title: Bryostatin-1 causes radiosensitization of BMG-1 malignant glioma cells through differential activation of protein kinase-Cδ not evident in the non-malignant AA8 fibroblasts.
abstract: Bryostatin-1 (bryo-1), a non-phorbol ester, is known to sensitize mammalian cells against certain chemotherapeutic drugs. We assessed its ability to modify radiation response of mammalian cells using Chinese hamster fibroblasts AA8 cells and human malignant glioma BMG-1 cells. In the malignant glioma BMG-1 cell line, bryo-1 pre-treatment significantly enhanced radiation-induced growth inhibition and cytogenetic damage, and further reduced the clonogenic cell survival as compared to cells irradiated at the clinically relevant dose of 2 Gy. PKCδ expression increased significantly when bryo-1 pre-treated BMG-1 glioma cells were irradiated at 2 Gy and induced prolonged ERK-1/2 activation associated with p21 overexpression. Silencing PKCδ resulted in inhibition of bryo-1-induced radiosensitization. In contrast, bryo-1 failed to alter radiosensitivity (cell survival; growth inhibition; cytogenetic damage) or activate ERK1/2 pathway in the AA8 fibroblasts despite PKCδ phosphorylation at its regulatory (Y155) domain, indicating alternate mechanisms in these non-malignant cells as compared to the glioma cells. This study suggests that bryo-1 may effectively enhance the radiosensitivity of malignant cells and warrants further in-depth investigations to evaluate its radiosensitizing potential in various cell types.
authors.affiliation: Natural Radiation Response Mechanisms Group, Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig. S K Mazumdar Road, Timarpur, Delhi, 110054, India.
authors.forename: Raghubendra Singh
authors.initials: RS
authors.lastname: Dagur
authors.forename: Shashank
authors.initials: S
authors.lastname: Hambarde
authors.forename: Sudhir
authors.initials: S
authors.lastname: Chandna
mesh_terms: D000818:Animals; D054713:Bryostatins / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D006224:Cricetinae; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D005910:Glioma / Q000378:metabolism*; D006801:Humans; D051745:Protein Kinase C-delta / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015854:Up-Regulation
chemical_list: D054713:Bryostatins; D011838:Radiation-Sensitizing Agents; C046785:bryostatin 1; D051745:Protein Kinase C-delta