Abstract
Summary
This study was designed to test the effect of the sequential administration of poly I: poly C on the growth rate and morphology of DBA mouse mammary adenocarcinoma. Treatments with poly I: poly C (150 μg ip per dose) started (a) 24 hr after implantation; (b) when the size of tumors reached 0.6—1.0 cm3, or (c) 1.8—2.0 cm3. Controls were injected with 0.15 ml phosphate-buffered saline (placebo). In all groups the treatment continued at 48-hr intervals for 18—22 days. Treatments starting 24 hr after implantation resulted in a temporary arrest of the growth of tumor implants followed by a significantly decreased volume-doubling time (for tumors 0.5 and 1.0 cm3 in size p <0.001). The treatment of established tumors was more effective in small tumors. The fractional survival of tumor tissue was significantly lower in tumors measuring 0.6—1.0 cm 3 (0.070) than in tumors 1.8—2.0 cm3 in size (0.231). All groups of mice treated with poly I: poly C showed a significantly longer survival time (p < .01). Increased interferon levels were observed after the first injection of poly I: poly C but not after a series of injections. The regression of tumors was most significant at the beginning of treatment. Extensive necrotic lesions were observed in histologic sections of tumors treated with poly I: poly C. There was no morphologic evidence suggesting the damage of the tumor tissue by induced cell-mediated immune response, and there was no indication that lymphocytes play some crucial role in the genesis of the inhibitory effect of poly I: poly C on isologous DBA tumors.
The authors express appreciation to Dr. J. Vilcek, Department of Microbiology of the New York University Medical Center for performing the interferon assays and to Dr. Samuel Baron, of the National Institutes of Health, Bethesda, MD for reading the manuscript and comments.
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