Monitoring tumour microenvironment changes during anti-angiogenesis therapy using functional MRI

This study aims to explore the feasibility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) in assessing vessel function and tumour aggressiveness during anti-angiogenesis treatment. A colon cancer xenograft model was established in BALB/C nude mice with the HCT116 cell line. Sixteen mice were randomly divided into Group A and Group B, which were treated with saline or bevacizumab by intraperitoneal injection on the 1st, 4th, 7th, 10th and 13th days and underwent DCE-MRI and BOLD-MRI examinations before and on the 3rd, 6th, 9th, 12th and 15th days after treatment. Group C was treated with oxaliplatin monotherapy, and Group D was treated with bevacizumab and oxaliplatin as a point of comparison for therapeutic effects. The pathological examinations included HE, HIF-1α, fibronectin and TUNEL staining, as well as α-SMA and CD31 double staining. One-way analysis of variance and correlation analysis were the main methods used for statistical analysis. Group D manifested the highest tumour inhibition rate and smallest tumour volume on day 15, followed by Group C, Group B and Group A. Ktrans (F = 81.386, P < 0.001), Kep (F = 45.901, P < 0.001), Ve (F = 384.290, P < 0.001) and R2* values (F = 89.323, P < 0.001) showed meaningful trends with time in Group B but not Group A. The Ktrans values and tumour vessel maturity index (VMI) were higher than baseline values 3–12 days after bevacizumab treatment. The CD31 positive staining rate and VMI had the strongest correlations with Ktrans values, followed by AUC180, Ve and Kep values. The R2* value positively correlated with the positive staining rates of HIF-1α and fibronectin. Intermittent application of low-dose anti-angiogenic inhibitor treatment may help improve the effect of chemotherapy by reducing hypoxia-related treatment resistance and improving drug delivery. DCE-MRI is useful for evaluating vessel maturity and vascular normalization, while BOLD-MRI may help to predict tumour hypoxia and metastatic potential after anti-vascular treatment.