Potential of a Cetuximab‐based radioimmunotherapy combined with external irradiation manifests in a 3‐D cell assay

Abstract

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [ 90 Y]Y-CHX-A 00 -DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD 50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A 00 -DTPA-C225 (DTPA-C225), [ 90 Y]Y-CHX-A 00 -DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD 50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 mg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD 50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

Evaluation of spheroid head and neck squamous cell carcinoma cell models in comparison to monolayer cultures

“…To date, a certain number of studies on HNSCC spheroids have been published (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46) but there is little knowledge on contraposing 2D to 3D cell cultures. These previous studies have focused on novel drug treatments or molecular expression patterns in 3D cell models.…”

Spheroid-based 3D Cell Cultures Enable Personalized Therapy Testing and Drug Discovery in Head and Neck Cancer

“…Therefore, predicting clinical response of new agents tested in 2D cellular assays is limited (32). Although 3D cell culture models are commonly seen to be superior to monolayer cultures as a more reliable drug screening tool, there are only a few studies that deal with spheroids in head and neck cancers (27,33,(52)(53)(54).…”

Improving external beam radiotherapy by combination with internal irradiation

“…However, SAS and FaDu were already controlled after RIT treatment alone in spheroids as well as 2D cultures. 58,59 The obviously higher RIT efficacy in vitro than in xenografts may be explained by differing RIT doses used in the studies. Regardless of the limitations of efficacy tests, in vitro cell culture models offer important possibilities to study other end points such as cellular binding and uptake 55,57,59 as well as downstream signalling.…”

“…58,59 The obviously higher RIT efficacy in vitro than in xenografts may be explained by differing RIT doses used in the studies. Regardless of the limitations of efficacy tests, in vitro cell culture models offer important possibilities to study other end points such as cellular binding and uptake 55,57,59 as well as downstream signalling. 32,57,58 Accordingly, in vitro models should be used to uncover underlying mechanisms and can give indications on efficacy.…”