Synergistic Anti-Lung Cancer Effects of Cytarabine and a NCBI-Registered Streptococcus via Modulation of Apoptotic and Survival Pathways.

Lung cancer remains one of the leading causes of cancer-related mortality worldwide, and although Cytarabine (CYT) exhibits anticancer activity, its clinical application is often restricted by dose-dependent toxicity. In this study, we investigated the synergistic anticancer potential of the NCBI-registered probiotic Streptococcus thermophilus Ab.342 SH (GenBank accession no. PX426457) in combination with CYT against human lung adenocarcinoma A549 cells. Following molecular identification of the probiotic isolate, A549 cells were treated with different concentrations of bacterial cell-free supernatant (CFS), CYT, or their combination, while human umbilical vein endothelial cells (HUVECs) were used to evaluate selective cytotoxicity. Cell viability was assessed using the MTT assay, apoptosis-related gene expression was analyzed by qRT-PCR, and apoptotic cell death was confirmed by Annexin V-FITC/PI flow cytometry. The CFS alone reduced A549 cell viability in a dose-dependent manner without significant cytotoxicity toward HUVECs. CYT monotherapy exhibited an IC₅₀ of approximately 40 μg/mL, whereas combination treatment with S. thermophilus CFS (OD₆₀₀ = 1.2) reduced the IC₅₀ to 145 ng/mL, representing an approximately 276-fold dose reduction. Combined treatment significantly upregulated PTEN, BAX, CASP3, CASP8, CASP9, P53, P21, and FAS expression while suppressing AKT, mTOR, BCL-2, and IκB, accompanied by a marked increase in apoptotic cells. These findings demonstrate that S. thermophilus Ab.342 SH markedly enhances the anticancer efficacy of CYT while substantially reducing the required drug dosage, supporting the potential application of probiotic-based adjuvant therapy for safer and more effective lung cancer treatment.