Monitoring the response of orthotopic bladder tumors to granulocyte macrophage colony-stimulating factor therapy using the prostate-specific antigen gene as a reporter.

PURPOSE Although orthotopic animal models of cancer best reflect the disease in humans, a major drawback of these models is the inability to monitor tumor growth accurately. Our aims were to produce a bladder tumor cell line (MB49) that secreted human prostate-specific antigen (PSA), analyze the feasibility and accuracy of PSA as a biomarker for monitoring orthotopic bladder tumor growth, and evaluate the effectiveness of granulocyte macrophage colony-stimulating factor (GM-CSF) gene therapy using this model. EXPERIMENTAL DESIGN PSA secretion was assessed after both s.c. and orthotopic implantation of MB49-PSA cells in C57BL/6 mice. PSA levels in mouse serum and urine samples were monitored at 2- to 3-day intervals by ELISA. Using the orthotopic model, mice with confirmed tumors were given liposome-mediated GM-CSF gene therapy twice a week for 3 weeks intravesically and PSA levels monitored. RESULTS The MB49-PSA cells behaved similarly as the parental cell line and produced high levels of PSA both in vitro and in vivo. In the s.c. model, the level of PSA produced correlated with tumor volume (r = 0.96). In the orthotopic model, PSA could be detected in serum and urine on the fourth day after implantation. PSA levels over the treatment period indicated that tumor growth was inhibited by GM-CSF gene therapy. Up to 50% of the treated mice were cured. Cytokine array analysis revealed that GM-CSF gene therapy induced the production of other cytokines and chemokines. CONCLUSIONS MB49 cells modified to secrete PSA are a reliable method to evaluate therapeutic modalities for bladder cancer.