Induction of cyclopamine resistance in desmoplastic medulloblastoma cells increases their cancer stem-like cell compartment and their in vitro tumorigenic potential

Abstract

Current treatment against medulloblastoma, one of the most frequent tumors in childhood and early adolescence, is not effective enough, presenting long time relapses in addition to side effects in growth and intellectual outcome of patients. Among the different types of medulloblastoma, we focused on the sonic hedgehog (Shh) type of this disease. Cyclopamine inhibits the Shh pathway. Medulloblastoma very often presents chemotherapy resistance. We tried, in this work to understand the mechanism of cyclopamine resistance in Shh meduloblastoma. In our study we induced cyclopamine resistance to Daoy desmoplastic Shh type medulloblastoma cells by treating them with this drug for a long period of time. Cellular assays (proliferation, clonogenicity, and migration), together with qRT-PCR molecular experiments allowed us to verify the different behaviour of the cells after each cyclopamine exposure. The results highlight the evidence that cells became resistant because they were able to grow in soft agar without attachment, to migrate and to overexpress genes related to cancer stem-like cell phenotypes. The resistance induced seems to have a cyclic behaviour, as according with the results Daoy cells might sustain a subgroup of cancer stem-like cells in the tumor that never disappear despite cyclopamine treatments. Induction of cyclopamine resistance in desmoplastic Shh medulloblastoma cells increases their cancer stem-like cell compartment and their in vitro tumorigenic potential. Further studies are required to properly understand the mechanisms of cyclopamine resistance and the possible ways to overcome it.