大多數帶有 EGFR 突變的肺癌患者對於表皮生長因子受體酪氨酸激酶抑製劑 (EGFR-TKIs) 治療都有很好的效果，但無可避免地，肺癌患者在接受 EGFR-TKIs 治療後往往會產生對 EGFR-TKIs 的抗藥性，而其背後的潛在機制仍尚未被釐清。
在本研究中，我們發現腦源性神經滋養因子 (BDNF) 透過表觀遺傳的調控在 EGFR-TKI 耐藥性的肺癌細胞中高度表達，此調控機制類似於神經幹細胞 EGFR 突變的肺癌患者對於 EGFR-TKIs 治療都有很好的效果，但無可避免地，肺癌患者在接受 EGFR-TKIs 治療後往往會產生對 EGFR-TKIs 的抗藥性，而其背後的潛在機制仍尚未被釐清。
在本研究中，我們發現腦源性神經營養因子 (BDNF) 透過表觀遺傳的調控在 EGFR-TKI 耐藥性的肺癌細胞中高度表達，此調控 BDNF 表現量的機制類似於神經幹細胞分化至星狀膠細胞譜系的分化過程。我們也發現BDNF的過表達會誘導上皮-間充質轉換 (EMT)，並賦予肺癌細胞在低量血清和 EGFR-TKIs 藥物處理的條件壓力下有更好的存活能力。除此之外，我們還觀察到源自於癌細胞的 BDNF 可以促進纖維母細胞的生長並增強 FGF2 的表達，而纖維母細胞分泌的 FGF2 可以進一步滋養肺癌細胞的生長。在異種移植的動物模型中，我們發現腫瘤在 EGFR-TKIs 的處理下會有著豐富的 BDNF 和 FGF2 表達。
我們的研究結果表明，肺癌細胞分泌的 BDNF 和纖維母細胞分泌的 FGF2 之間的串擾為 EGFR-TKI 耐藥性提供了新的機制，這個交互作用的機制可以提供肺癌新的治療標靶和作為分子標記物的潛力。

Most of lung cancer patients harboring activating EGFR mutations can benefit from the treatment of EGFR-tyrosine kinase inhibitors (TKIs). However, resistance to EGFR-TKIs inevitably occur, yet the mechanism behind this is still elusive. Here, I report that brain-derived neurotrophic factor (BDNF) is highly expressed in EGFR-TKI resistant lung cancer cells through an epigenetic control, which regulates BDNF expression through a similar process of neural stem cell differentiation to astrocyte lineage. We found that overexpression of BDNF can induce epithelial-to-mesenchymal transition (EMT) and endow lung cancer cell with high survival ability under low-serum stress and EGFR-TKI selection. Meanwhile, we observed that cancer derived BDNF can promote growth of fibroblasts and enhance FGF2 expression. FGF2 secretion from fibroblasts can further nourish growth of lung cancer cells. In a xenograft animal model, we found that BDNF and FGF2 can be enriched in tumors under EGFR-TKI selection. Our findings suggest that the crosstalk between BDNF and FGF2 in lung cancer and fibroblast cells provide a novel mechanism for EGFR-TKI resistance. This crosstalk may serve as novel therapeutic target and biomarker for lung cancer treatment.

Abstract - 1
中文摘要 - 2
致謝 - 3
Introduction - 6
Lung Cancer - 6
EGFR mutation and TKIs treatment in lung cancer - 6
EMT mediated the EGFR-TKI resistance in EGFR-mutated lung cancer cells - 7
Brain-derived neurotrophic factor (BDNF) - 8
Tumor microenvironment (TME) - 9
Cancer-associated fibroblast (CAF) - 10
Materials and Methods - 11
Cell Culture - 11
Quantitative Real-Time PCR assays (RT-qPCR) - 11
BDNF ELISA - 12
Chromatin Immunoprecipitation Quantitative PCR assays (ChIP-qPCR) - 12
Lentiviral Infection - 12
Clonogenic Assay - 13
Lung Cancer Cells Co-cultured With Fibroblasts Conditioned Media (CM) - 13
Fibroblasts Co-cultured With Lung Cancer Cells Conditioned Media (CM) - 14
Immunoblotting - 14
Statistical Analysis - 14
Results - 16
BDNF is elevated in lung cancer cells under EGFR-TKI resistance - 16
Epigenetic regulation of BDNF during differentiation and EGFR-TKI resistance - 17
BDNF regulates growth of lung cancer cells - 17
TGF-β induces EMT feature and upregulates BDNF expression in lung cancer cells - 18
BDNF secretion from lung cancer cells enhances the proliferation of fibroblasts - 18
FGF2 secretion from fibroblasts promotes survival of lung cancer cells - 19
FGFR1 expression in EGFR-TKI resistant lung cancer cells - 20
BDNF expression is associated with poor survival in lung cancer patients - 20
Summary - 22
Figures - 23
References - 52

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