Fibrotic Response Induced by Anti-CSF-1R Treatment Promotes Glioblastoma Recurrence

Background Introduction

Glioblastoma (GBM) is a highly aggressive and malignant primary tumor of the central nervous system. Although current standard treatments include surgical resection, Temozolomide chemotherapy, and fractionated radiotherapy, the median survival for patients is just over 14 months, with a five-year survival rate of less than 5%. Nearly all cases of glioblastoma inevitably relapse post-treatment. The limited efficacy of traditional treatments is mainly due to the high genetic instability and cellular plasticity of glioblastomas, resulting in high intra-tumoral heterogeneity and the emergence of treatment-resistant subclonal cells.

To address this problem, researchers have proposed an alternative strategy: targeting tumor-associated macrophages and microglia by inhibiting the Colony Stimulating Factor 1 Receptor (CSF-1R). CSF-1R inhibitors have been shown in various models to reprogram these immune cells, leading to tumor size reduction and significantly extending the survival of mice. However, in long-term experiments, approximately 50% of mice eventually relapsed after tumor regression, with recurrent tumors closely related to fibrotic scar areas. These results suggest that treatment-induced fibrosis may play a key role in tumor recurrence. However, the specific mechanisms of this fibrotic response and its impact on GBM treatment outcomes remain unclear.

To better understand this problem, a research team from several institutions, including the University of Lausanne, published a study in the journal “Cancer Cell.” They conducted a detailed multi-omics analysis of changes in the glioblastoma tumor microenvironment (TME) following anti-CSF-1R treatment, focusing especially on the molecular characteristics and potential roles of fibrotic areas formed post-treatment. This study indicates that the fibrotic response triggered by multimodal treatment may play a crucial role in tumor recurrence, and inhibiting this response can enhance the effectiveness of anti-CSF-1R treatment.

Research Process

Experimental Design and Multi-Omics Analysis

This study systematically explored the complex cellular and molecular composition of GBM fibrosis under anti-CSF-1R treatment using a multi-omics strategy. The study used a platelet-derived growth factor (PDGF)-driven GBM mouse model, which simulates the human glioblastoma phenotype under specific genetic mutations. The study followed several main steps:

1. Anti-CSF-1R Drug Treatment and Fibrosis Observation: Researchers treated the mouse model with the CSF-1R inhibitor BLZ945 and systematically monitored the tumor regression, dormancy, and recurrence states, as well as the distribution of fibrotic areas, using MRI and immunofluorescence (IF) staining at different time points post-treatment.

2. Spatial Multi-Omics Analysis: The researchers performed high-throughput single-cell RNA sequencing (scRNA-seq), proteomic mass spectrometry, and spatial transcriptomics analysis on the tumor microenvironment at various pre- and post-treatment time points to reveal the fibrotic characteristics of different regions within the tumor tissue and the distribution and expression changes of various cell subpopulations.

3. Cellular Spatial Relationship Analysis: Using high-dimensional immunofluorescence digital pathology image analysis and cellular proximity network analysis, the researchers examined the spatial relationships between tumor cells and fibrosis-related cells (such as astrocytes, macrophages, T cells, etc.) at different treatment stages, uncovering the mechanism by which fibrotic zones act as “survival niches” protecting tumor cell survival.

4. Targeted Fibrosis Therapy: Based on the mechanistic analysis of fibrosis from multi-omics data, researchers designed a treatment plan combining TGF-β signaling pathway and inflammation signal inhibitors to determine if fibrosis inhibition could extend the survival of mice.

Key Experimental Steps and Techniques

Various innovative experimental techniques and analysis methods were applied in this study. High-throughput single-cell RNA sequencing and spatial transcriptomics (ST) revealed the cellular heterogeneity and functional characteristics of fibrotic regions. Researchers used high-dimensional immunofluorescence digital pathology image technology, along with machine learning, to annotate fibrotic regions and analyze single-cell spatial positions, quantifying the distribution patterns of different cell types in the fibrotic zones. Additionally, researchers applied proteomic mass spectrometry to compare the protein composition of fibrotic and non-fibrotic areas, revealing specific matrix proteins and signaling pathways characteristic of fibrotic regions. Lastly, NicheNet analysis was used to calculate signal transmission between cells, assessing the signaling connections of different cell types involved in the fibrotic response.

Experimental Results

Formation and Characteristics of Fibrotic Regions

The study found that anti-CSF-1R treatment leads to the formation of fibrotic regions enriched with extracellular matrix (ECM) proteins such as collagen I and IV during the regression of GBM tumors. These areas are surrounded by astrocytes and contain numerous “reactive” macrophages and T cells. Detailed spatial analysis showed that surviving tumor cells often resided within these fibrotic regions, presenting a non-proliferative “dormant” state. Compared with non-fibrotic areas, fibrotic regions exhibited higher intercellular signaling activity, especially in TGF-β signals and inflammation-related signaling pathways.

Fibrotic Regions Promote Tumor Cell Recurrence

Further proteomic and transcriptomic analyses revealed that fibrotic regions can protect tumor cells from immune cell attacks and provide a favorable “niche” for tumor recurrence. After stopping anti-CSF-1R treatment, fibrotic regions gradually deteriorated, while surviving tumor cells revived from dormancy and began to proliferate, ultimately leading to tumor recurrence.

Targeted Fibrosis Treatment Enhances Anti-CSF-1R Therapy Effectiveness

Based on the role of fibrosis in promoting tumor recurrence, researchers designed a combination therapy strategy incorporating TGF-β receptor inhibitor (Galunisertib) and corticosteroid medication (Dexamethasone) into anti-CSF-1R treatment. The results showed that this combination treatment significantly reduced fibrosis formation and extended the disease-free survival of mice. Moreover, inhibition of the fibrotic response also decreased the relapse rate of tumors, significantly enhancing the efficacy of anti-CSF-1R therapy.

Research Conclusions and Significance

This study unveiled the critical role of the fibrotic response induced by anti-CSF-1R treatment in glioblastoma recurrence. The findings suggest that fibrotic areas can promote the long-term survival and recurrence of tumors by protecting dormant tumor cells and evading immune surveillance. Through multi-omics approaches, researchers not only revealed the cellular and molecular mechanisms of treatment-induced fibrosis but also proposed a new therapeutic strategy—using TGF-β inhibitors and anti-inflammatory drugs jointly to inhibit the fibrotic response and enhance anti-tumor efficacy. This discovery offers new perspectives for future GBM treatment and indicates the need for early intervention in the fibrotic response during clinical treatment to prevent tumor recurrence.

Research Highlights

1. Fibrotic Response Induced by Multimodal Treatment: The study systematically analyzed fibrotic responses induced by different anti-glioma treatments, discovering that whether it is immunotherapy, radiotherapy, or surgical resection, they all trigger fibrotic responses in the glioma microenvironment.

2. Fibrosis as a “Survival Niche” for Tumor Recurrence: Multi-omics analysis revealed that fibrotic areas provide a protective barrier for dormant tumor cells, shielding them from immune cell attacks and offering advantageous conditions for recurrence after treatment cessation.

3. Effectiveness of Combination Therapy Strategy: By inhibiting TGF-β signaling and inflammatory responses, the study proposed a new therapeutic strategy that significantly reduced tumor recurrence rates and extended mouse survival.

4. Innovativeness of Research Methods: The study employed several cutting-edge techniques, including high-throughput single-cell transcriptomics, spatial transcriptomics, proteomic mass spectrometry, and machine learning image analysis, providing data support for in-depth exploration of treatment-induced tumor microenvironment changes.

Research Outlook

This study expands the understanding of fibrotic responses during anti-tumor treatment and provides potential therapeutic targets for improving anti-glioblastoma efficacy clinically. However, further research is needed to delve into the molecular mechanisms by which fibrotic regions promote tumor recurrence and to optimize the combinations and timing of anti-fibrosis treatment plans in preclinical research. Future studies could focus on how to inhibit these fibrotic responses in clinical treatment to delay or even prevent tumor recurrence, thereby offering patients longer survival periods and a higher quality of life.