Motivated by the theory that tumor cells might shed anionic macromolecules from their surfaces into the blood, a microassay for polyanions based on the spectral shift of carbocyanine dye was adapted to the analysis of serum from healthy and tumor-bearing mice, incubated with and without sialidase. Carbocyanine dye-binding polyanion, compared with sodium pectin as a standard, was 131 µg/ml serum from healthy C57BL × DBA/2 F1 (hereafter called BD2F1) mice, 270 µg/ml in L1210 (ascites) leukemia, and 277 µg/ml in mice given s.c. injections of Lewis lung tumor. Non-tumor-bearing, traumatized controls, given i.p. injections of CCl4 to simulate the gross pathology of ascitic tumor growth and s.c. injections of Sephadex gel to simulate the trauma of solid tumor growth, gave carbocyanine dye-binding polyanion values of 173 and 166 µg/ml, respectively. The difference in carbocyanine dye-binding reactivity of serum with and without sialidase incubation gave the sialopolyanion fraction, values of which ranged from 29 to 35 µg/ml serum for healthy or traumatized mice and 135 and 169 µg/ml in mice bearing L1210 leukemia and Lewis lung tumor, respectively.

Sialopolyanion values, measured as a function of time after i.v. implantation of 104 leukemic cells or 106 Lewis lung tumor cells (implanted i.m.), showed a significant elevation in 2 days, whereas it was 8 days before the white blood cell count in leukemic mice increased, and more than 5 days before the Lewis lung tumor became palpable.

Differences between sialopolyanion values of serum from mice bearing a variety of tumors and the corresponding healthy host were similar to those seen for healthy BD2F1 mice and the hosts bearing the L1210 leukemia or Lewis lung tumor.

In support of the theory that tumor cells shed anionic material into the blood in vivo, it was found that the undiluted ascites plasma, from which Krebs tumor cells had been deposited by centrifugation, contained 27% more carbocyanine dye-binding polyanion and 42% more sialopolyanion than did plasma from which Krebs cells had been settled by gravity.

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Supported by Contract NO1-CM-33728 with Division of Cancer Treatment, National Cancer Institute, NIH, Department of Health, Education and Welfare, Bethesda, Md. 20014. Presented in part at the 64th Annual Meeting of the American Association for Cancer Research, April 11, 1973.

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