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Document Type

Dissertation - University Access Only

Award Date

2013

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Advisor

Fathi T. Halaweish

Abstract

Cucurbitacins are highly oxygenated tetracyclic triterpene natural products. They are known for their broad spectrum biological activities. Cucurbitacins showed potential activity towards different cancer cell lines with lack of investigation of their activity towards treatment of melanoma. Melanoma is the most lethal type among skin cancers, causing about 75 % of skin cancer deaths. B-Raf mutations show high incidence in melanoma. Inhibition of Mitogen Activated Protein Kinase (MAPK) signal transduction pathway can subsequently lead to induce apoptosis assisting in the treatment of melanoma. Initially, the binding affinity of cucurbitacins towards mutant B-RAF V600E receptor was studied using in-silico modeling techniques, showing the potential of cucurbitacins to bind to B-RAF V600E. In addition, cucurbitacins caused cytotoxicity in A-375 and SK-MEL28 cell lines with IC50 ranging from 0.32-1.59 μM. The study was extended to investigate the binding affinity of cucurbitacins towards MAPK pathway using in-cell based ELISA, showing the ability of cucurbitacins to inhibit phosphorylated ERK and surprisingly, ERK expression. The promising activity of cucurbitacins drew the attention towards optimizing the selectivity, by assigning the important chemical functionalities responsible for the activity, via molecular modeling. This approach resulted in assembling of a side chain at C-17 possessing α, β-unsaturated ketone at ring D of steroidal skeleton using structural based drug design approach. Three main sites were studied synthetically; 1) Assembling different functionalities at C-25 via Aldol reaction, 2) Thiophenol and azide addition reactions on C-24, 3) Trans, pseudo, and cis configuration of B/C ring juncture of the steroidal skeleton. Twelve synthetic steps were carried out resulting in 20 novel intermediate and final steroidal based analogs. These analogs were biologically screened using cytotoxicity and in-cell based ELISA assays, to show the potential of analogs possessing pseudo-cis configuration and the actual side chain of cucurbitacins to inhibit cell growth of A-375 cell lines with IC50 ranging from 12.20 -19.90 μM. The novel synthesized analogs exhibited significant inhibition of phosphorylated ERK induced by epidermal growth factor without reduction in the ERK expression levels. This study produced novel steroidal scaffolds targeting the MAPK pathway, to be structurally optimized towards treatment of melanoma.

Library of Congress Subject Headings

Cucurbitaceae -- Therapeutic use
Melanoma -- Treatment

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

200

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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