Understanding the Molecular Mechanisms that Lead to Tumor Recurrence and Acquired Therapy Resistance in Cancer
Date
2023
Authors
Advisors
Journal Title
Journal ISSN
Volume Title
Repository Usage Stats
views
downloads
Abstract
Advances in anti-cancer therapies, including chemotherapies, targeted therapies, and immuno-therapies, have drastically improved patient outcomes over the last few decades. However, tumor recurrence and acquired drug resistance continue to be detrimental for cancer patients, accounting for the majority of cancer-related deaths. Drug resistance is a common phenomenon that occurs when pharmaceutical agents are tolerated by and no longer effective against their target. In the case of cancer, acquired drug resistance is when cancer cells are able to survive, actively proliferate, and migrate to distant sites in the presence of anti-cancer agents. As such, it is imperative that we understand the mechanisms that lead to acquired drug resistance and tumor recurrence and leverage this newfound understanding to improve treatment options and, ultimately, patient outcomes.
Recurrent tumors and drug resistant cancer cells arise from drug-tolerant persister cells (DTPs), a population of cells that is able to withstand and adapt to cancer treatment. APOBEC3 and NRF2 are proteins that are largely absent and inactive in primary non-small cell lung cancer and HER2+ breast cancer, respectively. Interestingly, both proteins are found in recurrent disease, specifically after targeted therapy. This suggests that the upregulation of APOBEC3 and NRF2 is an adaptive response to anti-cancer treatment. Further, this suggests that APOBEC3 and NRF2 are essential for drug-tolerant persister cell survival and subsequent recurrence. Understanding how these proteins are induced, regulated, and what their respective roles are in tumor evolution can provide insight into therapeutic potentials in both residual and recurrent disease. First, I explored the regulation and function of APOBEC mutagenesis during acquired resistance to epidermal growth factor receptor (EGFR) inhibitors in two non-small cell lung cancer cell lines, PC9 and HCC827. I assess the effects of EGFR inhibition on APOBEC3 expression and activity and find that this induces APOBEC3 activity. Moreover, I evaluate how sustained APOBEC3 activity promotes evolution of drug resistance in DTPs. Finally, I examine what mechanisms might play a role in acquired drug resistance when APOBEC3 is highly active. I show that while APOBEC activity does not accelerate acquired therapy resistance, A3B expression alters the evolutionary path that PC9 cells take to become gefitinib-resistant. Specifically, A3B expression is associated with the late acquisition of T790M mutations during the DTP state, supporting a model where induction of APOBEC activity promotes DTP survival, thereby facilitating the on-going evolution of drug-tolerant persister cells. Of note, I find that APOBEC3 activity is associated with squamous cell transdifferentiation in PC9 cells, suggesting that p63 and its target genes could be future biomarkers and therapeutic targets.
Second, I investigated the regulation of the transcription factor NRF2 in recurrent breast cancer cells. I assess KEAP1-mediated regulation of NRF2 and find that while KEAP1 knockout in primary and recurrent cells caused an increase in NRF2 and its target genes, NRF2 remained more elevated in recurrent cells, indicating that increased NRF2 levels and transcriptional activity in these cells are independent of KEAP1. Next, I looked at post-translational modifications on NRF2 to determine if this may be the cause of the differential NRF2 levels in primary and recurrent cells. I found that NRF2 in recurrent cells had higher levels of phospho-Ser364, potentially affecting NRF2’s stability. Finally, I evaluated regulation of NRF2 by Akt and GSK-3β. I found that inhibition of Akt had no effect on NRF2 levels. In contrast to this, I found that GSK-3β activity is inversely correlated with NRF2 levels, suggesting that low levels of GSK-3β activity is partially responsible for NRF2 stabilization in recurrent tumor cells.
In conclusion, I have modeled two adaptive mechanisms for tumor recurrence and acquired drug resistance in two different cancer types. I elucidated the mechanisms by which APOBEC3B and NRF2 are able to promote cancer cell evolution in drug-tolerant persister cells that eventually give rise to recurrences.
Type
Department
Description
Provenance
Citation
Permalink
Citation
Garcia, Nina Marie Geronimo (2023). Understanding the Molecular Mechanisms that Lead to Tumor Recurrence and Acquired Therapy Resistance in Cancer. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/30277.
Collections
Except where otherwise noted, student scholarship that was shared on DukeSpace after 2009 is made available to the public under a Creative Commons Attribution / Non-commercial / No derivatives (CC-BY-NC-ND) license. All rights in student work shared on DukeSpace before 2009 remain with the author and/or their designee, whose permission may be required for reuse.