Intratumoral depot interleukin-2 therapy inhibits tumor growth in Dunning adenocarcinoma of the prostate implanted subcutaneously in rats

The purpose of this study was to determine the effectiveness and toxicity of local continuous immuno-therapy of prostatic cancer. A group of 60 young male Copenhagen rats with Dunning adenocarcinoma of the prostate, implanted subcutaneously into both flanks, after proven tumor growth, were treated with either human interleukin-2 (IL-2) depot preparations(n = 30) or albumin (placebo) depot preparations (n = 30) implanted directly into one tumor site. IL-2 depots released IL-2 reliably for more than 24 days. The rat serum was tested during treatment for human IL-2, possibly absorbed from depots, and for rat interferon gamma. IL-2 treatment reduced tumor growth significantly (P < 0.001) compared with albumin-treated sites or untreated contralateral sites. No toxicity was observed during treatment. Neither human IL-2 nor rat interferon gamma was detected in the serum, which indicates an exclusively local IL-2 effect. IL-2 depot preparations reduce tumor growth in Dunning adenocarcinoma of the prostate significantly without toxicity.