Monitoring the therapy of human tumor xenografts in nude mice by the use of lactate dehydrogenase.

With the use of circulating human lactate dehydrogenase (LDH) as a tumor marker, growth and remission of human tumor lines SW480, HEp-2, and Clouser, implanted into female BALB/c athymic nude mice, were followed during therapy. Three types of therapy were used: X-radiation, cyclophosphamide, and diphtheria toxin. After therapy tumor sizes were measured with calipers and compared to changes in the levels of circulating human LDH. Changes in LDH levels paralleled changes in tumor size, but the enzyme fluctuations were more pronounced. Mice bearing intraperitoneally growing SW480 and HEp-2 tumors were effectively treated with diphtheria toxin, and the measurement of circulating LDH was examined as a parameter for gauging the effectiveness of chemotherapy on tumors that could not be visualized. Circulating human LDH can be used to detect intraperitoneal tumor growth and/or remission and to predict death of the animal due to the tumor.