Objective: Radioimmunotherapy (RIT) is a systemic therapy currently used in the treatment of patients
with lymphoma. RIT complexes consist of a targeting molecule, commonly an antibody, radionuclide chelates and a linker which can be a nanoparticle platform. Nanoparticles facilitate the attachment of multiple radionuclides and targeting groups to a single complex. Here the target affinity, duration of target
association and inhibition of colony formation of Cetuximab-resistant tumour cells with Cetuximabtargeted [177Lu]-AuNPs were investigated. Dose distribution in xenografts derived from EGFRoverexpressing cells was also determined.
Methods: Cetuximab-targeted [177Lu]-AuNPs were generated by functionalising 15nm AuNPs with the
chelator DOTA and Cetuximab and radiolabelling with 177LuCl3. KDis, a measure of affinity, was determined by competitive binding to EGFR expressing cells. Radio-sensitivity was determined in EGFR
expressing tumour cells including the Cetuximab resistant cell line HCT116 using a colony formation
assay. Dose distribution was measured in sections from xenografts grown in nude mice using autoradiography.
Results: KDis for the complex binding to EGFR on MDA-MB-468 cells was 20 nM. Loss of cell associated
[
177Lu] activity was biphasic with loss of about 50% of activity in about 4 h. Remaining activity dissociated
over a period of about 4 days. HCT8 and MDA-MB-468, but not HCT116 cells were sensitive to the growth
inhibitory effect of Cetuximab. However, treatment with Cetuximab-targeted [177Lu]-AuNPs inhibited
colony formation in all 3 cell lines. Dose distribution across sections from xenografts was found to
demonstrate a co-efficient of variation of 15%.
Conclusion: Cetuximab-targeted [177Lu]-AuNPs demonstrate high affinity for EGFR and could be an effective treatment for Cetuximab-resistant colorectal cancer cells. A strategy involving pre-treatment with
receptor targeted[177Lu] to improve RIT therapeutic ratios has the potential to enhance clinical outcomes.