Pro-Synergistic Interaction of Farnesene and Daunorubicin Enhances Apoptotic Vulnerability in U87MG Glioblastoma Cells.

Glioblastoma (GBM) remains one of the most lethal primary brain tumors, characterized by aggressive proliferation, marked therapeutic resistance, and limited responsiveness to standard chemoradiotherapy. Therefore, identifying combination strategies capable of enhancing cytotoxic efficacy while minimizing toxicity is of considerable interest. In this study, we investigated the antitumor potential of Farnesene, a sesquiterpene natural compound, alone and in combination with the anthracycline chemotherapeutic Daunorubicin in U87MG glioblastoma cells. MTT assays demonstrated that Farnesene exerts strong tumor-selective cytotoxicity, with an IC₅₀ value of 4.65 µM in U87MG cells compared with 264.0 µM in non-malignant HDFa fibroblasts. Daunorubicin also reduced viability in a dose-dependent manner (IC₅₀ = 9.81 µM in U87MG), although with lower selectivity. Fixed-ratio combination analyses revealed pronounced synergism, as evidenced by markedly negative Bliss scores, high Highest Single Agent (HSA) advantages, and Combination Index values below 1 at submaximal concentrations. Flow cytometry using Annexin V/PI staining confirmed that the combination significantly increased both early and late apoptotic populations relative to monotherapies. FDA/PI fluorescent imaging supported these findings, showing a substantial elevation in non-viable PI-positive cells, whereas Hoechst 33,258 staining indicated preserved nuclear morphology at 24 h, consistent with early apoptotic engagement rather than immediate genotoxic collapse. Our results suggest that Farnesene not only exhibits potent and selective cytotoxicity toward glioblastoma cells but also enhances Daunorubicin-induced apoptosis through synergistic interactions. These findings highlight the preclinical potential of this combination and provide a rationale for further mechanistic and in vivo evaluation in experimental GBM models.