SUMMARY Measurement of thymidylate synthase (hTS) using immunohistochemical techniques has been reported in several clinical studies. However, its value as a prognostic indicator is still not clear. To pursue this, we have developed a new rabbit polyclonal antibody, hTS7.4. The antigen was recombinant hTS containing an N-terminal His 6 -tag. Antiserum hTS7.4 detected recombinant hTS by ELISA at a titer of 1:100,000. Western blot analysis of several human cell lines showed a single band of the expected 36-kD molecular size. HeLa cells treated with the TS inhibitor 5-FUdR showed the expected additional band corresponding to the ternary complex of hTS-dFUMP-reduced folate. hTS7.4 detected TS in bacterial, rat, mouse, and monkey cell extracts, and hTS8.3 (a closely related antiserum) immunoprecipitated a 36-kD [ 35 S]-methionine-labeled protein from HeLa extracts. TS was detectable by indirect immunofluorescence in HeLa cells. Proliferating normal human fibroblasts in culture showed staining, but nonproliferating cells did not. Lymphocytes in the germinal center of human tonsil tissue, which are known to be proliferating, stained with hTS7.4 and also with monoclonal antibody TS106. TS may therefore be useful as an immunohistochemical marker of cell proliferation. Normal colon mucosa showed weak staining, whereas some colorectal cancer specimens stained very strongly with hTS7.4. A clinical study of colorectal cancer using this antibody is in progress.

CI-921, (9-[[2-methoxy-4-[(methylsulfonyl)amino]phenyl]amino]- N,5-dimethyl-4-acridinecarboxamide 2-hydroxyethanesulfonate (1:1)), an anilinoacridine derivative with activity in experimental solid tumors was studied in a multicenter phase II trial in patients with solid tumors. Eligible tumor types included cancers of the breast, stomach, pancreas, nonsmall cell lung, small cell lung, colon, head and neck area, and melanoma. Prestudy requirements included an ECOG performance status of < or = 2, no CNS metastases, and measurable disease. CI-921 was administered intravenously over 1-2 hours on days 1, 8, and 15 of a 35-day course at an initial dose of 270 mg/M2, with modification in subsequent courses based upon tolerance. Principal toxicities included leukopenia, marked phlebitis, and mild nausea and vomiting. One hundred fifty patients were entered of whom 132 were evaluable for response. There was one complete and one partial response among 19 patients with breast cancer, and two partial responses, one each among 14 head and neck and 36 nonsmall cell lung cancer patients.

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