SYSTEMIC INTERLEUKIN-2 THERAPY FOR HUMAN PROSTATE TUMORS IN A NUDE-MOUSE MODEL

Once the regional lymph nodes become involved in prostate carcinoma, 8 5% of patients develop distant metastases within 5 years, and metastat ic disease is difficult to treat. We have investigated the effect of s ystemic interleukin 2 (IL-2) treatment on metastatic prostate carcinom a using a xenograft tumor model. Cells from a PC-3/IF cell line, produ ced by intrafemoral injection of human PC-3 prostate carcinoma cells, were injected in the prostate of Balb/c nude mice, Prostate tumors and para-aortic lymph nodes were resected, and tumor cells were reculture d and passaged in the prostate in vivo to produce new cell lines. On d ay 6 following prostatic injection of these cell lines, mice were trea ted with i,p, injections of IL-2 at 25,000-50,000 units/day for 5 cons ecutive days. The effect of IL-2 on tumor progression was assessed, an d histological studies were performed on prostate tumor and lymph node sections. The tumor cell lines generated by serial prostate injection were tumorigenic and metastasized to regional para-aortic lymph nodes . Tumors of 0.4 cm were obtained by day 16 and grew to 1-1.5 cm by day 40 with metastasis to para-aortic lymph nodes. Following two to three weekly courses of 5 days of 25,000-40,000 units/day of IL-2, the grow th of prostate tumors was inhibited by 94%. Higher doses of 50,000 uni ts/ day were toxic. Histologically, prostate sections showed vascular damage manifested by multifocal hemorrhages and an influx of lymphocyt es and polymorphonuclear cells into disintegrating tumors and areas of necrosis containing numerous apoptotic cells. In contrast to control mice, para-aortic lymph nodes were not enlarged in responding mice. Th ese findings suggest that systemic IL-2 therapy can induce an antitumo r response in prostate tumors and control their growth and metastasis.