Use of a surrogate marker (human secreted alkaline phosphatase) to monitorin vivo tumor growth and anticancer drug efficacy in ovarian cancer xenografts?

Objectives. A limitation to preclinical evaluation of possible anticancer t herapy is the objective assessment of efficacy, especially in the presence of small tumor burden or inaccessible disease. This study is designed to te st whether human secreted alkaline phosphatase (SEAP) could be used as a so luble marker for in vivo tumor burden. Methods. A SEAP expression construct under control of the CMV promoter was created. The SEAP activity in the conditioned medium was evaluated at 24 h and 48 h after the A2780 cell line was transiently transfected with the SEA P vector using Superfect reagent. Stable transfection of A2780 was accompli shed by selection of transfectants in G418. SEAP activity of the stable tra nsfectant was determined in conditioned medium and its relationship to tumo r cell number was examined. A highly expressing stable transfectant was imp lanted into immunocompromised mice (2 x 10(6) subcutaneously and 5 x 10(6) intraperitoneally) and peripheral blood was obtained by orbital puncture ev ery 5 days. The relationship between blood SEAP activity and tumor burden w as studied. The usefulness of this marker in preclinical assessment of anti cancer drug efficacy was evaluated by studying the plasma SEAP activity in xenografted mice treated or not treated with paclitaxel. Results. After transient transfection of the A2780 cell line (5 x 10(5)) wi th the plasmid, SEAP activity was found in the medium at 24 h (482.0 +/- 2. 0 ng/ml) and 48 h (1296.0 +/- 1.0 ng/ml). The in vitro study using a stable transfectant demonstrated that SEAP activity was linearly related to cell numbers (r = 0.99). The in vivo study demonstrated that SEAP was detectable in plasma one day postinjection, long before measurable tumor or detectabl e intraperitoneal tumor was present. Once detectable SC tumor was present, the SEAP activity correlated well with tumor volume (r = 0.94-0.97). The pl asma SEAP level was reduced after xenografted mice were treated with paclit axel (20 mg/kg, weekly x5) compared with untreated mice in both SC and IP t umor models (P = 0.05, P = 0.025, respectively). Conclusion. These data suggest that the plasma SEAP activity can be used as an alternative to survival or tumor measurement in evaluating anticancer a gents for efficacy, especially in the case of minimal or inaccessible disea se. (C) 2000 Academic Press.