NOVEL STRATEGIES TO OVERCOME CARBOPLATIN RESISTANCE IN TRIPLE NEGATIVE BREAST CANCER USING PATIENT DERIVED XENOGRAFTS

Author

Mohammad A. Al Zubi, Virginia Commonwealth UniversityFollow

DOI

https://doi.org/10.25772/ZSCR-RW26

Defense Date

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Integrative Life Sciences

First Advisor

J. Chuck Harrell, Ph.D.

Second Advisor

Jolene Windle, Ph.D.

Third Advisor

Joyce Lloyd, Ph.D.

Fourth Advisor

Mikhail Dozmorov, Ph.D.

Fifth Advisor

Paula Bos, Ph.D.

Abstract

Triple-negative breast cancer (TNBC) patients have a poor prognosis and rely on chemotherapeutic treatment as standard of care. Often, they develop chemotherapy resistance, which leaves them without more therapeutic options, like targeted therapy. New models have been developed to test targeted inhibitors in human tumors, and they are known as patient-derived xenografts (PDX). These tumors are obtained from patients, then established and maintained in mice where they areused for tumor studies. In this work, we characterized 14 PDXs for their primary tumor growth rate and investigated metastatic propensity using spontaneous and experiment metastasis models. We utilized RNA-sequencing to characterize contributions of human and mouse cells in the metastatic process. We then focused on characterizing the growth of the 14 PDXs in the liver after portal vein injection; several PDXs surprisingly failed to grow, and in others we noted morphological differences in the metastases such as “growth nodules or replacement growth” patterns. Since acquired chemotherapy resistance in metastases is a problem for TNBC patients, we identified models that were sensitive to carboplatin, and then developed isogenic carboplatin-resistant (CR) PDXs to study. Cytotoxic drug screens with 1,363 FDA approved drugs on these CR PDX cell suspensions in vitro identified a novel combination of erlotinib and napabucasin (EGFR and STAT3 inhibitors, respectively) that has the potential to overcome carboplatin resistance. Bulk and single-cell (sc) RNAseq analyses, combined with reverse phase protein array (RPPA) analyses, found a consistent positive correlation of EGFR and STAT3 expression. Analysis of gene expression data within an 855-patient dataset revealed that tumors which were EGFR^high and STAT3^high had a poorer outcome compared to other groups, suggesting dual targeting using erlotinib and napabucasin can have a high translational value. In vivo testing found effectiveness in inhibiting primary tumor growth with the combination compared to single agents. Finally, so that we can later combine cancer therapeutics with immune cell targeting, we obtained the immune-competent glowing head (GH) mouse, and tested primary and metastatic growth of multiple mouse mammary cancer cell lines and characterized liver metastasis models. Future studies aim to incorporate the models developed herein to identify novel effective therapeutic compounds for clinical trials.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

7-8-2020