Book of abstract 2008

Response to VEGF receptor inhibition and vascular disrupting therapy
of mouse tumours expressing only single isoforms of VEGF-A
Simon Akerman, Neil A. Cross, Katie L. Pettyjohn, Leigh J. Williams, Matthew Fisher,
Helen Evans, Meit A. Bjorndahl, Sheila Harris, Paul R. Barber, Chryso Kanthou, Vivien
E. Prise, Sally A. Hill, Gillian M. Tozer
Cancer Research UK Tumour Microcirculation Group, Academic Unit of Surgical Oncology, University
of Sheffield, Royal Hallamshire Hospital, Sheffield, S10 2JF
Mouse fibrosarcomas expressing only single VEGF-A isoforms (120, 164 or 188), or all
isoforms (w/t) under endogenous promoter control have been developed. Subcutaneous
VEGF120 tumours transplanted into SCID mice have poor vessel wall development, with
very few α-smooth muscle actin or desmin staining cells, indicative of lack of pericytes.
This is associated with susceptibility to vessel breakdown following treatment with the
prototype tumour vascular disrupting agent, combretastatin A4-phosphate (CA-4-P).
VEGF188 tumours have more uniform vascular networks and better-developed vessel
walls (positive staining for α-smooth muscle actin and desmin) than VEGF120 tumours
and are less responsive to CA-4-P. We tested the effect of chronic treatment with a VEGF
receptor inhibitor, SU5416, on angiogenesis in the different tumour types and subsequent
response to CA-4-P.
Measurements of angiogenesis and vascular response to CA-4-P in VEGF120, 164, 188
and w/t tumours were studied in SCID mice using dorsal skin flap window chambers.
Subcutaneously implanted tumours were studied for growth measurements and to
perform immunohistochemistry. In subcutaneous tumours, SU5416 (50 mgkg-1, i.p,
twice weekly) did not affect growth rates in any tumour line. There were higher levels
of α-smooth muscle actin staining in SU5416-treated VEGF120 tumours than untreated
tumours, implying greater vascular maturity, in terms of pericyte recruitment. Less effect
of SU5416 on pericyte staining was observed in the other tumour types. In the window
chamber, angiogenesis was inhibited in all VEGF-isoform tumours treated with SU5416,
as measured
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by total vessel length density versus time after transplantation. In VEGF120
tumours pre-treated with SU5416 (50 mgkg-1, i.p, twice weekly), CA-4-P (30 mgkg-1,
i.v) decreased red blood cell velocity after 1hr, but there was complete recovery by 24hrs.
In contrast, in VEGF120 tumours either pre-treated with vehicle (twice weekly), or
untreated tumours, CA-4-P caused rapid vascular shutdown and haemorrhage with no
recovery after 24hrs. SU5416 had less effect on response to CA-4-P treatment in the other
tumour types, in keeping with the results for pericyte staining.
The VEGF receptor inhibitor SU5416 caused a significant ‘normalization’ of the
vasculature in VEGF120 tumours, involving an increased proportion of tumour vessels
that are stabilised by pericytes, and resulting in a poor response to CA-4-P. These results
suggest that response to vascular disrupting agents is strongly influenced by pericyte
investment and that vascular normalisation may be an undesirable effect of anti-angiogenic
agents such as SU5416.
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This work was funded by Cancer Research UK