietic stem cell disease resulting from a reciprocal translocation that gives rise to BCR-ABL, a constitutively active tyrosine kinase. Imatinib and other tyrosine kinase inhibitors are currently standard therapy; however, point mutations often lead to drug resistance and disease relapse often occurs due to the persistence of quiescent leukemia stem cells that are shielded by stromal factors within the bone marrow microenvironment. In an effort to develop new therapies capable of eradicating these elusive cells, a novel approach has been proposed in which the biochemical properties of cancer cells are targeted. It has been established that one such property is oxidative stress due to the increased production of reactive oxygen species, which makes cancer cells especially dependent on their antioxidant systems to maintain redox homeostasis. Recent studies demonstrate that chaetocin, a mycotoxin produced by Chaetomium species fungi, possesses potent and specific antimyeloma activity due in part to its ability to inhibit thioredoxin reductase-1, a central oxidative stress remediation enzyme. In this study, the effectiveness of chaetocin against leukemia stem cells has been investigated using in vitro and in vivo murine chronic myelogenous leukemia models. Our results indicate that: chaetocin and imatinib function synergistically in decreasing cell viability, inducing apoptosis, and inhibiting the colony formation of chronic myelogenous leukemia cells in vitro; that chaetocin in combination with imatinib reduces leukemia stem cell frequency in vivo; that chaetocin increases intracellular reactive oxygen species levels; and that chaetocin does not disrupt the proliferation and differentiation of normal murine hematopoietic stem cells. Surprisingly, our results also show that while bone marrow stromal factors inhibit the activity of imatinib, they potentiate the activity of chaetocin, indicating that chaetocin could potentially be used to target leukemia stem cells within the bone marrow niche.