New anti-glioblastoma strategy with natural compounds sclareol and doxorubicin

Background: Doxorubicin (DOX) has been very effective against glioblastoma invitro. Its application in vivo is hampered because it cannot pass the blood–brainbarrier (BBB). Significant research efforts are invested to overcome this limitation.Sclareol (SC) is an aromatic compound naturally found in clary sage. Thecombination of SC and DOX showed promising effects in different tumor types invitro and in vivo. Therefore, we tested their combination and innovative hybridmolecules (SC:DOX) on glioblastoma cells with the expression of P-glycoprotein, amajor component of BBB and cancer multidrug resistance marker. Methods:Cytotoxicity and selectivity towards glioblastoma cells of SC, DOX, theircombination, and SC:DOX were examined by MTT assay. The effect of SC on DOXaccumulation was determined by flow cytometry. We also studied SC:DOXaccumulation, cellular uptake, localization imaging, and DNA damage induction.Results: The effects of simultaneous SC and DOX treatments demonstrated theconsiderable potential of SC to reverse DOX resistance in glioblastoma cells andincrease DOX accumulation. SC:DOX hybrids, named CON1 and CON2 were lesscytotoxic than DOX, but with reduced resistance and increased selectivity towardsglioblastoma cells. Cellular uptake of CON1 and CON2 was increased in glioblastomacells compared to DOX. Perinuclear localization of CON1 and CON2 vs. nuclearlocalization of DOX as well as no DNA damaging effects suggest a differentmechanism of action for SC:DOX. Conclusion: The combination of SC and DOX, andtheir innovative hybrids, could be considered a promising strategy that can overcomethe limitations of DOX application in glioblastoma.