SP1 and cancer: PPARƔ primarily inhibits the growth of cancer cells; emodin decreases IGFBP1 [104]; cladosporol, rosiglilazone and a bis-indole PPARƔ ligand induce p21 [105,106,107]; and thiazolidinediones (TZDs) decrease an insulin receptor [108] via PPARƔ/Sp1 in cancer cell lines (Figure 5).