Influence of irradiation on the metabolism of melanoma cells and development of corresponding in vitro and in vivo models for the characterization of radiopharmaceuticals

Aim:

Irradiation is an effective implement for the therapy of solid tumors. But often single cells elude this treatment and constitute a basis for recurrence of the primary tumor and formation of metastases. One possible explanation for this observation could be predicted on irradiationdependent metabolic changes which lead to a predisposition of certain cells to show enhanced survival and migratory activity. The aim of our study was to investigate metabolic properties of irradiated melanoma cells which should further enable us to develop and validate appropriate in vitro and in vivo models for the characterization of new radiopharmaceuticals for diagnosis and therapy of metastases and solid tumors.

Materials and methods:

We applied different singledose X‐ray irradiation (1, 2, 5, 7, 10, and 20 Gy) to murine B16‐F10 melanoma cells. At several timepoints we analyzed cell viability, growth properties, clonogenic regrowth capability, cellular proliferation, and expression of cell cycle markers. Furthermore, we analyzed the cellular uptake of the radiotracers 2‐[18F]Fluor‐2‐desoxy‐D‐glucose and 3‐O‐Methyl‐[18F]fluor‐L‐DOPA, providing information about the glucose and amino acid metabolism before and after irradiation. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of untreated and irradiated melanoma cells to form lung metastases. Results: In a dosedependent manner we detected a decrease in the growth properties, viability and tracer uptake of the melanoma cells, particularly, in the period 3 to 6 days after irradiation. In contrast, already one day after irradiation cell cycle analyses showed an increase in the number of G2/M phase cells and the expression of G2‐phase markers in irradiated compared to untreated cells. Additionally, in vitro analyses showed an influence of irradiation concerning the extent to form lung metastases in the mouse.

Conclusion:

Our results indicate that metabolic changes in melanoma cells after irradiation can be analyzed by a set of different in vitro and in vivo approaches, even in a dose‐dependent manner. Using this experimental approach, we are able to characterize new radiotracers and, furthermore, to investigate metabolic effects of applied radiopharmaceuticals in combination with experimental radiation therapy.