Macrophages and tumour revascularisation following treatment with vascular disrupting agents

Abigail Welford, Seth Coffelt, Claire Lewis, Gillian Tozer

University of Sheffield, UK

Proffered paper presentation

Background
Combretastatin A-4-phosphate (CA-4-P), a tubulin-binding, vascular-disrupting agent (VDA), induces rapid and selective tumour vascular shutdown and secondary tumour cell death. However, acute revascularisation contributes to treatment resistance. It is hypothesised that VDA-induced haemorrhagic necrosis and hypoxia stimulate tissue infiltration by tumour-associated macrophages (TAMs), which promote tumour revascularisation and recovery.

Objectives
To determine if macrophages infiltrate tumours in response to CA-4-P treatment and, if so, whether they assist in tumour revascularisation.

Method and Conclusions

Late stage Polyoma Middle T (PyMT) spontaneous murine breast adenocarcinomas were excised from CA-4-P- and saline-treated mice. Twelve hours following a single injection of 100mg/kg CA-4-P, there was significant tumour necrosis (34.03 8.52%) compared with 1.99 0.33% in saline controls. At 24 hours, necrosis had reduced to 5.27 1.93% in treated tumours, suggesting very rapid recovery. This was accompanied by tumour infiltration of F4/80+ macrophages; 3.66 0.24% at 12 hours; 2.98 0.54% at 24 hours, compared with 1.18 0.08% and 0.71 0.21% in saline controls. Macrophages were primarily located in stromal regions between tumour lobules and showed co-localisation with CA4-P-induced hypoxia. A subset were Tie2+, and expressed MMP-9, a potently angiogenic molecule, which increases the bioavailability of VEGF. Results suggest involvement of macrophages in tumour revascularisation following VDAs. Further exploration in macrophage-depleted mouse models is planned to determine whether inhibition of macrophage infiltration would be advantageous in combination with VDA therapy, in order to impede revascularisation and increase efficacy.

Acknowledgements

Funded by Cancer Research UK