A Caco-2 and Bifidobacterium bifidum co-culture model to assess lapatinib’s effects on intestinal microbiota and cell viability

Background: Lapatinib (LAP), a tyrosine kinase inhibitor (TKI) used to treat ErbB2-overexpressing breast cancer, is frequently associated with diarrhoea reported in 58–78 % of patients. Decreased Bifidobacterium spp. levels in TKI-treated patients have been observed, suggesting a link between LAP and gut microbiota alterations, but the underlying interactions remain unclear. The present study established a Caco-2/Bifidobacterium bifidum (BB) co-culture model to examine the effects of LAP on intestinal epithelial cell viability, bacterial viability, and bacterial adhesion. Methods: BB morphology was confirmed by Gram staining and scanning electron microscopy. Caco-2 cells, representing the intestinal epithelium, were co-cultured with BB at different bacterial concentrations and treated with LAP. Caco-2 cell viability was assessed using an MTS assay; BB viability was determined with a bacterial viability assay, while bacterial adhesion was quantified by recovering adhered BB following LAP treatment and enumerating colony-forming units (CFU). Results: LAP reduced Caco-2 cell viability at all bacterial concentrations, although differences were not statistically significant (p > 0.05). Although not statistically significant, a higher BB concentration (1 × 10^8 CFU/mL) was associated with slightly greater cell viability (86.60 % ± 2.73). While LAP initially decreased BB viability, bacterial proliferation subsequently increased, reaching 115.66 % ± 6.25 by 96 hours. A high number of viable, adhered BB was recovered from Caco-2 cells even after LAP treatment, indicating that bacterial-host interactions persisted despite drug exposure. Conclusions: LAP suppresses epithelial cell viability and transiently reduces BB growth, but BB rapidly recovers and maintains adhesion to Caco-2 cells. LAP may induce epithelial stress that modifies surface properties, thereby favouring adhesion without preserving barrier integrity. Further studies assessing tight-junction proteins and permeability are needed to confirm whether BB adhesion mitigates LAP-induced epithelial disruption.