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

Abstract

The purpose of this study was to determine the effectiveness and toxicity of local continuous immunotherapy 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 γ. 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 γ 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.