title: Increased betulinic acid induced cytotoxicity and radiosensitivity in glioma cells under hypoxic conditions.
abstract: BACKGROUND
  Betulinic acid (BA) is a novel antineoplastic agent under evaluation for tumor therapy. Because of the selective cytotoxic effects of BA in tumor cells (including gliomas), the combination of this agent with conservative therapies (such as radiotherapy and chemotherapy) may be useful. Previously, the combination of BA with irradiation under hypoxic conditions had never been studied.
  
  
  METHODS
  In this study, the effects of 3 to 30 μM BA on cytotoxicity, migration, the protein expression of PARP, survivin and HIF-1α, as well as radiosensitivity under normoxic and hypoxic conditions were analyzed in the human malignant glioma cell lines U251MG and U343MG. Cytotoxicity and radiosensitivity were analyzed with clonogenic survival assays, migration was analyzed with Boyden chamber assays (or scratch assays) and protein expression was examined with Western blot analyses.
  
  
  RESULTS
  Under normoxic conditions, a half maximal inhibitory concentration (IC50) of 23 μM was observed in U251MG cells and 24 μM was observed in U343MG cells. Under hypoxic conditions, 10 μM or 15 μM of BA showed a significantly increased cytotoxicity in U251MG cells (p = 0.004 and p = 0.01, respectively) and U343MG cells (p < 0.05 and p = 0.01, respectively). The combination of BA with radiotherapy resulted in an additive effect in the U343MG cell line under normoxic and hypoxic conditions. Weak radiation enhancement was observed in U251MG cell line after treatment with BA under normoxic conditions. Furthermore, under hypoxic conditions, the incubation with BA resulted in increased radiation enhancement. The enhancement factor, at an irradiation dose of 15 Gy after treatment with 10 or 15 μM BA, was 2.20 (p = 0.02) and 4.50 (p = 0.03), respectively. Incubation with BA led to decreased cell migration, cleavage of PARP and decreased expression levels of survivin in both cell lines. Additionally, BA treatment resulted in a reduction of HIF-1α protein under hypoxic conditions.
  
  
  CONCLUSIONS
  Our results suggest that BA is capable of improving the effects of tumor therapy in human malignant glioma cells, particularly under hypoxic conditions. Further investigations are necessary to characterize its potential as a radiosensitizer.
authors: Department of Radiotherapy, Martin-Luther-University Halle-Wittenberg, Dryanderstr, 4, 06110 Halle, Germany. matthias.bache@medizin.uni-halle.de
authors: Matthias
authors: M
authors: Bache
authors: Martin P
authors: MP
authors: Zschornak
authors: Sarina
authors: S
authors: Passin
authors: Jacqueline
authors: J
authors: Kessler
authors: Henri
authors: H
authors: Wichmann
authors: Matthias
authors: M
authors: Kappler
authors: Reinhard
authors: R
authors: Paschke
authors: Goran N
authors: GN
authors: Kaluđerović
authors: Harish
authors: H
authors: Kommera
authors: Helge
authors: H
authors: Taubert
authors: Dirk
authors: D
authors: Vordermark
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002465:Cell Movement; D002470:Cell Survival; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D000860:Hypoxia; D053978:Pentacyclic Triterpenes; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D014315:Triterpenes / Q000494:pharmacology*; D014945:Wound Healing; D000094062:Betulinic Acid
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D053978:Pentacyclic Triterpenes; D011838:Radiation-Sensitizing Agents; D014315:Triterpenes; D000094062:Betulinic Acid