Research in mice at the Mayo Clinic in Rochester, Minnesota, has shown that rapamycin boosts the therapeutic effect of radiation by delaying the regrowth of brain tumours after treatment.
Their findings are being presented at the EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics, in Frankfurt, Germany.
Lead investigator Dr Jann Sarkaria, assistant professor and consultant in the clinic's Department of Oncology, told a news briefing today (Thursday 21 November) that combined rapamycin and radiation treatment delayed regrowth of glioblastoma multiforme (GBM) human tumours in mice for an average 19 days compared to treatment with rapamycin alone. In contrast, radiation treatment alone or rapamycin alone had no effect on tumour growth compared to control treatment.
Rapamycin inhibits the activity of a protein, mTOR, which functions in a signalling pathway to promote tumour growth. Rapamycin binds to a receptor protein (FKBP12) and the rapamycin/FKB12 complex then binds to mTOR and prevents interaction of mTOR with target proteins in this signalling pathway.
"It's already known that rapamycin specifically inhibits mTOR and that mTOR is important in regulating cell growth and proliferation. Many GBM tumours have genetic changes that hyperactivate mTOR signalling, and these are the tumours most likely to respond to rapamycin therapy," said Dr Sarkaria.
"But, the exciting finding from our study is that this is the first evidence that mTOR is involved in the cellular response to radiation. It's not clear yet how it works but we think rapamycin slows tumour proliferati
Contact: Margaret Willson
European Organisation for Research and Treatment of Cancer