This study evaluated the effects of PGA1 on B-16 melanoma-bearing mice. Intraperitoneal injection of PGA1 (10 μg/day) significantly inhibited the rate of melanoma growth measured both as delay in the rate of appearance and decrease in the tumor volume. In contrast to the diluent control-treated mice, by 17 days, less than half of the PGA1 - treated animals developed measurable (>2mm) subcutaneous tumors. In addition to its effect on tumor size, PGA1 was also effective in stimulating both the humoral and cellular components of the immune response. B-16 tumor-bearing mice were shown to be immunosuppressed, in that they had decreased anti-sRBC hemagglutinin titers, decreased splenic plaque-forming cells, suppressed delayed hypersensitivity responses, and delayed rejection of skin allografts from BALB/c mice. Although, PGA1 had relatively little effect on normal mice, this prostaglandin substantially improved all these immunologic parameters in tumor-bearing animals.
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