Yes it has. There are several papers discussing this. Perhaps this review might be a good starting point: http://neuro-oncology.oxfordjournals.org/content/early/2015/07/14/neuonc.nov125.long
Thank a lot for the response. Unfortunately my library does'n offer that journal. I've read several papers on the subject, but just one reports a clear image of the barrier (Gatenby and Gawlinsky, 1996) and is not specific for GBM.. Have you read papers, specifically dedicated to GBM and clearly showing in a real picture of the Warburg barrier?