BACKGROUND: Immunosuppressive therapy is a risk factor for the increased incidence and metastatic progression of malignancies in organ graft recipients. Transforming growth factor (TGF)-beta(1) has been associated with tumor invasion and metastasis, and we have implicated cyclosporine-associated TGF-beta(1) hyperexpression in tumor progression in mice. METHODS: BALB/c mice or severe combined immunodeficient-beige mice were treated with 2 or 4 mg/kg of tacrolimus, and the effect of treatment on mouse renal cancer cell pulmonary metastasis was investigated. We also determined whether tacrolimus induces TGF-beta(1) expression. Spleens from tacrolimus-treated mice were analyzed for level of expression of TGF-beta(1) mRNA with the use of competitive-quantitative polymerase chain reaction assay, and circulating levels of TGF-beta(1) protein were measured with the use of an enzyme-linked immunosorbent assay. RESULTS: Treatment with tacrolimus resulted in a dose-dependent increase in the number of pulmonary metastases in the BALB/c mice (197+/-16 in untreated mice, 281+/-26 in mice treated with 2 mg/kg of tacrolimus, and 339+/-25 in mice treated with 4 mg/kg of tacrolimus; no treatment vs. 4 mg/kg tacrolimus, Bonferroni's P<0.001) and in the severe combined immunodeficient-beige mice (117+/-18 in untreated mice, 137+/-19 in mice treated with 2 mg/kg of tacrolimus, and 216+/-29 in mice treated with 4 mg/kg of tacrolimus; no treatment vs. 4 mg/kg tacrolimus, P<0.05). Treatment with 4 mg/kg but not 2 mg/kg of tacrolimus resulted in a significant increase in the levels of expression of TGF-beta(1) mRNA and circulating levels of TGF-beta(1) protein. CONCLUSIONS: Tacrolimus has a dose-dependent effect on tumor progression and TGF-beta(1) expression, and tacrolimus-induced TGF-beta(1) overexpression may be a pathogenetic mechanism in tumor progression.
