Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Pharmaceutical Sciences

First Advisor

Fei Chen

Abstract

ABSTRACT

EXPLORATION OF CANCER PROLIFERATIVE SIGNALING IN CHEMOTHERAPY DRUG RESISTANCE AND MDIG-INDUCED TUMORIGENESIS

by

KAI WU

August 2016

Advisor: Dr. Fei Chen

Major: Pharmaceutical Sciences

Degree: Doctor of Philosophy

Aberrant intracellular signaling pathway is one of the major driving forces of malignancy through multiple stages of human cancers. Our study demonstrates that in cancer cells, the signaling pathways are profoundly and actively intertwined with each other so they can synergistically affect cell biology, including promoting development of malignancy and compensating the loss of proliferation or survival signals in responses to anti-tumor drug. Moreover, cancer cells can also adopt “non-canonical” mechanisms to modulate the activities of key protein regulators so the whole signaling pathway is strengthened.

In the first project, we performed integrative studies to investigate the oncogenic role of a WTC (World Trade Center) dust-induced regulator, mdig, in multiple myeloma (MM). MM is a malignancy of plasma cells located within bone-marrow compartment and several post 9/11 health surveillance programs and epidemiological studies suggested an increased incidence rate of multiple myeloma (MM) among the individuals who intensively exposed to WTC dust. However, the potential connections between WTC dust and MM remain to be elucidated. Expressions of mdig were investigated in bronchial epithelial cells, B cells, MM cell lines and in the bone marrow specimens from the MM patients. We found that WTC dust is potent in inducing mdig protein and/or mRNA in bronchial epithelial cells, B cells and MM cell lines. An increased mdig expression in MM bone marrow was observed, which is associated with the disease progression and prognosis of the MM patients. Using integrative genomics and proteomics approaches, we further demonstrated that in MM cell lines, mdig directly interacts with c-myc and JAK1, which contributes to hyperactivation of the JAK-STAT3 signaling important for the pathogenesis of MM. Genetic silencing of mdig reduced activity of the major downstream effectors in the JAK-STAT3 pathway. Our results indicate that WTC dust induced-mdig overexpression bridges c-myc pathway and STAT3 pathway in MM, which is essential for the tumorigenesis of MM.

In the second project, we focused on the underlying mechanisms of both primary and secondary resistance to EGFR TKI (Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor), including gefitinib, in NSCLC (Non-small cell lung cancer), which are two major obstacles compromising the clinical success of targeted therapy. In the part studying primary resistance, we observed that JAK2-STAT3 signaling axis in non-sensitive lung cancer cell lines is highly refractory to gefitinib treatment. Follow-up experiments further revealed a unique STAT3-dependent Akt restoration pattern in non-sensitive lung cancer cells, which impairs the efficacy of gefitinib. Mechanistically, gefitinib increased physical binding between EGFR and STAT3, which de-repressed STAT3 from SOCS3, an upstream suppressor of STAT3. Such a de-repression of STAT3 in turn fostered Akt activation. Genetic or pharmacological inhibition of STAT3 abrogated Akt activation and combined gefitinib with STAT3 inhibition synergistically reduced the growth of the tumor cells. In order to study the mechanisms of secondary resistance (acquired resistance), we established a gefitinib-resistant lung cancer (GR) cell line. Through profiling the gene expression pattern and investigating the alterations of intracellular signaling pathways, we discovered multiple resistance mechanisms in GR cells, including a unique hyperactivation pattern of STAT3. A rational co-inhibition of STAT3 and EGFR simultaneously suppressed several survival-related pathways in GR cells. As a result, such combinational targeting re-sensitized the GR cells to gefitinib treatment. Taken together, our study has unraveled novel mechanisms of resistance to EGFR TKI in lung cancer and has provided important information for rationale-based combinational targeting strategies to overcome drug resistance.

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