IFN-alpha-2b-induced signal transduction and gene regulation in patient peripheral blood mononuclear cells is not enhanced by a dose increase from 5 to 10 megaunits/m2.

Purpose: The precise molecular targets of IFN-alpha therapy of melanoma are unknown but likely involve signal transducer and activator of transcription (STAT) 1 signal transduction within host immune effector cells. We hypothesized that intermediate and high doses of IFN-alpha would be equally effective in activating patient immune cells.

Experimental Design: Eleven metastatic melanoma patients who were enrolled in a clinical trial of bevacizumab in combination with escalating doses of IFN-alpha-2b (5 megaunits/m(2) and then 10 megaunits/m(2)) were included in the study. Peripheral blood mononuclear cells (PBMC) were procured from patient blood just before therapy and again 1 h after each dose of IFN-alpha-2b and analyzed for the presence of phosphorylated STAT1, phosphorylated STAT2, and the induction of IFN-stimulated gene (ISG) transcripts.

Results: Phosphorylated STAT1 was significantly greater at the 5 megaunits/m(2) dose compared with the 10 megaunits/m(2) dose of IFN-alpha-2b (P = 0.02). In contrast, no significant difference in phosphorylated STAT2 was observed at a dose of 5 megaunits/m(2) compared with 10 megaunits/m(2) (P = 0.20). There were also no significant differences in the induction of ISGs within PBMCs between the two doses (P > 0.4 for all ISGs). Suppressor of cytokine signaling 1 and 3 (two inhibitors of IFN-alpha signaling) transcripts were significantly higher among patient PBMCs following the 10 megaunits/m(2) dose of IFN-alpha (P < 0.001).

Conclusion: These results suggest that lower doses of IFN-alpha-2b are as effective as higher doses with respect to the induction of Janus-activated kinase-STAT signal transduction and the transcription of ISGs within immune effector cells.