New insights into the anticancer activity of carnosol: p53 reactivation in the U87MG human glioblastoma cell line

Glioblastoma multiforme (GBM) is an aggressive brain tumour with high resistance to radio- and chemotherapy. As such, increasing attention has focused on developing new therapeutic strategies to improve treatment responses. Recently, attention has been shifted to natural compounds that are able to halt tumour development. Among them, carnosol (CAR), a phenolic diterpene present in rosemary, has become a promising molecule that is able to prevent certain types of solid cancer. However, no data are available on the effects of CAR in GBM. Here, CAR activity decreased the proliferation of different human glioblastoma cell lines, particularly cells that express wild type p53. The p53 pathway is involved in the control of apoptosis and is often impaired in GBM. Notably, CAR, through the dissociation of p53 from its endogenous inhibitor MDM2, was able to increase the intracellular p53 levels in GBM cells. Accordingly, functional reactivation of p53 was demonstrated by the stimulation of p53 target genes' transcription, the induction of apoptosis and cell cycle blockade. Most importantly, CAR produced synergistic effects with temozolomide (TMZ) and reduced the restoration of the tumour cells' proliferation after drug removal. Thus, for the first time, these data highlighted the potential use of the diterpene in the sensitization of GBM cells to chemotherapy through a direct re-activation of p53 pathway. Furthermore, progress has been made in delineating the biochemical mechanisms underlying the pro-apoptotic effects of this molecule.