B20
Systematic optimisation of in vivo imaging of αvβ6 in cancer
Antonio Saha, David Ellison, Mather Stephen, Hart Ian, Marshall John
Queen Mary's, University Of London, London, UK
Background
The epithelial-specific integrin αvβ6 usually is undetectable on normal, adult, human tissue but upregulated during tissue re-modelling and carcinogenesis. We identified a 20mer peptide (A20FMDV2) that, in vitro, binds strongly and specifically (>100-fold) to αvβ6 but not other RGD-directed integrins (αvβ3, αvβ5, αvβ8 or α5β1). When [18F]A20FMDV2 was injected into mice bearing both A375P puro(β6-negative) and A375Pβ6(β6-positive) tumours uptake in A375Pβ6 was 0.66% Injected Dose/g (%ID/g) at one hour, thrice as much as in A375Ppuro. We sought to improve this level of peptide localisation to αvβ6-positive tumours
Method
A20FMDV2 conjugated to the chelating agent DTPA was labelled with Indium-111 and injected into athymic mice bearing both A375Ppuro and A375Pβ6 tumours. We tested 1) strain of mouse (CD1, BalbC/nu, ICRF nude) 2) peptide specific activity 3) kinetics of uptake 4) specificity of uptake and 5) NanoSPECT/CT imaging. Immunohistochemistry was used to examine endogenous αvβ6 expression in mouse tissues.
Results
Ratio of uptake of [111In]-DTPA-A20FMDV2 by A375Pβ6 vs A375Ppuro tumours was 7:1, at 2%ID/g, and was not affected by mouse strain. Peak uptake required injection of 4g peptide labelled with 10MBq Indium-111 and occurred at 1h. Such uptake was eliminated completely by pre-injection of 100-fold mass of cold peptide. Biodistribution and imaging showed significant uptake in the stomach and gut that correlated with endogenous αvβ6 expression. Selective imaging of the A375Pβ6 tumour versus the A375Ppuro tumour was achieved easily by NanoSPECT/CT.
Conclusion
DTPA-A20FMDV2 is the first peptide described for the successful imaging, by SPECT, of αvβ6-positive cancers.
