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Effects of affinity on binding of HER2-targeting Affibody molecules: model experiments in breast cancer spheroids
O F Qvarnström1, M Simonsson, J Carlsson
1Section of Oncology, Department of Radiology, Oncology and Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-751 85 Uppsala, Sweden.
Abstract:
Binding of a targeting agent in tumor tissue is influenced by many factors such as molecular weight, charge and affinity of the targeting agent and vascularization of the tumor. In this study, we analyzed tumor cell binding of three HER2-specific and radiolabeled Affibody molecules with different affinities. The Affibody molecules had affinities in the range of 0.12-3.8 nM. Cellular binding was analyzed, after 2 h of incubation, in tumor spheroids composed of BT474 breast cancer cells, which highly express HER2. Binding was, due to the binding-site barrier, limited to the outer 15 ± 5 µm rim of the spheroids, independent of affinity when the concentration of the substances was low. When the concentration was high, the binding site barrier was overcome and the binding occurred approximately 35 ± 5 µm into the spheroids for the two high affinity substances and 50 ± 5 µm for the low affinity substance. The lower affinity might allow for penetration into deeper regions due to less firm binding. We conclude that there is a binding site barrier within tumor spheroids which can be overcome by increased concentration of substance and modified by affinity.
Insights
Tumor targeting agents like Affibody molecules face a binding site barrier in spheroids. Higher concentrations and lower affinity can improve penetration into deeper tumor regions.
Area of Science:
- Oncology
- Biochemistry
- Radiopharmaceutical Science
Background:
- Targeting agents for tumor therapy are affected by factors like molecular weight, charge, affinity, and tumor vascularization.
- Understanding these factors is crucial for optimizing drug delivery and efficacy in cancer treatment.
Purpose of the Study:
- To analyze the tumor cell binding of three HER2-specific Affibody molecules with varying affinities.
- To investigate the influence of Affibody affinity and concentration on penetration into tumor spheroids, considering the binding-site barrier.
Main Methods:
- Radiolabeled HER2-specific Affibody molecules with affinities ranging from 0.12-3.8 nM were used.
- Tumor spheroids composed of BT474 breast cancer cells (high HER2 expression) were incubated with Affibody molecules for 2 hours.
- Cellular binding was quantified at different depths within the spheroids under varying concentrations.
Main Results:
- Binding was initially limited to the outer 15 ± 5 µm rim of spheroids due to the binding-site barrier, irrespective of affinity at low concentrations.
- At high concentrations, the binding site barrier was overcome, with binding reaching approximately 35 ± 5 µm for high-affinity molecules and 50 ± 5 µm for the low-affinity molecule.
- Lower affinity demonstrated potential for deeper penetration into tumor spheroids.
Conclusions:
- A significant binding site barrier exists within tumor spheroids, limiting the penetration of targeting agents.
- Increased concentration of the targeting agent can overcome this barrier.
- Affinity plays a crucial role, with lower affinity potentially facilitating deeper drug penetration for enhanced therapeutic outcomes.
