Evaluating fulvestrant-resistance in HCC1428 breast cancer cells
(2019) MOBN02 20182Degree Projects in Molecular Biology
- Popular Abstract
- Overcoming drug resistance in breast cancer
Breast cancer remains the most common malignancy in women worldwide with over 2 million newly diagnosed cases in 2018, accounting for almost a quarter of all cancer cases in women. More than 70% of breast tumors depend on estrogen for survival and growth, which led to the development of targeted therapy against the associated cellular hormone receptor by inhibiting its activity or lowering its amount by degradation. Disease can effectively be controlled by this approach in many patients, however, in the majority of metastatic patients, the disease progresses during therapy and eventually they become resistant to the treatment.
In my thesis, I have looked at possible resistance-driving... (More) - Overcoming drug resistance in breast cancer
Breast cancer remains the most common malignancy in women worldwide with over 2 million newly diagnosed cases in 2018, accounting for almost a quarter of all cancer cases in women. More than 70% of breast tumors depend on estrogen for survival and growth, which led to the development of targeted therapy against the associated cellular hormone receptor by inhibiting its activity or lowering its amount by degradation. Disease can effectively be controlled by this approach in many patients, however, in the majority of metastatic patients, the disease progresses during therapy and eventually they become resistant to the treatment.
In my thesis, I have looked at possible resistance-driving mechanisms to the drug fulvestrant in a selected breast cancer cell model that has previously been made resistant to this drug and can now grow in its presence. Fulvestrant is the only FDA-approved selective estrogen receptor degrader drug and its unique mode of action lowers cellular estrogen receptor levels by inducing its degradation upon drug binding and inhibits any further signaling activity. However, there is something striking about the investigated drug-resistant cell model: Its estrogen receptor level is not decreased as expected with fulvestrant, showing that the receptor is still present. It is however not functional. Immediately when the drug is removed, the estrogen receptor levels go up – even higher than in original fulvestrant-sensitive cells and the receptor function is active. With a non-active estrogen receptor, the fulvestrant-resistant cells must have found an alternative signaling route for driving their growth.
What did I find out?
I confirmed that resistant cells grow in the presence of the drug and also independently of estrogen by quantifying growth curves in untreated and fulvestrant-treated conditions. I assessed receptor protein levels and saw that treatment with a higher fulvestrant dose did not decrease receptor levels any further, ruling out that the fulvestrant dosage used was insufficient to degrade existing receptors. Next, I studied whether the abundant receptor in resistant cells was functioning normally by using an assay that correlates intensity of a light signal to the magnitude of receptor activity. The readout showed an inactive estrogen receptor with fulvestrant treatment. However, when the drug was removed in those cells, they showed a significant increase in receptor activity. That indicates that the receptor inactivity is a regulated, reversible condition. Further, I investigated possible changes in alternative signaling pathways which resistant cells could use to bypass estrogen-dependence for their growth. More work is needed to draw conclusions from these experiments, but one of the pathways that we studied showed no hyperactivation and is thus likely not a driver for resistant cell survival. More, I explored differences in gene expression between normal and resistant cells: I checked selected genes that are affected by estrogen. Such estrogen receptor target genes were generally, but not exclusively, downregulated in the resistant cells, probably due to impaired estrogen-receptor activity. However, this remains to be investigated further. I also identified enriched, functionally related gene groups in resistant cells involving genes in cell cycle and DNA repair. Both gene groups are interesting subjects for further studies in search of candidate genes that might drive resistance. I similarly investigated selected influencing and interacting proteins that regulate estrogen receptor activity. All in all, I observed an upregulation of stimulating factors and a decrease in repressors in fulvestrant-treated resistant cells. An imbalance could drive resistance, but further bioinformatic analysis is needed here. In conclusion, my data suggests that the estrogen receptor expressed by this fulvestrant-resistant cell model is inactivated when fulvestrant is present, but quickly gets activated when fulvestrant-pressure is removed. Unravelling the underlying molecular mechanisms in progression and treatment resistance in metastatic breast cancer will improve patient care and treatment in the future.
Master’s Degree Project Molecular Biology 45 credits 2019
Department of Biology, Lund University
Advisor: Gabriella Honeth
Molecular therapeutics in breast cancer, Department of Oncology and Pathology, Medical Faculty, Lund (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/8975080
- author
- Bodily, Lisa
- supervisor
- organization
- course
- MOBN02 20182
- year
- 2019
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 8975080
- date added to LUP
- 2019-05-06 14:44:10
- date last changed
- 2019-05-06 14:44:10
@misc{8975080,
author = {{Bodily, Lisa}},
language = {{eng}},
note = {{Student Paper}},
title = {{Evaluating fulvestrant-resistance in HCC1428 breast cancer cells}},
year = {{2019}},
}