GABAB receptor regulates proliferation in the high-grade chondrosarcoma cell line OUMS-27 via apoptotic pathways

Background: High-grade chondrosarcoma, which has a high incidence of local recurrence and pulmonary metastasis despite surgical resection, is associated with poor prognosis. Therefore, new and effective adjuvant therapies are urgently required for this disease. Gamma-aminobutyric acid (GABA), which acts as a neurotrophic factor during nervous system development, is related to the proliferation and migration of certain cancer cells. The GABAergic system, which is composed of GABA, the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), and GABA receptors, has an important function in nerve growth and development of neural crest. Therefore, the GABAergic system may play important functional roles in the proliferation of chondrosarcoma cells, which are derived from neural crest cells. We examined the anti-tumor effects of the GABAergic system on a chondrosarcoma cell line. Methods: We evaluated the underlying mechanisms of the anti- tumor effects of the GABAergic system, such as the involvement of different signaling pathways, apoptosis, and cell cycle arrest, in the high-grade chondrosarcoma cell line OUMS-27. In addition, we performed whole-cell patch-clamp recordings for Ca2+ currents and evaluated the changes in intracellular Ca2+ concentration via Ca2+ channels, which are related to the GABA(B) receptor in high-grade chondrosarcoma cells. Results: The GABA(B) receptor antagonist CGP had anti- tumor effects on high-grade chondrosarcoma cells in a dose-dependent manner. The activities of caspase 3 and caspase 9 were significantly elevated in CGP-treated cells compared to in untreated cells. The activity of caspase 8 did not differ significantly between untreated cells and CGP-treated cells. However, caspase 8 tended to be up-regulated in CGP-treated cells. The GABA(B) receptor antagonist exhibited anti- tumor effects at the G1/S cell cycle checkpoint and induced apoptosis via dual inhibition of the PI3/Akt/mTOR and MAPK signaling pathways. Furthermore, the changes in intracellular Ca2+ via GABA(B) receptor-related Ca2+ channels inhibited the proliferation of high-grade chondrosarcoma cells by inducing and modulating apoptotic pathways. Conclusions: The GABA(B) receptor antagonist may improve the prognosis of high-grade chondrosarcoma by exerting anti- tumor effects via different signaling pathways, apoptosis, cell cycle arrest, and Ca2+ channels in high-grade chondrosarcoma cells.