NSC114792 selectively inhibits persistently-active JAK3/STAT signaling in cancer cells. The Hodgkin's lymphoma cell lines L540 (A) and HDLM-2 (B), the breast cancer cell line MDA-MB-468 (C), and the prostate cancer cell line DU145 (D) were cultured for 24 hours in the presence of either vehicle (DMSO) alone, NSC114792 at various concentrations up to 20 μmol/L, or the pan-JAK inhibitor AG490 (150 μmol/L). Whole-cell extracts were processed for Western blot analysis using antibodies specific for the molecules indicated. Treatment with NSC114792 did not alter the levels of phospho-JAK1 and -JAK2 (B-D, lanes 1-4), but it did potently inhibit phospho-JAK3 in a dose-dependent manner (A, lanes 5 and 6). Consistently, the compound decreased phospho-STAT3 only in L540 cells, which exhibit persistent JAK3 activation (lanes 7 and 8). In contrast, AG490 non-selectively decreased the phosphorylation of JAK kinases and thus led to a block in phospho-STAT3 in all cell lines tested. NSC114792 did not alter the levels of other activated oncogenic kinases, including phospho-Src (lanes 9 and 10), phospho-Lyn (lanes 11 and 12), phospho-Akt (lanes 13 and14), and phospho-ERK1/2 (lanes 15 and 16). None of these kinases were affected by treatment with NSC114792 at concentrations up to 20 μmol/L.