Normal tissues toxicities triggered by combined anti-angiogenic and radiation therapies: hurdles might be ahead

Abstract

Background: Combined-modality therapy is a promising approach to improve the therapeutic index of radiotherapy. However, these improvements could come at the cost of increased toxicities. Clinical trials evaluating anti-tumour efficacy of bevacizumab combined with radiotherapy have encountered unexpected side effects. This study is the first systematic evaluation of normal tissue toxicity triggered by anti-angiogenic agents combined with radiation therapy in mice.

Methods: Effect of a mouse anti-VEGF antibody was monitored on acute toxicity studying radiation-induced intestinal ulceration (12 Gy TBI); on subacute toxicity using a model of oral mucositis (16.5 Gy); on late radiation injuries by monitoring lung fibrosis (bleomycin and 19 Gy).

Results: Combination of irradiation with anti-VEGF antibody enhanced intestinal damages with severe epithelial ulcerations, had no adverse impact on oral mucositis and dramatically worsened the fibrotic picture induced by bleomycin and irradiation to the lung.

Interpretation: These reports bring to light the important questions about safety and underscore the need for appropriate preclinical modelling of the impact on normal tissues of novel drug-radiation regimens. Our findings also highlight the complexity of anti-VEGF action, which could in defined conditions exert tissue-specific protection. The findings indicate that the combination of targeted drugs with radiotherapy should be approached with caution.

Figure 1

Acute toxicity: six groups of treatment were compared: (1)12 Gy TBI; (2) anti-VEGF antibody at 5 mg kg⁻¹ twice weekly beginning 24 h before 12 Gy TBI; (3)TNBS (150 mg kg⁻¹); (4) TNBS before 12 Gy TBI; (5) TNBS before anti-VEGF antibody twice weekly; (6) TNBS before anti-VEGF antibody twice weekly and TBI 12 Gy. Mice were killed 24 h and 72 h after according to the schedule shown (A). At 24 h after irradiation small intestine histology (transversal sections) shows crypt dilatation, mucosal thickness and villi shortening. Anti-VEGF antibody enhances damages (B). At 24 h after irradiation colon histology (longitudinal sections) shows that mouse anti-VEGF antibody increases dramatically irradiation and TNBS-induced lesions (C).

Figure 2

Monitoring subacute toxicity: oral mucositis was obtained after local snout irradiation at 16.5 Gy (A). We compared mice treated with or without anti-VEGF antibody at 5 mg kg⁻¹ twice weekly beginning 24 h before irradiation. Intensity of the damages was monitored using Parkins score every day (B). Animals were killed and sampled at day 10 and 22 and histopathological analysis performed on HES section (C).

Figure 3

Late toxicity: effect of murine anti-VEGF antibody on the development of bleomycin and radiation-induced lung fibrosis was investigated. Lung fibrosis was generated using a radio-mimetic agent bleomycin and a single dose of irradiation (19 Gy) that allows, respectively, occurrence of fibrosis within 30 days and 15 weeks. Treatment schedule is shown in (A) and (C). Mice were killed and lungs collected for histopathological analysis at indicated times (B) and (D).