Radiolabelled affibody molecules for imaging EGFR expression in tumours

Affibody molecules are promising scaffold-based targeting proteins for radionuclide imaging and cancer therapy. This thesis is based on 5 original research articles (Papers I-V), with the primary focus being placed on the optimization of molecular design of EGFR-binding affibody variants for high contrast imaging of epidermal growth factor receptor (EGFR) expression in tumours. The goal of my studies was to investigate the effect of labelling chemistry on the targeting properties of the anti-EGFR affibody molecule ZEGFR:2377 labelled with technetium-99m (99mTc) for single-photon emission computed tomography (SPECT), gallium-68 (68Ga), zirconium-89 (89Zr) and gallium-66 (66Ga) for positron-emission tomography (PET) to select radiolabelled variants providing the best imaging contrast. In Paper I, we showed the feasibility of stably labelling the anti-EGFR affibody molecule ZEGFR:2377 with 99mTc using a peptide-based cysteine-containing chelator and evaluated the imaging of EGFR expression in tumours using the [99mTc]Tc-ZEGFR:2377 affibody molecule. In Paper II, the effect of the composition of cysteine-containing peptide-based chelators on the biodistribution of 99mTc-labelled anti-EGFR affibody molecules was investigated. We evaluated whether the use of glutamate-based chelators improved the imaging properties of 99mTc-labelled ZEGFR:2377. In Paper III, the use of cyclic (FSC) versus noncyclic chelators (DFO) as bifunctional chelators for radiolabelling the anti-EGFR affibody molecule ZEGFR:2377 with 89Zr was investigated. The in vitro and in vivo properties of the resulting DFO- and FSC-ZEGFR:2377 molecules labelled with 89Zr were studied. In Paper IV, the targeting properties of [68Ga]Ga-DFO-ZEGFR:2377 were evaluated and compared directly with the properties of [89Zr]Zr-DFO-ZEGFR:2377 at 3 h after injection. In Paper V, the targeting properties of [66Ga]Ga-DFO-ZEGFR:2377 were evaluated and compared directly with the properties of [68Ga]Ga-DFO-ZEGFR:2377 and [89Zr]Zr-DFO-ZEGFR:2377 at 3 and 24 h after injection, respectively.N