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Updated: Oct 24, 2026
Therapy Testing in a Spheroid-based 3D Cell Culture Model for Head and Neck Squamous Cell Carcinoma
Published on: April 20, 2018
[3H]gemcitabine uptake by nucleoside transporters in a human head and neck squamous carcinoma cell line
J R Hammond1, S Lee, P J Ferguson
1Department of Pharmacology and Toxicology, University of Western Ontario, London, Ontario, Canada.jhammo@julian.uwo.ca
Abstract:
Cellular uptake of many chemotherapeutic nucleoside analogs is dependent on the activity of a family of nucleoside transport proteins located in the cell plasma membrane. In the present study, we examined the role of these transporters in the accumulation of gemcitabine by a human head and neck squamous carcinoma cell line. The uptake of [3H]gemcitibine was compared with that of [3H]uridine and [3H]formycin B in the parent cell line (HN-5a) and in a gemcitabine-resistant variant (GEM-8e). The HN-5a and GEM-8e cells were similar in their transport characteristics and expressed predominantly the es (equilibrative, inhibitor-sensitive) transporter subtype; less than 10% of the influx of [3H]formycin B or [3H]uridine was mediated by the ei (equilibrative inhibitor-resistant) system, and there was no evidence for Na+-dependent nucleoside transporters. [3H]Gemcitabine (10 microM) entered these cells via both the es and ei transporters with an initial rate of uptake similar to that seen with the use of [3H]formycin B or [3H]uridine. In addition, ATP-replete cells accumulated significantly less [3H]gemcitabine than did ATP-depleted cells, which is indicative of an active efflux mechanism for gemcitabine. These results show that gemcitabine is a substrate for both the es and ei nucleoside transporters of HN-5a and GEM-8e cells and that gemcitabine resistance of the GEM-8e cells cannot be attributed to changes in transporter activity. Further studies to define the characteristics of the putative efflux mechanism are clearly warranted because this system has the potential to significantly affect the clinical efficacy of gemcitabine.
Insights
Gemcitabine enters cancer cells via nucleoside transporters, but an active efflux mechanism may reduce its effectiveness. Gemcitabine resistance in head and neck cancer cells is not due to altered transporter activity.
Area of Science:
- Pharmacology
- Molecular Biology
- Oncology
Background:
- Cellular uptake of nucleoside analogs, like gemcitabine, is crucial for chemotherapy.
- Nucleoside transport proteins in the cell membrane mediate this uptake.
- Understanding these transporters is key to optimizing gemcitabine efficacy.
Purpose of the Study:
- To investigate the role of nucleoside transporters in gemcitabine accumulation in head and neck squamous carcinoma cells.
- To compare transporter activity in a parent cell line (HN-5a) and a gemcitabine-resistant variant (GEM-8e).
Main Methods:
- Utilized radiolabeled gemcitabine, uridine, and formycin B to assess nucleoside transport.
- Compared uptake in parent (HN-5a) and gemcitabine-resistant (GEM-8e) cell lines.
- Investigated the influence of cellular ATP levels on gemcitabine accumulation.
Main Results:
- Both HN-5a and GEM-8e cells predominantly express equilibrative, inhibitor-sensitive (es) and equilibrative, inhibitor-resistant (ei) nucleoside transporters.
- Gemcitabine uptake occurred via both es and ei transporters, similar to uridine and formycin B.
- ATP-depleted cells showed higher gemcitabine accumulation, indicating an active efflux mechanism.
Conclusions:
- Gemcitabine is a substrate for both es and ei nucleoside transporters in these cell lines.
- Gemcitabine resistance in the GEM-8e variant is not caused by altered nucleoside transporter activity.
- An active efflux mechanism for gemcitabine warrants further investigation due to its potential impact on clinical efficacy.
