| Angiogenesis is required for normal physiology but also contributes to the pathogenesis of diseases including cancer. Existing antiangiogenic drugs have been only modestly successful and have significant side effects. Thus, this thesis is an effort to identify and understand the mechanism of new inhibitors of angiogenesis.;In one approach, 741 binary combinations of clinical drugs were screened for synergistic inhibition of endothelial cell (EC) proliferation. Itraconazole, an antifungal, and cyclosporin A (CsA), an immunosuppressant, had significant synergy in inhibiting EC proliferation, tube formation, and sprouting. The mechanisms of CsA and itraconazole in antiangiogenesis were investigated. A non-immunosuppressive analog of CsA, N-MeVal-4-CsA, retained potent in vitro and in vivo antiangiogenic activity indicating that immunosuppression and antiangiogenesis have distinct mechanisms. Cyclophilins are inhibited by both CsA and N-MeVal-4-CsA suggesting they may be the relevant target of CsA for its antiangiogenic activity.;Itraconazole inhibited the signaling of the VEGF receptor 2 (VEGFR2), a key receptor in angiogenesis, and blocked its cell surface expression and the maturation of its N-linked sugars. This suggests that itraconazole may inhibit intracellular trafficking. A study of the itraconazole structure activity relationship showed that the cis stereoisomers of itraconazole were more potent against EC proliferation than the trans series and revealed trends for potency against glycosylation and EC proliferation with respect to the sec-butyl side chain. Analogs with increased antiproliferative activity were identified.;A screen of 47 clinically approved steroids identified 13 compounds with IC50s for EC proliferation of < 5 muM. Other than four cardiac glycosides, these hits universally inhibited cholesterol trafficking whereas a subset inhibited mTOR signaling (itraconazole inhibits both), suggesting these activities are not always linked but that the former may be common to all antiangiogenic steroids. The most potent non-cardiac glycoside hit, danazol, was further characterized.;The findings of this work pertaining to the mechanism or activity of clinical drugs have the potential to motivate phase II clinical trials since these drugs have been deemed safe in humans. Those compounds which are analogs of known drugs but with increased potency or unique activities may serve as lead compounds for further medicinal chemistry or mechanistic exploration. |
