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Doctor of Philosophy



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The current GAG anticoagulants such as heparin, heparin derivatives, and vitamin K antagonists, such as warfarin continue to be the backbone of anticoagulant therapy. These drugs act through an indirect mechanism to convey inhibition of several coagulation enzymes. However, xv their use leads to several serious adverse effects, such as excessive bleeding risk and unpredictability of patient response. Regardless of their clinical achievement, every individual agent is accompanied by several side effects, particularly major/minor bleeding, thrombocytopenia, drug-food or drug-drug interactions, or absence of antidote. Of all these side effects, bleeding, and a lack of an effective antidote to reverse excessive anticoagulation continue to challenge the recently introduced target specific anticoagulants such as fondaparinux, dabigatran, apixaban, and rivaroxaban, despite their overall improved safety profile in comparison heparins and coumarins anticoagulant derivatives. Several lines of evidence have suggested that factor XIa (FXIa) is a promising target for developing a new line of anticoagulants with a potentially minimal risk of bleeding [6, 7]. For example, hemophilia C patients with congenital FXI (Factor XI) deficiency are known to suffer minimal bleeding, and the severe deficiency of FXI has been resolved through FXI concentrates [8–10]. Epidemiologic studies show that FXI-deficient patients are relatively less susceptible to venous thrombosis [11] and ischemic stroke [12]. On the other hand, excessive levels of FXIa enhanced women’s risk for cardiovascular diseases [13]. Animal arterial, venous, and cerebral thrombosis models have supported these human studies and validated FXIa as an attractive drug target [14]. FXI-null mice do not develop clots in the FeCl3-induced carotid artery model while showing no effect on bleeding time [15]. Lastly, FXIa inhibition appears to only interrupt the pathological coagulation process (thrombosis) but not the physiological process (hemostasis) [16, 17]. To develop a new line of anticoagulants, we recently introduced non-saccharide glycosaminoglycan mimetics (NSGMs) sulfated pentagalloyl glucopyranoside (SPGG) that bind to coagulation factors and induce inhibition, which potently inhibited FXIa [6,7]. Structurally, xvi SPGG is a mixture that consists of more than a thousand species. In the process to improve potency, the Desai lab designed a pure SPGG analog, Sulfated Chiro-inositol (SCI). The basic principle used in the design of SCI was that an appropriate anionic scaffold would target the highly electropositive heparin-binding site(s) of FXIa, resulting in allosteric dysfunction of its catalytic function. Since SPGG inhibition of human FXIa had shown promising plasma and whole blood anticoagulant potential, and the SCI is an analog of SPGG, the specific hypothesis of the proposed project is that SCI will target FXIa [6, 7]. Hence, we wanted to respond to a few fundamental questions: Is the SCI selectively targeting FXIa? Can FXIa inhibition by SCI be reversed? To address these critical questions to improve our understanding of the novel allosteric mechanism of FXIa inhibition by SCI, the following proposed studies will be conducted. Furthermore, the laboratory of my advisor Dr. Umesh Desai discovered G2.2 as an anticancer agent. The G2.2 preliminary experimental investigations that were performed on animals revealed that G2.2 displayed no vascular bleeding properties. Also, G2.2 was tested in several cancer cell lines (HT29, HCT116) and was found to selectively inhibit the growth and self-renewal of cancer stem cell-like (CSC). Our hypothesis of the second proposed studies is that these small NSGMs molecules will bind to plasma proteins, affecting their signaling pathway downstream and inducing some changes in physiological hemostasis. Thus, it is essential to understand the molecular interaction of SCI and G2.2 with FXIa and other plasma proteins and evaluate the nature of allosteric inhibition. In these proposed studies, SCI and anticancer agents will be evaluated for its anticoagulant activity in human pool platelet-poor plasma (PPP), (PT and, TT, APTT), direct enzyme inhibition, and fresh whole blood (TEG). Furthermore, the anticoagulant properties of these NSGMs will be determined and compared to the inhibition activity of enoxaparin. The second proposed study is xvii in vivo animal model tail bleeding and venous thrombosis assays will be employed. In addition, SCI and anti-cancer agents will be tested in male wild-type ICR male mice and rats to identify antithrombotic activity. The current proposed studies will provide a comprehensive understanding of the pharmacokinetics of these novel antithrombotic and anticancer agents in vitro, ex-vivo, and in vivo levels. Moreover, these studies' outcomes will help determine the potent anticancer agent with low anticoagulant activity. However, there is a possibility that we may identify some anticancer agents that also have anticoagulant activity.


© Elsamani I Abdelfadiel

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