The role of the tumor microenvironment in the progression of desmoplastic cancers in subcutaneous and orthotopic injection models

Abstract

Cancer remains one of the leading causes of mortality worldwide, with an estimated 10 million deaths in 2022 according to the World Health Organization. Despite significant advances in cancer research and treatment, certain types of cancer, particularly those characterized by a dense stromal reaction, continue to pose significant challenges in terms of treatment efficacy and patient outcomes. This thesis focuses on three such desmoplastic cancers: lung cancer, hepatocellular carcinoma (HCC), and pancreatic ductal adenocarcinoma (PDAC). While PDAC and certain forms of lung cancer are highly desmoplastic, HCC shows significantly less desmoplastic activity with little intratumoral extracellular matrix (ECM), though its characteristic capsule formation should be noted. These cancers are known for their aggressive nature, poor prognosis, and resistance to conventional therapies, largely due to their complex tumor microenvironment (TME). The urgent need for new therapeutic strategies for these cancer types stems from their unique biological characteristics. Lung cancer, particularly non-small cell lung cancer (NSCLC), the leading cause of cancer-related deaths globally, often develops resistance to targeted therapies. HCC, typically arising in the context of chronic liver disease, presents challenges due to its heterogeneity and the compromised liver function of patients. PDAC is notorious for its late diagnosis and extreme resistance to current treatment modalities, largely attributed to its dense stromal component. This study investigates the complex roles of cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs) in the progression of these desmoplastic cancers. Various subcutaneous and orthotopic injection models were established to study tumor-stroma interactions in vivo. A key aspect involved using a bi-transgenic Col3a1-CreERT2/TGFβRII fl/fl mouse model to selectively inactivate TGF-β signaling in CAFs, revealing its impact on tumor growth and the TME. The study also explored innovative therapeutic strategies, Fra-2 antisense oligonucleotide and the mTOR inhibitor rapamycin, to target different components of the tumor microenvironment. Combination therapy showed promising results in reducing tumor burden and modulating the TME in an orthotopic HCC model. The post-treatment mRNA expression profiles unveiled striking alterations, with notable changes in collagen transcripts. Histological examination provided additional data on collagen distribution within the tumor tissue, confirming this observation. Combination therapies elicited more pronounced effects on several measured parameters compared to single-agent treatments, highlighting synergistic effects. Additionally, novel murine models for HCC and PDAC research were established, and a new Col3a1-CreERT2/iDTR mouse strain was developed for future CAF depletion studies. The findings highlight the intricate interplay between tumor cells and stromal components, offering insights into potential therapeutic approaches for desmoplastic cancers and paving the way for more effective treatment strategies in these challenging malignancies.