Adipocyte Secretome Increases Radioresistance of Malignant Melanocytes by Improving Cell Survival and Decreasing Oxidative Status.

Pedro Coelho,Armanda Monteiro,Mónica Vieria,Gabriela Pinto,Rúben Fernandes,Isabel Faria,Cristina Prudêncio,Liliana Silva,Raquel Soares

doi:10.1667/rr14551.1

Abstract

Radiotherapy is a treatment option for the majority of malignancies. However, because melanoma is known to be radioresistant, the use of ionizing radiation as an adjuvant therapy in cutaneous melanoma patients is ineffective. Obesity has now been recognized as a risk factor for melanoma. High adiposity is generally associated with a more pro-oxidative status. Oxidative stress is a major player in radiation therapy and also a common link between obesity and cancer. Several adipocyte-released proteins are known to have a role in controlling cellular growth and pro-survival signaling. For that reason, we investigated the influence of 3T3-L1 mature adipocyte secretome in B16-F10 malignant melanocyte radiosensitivity. We evaluated B16-F10 cell survival and redox homeostasis when exposed to four daily doses of ionizing radiation (2 Gy per day) up to a total of 8 Gy in a medical linear accelerator. B16-F10 melanocytes exhibited slight alterations in survival, catalase activity, nitrative stress and total oxidant concentration after the first 2 Gy irradiation. The motility of the melanocytes was also delayed by ionizing radiation. Subsequent irradiations of the malignant melanocytes led to more prominent reductions in overall survival. Remarkably, 3T3-L1 adipocyte-secreted molecules were able to increase the viability and migration of melanocytes, as well as lessen the pro-oxidant burden induced by both the single and cumulative X-ray doses. In vitro adipocyte-released factors protected B16-F10 malignant melanocytes from both oxidative stress and loss of viability triggered by radiation, enhancing the radioresistant phenotype of these cells with a concomitant activation of the AKT signaling pathway. These results both help to elucidate how obesity influences melanoma radioresistance and support the usage of conventional medical linear accelerators as a valid model for the in vitro radiobiological study of tumor cell lines.

Highlights

Melanoma is one of the world’s most rapidly increasing malignancies [1] The number of reported cases increasing for the last few decades
Exposure to radiation (2 Gy) slowed down B16-F10 motility towards the injury void space, 4 h postirradiation, but this effect was reversed when 3T3-L1 conditioned media (CM) was present (Fig. 2A). These results indicate that adipocyte-released molecules can protect melanoma cancer cells from X-ray radiation damages, both reducing antioxidant status and enhancing cell migration
Our results disclosed an increased metabolic activity of irradiated melanocytes when treated with adipocyte conditioning media (3T3-L1 CM)

Summary

Introduction

Melanoma is one of the world’s most rapidly increasing malignancies [1] The number of reported cases increasing for the last few decades. Over 176,000 new cases of melanoma are reported annually in Europe and the U.S [2, 3]. Melanoma treatment has remained the same for the last few decades: surgical excision of the malignant mass is still the most effective treatment in primary melanomas [4]. Radiationinduced ionization of regulatory proteins and DNA might render the cells unviable and culminate in cellular death [5]. Ionizing radiation can indirectly cause cellular damage. The formation of highly reactive oxygen and nitrogen radicals increases the intracellular oxidative stress, depleting the antioxidant defenses, which subsequently react with many cellular components (DNA, proteins, lipids) leading to unrecoverable damage [6]

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Conclusion