Pharmacokinetic studies and synergistic antitumor effects of cannabichromene and cannabidiol in drug-resistant breast cancers.

Triple-negative breast cancer (TNBC) is highly aggressive with limited treatment options, and resistance to doxorubicin (DOX) further compromises outcomes. Cannabinoids such as cannabichromene (CBC) and cannabidiol (CBD) possess anticancer properties, but their combined effects in resistant TNBC remain unexplored. This study evaluated the antitumor efficacy of a CBC + CBD combination against DOX-resistant (DOX-RT) TNBC using in vitro, in vivo, and pharmacokinetic models. Cytotoxicity was assessed in DOX-RT MDA-MB-231 cells using 2D and 3D assays, with synergy confirmed by combination index (CI) analysis. Cell cycle and invasion assays were performed. Xenograft studies were conducted in BALB/c nude mice bearing DOX-RT tumors treated intraperitoneally with CBC (10 mg/kg), CBD (20 mg/kg), or CBC + CBD. Pharmacokinetics were evaluated in rats, complemented by GastroPlus™ simulations. CBC + CBD synergistically inhibited cell growth induced G0/G1 arrest, and reduced invasiveness by ~ 55% in a Transwell Matrigel invasion assay. In xenografts, combination therapy reduced tumor volume by two-folds compared to single treatments and fourfolds versus control. Western blotting revealed downregulation of MEK/ERK, PI3K/AKT/mTOR, Cyclin D1, CDK6, SOD2, and NF-κB. Pharmacokinetic studies showed co-administration increased Cmax and AUC without altering Tmax, supported by simulations predicting enhanced jejunal absorption. CBC + CBD co-therapy demonstrates synergistic efficacy against resistant TNBC by inhibiting oncogenic pathways and enhancing systemic exposure. This first study of its kind highlights CBC + CBD as a promising strategy to overcome DOX resistance in TNBC.