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Penetration and binding of epidermal growth factor-dextran conjugates in spheroids of human glioma origin
1Department of Radiation Sciences, Uppsala University, Sweden.
Abstract:
Targeting with toxic EGF-based conjugates against tumour cells with amplified EGF-receptors might be a possible approach towards improved therapy of certain malignancies such as gliomas and squamous carcinomas. In this study, the penetration and binding of 125I delivered by EGF-dextran conjugates were analysed in cultured spheroids applied as a tumour nodule model. The spheroids consisted of human glioma cells, U-343MGaCl2:6, with large amounts of EGF-receptors. The penetration and binding patterns of 125I delivered by 125I-EGF and 125I-dextran were analysed for comparison. The EGF-dextran associated 125I-activity showed a rather slow penetration but after some hours significant amounts of radioactivity had reached the deeper regions and good penetration was obtained within 5 hours. The penetration seemed somewhat faster when the 125I-activity was delivered with EGF possibly dependent on the lower molecular weight allowing for faster diffusion. Furthermore, EGF-dextran associated 125I seemed to penetrate somewhat faster after the EGF-receptors were blocked with non-radioactive EGF, probably due to the lack of binding preventing free diffusion. After administration of 125I-EGF-dextran or 125I-EGF, the binding patterns were superimposed on the penetration patterns. In the penetration studies, the superimposed accumulations due to binding were removed by presaturation of the receptors with non-radioactive EGF. After a 1 hour incubation, binding of EGF-dextran associated 125I-activity could be seen only in an outer region, with an approximative thickness of 50 microns, of the viable cell layer. Extensive receptor specific binding in the deeper regions, at a depth of 100-200 microns, was seen after several hours incubation. In addition, low levels of non-specific binding in the central regions were seen when the 125I-activity was delivered with dextran without EGF. A similar low background binding was seen also in the centre of spheroids incubated with 125I-EGF-dextran or 125I-EGF after saturation of the receptors with non-radioactive EGF. However, the major amount of radioactivity delivered as 125I-EGF-dextran or 125I-EGF had a receptor specific binding and, also in inner regions, it could be displaced by non-radioactive EGF. Thus, EGF-dextran, which is a candidate compound for targeted therapy, allowed penetration of the applied radioactivity and binding could be observed, after some hours, also in the inner regions of the spheroids.
Insights
Targeting tumors with Epidermal Growth Factor (EGF)-based conjugates shows promise for cancer therapy. EGF-dextran conjugates effectively penetrate tumor spheroids and exhibit receptor-specific binding in deeper regions after several hours.
Area of Science:
- Oncology
- Bioconjugation Chemistry
- Radiopharmaceutical Therapy
Background:
- Tumor cells with amplified Epidermal Growth Factor Receptors (EGFR) are targets for novel cancer therapies.
- EGF-based conjugates offer a potential strategy for targeted delivery of therapeutic agents to malignancies like gliomas and squamous carcinomas.
Purpose of the Study:
- To evaluate the penetration and binding characteristics of Iodine-125 (125I) delivered via Epidermal Growth Factor (EGF)-dextran conjugates in a tumor spheroid model.
- To compare the behavior of 125I-EGF-dextran with 125I-EGF and 125I-dextran to understand the role of EGF and molecular weight in delivery and binding.
Main Methods:
- Utilized cultured human glioma cell spheroids (U-343MGaCl2:6) overexpressing EGF receptors as a tumor nodule model.
- Administered radiolabeled tracers: 125I-EGF-dextran, 125I-EGF, and 125I-dextran.
- Analyzed penetration and binding patterns using techniques that allowed for the removal of non-specific binding via receptor saturation with unlabeled EGF.
Main Results:
- EGF-dextran associated 125I demonstrated significant penetration into deeper spheroid regions within 5 hours.
- Receptor-specific binding of 125I-EGF-dextran was observed in outer regions after 1 hour, extending to deeper regions (100-200 microns) after several hours.
- Non-specific binding was minimal, particularly when receptors were saturated, and the majority of radioactivity showed EGF receptor-dependent binding.
Conclusions:
- EGF-dextran conjugates facilitate the penetration of radioactivity into tumor spheroids.
- Significant EGF receptor-specific binding occurs in both superficial and deeper regions of the tumor model, supporting their potential in targeted therapy.
- EGF-dextran conjugates represent a viable candidate for targeted cancer therapy, demonstrating effective delivery and specific binding within tumor models.