Cure of human melanoma lung metastases in nude mice with chronic indomethacin therapy combined with multiple rounds of IL-2: characteristics of killer cells generated in situ

We have shown that macrophage-derived prostaglandin (PG)E2 inactivates all interleukin 2 (IL-2) dependent killer cell lineages in the tumor-bearing host, so that chronic indomethacin therapy (CIT) combined with multiple rounds of IL-2 can cure experimental and spontaneous metastases of a variety of murine tumors. We tested the efficacy of this therapy on experimental human melanoma metastasis in nude mice and characterized the killer cells generated in situ. BALB/c nude mice were injected i.v. with 2 x 10(6) human lung-metastasizing line P52, MeWo melanoma cells. After 5 weeks, when lung nodules were well established, mice received vehicles alone (control) or were given (a) CIT (14 micrograms/ml in drinking water); (b) three rounds of IL-2, 25,000 Cetus U, 8 hourly i.p. (days 40-44, 50-54, 60-64); (c) CIT + three rounds of IL-2; (d) CIT + four rounds of IL-2 (round 4 on days 70-74); and (e) CIT + five rounds of IL-2 (round 5 on days 80-84). Control and experimental mice were killed on day 71 to score lung colonies and evaluate killer activity in splenic and lung lymphocytes and macrophages against murine YAC-1 lymphoma and B16F10 melanoma, human P52 melanoma, K562 erythroleukemia, and Raji lymphoma targets. Killer cells for P52 were phenotyped for Thy-1, Lyt-2, and asialo-GM-1 markers by ab + C'-mediated deletion of killer function. Mice in all groups were also kept for survival. CIT alone improved splenic NK activity but marginally reduced the lung colony counts or prolonged the survival time. Three rounds of IL-2 alone reduced the median colony counts by 50% and prolonged the survival by 2 weeks, but resulted in no long-term, disease-free survival, in spite of significant activation of LAK cells with Thy-1-, Lyt-2-, AGM-1+ phenotype in the spleen. CIT + 3 rounds of IL-2 reduced the median colony counts from 40 to 0 and improved the survival from a median of 66 (control) to 120 days (40% surviving 260 + days). CIT + four or five rounds of IL-2 caused long-term (260 + days) survival of 80% mice, most surviving 400 + days. The combination therapy activated killer lymphocytes (Thy-1-, Lyt-2-, AGM-1+) and, to a smaller extent, macrophages (AGM-1 +/-) in the spleen and the lungs, showing a high cytocidal ability for all the targets.(ABSTRACT TRUNCATED AT 400 WORDS)