Cancer is the second leading cause of death in the United States (more than half a million people each year), and even with billions of dollars in medical effort patients are rarely cured. This dissertation research is devoted to meeting this medical need by providing new cancer therapeutics that are more potent and safer than current chemotherapies. This is achieved by using two state of the art anticancer “warheads”: 1) gold nanoparticle (AuNP) technology and 2) a new class of epigenetic anticancer small molecules, histone deacetylase inhibitors (HDACi). These warheads are then selectively delivered to cancer cells via “homing devices” targeted to receptors that are overexpressed in the cancers. This work primarily focuses on the androgen receptor (AR) to target prostate cancer. The 1st chapter sets the stage, providing scientific rationale and background for the central hypothesis: small molecules that engage the AR can, upon conjugation to a therapeutic agent, enable selective delivery of that agent to prostate cancer cells. Chapter 2 delves into the structural molecular biology of the androgen receptor. There is a survey of the crystallographic data for all nuclear receptors, providing structural information which is used to build AR homology models for antagonist and inverse agonist modes of ligand binding. These models are used to design AR targeting ligands (Chapters 3, 5, 6 and 7). The application of the targeting technology is illustrated by attaching them to AuNPs for selective delivery to prostate cancer cells (Chapter 3). Next, in order to appreciate the importance of using targeting agents in HDACi cancer therapeutics, we reviewed this recently emerged field in Chapter 4. In this chapter we argue that the failure of HDACi in solid tumors, despite more than 500 clinical trials in the last decade, is primarily due to an inability of these small molecules to accumulate at effective concentrations in the cancer. We provide an analysis of the paradigms being pursued to overcome this barrier, including HDAC isoform selectivity, localized administration, and targeting cap groups to achieve selective tissue and cell type distribution. In Chapter 5, this last approach (targeting cap groups, or a “homing device”) is illustrated with HDACi targeted to prostate cancer via antiandrogens that bind the AR. The second generation of improved “homing devices” is disclosed in Chapter 6 (for both AuNPs and HDACi), in addition to preliminary ADMET data and safety studies in mice. Excitingly, our three dimensional understanding of binding to the AR allowed design and structure-activity-relationship studies that lead to the first reported examples of AR inverse agonists (Chapter 7) Several points of significance: • AuNP targeted to AR ∙ have the strongest binding affinity ever reported (IC50 ~14 picomolar) ∙ are actively recruited to prostate cancer cells ∙ overcome treatment resistance in advanced prostate cancer cells ∙ exhibit nanomolar anticancer potency ∙ resolved the identity of the “membrane AR” as the GPRC6A • HDACi targeted to AR ∙ have HDACi activity and AR binding affinity superior to their clinical precursors ∙ exhibit potent AR antagonist activity ∙ induce AR translocation to the nucleus in a HDACi dependent fashion ∙ selectively and potently kill prostate cancer cells that express AR ∙ are safer than Tylenol®, as tested in small animals • Pure AR binding ligand studies ∙ resulted in the discovery of the first examples of AR inverse agonists, which are vastly more potent that clinically available antiandrogens for prostate cancer ∙ work via a never-before-seen mechanism of action, by localizing to the nucleus and recruiting corepressors to actively shut off AR genes

The enhanced expression of histone deacetylases (HDACs) in a variety of malignancies drew attention to investigate a new category of anti-cancer drugs that are based on the inhibition of those enzymes. Valproic acid (VPA) is a well-known antiepileptic drug that exhibits antitumor activities through inhibition of HDACs class I and IIa. Cancer stem cells (CSCs) have been recognized to drive the tumor growth and progression hence; attention has been given to target this small subpopulation of CSCs rather than the whole bulk tumor cells. CD133 is considered to be a CSC marker in several tumors and its transcription is strongly influenced by epigenetic changes that will be altered upon administration of histone deacetylase inhibitors (HDACi) in cancer treatment. Therefore, we evaluated the epigenetic and cytotoxic effects of treatment with 1 mM VPA in combination with other chemotherapeutics and its influence on the expression of CD133 in human neuroblastoma (NB) cell lines. Our results revealed that addition of VPA to DNA-damaging chemotherapeutics induced a synergistic anti-tumor effect that was associated with caspase-3 dependent induction of apoptosis in UKF-NB-4 cells. This synergism was related to the increase of the acetylation status of histones H3 and H4 and was only produced either by...