Abstract

High-risk human papillomaviruses (HPV) are the causative agents of virtually all cases of cervical cancer and up to 80% of head and neck squamous cell carcinoma (HNSCC). Current treatment options include chemo- and radiotherapy, though the effectiveness of these therapies is limited by the viral oncoprotein E6, which disrupts apoptotic pathways by binding to and accelerating the degradation of molecules such as p53 and caspase- 8. Our hypothesis was that inhibiting E6 and rescuing the apoptotic mediators would increase the effectiveness of apoptotic agents. The aims of this study were to first, develop an HPV+ HNSCC xenograft model to test small E6 inhibiting molecules; and second, to evaluate the antitumor efficacy of lead molecules in an established in vivo model. We fulfilled the first aim by optimizing an HNSCC xenogral model using UM-SCC47 cells, incorporating Matrigel, and applying luciferase technology. Our lab has identified two E6 inhibitors from two different sources: spinacine was identified following screening of the TimTec Actiprobe 2K library, and 30-hydroxygambogic acid (GA-OH) was identified following screening of the Kansas University 5K library with subsequent follow-up. Both compounds were shown to rescue the apoptotic signaling molecules and to re-sensitize cancer cells to apoptosis in vitro. To further explore the therapeutic potential of these small molecules, we determined their toxicity and antitumor efficacy in vivo. Spinacine exhibited no toxicity to mice at doses up to and including 20 mg/kg but did not yield evidence of efficacy on tumor growth either alone or when combined with apoptotic agents. Subsequently, our lab demonstrated that GA-OH had higher specificity and effectiveness than our previous lead molecules in vitro. Therefore, we assessed GA-OH’s toxicity and evaluated the effectiveness of GA-OH in combination with chemotherapy. Behavioral/physical assessments, body weight, organ necropsy, and blood tests, with the possible exception of creatine kinase, all pointed towards lack of significance toxicity, predicting tolerance. Moreover, we were able to demonstrate that our animal model was functional, and that cetuximab slowed and regressed tumor growth. We found that GAOH alone did not slow tumor growth; however, when combined with cisplatin, GA-OH enhanced cisplatin’s efficacy in HPV+ HNSCC in vivo.

LLU Discipline

Biochemistry

Department

Basic Sciences

School

School of Medicine

First Advisor

Penelope J. Duerksen-Hughes

Second Advisor

Eileen Brantley

Third Advisor

Sanjay Chanda

Fourth Advisor

Valery Filippov

Fifth Advisor

Mark E. Reeves

Sixth Advisor

Julie Unternaehrer

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2023

Date (Title Page)

6-2024

Language

English

Library of Congress/MESH Subject Headings

Apoptosis; Squamous Cell Carcinoma of Head and Neck; Human Papillomavirus Viruses; Oncogene Proteins

Type

Dissertation

Page Count

xvi, 167 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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