Capacity of murine IL-12 to inhibit the development of primary melanoma tumors and to prevent lung metastases in the melanoma-challenged mice DavidP.Shrayer 1 ,HendrikBogaars 1 ,BernardCole 2 ,StanleyF.Wolf 3 , and Harold J. Wanebo 1 1 Departments of Surgery and Pathology, Roger Williams Medical Center, Brown University, Providence, RI, 02908, 2 Department of Community Health, Brown University, Providence, RI, 3 Genetic Institute, Inc., Cambridge, MA, 02140. Correspondence to Dr. David Shrayer, Departments of Surgery and Pathology, Roger Williams Medical Center, Brown University, 825 Chalkstone Avenue, Providence, RI 02908. Phone: (401)456-6526. Fax: (401) 456-2035. E-mail: David_Shrayer@brown.edu. (Received 1/12/2001; accepted 2/20/2001; updated 3/14/2001) Interleukin-12 (IL-12) has the capacity to activate cytotoxic lymphocytes, stimulate natural killer cells, induce the production of INF-, and be synergistic with IL-2. We have evaluated this cytokine in an experimental model for metastatic melanoma that approximates the major clinical stages of metastatic dissemination. To develop primary melanoma tumors, mice were injected subcutaneously with 5Â10 5 cells in a volume of 25 l into the middle of the tail (11). In a month, mice were started to be treated for 4 weeks with recombinant murine IL-12 (R mIL-12) at the following doses: 0, 0.5, 2.5, 5.0, 15.0, and 50 g/kg. Diameters of the primary melanoma tumors were measured at weekly intervals. At the end of 13 weeks (9 weeks from the start of treatment with R mIL-12), all surviving mice were sacrificed. Pathological examination of lung metastases (macroscopy) was done with all dead or sacrificed mice. Treatment of mice bearing melanoma at a dose of 300 ng/mouse (15 g/kg) inhibited development of primary tumors in 40% of mice. The primary tumor diameters were significantly lower in the group treated with 300 ng/ mouse (15 g/kg) in comparison to controls. At the end of the observation period, groups treated with 0.5, 2.5, 15.0, and 50 g/kg had mean primary tumor diameters smaller than the control group. Evaluation of IL-12 therapy on primary tumor growth, mean diameters of primary tumors, survival rate, and development of lung metastases showed that the best results were observed using 300 ng/mouse (15 g/kg) R mIL-12. Keywords: IL-12, lymphokines, melanoma, metastasis. INTRODUCTION Lymphokine therapy can significantly affect cancer growth primarily by modulating the cellular response, and secondarily by in- creasing antibody production and stimulat- ing the secretion of lymphokines. Interleukin-12 (IL-12) which was described some years ago (1±3) has the capacity to activate cytotoxic lymphocytes, stimulate natural killer cells, induce the production of IFN-, and be synergistic with IL-2. Both human and murine IL-12 are heterodimeric cytokines with p35 and p40 subunits (2,3). Because human IL-12 did not elicit re- sponses in murine T cells and NK cells (3), mouse-model experiments were performed with murine IL-12. Experimental pulmonary metastases or subcutaneous growth of the B16 F10 melanoma were markedly reduced in mice treated intraperitoneally with murine recombinant IL-12 (R mIL-12), resulting in an increase of survival time. The therapeutic effectiveness of IL-12 was dose dependent with maximal effects observed at a dose of 1 g per injection (4). R mIL-12 did not directly alter BL-6 murine melanoma cells in vitro but delayed emergence of detectable tumor after intradermal injection of BL-6 in an established model (5). Antitumor activ- ity of R mIL-12 (0.1±1.0 g/day) against MC-38 colon adenocarcinoma and MCA-105 and MCA-207 methycholanthrene-induced Journal of Experimental Therapeutics and Oncology 2: 93±99, 2002 D 2002 Blackwell Publishing Inc. Journal of Experimental Therapeutics and Oncology Vol. 2 2002 93