Therapeutic Effect Reflected by Plasma Levels of a Viral Protein during Combination Chemotherapeutic Treatment of Mammary Tumor-bearing Mice

Plasma concentrations of gp52, a M r 52,000 glycoprotein of the mouse mammary tumor virus, have been measured during cyclophosphamide, doxorubicin (adriamycin) and 5-fluorouracil (CAF) treatment of mammary tumor-bearing CD8F1 mice. The value of plasma concentrations of gp52 as an indicator of CAF-mediated changes in tumor status was supported by each of the following findings: ( a ) CAF treatment did not interfere with the detection of elevated viral antigen levels in the plasma of tumor-bearing mice; ( b ) at 9–11 days after initiation of treatment, a significantly lower mean gp52 level, observed in the group of CAF-treated mice, provided definitive evidence of therapeutic effect; and ( c ) serial determinations of plasma gp52 levels in individual mice before, during, and after treatment provided a relative measure of therapeutic effect for each individual that was a reflection of corresponding changes in tumor size. Changes in viral antigen levels ( i.e. , decrease or increase) reflected inhibited tumor growth, as well as tumor regression. These findings demonstrate that plasma concentrations of gp52 can be utilized to provide an alternative measure of therapeutic effect in CAF-treated mice bearing significant tumor loads.