Cannabidiol selectively downregulates FAM111B expression and induces apoptosis in fibrosarcoma cells: an in vitro study

Fibrosarcoma is a rare and aggressive soft tissue sarcoma with limited therapeutic options and poor outcomes in advanced disease. Family with sequence similarity 111 member B (FAM111B) has emerged as a pro-tumorigenic factor associated with dysregulated cell survival and proliferation. Cannabidiol (CBD), a non-psychoactive phytocannabinoid, exhibits anticancer activity in multiple malignancies, but its effects on FAM111B expression and downstream pathways in fibrosarcoma remain unclear.

The effects of CBD were evaluated in human fibrosarcoma (HT1080) cells and non-cancerous human fibroblasts (FG0). Cell metabolic activity was assessed using an MTT assay. Gene and protein expression were determined by real-time quantitative PCR and Western blotting, respectively. Apoptosis and cell-cycle distribution were assessed by flow cytometry using Annexin V-FITC/propidium iodide (PI) and PI staining alone, respectively. Statistical analyses were performed using an unpaired Student's t-test or a two-way analysis of variance (ANOVA) followed by Šídák's post hoc multiple comparisons test, as appropriate.

CBD reduced metabolic activity in both HT1080 and FG0 cells in a dose-dependent manner, with comparable IC₅₀ values (28.95 ± 3.15 µM and 30.75 ± 9.12 µM, respectively), indicating limited selectivity based on metabolic activity alone. CBD significantly reduced FAM111B mRNA expression by approximately 3-fold in HT1080 cells and 2-fold in FG0 cells; however, a significant reduction in FAM111B protein expression was observed only in HT1080 cells, CBD treatment was associated with marked downregulation of BAG3 and Cyclin B1 proteins, increased apoptosis (Annexin V-positive cells: 3.55 ± 0.78% vs. 13.20 ± 4.56%), and altered cell-cycle progression characterized by increased Sub-G1 (3.44 ± 1.10% vs. 18.37 ± 0.83%) and G0/G1 (28.30 ± 1.57% vs. 39.17 ± 0.85%) populations, with corresponding reductions in the S- and G2/M-phase populations. These effects were markedly attenuated in non-cancerous fibroblasts.

CBD exerts context-dependent anticancer effects in HT1080 fibrosarcoma cells by selectively suppressing FAM111B protein expression, promoting apoptosis, and disrupting cell-cycle progression. These findings identify FAM111B- and BAG3-associated pathways as potential therapeutic vulnerabilities and support further investigation of CBD as a modulator of stress-adaptive and proliferative signaling in preclinical fibrosarcoma models.