TMC-264, a novel inhibitor of STAT6 activation produced by Phoma sp. TC 1674

A novel inhibitor of STAT6 activation, named as TMC-264 (1), was discovered from the fermentation broth of Phoma sp. TC 1674. Based on spectroscopic analyses, TMC-264 was found to be a novel tricyclic polyketide with chloro-1H-dibenzo[b,d]pyran-4,6-dione. TMC-264 suppressed expression of IL-4 driven luciferase and germline Cepsilon mRNA with IC50 values of 0.3 microM and 0.4 microM, respectively. TMC-264 exhibited a potent inhibitory activity against tyrosine phosphorylation of STAT6 with an IC50 value of 1.6 microM, whereas TMC-264 weakly inhibited tyrosine phosphorylation of STAT5 with an IC50 value of 16 microM, but did not inhibit the phosphorylation of STAT1 up to 40 microM. TMC-264 blocked formation of the complexes between phosphorylated STAT6 and STAT6 oligonucleotides in a dose dependent manner, while TMC-264 did not affect the formation of phosphorylated STAT1/STAT1 oligonucleotides complexes. These results suggested that TMC-264 selectively inhibited IL-4 signaling by interfering both of phosphorylation of STAT6 and binding of the phosphorylated STAT6 to the recognition sequence.