Low Dose Cyclophosphamide Modulates Tumor Microenvironment by TGF-β Signaling Pathway

Area of Science:

• Oncology
• Immunology
• Pharmacology

Background:

• The tumor microenvironment significantly influences cancer progression and treatment resistance.
• Cyclophosphamide (CTX) is a cytotoxic chemotherapy agent, with metronomic scheduling (low, continuous doses) showing potential but with incompletely understood mechanisms.
• Previous research suggests metronomic CTX targets endothelial cells and regulatory T cells (Tregs).

Purpose of the Study:

• To investigate the anti-tumor activity and immunomodulatory effects of two metronomic cyclophosphamide schedules.
• To explore the impact of metronomic CTX on the tumor microenvironment and immune cell populations.
• To evaluate the toxicity and anti-metastatic potential of metronomic CTX in a Lewis lung cancer model.

Main Methods:

• Nude mice with Lewis lung cancer were treated with metronomic CTX regimens and maximum tolerated dose (MTD) regimens.
• Toxicity was assessed via survival, weight loss, and histopathology.
• Immune cell populations (CD4+, CD8+, CD4+CD25+FoxP3+ T cells) were analyzed by flow cytometry.
• Tumor microenvironment changes, including myofibroblasts, E-cadherin, N-cadherin, and TGF-β pathway components, were evaluated.

Main Results:

• Metronomic CTX restored immune function by increasing CD4+/CD8+ T cell ratios and depleting Tregs in circulation, spleen, and tumor sites.
• Low-dose CTX reduced myofibroblasts and altered E-cadherin/N-cadherin levels in primary tumors and lung metastases.
• These changes were associated with downregulated TGF-β receptor 2 expression, suggesting TGF-β pathway involvement.

Conclusions:

• Metronomic cyclophosphamide demonstrates significant anti-tumor activity by enhancing anti-tumor immunity and modulating the tumor microenvironment.
• The findings suggest that metronomic CTX employs molecular mechanisms beyond targeting angiogenesis and Tregs, including TGF-β pathway modulation.
• Low-dose metronomic CTX offers a promising therapeutic strategy with potential to overcome cancer progression and therapy resistance.