Probiotics, particularly Lactobacillus species, show promise as adjuvants in cancer therapy due to their pro-apoptotic effects. This study investigated the synergistic impact of Lactobacillus fermentum (Ab.RS23) and vincristine sulfate on colorectal (HT-29) and breast (MCF-7) cancer cells.

Cells were treated with vincristine, L. fermentum, or both. Cell viability was measured by MTT assay. Apoptosis was analyzed via Annexin V-FITC/PI flow cytometry. Gene expression changes were evaluated by RT-qPCR.

Co-treatment reduced the IC₅₀ of vincristine by 8-fold in HT-29 and 13-fold in MCF-7 cells. Apoptotic signaling was enhanced, with pro-apoptotic pathways upregulated and survival pathways downregulated.

L. fermentum enhanced vincristine-induced apoptosis and reduced the required drug dose, which may contribute to lowering vincristine-associated toxicity. These findings require confirmation through in vivo studies.